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Repurposing of COVID-19 single-use face masks for pavements base/subbase
Abstract
The coronavirus (COVID-19) pandemic has not only created a global health crisis, but it is also now threatening the environment. A multidisciplinary collaborative approach is required to fight against the pandemic and reduce the environmental risks associated with the disposal of used personal protective equipment (PPE). This paper explores an innovative way to reduce pandemic-generated waste by recycling the used face masks with other waste materials in civil constructions. In this research, for the first time, a series of experiments, including modified compaction, unconfined compression strength and resilient modulus tests, were conducted on the blends of different percentages of the shredded face mask (SFM) added to the recycled concrete aggregate (RCA) for road base and subbase applications. The experimental results show that RCA mixed with three different percentages (i.e., 1%, 2% and 3%) of SFM satisfied the stiffness and strength requirements for pavements base/subbase. The introduction of the shredded face mask not only increased the strength and stiffness but also improved the ductility and flexibility of RCA/SFM blends. The inclusion of 1% SFM to RCA resulted in the highest values of unconfined compressive strength (216 kPa) and the highest resilient modulus (314.35 MP). However, beyond 2%, increasing the amount of SFM led to a decrease in strength and stiffness.
... Recycled C&D materials, such as recycled concrete, recycled rock, recycled brick, reclaimed asphalt, and recycled glass, are increasingly being assessed for their suitability in various civil engineering applications, such as roads, pavements, footpaths and concretes [9][10][11]. Incorporating these reclaimed materials into civil engineering projects offers an eco-friendly alternative, significantly reducing carbon emissions compared to virgin quarried materials [12][13][14][15]. ...
... Notably, compaction, unconfined compression strength, resilient modulus, and permanent deformation tests were performed on three identical replicate specimens for each mixture. To prevent segregation and ensure uniform mixing, the technique proposed in [64] and [10] was adopted. For every layer, the mixed materials were meticulously poured into the mould while keeping the scoop in close proximity to the top layer of the sample. ...
... Conversely, the decline in MDD can be attributed to the lower density exhibited by PP fibres in comparison to the recycled coarse aggregate. Similar results were reported in [10,11,68] for the introduction of highdensity polyethylene, low-density polyethylene, polyethylene terephthalate, and polypropylene into the recycled C&D aggregates. content. ...
... To attain a uniform blend of construction materials and DMF, the initial step involves removing the rubber ear loops and metal strips located at the nose bridge of the masks. Following that, manual shredding is conducted, with scholars reporting various dimensions such as 10 mm × 10 mm [39], 10 mm × 20 mm [40], 20 mm × 4 mm [41], 20 mm × 5 mm [35,[42][43][44], 20 mm × 20 mm [40], 40 mm × 10 mm [45], 60 mm × 15 mm [45]. Besides, several researchers possessed additional process after shredding DM. ...
... Saberian et al. [44] examined the mechanical performance of DMF in road subbases and base courses, focusing on parameters like unconfined compressive strength and elastic modulus. They found that incorporating just additional 1 % of DMF (by weight of soil) substantially increased the unconfined compressive strength (UCS) to 216 kPa and raised the elastic modulus to 314.35 MPa. ...
... The significant variations observed primarily stem from the utilization of distinct materials. Saberian et al. [44] employed recycled concrete aggregate (RCA) and DMF (0 %, 1 %, 2 % and 3% by weight of RCA). In contrast, Abdullah et al. [54] utilized locally purchased clay along with DMF (0.5 %, 1 % and 2 % by weight of dry soil). ...
In recent years, with the heightened of public health protection awareness, masks have become an important protective equipment. The accumulation of discarded masks (DM) poses an impact to environment and resource. Recycling DM has become a prime focus of sustainable development research. This investigation introduces a review of the recycling of DM in civil engineering and presents a novel modification of discarded mask fibers (DMF) to enhance the mechanical property of cement paste. In the review section: (1) The masks are divided into three classes by integrating relevant standards and considering mask protective characteristics; (2) Various disposal techniques for recycling DM are categorized in shredding, hot processing, paper shredding, and crushing; (3) The impact of incorporating DMF in concrete, mortar, asphalt, road subbases and base courses are discussed. The enhancement of applying DMF into composite materials varies depending on the specific application. In the experimental research section, the silane coupling agent (SCA) is introduced as a modification to improve the weak bonding between DMF and composite materials. The SCA-modified polypropylene (PP) fibers were conducted as a control group. The results indicate that the compressive strength of cement paste with both SCA-modified DMF and PP fibers increased by 12.29 % and 26.10 %, respectively. Finally, several future opportunities in recycling of DM in Civil Engineering were drawn.
... The use of masks is at its peak due to the universal masking of the COVID-19 pandemic. Now, approximately 4 billion surgical masks are used globally each day, and the majority (80%) of those synthetic products, along with other PPE, end up in the water, which is hazardous from an environmental standpoint (Das et al. 2020;Ma et al. 2021;Saberian et al. 2021), which raises the oceans' microplastic and chemical levels due to mechanical, chemical, and natural degradation of the mask over time, with the filter layer producing more microplastic synthetic polymers like polylactic acid, polyethylene oxide, and polyvinyl alcohol and natural polymers like gelatin, alginate, chitosan, and collagen are used for this purpose (Silva et al. 2020;Haque et al. 2021;Wu et al. 2022). ...
... Extended use and reuse of those masks also reduce certain amount of those plastics from going into the environment (Das et al. 2020;. Those face masks can be further used in 1 to 2% of a construction site, which will increase the strength of the concrete due to their reinforcement power and also reduce a few portions from going into the environment (Kilmartin-Lynch et al. 2021). ...
Masks are face coverings that give protection from infectious agents, airborne pathogens, bacteria, viruses, surgical fog, dust, and other chemical hazards by acting as a barrier between the wearer and the environment. In the COVID-19 pandemic, this major personal protective equipment’s became essential part of our daily life. The aim of this review is to analyze and discuss the different types of masks with their pros and cons, manufacturing procedures, evaluation criteria, and application with some of the sterilization process for reuse and smart mask. The review used a thorough examination of the literature to analyze the preventive effects of surgical, N95, smart mask, and potential environmental damage from those masks. Several studies and evidence were also examined to understand the efficiency of different mask on different environment. N95 respirators are capable of filtering out non-oil-based 95% air-born particles, and surgical masks act as a protective barrier between the wearer and the environment. The application of spoon bond and melt blown techniques in the fabrication process of those masks improves their protective nature and makes them lightweight and comfortable. But the high demand and low supply forced users to reuse and extend their use after sterilizations, even though those masks are recommended to be used once. Universal masking in the SARS-COV-2 pandemic increased the chance of environmental pollution, so the application of smart masks became essential because of their high protection power and self-sterilizing and reusing capabilities.
Graphical abstract
... To control the spreading of COVID-19, it was advised that every person should wear a face mask, triggering the demand for face masks to grow at an unpredictable rate, followed by daily disposal of enormous amounts of face masks [5,17]. Nonwoven fabrics are used for the production of both respirator masks and surgical masks. ...
... Mechanically recycled waste polymeric materials such as PP and polyurethane have previously been used in construction and building materials [9,12]. Such materials have been used to manufacture construction materials with attractive properties at relatively low costs [17]. Since construction activities are responsible for consuming about 40% of natural resources, using PP-based nonwoven fabrics from disposable facemasks holds promise to cater to the hefty volume of input materials required for such industries. ...
Rapid spread of COVID-19 disease worldwide resulted in a dramatic increase in face mask consumption. Single-used surgical face masks are manufactured using plastic fibres such as polypropylene (PP) or polyester, which cause severe environmental concerns when accumulated in landfills, primarily due to their non-degradability. Furthermore, plastic fibres are derived from petroleum, a depleting resource at an alarming rate, due to which preserving is highly recommended. Massive consumption and subsequent disposal of single-use surgical face masks urge seeking alternative solutions to conserve resources and manage the ever-growing waste issue. This study investigates the feasibility of recycling surgical facemasks. Single-use surgical face masks were subjected to mechanical recycling through melt extrusion. FTIR and TGA tests were conducted to establish the raw material’s chemical composition and thermolytic properties. Facemasks were initially shredded and melt-extruded to obtain filaments, which were subsequently pelletised. The pellets were hot-pressed using the compression moulding technique to make sheet-like panels. Tensile testing of the recycled sheet-like material exhibited failure stress of ~23 MPa and a failure strain of ~2.2%. While the failure stress was similar to the virgin PP material, the failure strain reduced significantly upon recycling. The material’s thermal conductivity was measured to be 0.404 W m−1 K−1 using Lee’s Disc Method. Thermal conductivity was increased significantly than the virgin PP material. The recycled material can be used in sheet form for applications such as thermal insulation and partition boards with further improved strength and thickness. Additionally, recycled pellets have the potential to be used as 3D printing feedstock, thereby enabling utilisation in bulk quantities.KeywordsFace mask wasteCOVID-19Waste managementRecyclingEnvironmental pollutionPolypropylene
... During the COVID-19 pandemic, WHO introduced guidelines on the utilisation of personal protective equipment (PPE) and requested that the production of PPE, including face masks, should be increased by 40% [1]. Most countries agreed to the recommendations of the WHO and implemented a policy of mandatory mask-wearing in public areas in response to this public health emergency of international concern [2][3][4]. The main part of the medical three-layer masks consists of a layer of melt-blown fabric and two layers of spun-bond fabric made of ultra-fine polypropylene (PP) nonwoven fibres [5]. ...
... As a means of alleviating such negative effects, researchers were working toward reusing discarded masks in civil construction projects such as concrete [11], pavement base/subbase layers [4], subgrade layer and soil stabilisation [18]. However, there is limited research on the use of waste masks in different types of asphalt mixtures. ...
Since COVID-19 was declared a global pandemic, the production, consumption, and discard of personal protective equipment (PPE), such as face masks, have been rapidly increasing. The massive amount of face mask waste poses a severe threat to the ecology, environment, and public health. Alleviating the adverse effects of mask waste requires the cooperation of professionals from various fields. To reduce the epidemic-generated waste and improve the performance of stone mastic asphalt (SMA) mixes, in this study, comprehensive laboratory experiments, including volumetric assessment, Marshall stability and flow, resilient modulus, dynamic creep, moisture susceptibility, and binder drain-off test were carried out on SMA specimens prepared with 0.3%, 0.5%, 0.7%, and 1.0% of mask fibre (MF) by weight of asphalt mixture. The results were compared with the control SMA specimen (i.e., SMA mixed with 0.3% cellulose fibre (CF)) that complied with the road industry regulations and standards. The results of the study illustrated that the introduction of MF into the SMA mix improved the stability, resilient modulus, indirect tensile strength, resistance to permanent deformation, resistance to moisture damage and binder drain-off performance. Experimental results indicated that the inclusion of 0.3% and 1.0% MF in SMA complied with industry requirements and suggested that MF could be used instead of virgin CF as a fibre additive. Considering the available supply, performance and industry standards, SMA containing 0.3% MF demonstrates more potential for pavement applications.
... The study showed the benefit of recycling disposable face masks in improving the mechanical performance of concrete, and such concrete can be used in buildings and structural applications. Saberian et al. [25] proposed the recycling of surgical face masks with recycled concrete aggregate in pavement applications. The results of the study showed that the blend of waste mask and recycled aggregates provides sufficient stiffness and strength for application in the pavement base/subbase. ...
With the advent of the COVID-19 pandemic, the global consumption of single-use surgical masks has risen immensely, and it is expected to grow in the coming years. Simultaneously, the disposal of surgical masks in the environment has caused plastic pollution, and therefore, it is exigent to find innovative ways to handle this problem. In this study, surgical masks were processed in a laboratory using the mechanical grinding method to obtain recycled surgical masks (RSM). The RSM was added in doses of 0%, 1%, 2%, 3%, and 4% by volume of geopolymer bricks, which were synthesized with ground granulated blast furnace slag (GGBS), rice husk ash (RHA), sand, and sodium silicate (Na 2 SiO 3) at ambient conditions for a duration of 28 days. The developed bricks were tested for compressive strength, flexural strength, density, water absorption, efflorescence, and drying shrinkage. The results of the study reveal that compressive strength and flexural strength improved with the inclusion of RSM in the bricks. The highest values of compressive strength and flexural strength were 5.97 MPa and 1.62 MPa for bricks with 4% RSM, respectively. Further, a reduction in the self-weight of the bricks was noticed with an increase in RSM. There was no pronounced effect of RSM on the water absorption and efflorescence properties. However, the RSM played a role in reducing the drying shrinkage of the bricks. The sustainability analysis divulges the catalytic role of RSM in improving material performance, thereby proving to be a potential candidate for low-carbon material in the construction industry.
... The incorporation of shredded FM fibers has been identified as a source to counteract the loss of ductility in fat clay that occurs as a result of the formation of a brittle solidified soil-cementitious gel matrix due to pozzolanic reactions. Researchers have investigated the utilization of discarded FM for soil stabilization to alleviate the waste management burden arising from their significant use during and after the COVID-19 pandemic while simultaneously improving the soil's shock load-bearing capacity (Saberian et al. 2021;Rehman and Khalid 2022). Consequently, the utilization of used FMs in proposed soil stabilizers is a value addition on both waste management and balanced stabilization accounts. ...
This study proposes a novel approach by integrating geopolymerized bagasse ash (GBA) and geopolymerized quarry dust (GQD) along with shredded facemasks (FM) for the balanced amelioration of fat clay. Extensive geotechnical testing and mineralogical and microstructural analyses were conducted to assess the performance of the proposed multi-waste fat clay stabilizer. GBA and GQD were found to reduce the liquid limit (wL) and plasticity index (IP) of fat clay up to 12% and 30% of their weight by soil, respectively, based on which composite binary additive (CBA) was devised for which optimum binary additive (OBA) was found at 20% of CBA. The strength characteristics, i.e., unconfined compressive strength (qu), CBR value, and yield stress (σy) of soil treated with OBA were observed to be significantly higher than that of untreated soil. Meanwhile, the combination of OBA and FM increased the strength more than OBA up to 0.2% of FM, after which a slight decrease was observed. The stress–strain curve, brittleness index (IB), and ductility index (ID) of the OBA-treated fat clay showed a brittle failure response, which was transformed into a ductile response as FM increased in OBA cum FM stabilizer. Microstructural analysis showed the formation of flocculation, reticulation, and cementitious gel in the treated soil. Mineralogical and elemental analyses confirmed the formation of (N, C)–A–S–H gel in the fat clay, primarily responsible for the strength gain of the treated soil. The microstructural analysis also evidenced the FM strings in the microstructure responsible for maintaining the ductility of soil. Also, the proposed multi-waste recycling has significant implications for waste management, as its implementation for the construction of a two-lane subgrade covering a distance of 1 km may enable the repurposing of 1188.58 tons of assorted solid waste.
... Considering the laboratory and government regulations during the COVID-19 pandemic, new disposable FM was utilized for testing, and the physical parameters are presented in Table 2. Meantime, Saberian et al. pointed out that masks treated with thermal disinfection and brand-new masks had little effect on tensile strength and elongation at break [13]. In the process of mask crushing, the metal strips and mask belts need to be taken out, and then crushed into mask fragments of any shape and size with a width of no more than 0.2 cm and a length of 0.5 cm in Figure 1. ...
In order to alleviate the environmental impact of mask waste, 5%, 10%, and 15% shredded face masks (SFM) were added to 70# base asphalt, respectively, and the feasibility of applying masks in asphalt modification was evaluated by temperature sweep, frequency sweep, MSCR, and time scan tests. The complex modulus, rutting factor, and average percent recovery were all improved by SFM modification, while the non-recoverable creep compliance and phase angle were also reduced. Effective enhancements were made to resistance to rutting and creeping. Additionally, 5% SFM-modified asphalt had a 5.4% increment in fatigue life compared to the original binder, whereas 10% and 15% SFM-modified asphalt had a decrease in fatigue life of 11.5% and 29.0%, respectively. The test results provide a reference for the engineering application of waste mask modified asphalt and have potential environmental benefits.
... The most ideal way to treat plastic waste is to recycle it. It can disinfect and decompose waste medical masks into particles or fragments, and then mix them evenly with other materials to make other plastic products, making waste masks reusable [11][12][13]. Chemical method recycling refers to the preparation of fuel oil under high-temperature catalytic conditions after disinfection, and the process conditions are relatively complex [14][15][16]. ...
The COVID-19 leads the use and waste of a large number of polypropylene-based masks, and improper or arbitrary disposal of waste masks will cause serious environmental pollution. In order to utilize waste masks as resources, this work prepared oil soluble crude oil fluidity improvers using waste masks as a raw materials. The effect of the layers and their mixture of masks on reducing crude oil viscosity was evaluated, and then the most effective one was compounded with other oil soluble viscosity reducers and polymers to enhance its impact on the viscosity and pour point of crude oil. The results show that the tri-component, composed of oil PP-2, polyethylene glycol and sodium dodecylbenzene sulfonate (named as CPPA), can reduce the viscosity of crude oil by 72.9%, depress the pour point by 7°C, reflecting excellent functional efficiency. DSC analysis shows that CPPA can reduce the wax precipitation point. CPPA can eutectic with wax crystals in crude oil, resulting in wax crystal disorder, changing intermolecular forces, and changing the crystal form of wax, thereby reducing the pour point. CPPA also interferes with the hydrogen bonds between polycyclic aromatic hydrocarbons and colloidal macromolecules, thereby reducing viscosity. In addition, the viscosity reduction effects of other oil samples from CPPA have also been studied, indicating that CPPA has certain universal applicability, which has explored a feasible path for the resource utilization of waste masks.
... [5] At the same time, the waste of resources caused by a large number of disposable FMs is increasingly serious, so how to efficiently and cleanly deal with the disposable FMs produced in daily life has become an urgent problem. So far, researchers have made some progress in the recycling of discarded FMs: Saberian [6] removed the ear hook and nose clip of FMs, cut them into 2 × 0.5 cm fiber fragments, mixed them into recycled concrete aggregate with different mass percentages, and then cured the prepared concrete samples. A series of tests showed that the introduction of FM fragments improved the strength and rigidity of concrete. ...
Conducting polymer composites possessing excellent electromagnetic interference shielding effectiveness (EMI SE) are effective methods to prevent the harm caused by electromagnetic pollution. Since COVID‐19 in 2019, people have made a lot of progress in the recycling of waste face masks (FMs). Besides, effective measures are needed to reduce the harm of microplastics (MPs) pollution in the water environment. However, so far, no publications are available in the literature that simultaneously solve the problem of electromagnetic pollution, FM pollution, and MP pollution. Herein, FMs, polystyrene MPs (PS MPs), and graphene (Gr) were used to fabricate EMI shielding composites with isolated conductive network structures via the adhesion of polydopamine (PDA). The effects of isolated conductive networks, different sizes of PS MPs, and different layers of FMs on the adsorption properties of FMs‐PDA‐Gr, as well as electrical performance for the obtained polypropylene‐PDA‐Gr composites, were studied. The composites displayed EMI SE for 29.3 dB in X‐band with 2 vol.% Gr content due to the isolated conductive network structure, which may be useful to the simultaneous elimination of garbage from electromagnetic pollution, FMs pollution, and MPs pollution to a certain degree.
... The descriptions of recycling practices are much more limited in our dataset. This theme covers descriptions of recycling bins that have been placed in shops (e.g., ReWorked, descriptions of items made from recycled FM (see Saberian et al., 2021), descriptions of FM made from recycled items (as in 7), but the articles from our dataset also point out the difficulties of recycling FM, as in example (9): (9) With face-coverings here to stay, conservationists are calling for recyclable alternatives: Professor Mark Miodownik, a mechanical engineer at University College London's Plastic Waste Innovation Hub, said masks were very difficult to recycle, meaning they were incinerated, sent to landfill or littered. "It's technically possible to recycle any plastic. ...
IntroductionThe environmental impact of waste caused by single-use masks or face coverings is an under-considered effect associated with the COVID-19 pandemic. The combination of the protective purpose of face masks and their potential environmental impacts through littering or waste management means the wearing of face masks is simultaneously associated with the health crisis and creation of a new environmental challenge, combining two strands of journalism.Methods
Our study demonstrates how the discourse in British and Irish newspapers in the March 2020-December 2021 time frame relates to this problem. By a combination of quantitative and qualitative discourse analysis, we identify concepts commonly associated with the terms “face-covering” and “mask,” particularly concerning whether they refer to a disposable or reusable item.ResultsResults suggest that the newspaper discourse generally favored references to single-use surgical masks. Newspapers reported on the environmental impact of face masks only in very limited ways.DiscussionWe propose that the increase in waste caused by face masks can be related to prevailing representations of single-use surgical masks and limited attention paid to environmental concerns.
... An increasingly important priority worldwide is to transform waste into a valuable resource for other applications, supporting the circular economy. The cement and concrete industry is one of the major sectors that is actively contributing toward a closed loop circular economy by incorporating a range of industrial byproducts and waste materials [1][2][3], such as, fly ash (FA) [4,5], slag [6,7], waste tire rubber [8][9][10][11][12], recycled concrete aggregate [13,14], organic waste [15] and medical waste [16][17][18][19]. However, the production of cement accounts for around 5-7% of global greenhouse gas emissions [20,21]. ...
The cement industry is responsible for about 5–7% of global greenhouse gas emissions and with the rapid rise in global warming, it is imperative to produce an ecofriendly alternative to Portland cement. Fly ash (FA) is an abundantly available and least utilized industrial byproduct with good pozzolanic properties that can help reduce the carbon footprint of cement composites. We investigated replacing 80% of the cement content with different blends of FA, nanosilica (NS) and silica fume (SF). Hydrated lime and a set accelerator were used to increase the pozzolanic reactivity of the blended cement composites. The portlandite released with 20% cement content was insufficient for the pozzolanic reaction of the blended cement composites containing FA and SF, requiring externally added hydrated lime. The addition of a set accelerator significantly increased the pozzolanic reaction and the resultant compressive strength, and these increased with the increasing content of the set accelerator. The replacement of SF with NS led to a remarkable increase in the pozzolanic reaction. The corresponding compressive strength of FA mixed with cement composites increased with increasing percentage composition of NS.
Disposable Surgical Face Masks (SFMs) are being used in the fight against Corona VIrus Disease-19 (COVID-19) during the pandemic. Since SFMs are made of polymers, their mass production causes severe environmental pollution. To reduce the SFM pollution, we have synthesized ash from the SFMs by incineration. A simple solution casting method is used to blend the surgical face mask ash (SFMA) with biodegradable hydroxypropyl methylcellulose polymer (HPMC). We have successfully adopted the Thermally Induced Phase Separation (TIPS) method to fabricate HPMC–SFMA films using water as the solvent. The successful incorporation of SFM-derived ash into the HPMC matrix was confirmed by FT-IR and FE-SEM characterization techniques. The addition of SFMA to the HPMC matrix has implications for Young’s modulus, as well as their biodegradation behavior. The incorporation of SFMA in the HPMC matrix changes its stiffness and elasticity, potentially affecting the film’s mechanical performance. Furthermore, while HPMC is biodegradable, the inclusion of SFMA hinders its biodegradation rate and enhances the life span of HPMC. Hence, the HPMC–SFMA films would be a promising candidate for agricultural mulching and this work leads to a conceptual basis for the production of novel materials in agricultural mulching.
Since the outbreak of the COVID-19 pandemic, the discarded face masks have attracted widespread attention in society. In line with sustainable development, a physicochemical treatment method was used to recycle discarded face masks into styrene–butadiene–styrene (SBS) modified bitumen. Utilizing the highly adhesive polydopamine-polyethyleneimine (PDA-PEI) coating, it has improved the surface damage of the discarded face mask fibers (DFMF) caused by natural aging and mechanical fragmentation, simultaneously strengthening the connection between the fibers and bitumen. At 46 °C, the 2% embellish-face mask fiber (E-FMF)/SBS modified bitumen, compared to the 2%DFMF/SBS modified bitumen, exhibited improvements in complex modulus (G*), elastic modulus (G′), and loss modulus (G″) by 12.27%, 16.39%, and 13.35%, respectively. Furthermore, at 0.1 kPa and 3.2 kPa, the creep recovery rate (R) increased by 23.3% and 32%, and the average creep compliance (Jnr) decreased by 54.7% and 64%. It was demonstrated that DFMF adhered with the coating, were more effective in improving the mechanical properties, deformation resistance, and shear resistance of the bitumen. This approach enriches the application scenarios of discarded single-use face masks and supports environmental protection and road construction.
Graphical Abstract
Cementitious composites (CC) have continuously advanced in recent years, owing to their abundant resources, well-established production methods, and remarkable versatility in civil engineering and construction applications. However, one aspect of CC that has received significant attention and improvement is its microstructure, primarily due to its inherent heterogeneity. At the microscale level, incorporating multiple independent polypropylene (PP) fibers into CC has demonstrated the potential to address its intrinsic weaknesses effectively. A novel research area involves integrating recycled PP fibers from single-use facemasks (SUF) into CC, producing environmentally friendly fiber-reinforced cementitious composites (FRCC) which can enhance microstructure characteristics. This study utilized locally available CC constituents combined with PP fibers sourced from SUF, resulting in a specimen with a fiber volume content of 0.40%. Scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS) were employed to analyze the microstructure and elemental composition of the specimen. The findings indicate that incorporating PP fibers from SUF resulted in notable improvements in the CC microstructure than the adjacent host cementitious matrix by producing a denser cement matrix, effectively reducing micropores and voids, exhibiting smaller microcracks, and establishing good fiber-matrix compatibility.
The overall objective of this work was to conduct a critical literature review on the application of the circular economy (CE) hierarchy for the management of COVID-19 healthcare waste (HCW). To describe the problem created by COVID-19 HCW, first, the subsystems of the overall management system, including generation, segregation, classification, storage, collection, transport, treatment and disposal, were reviewed and briefly described. Then, the CE hierarchy using the 10R typology was adapted to the management of COVID-19 HCW and included the strategies Refuse, Reduce, Resell/Reuse, Repair, Reprocess, Refurbish, Remanufacture, Repurpose, Recycle and Recover (energy). Disposal was added as a sink of residues from the CE strategies. Using the detailed 10R CE hierarchy for COVID-19 HCW management is the novelty of this review. It was concluded that R-strategy selection depends on its position in the CE hierarchy and medical item criticality and value. Indicative HCW components, which can be managed by each R-strategy, were compiled, but creating value by recovering infectious downgraded materials contaminated with body fluids and tissues is not currently possible. Therefore, after applying the circular solutions, the end of pipe treatment and disposal would be necessary to close material cycles at the end of their life cycles. Addressing the risks, knowledge gaps and policy recommendations of this article may help to combat COVID-19 and future pandemics without creating environmental crises.
During the pandemic period, people have used various personal protective equipment including gloves, facemask and face shields. Among them, disposable facemask play a critical role to control the spread of COVID-19, that situation lead to occurring huge amount waste materials. Hence, there is urgent need to evaluate and suspend such waste materials from environment. Herein, we have investigated the potential use of disposable facemask as oil sorbent material for efficient oil/water separation. Due to their hydrophobic/oleophilic character of PP based disposable facemask. Some structural characterization techniques are employed to examine the facemask. A number of tests including absorbency, oil/water separation stability in oils and waters, selective removal of oils in different water medium have been systematically investigated. The outcomes show that waste facemask have great potential in the field of oil-water separation that achieve selectively separate the oil from oily wastewater.
There are numerous manuals to guide practitioners in utilizing traditional additives in the construction of road, rail and dam construction but they fall short of specific guidance for non-standard additive-based ecofriendly and cost-effective soil stabilization. Increased attention has recently been on the use of non-standard additives for stabilizing weak soils due to environmental and cost concerns associated with traditional additives. We summarize the specific guidelines of using environmental-friendly enzymes to treat weak soils. We elaborate on the requirements and specifications for the Eko-Soil multi-enzyme product that is manufactured from water and proteins extracted from fermented exudes of plants. Specific tests (laboratory and field) and conditions required for soil stabilization using Eko-Soil enzyme are elaborated using the experience of past construction projects. The guide also elaborates enhancing the efficiency of enzymatic soil stabilization by correctly incorporating the required mixing proportions and pre-requisite condition tests. Professionals and practitioners will benefit from using novel eco-friendly sustainable stabilization techniques in the treatment of weak soils covering many applications including roads, foundations, water containment areas, landfills, working platforms and slope erosion control.
Alum sludge is a typical by-product of the water industry. The traditional sludge management method, disposing of sludge in landfill sites, poses a critical environmental and economic concern due to a significant increase in sludge amount and disposal cost. In this paper, the feasibility of reusing sludge as cement replacement is investigated, and the physical performance and microstructure modification of concrete products made with sludge is discussed. The obtained results indicated that a satisfying pozzolanic reactivity of sludge after calcination at high temperatures and grinding to the appropriate size was identified. When 10% cement was replaced with sludge, the reaction degree of sludge was up to 39%, and the obtained concrete blocks exhibited superior mechanical performance. Based on the microstructural analysis, e.g., x-ray diffraction, thermogravimetric analysis, and advanced nanoindentation method, the high aluminum content in sludge was incorporated into C–(A)–S–H gel; the original “Al-minor” C–(A)–S–H gel in pure cement paste was converted to ‘Al-rich’ C–(A)–S–H gel. Also, sludge promoted the formation of aluminum-bearing hydrates, such as ettringite and calcium aluminate hydrates (C–A–H). Although the Al incorporation had no significant effect on the hardness and modulus of C–(A)–S–H gel, the homogeneous mechanical properties (hardness and modulus measured with nanoindentation) of binder paste degraded with increasing sludge ash content above 10%, attributing to the lower hardness of unreacted sludge than cement clinker and the relatively lower reaction degree. Using sludge in concrete products offers an economical and environmentally friendly way to dispose of sludge and preserve diminishing natural resources. Also, the reduction of cement usage may contribute to achieving carbon neutrality.
Delay in construction projects is a significant issue and concern for most construction companies. Many studies have addressed this issue by identifying the top-ranked causes, which vary according to project type, location, and the research method used. The combined factors of delay/time overrun need further analysis to understand the top-ranked factors considering the project context. We identified 360 delay/time overrun factors of construction projects from articles published in the past 10 years in top-quality journals ranked as per scientific journal ranking (SJR). The factors were then coded and classified into categories based on their impact and the description in NVIVO software. Finally, the categories were analyzed and ranked by the relative importance index using SPSS software to identify the critical ones in global construction projects. In addition, the developed and developing countries affected by these delay factors were determined. The results revealed that the top five important factors are located under the following categories: orders and requirements; experience and productivity; financial problems; planning; and lastly both external and management categories. These categories were the highest ranking among the five top factors found in the reviewed studies and affect both developed and developing countries.
Alkali–silica reaction (ASR) is one of the most recognized chemical reactions that lead to the deterioration and premature failure of concrete. The severity of ASR is largely dependent on the expansive nature of the reaction product (ASR gel). As such, it is important to expound the developed knowledge on the formation, structure, composition, and swelling mechanism of ASR gel, to provide a greater understanding of ASR deterioration and to facilitate the development of more reliable prediction and mitigation methods. We present a summary of existing methods for assessing ASR and the state-of-the-art techniques that use neutron and X-ray scattering methods to characterize the nano- and microstructural properties of concrete and elucidate the potential transport dynamics of reactants that determine the mechanism and extent of ASR.
The alkali–silica reaction (ASR) can cause expansion, cracking, and degradation of the mechanical properties of affected concrete. Concerns about the safety of ASR-damaged reinforced concrete structures have driven the demand for studying the effects of ASR on residual load capacity of the deteriorated structure. Conventionally, field load testing methods are used to assess the residual load capacity of ASR-affected structures. In this study, a novel accelerated laboratory test using the LVSA 50/70 autoclave to accelerate ASR was applied to investigate the flexural and shear behavior of small-scale reinforced concrete beams affected by ASR. The specimens were subjected to three cycles of 80 °C steam curing at atmospheric pressure in the autoclave, with 60 h/cycle. Significant expansion and ASR damage were observed. Load carrying capacity tests on the small-scale reinforced concrete beams showed that, at the expansion levels achieved, the flexural capacity of the reinforced concrete beams was not significantly affected. Shear resistance of the reinforced concrete beams, however, was found to increase compared with their 28-day counterparts, which could be attributed to the prestressing effect due to ASR expansion. It appears that the multicycle 80 °C steam-curing autoclave test is suitable for investigating ASR deterioration of actual concrete mixes within a short period of time. ASR effects on the load carrying capacity of reinforced concrete elements at higher expansion levels, however, need further investigation.
A machine learning (ML) technique was used to assist in the dynamic analysis of mixed geometric and material nonlinearities of real-life engineering structures. Various types of inputs of system properties were considered in the 3D dynamic geometric elastoplastic analysis, giving a series of realistic nonlinear descriptions of complex, large deformation structural behaviors. To resolve the numerical challenges of solving the mixed nonlinear problems, a newly established ML technique using a new cluster-based extended support vector regression (X-SVR) algorithm was applied. With this technique, a surrogate model can be built at each time step in the Newmark time integration process, which can then be used to predict the deflection, force and stress of the relevant structural performance at different loading time stages. To demonstrate the accuracy and efficiency of the proposed framework, practical engineering applications with linear and nonlinear properties are fully demonstrated, and the nonlinear behavior of the structure under predicted working conditions in the future was predicted and verified in numerical studies.
Microbially induced calcium carbonate precipitation is effective in achieving self-healing of concrete cracks when the bacteria are well protected in concrete with a high pH and dense microstructure. Calcium alginate hydrogels are appropriate for encapsulating bacteria in concrete due to the mild environment with rich moisture in the hydrogels. Nevertheless, the low alkaline tolerance and breakage ratios of the hydrogels after concrete cracking restrict their applications in concrete. To address these problems, nanosilica was doped into calcium alginate hydrogels with encapsulated bacterial spores to react with the Ca(OH) 2 surrounding hydrogels in concrete. Due to the modification by nanosilica, the bond of the hydrogels with cement matrix was enhanced as needle-like C–S–H was generated at the interface after hydration for 7 days. Moreover, the urease activity of the encapsulated spores in the modified hydrogels was higher than that in plain hydrogels after submersion in saturated Ca(OH) 2 solution or simulated concrete solution for 7 days. Therefore, it can be concluded that nanosilica holds promise for modifying hydrogels to improve the effectiveness of encapsulated bacterial spores for self-healing of concrete.
The alkali–silica reaction (ASR) is one of the most harmful distress mechanisms affecting concrete infrastructure worldwide. The reaction leads to cracking, loss of material integrity, and consequently compromises the serviceability and capacity of the affected structures. In this study, a modeling approach was proposed to simulate ASR-induced expansion considering three-dimensional stress/restraint conditions, and its impact on the structural capacity of reinforced concrete members. Both the losses in concrete mechanical properties and prestressing effects induced by the expansion under restraints are taken into account in the model. Validation of the developed model is conducted using reliable experimental datasets derived from different laboratory testings and field exposed sites. With the capability of modelling both ASR-induced expansion and its impact on structural capacity, the model provides valuable results to specify effective repair and/or mitigation strategies for concrete structures affected by ASR.
Limestone calcined clay cement (LC3) is a new type of cement that contains Portland cement, calcined clay, and limestone. Compared with traditional cement clinker, LC3 reduces CO 2 emissions by up to 40%, and is a promising technology for the cement industry to achieve its emission target. We used a numerical approach to predict the optimum composition of LC3 mortar. The experiments were performed using central composite rotational design under the response surface methodology. The method combined the design of mixtures and multi-response statistical optimization, in which the 28-day compressive strength was maximized while the CO 2 emissions and materials cost were simultaneously minimized. The model with a nonsignificant lack of fit and a high coefficient of determination (R ² ) revealed a well fit and adequacy of the quadratic regression model to predict the performance of LC3 mixtures. An optimum LC3 mixture can be achieved with 43.4% general purpose cement, 34.16% calcined clay, 20.6% limestone and 1.94% gypsum.
The alkali–silica reaction (ASR) is a severe durability issue in cement-based materials. Although using calcium-rich supplementary cementitious materials (SCMs) such as ground granulated blast-furnace slag (GGBS) is beneficial for improving mechanical performance, it can lead to critical ASR-induced damage, primarily when high-reactive aggregates are used. We used alum sludge, a byproduct of drinking water treatment processes, and found it to have high efficiency in mitigating ASR in mortars containing GGBS as cement replacement and waste glass as high-reactive aggregate. The raw alum sludge was calcined for 2 h at 800 ℃ and ground to pass a 75-µm sieve. Ternary blended binders were made by replacing 10, 20 and 30% of cement with the mixture of alum sludge and GGBS (ratio 1:1). The mortar samples exhibited a considerable compressive strength and significant ASR resistance when 30% of cement was replaced with the mixture of alum sludge and GGBS compared with the reference samples. Microstructural characterization using X-ray diffraction, backscattered electron images and energy-dispersive X-ray spectroscopy indicated that increasing the aluminum content of the alum sludge could prevent the formation of detrimental Ca-rich and low-flowable ASR gels. The hindering effect was attributed to the alkaline binding ability and the extra precipitation of calcium aluminum silicate hydrate phases due to the abundant Al in the binder.
3D printing by means of fused filament fabrication involves extruding and depositing melted material in layers to produce a 3D part. Current 3D printing requires manual intervention from a human operator between prints, leading to inefficiency. The focus of this study was facilitating the automation of the additive manufacturing process. Based on suggestions for future works in this field, this study extended on automated 3D-part removal systems by implementing additional operations to automate the production process. The proposed system uses robotic arms and grippers to operate and maintain 3D printers; specifically, the removal of 3D-printed parts, the cleaning of printer beds, the application of glue to the printer beds to assist with print adhesion, and the monitoring of bed levelness. The importance of this contribution is the improved efficiency of 3D-printing production, allowing for continuous 3D-printer operation and decreasing the requirement for human interaction and monitoring in the production process. The system is demonstrated using a 7 degrees of freedom KUKA robotic arm and ROBOTIQ gripper to autonomously operate and maintain an Ender 3 V2 printer. Sensor data and information from the 3D printers was used to determine the required operation or function to be performed by the robotic system. Tasks were performed by automated movement sequences of the robotic arm and gripper using supplied data. System status was recorded for monitoring and alerting human operators when intervention was required. The implementation of these functions using an automated robotic system allows 3D-printing production to operate continuously for longer periods, increasing production efficiency as downtime and human involvement for maintenance between prints is minimized.
We investigated the formation of the conductive network of carbon nanotubes (CNTs) in alkali-activated nanocomposites for sulfate-sensing applications. The matrix was a one-part blend of fly ash and ground granulated blast-furnace slag, activated by sodium silicate and water. Sodium dodecylbenzenesulfonate was used as the surfactant for dispersion of the CNTs in the aqueous media. The nanocomposites were investigated by a laboratory-developed setup to study the electrical and sensing properties of the alkali-activated material. The electrical properties (i.e., conductivity) were calculated and assessed to discover the percolation threshold of the nanocomposites. Furthermore, the sensing behavior of nanocomposites was studied upon sulfate ( $${\mathrm{SO}}_{4}^{2-}$$ SO 4 2 - ) exposure by introduction of sulfuric acid ( $$({\mathrm{H}}_{2}{\mathrm{SO}}_{4})$$ ( H 2 SO 4 ) ) and magnesium sulfate ( $${\mathrm{MgSO}}_{4}$$ MgSO 4 ). The sensors were able to preliminarily exhibit a signal difference based on the introduced media ( $${\mathrm{H}}_{2}{\mathrm{SO}}_{4} \&\mathrm{ Mg}{\mathrm{SO}}_{4}$$ H 2 SO 4 & Mg SO 4 ), CNT content and $${\mathrm{H}}_{2}{\mathrm{SO}}_{4}$$ H 2 SO 4 volumetric quantity. The results of this research demonstrated a sensing potential of CNT alkali-activated nanocomposites and can be applied in the concrete structural health monitoring.
Lightweight concrete (LWC) has been used for more than 2000 years, and the technical development of waste-based LWC is still proceeding. Notably, the very first representative concrete mix of infrastructural LWC was introduced for building a family house in Berlin, Germany, a few decades ago. The unique and distinctive combination of waste-based LWC successfully creates an appealing alternative to traditional concrete aggregates in terms of durability, robustness, cost, energy-saving, transportation, environmental advantages, innovative architectural designs and implementations, and ease of construction. Numerous researchers have attempted to utilize waste materials to produce LWC, aiming to bring both ecological and economical solutions to the construction industry over the past few decades. Waste materials, such as crushed glass, waste tire rubber, masonry rubber, chip rubber, plastics, coconut shells, palm oil fuel ash, palm kernel shells, fly ash, and rice husks, possess lower specific gravity than traditional concrete aggregates. Thus waste-based LWC can be a significant replacement for conventional raw materials (cementitious material and aggregates) as it requires less strength than conventional concrete for both structural and non-structural applications. Although waste-based LWC is well recognized and has proven its scientific potential in a broad range of applications, there are still uncertainties and hesitations in practice. Therefore, the primary objective of this study was to demonstrate the current state-of-the-art understanding and advancement of waste-based LWC over the past decades. Furthermore, an equally critical discussion is reported to shed light on the potential benefits of LWC. We highlight how the performance of LWC has been enhanced significantly over the period, and understanding of the properties of waste-based LWC has advanced.
Waterborne coatings with intended functionalities have been designed by manipulating acrylic-based nanocomposites with different nanostructures. Taking advantage of the favorable structure of acrylic copolymers, three waterborne coatings with various desired properties were created through molecular engineering either by copolymerizing with other components or through nanocomposite formation. This approach was demonstrated by synthesizing acrylic-based waterborne coatings with three different nanostructures, namely homogeneous, worm-like, and spherical-like nanostructures. The properties of coating samples prepared by this new approach and by traditional physical blending were compared experimentally, which revealed that the incorporation of 3-methacryloxypropyltrimethoxysilane (MPS)-modified nanoparticle TiO 2 in an acrylic base enabled the formation of a nanocomposite with nanoparticles uniformly distributed in the acrylic base. The coating film with this acrylic-TiO 2 nanocomposite showed significantly better UV absorption performance than the coating made by physical blending. The copolymerization of acrylic copolymers with an organic polymer (alkyd) created a worm-like nanostructure of acrylic–alkyd composite that allowed uniform distribution of the acrylic–alkyd nanocomposite in a more closely packed dense coating film, leading to enhanced barrier property and significantly improved corrosion resistance as confirmed by electrochemical impedance spectroscopy and salt spray tests. The copolymerization of acrylic monomers with an inorganic polymer (polydimethylsiloxane [PDMS]) led to a spherical-like nanostructure of acrylic–PDMS composite film. The formation of this nanostructure arose from the migration of PDMS segments, and a PDMS-rich phase formed on the film’s surface, which resulted in a coating film with PDMS functionalities such as low dirt-picking behavior. Overall, these three cases demonstrated that acrylic copolymer are an excellent base for developing various nanocomposite waterborne coatings with different functionalities through copolymerization and that the nanocomposites with different nanostructures have a significant influence on the coatings’ performance.
Driven by government policy and incentives, solar power production has soared in the past decade and become a mainstay during the worldwide clean-power transition process. Among the various next-generation photovoltaic technologies, perovskite solar cells (PSCs) are the most important emerging area of research due to their outstanding power conversion efficiency and affordable scale-up operation. We adopted the nonlocal strain gradient theory and the first-order shear deformation plate theory to investigate the size-dependent free vibration behavior of PSCs. The size-dependency in the nanostructure of the PSCs was captured by coupling the nonlocal and strain gradient parameters. In accordance with the Hamilton principle, the governing equations set was derived. Subsequently, the Galerkin procedure was applied to address the dynamic characteristics analysis of PSCs with simply supported and clamped edges. Compared with the size-insensitive traditional continuum plate model, the current multiscale framework revealed a size effect on the free vibration of the PSC. Moreover, some parametric experiments were conducted to explore the impacts of scale length parameter, nonlocal parameter, and boundary conditions on the natural frequency of the PSC.
Partly replacing Portland cement (PC) with lower carbon footprint cementitious materials such as ground granulated blast furnace slag (slag) is considered as a practical method for reducing CO 2 emissions in the cement concrete industry. To mitigate the slow reactivity of slag in a cementitious system and enhance early-age strength, the addition of a chemical activator is a solution. However, the effect of the activator on creep behaviour of slag-blended cement concretes remains unclear. This work presents the effect of sodium sulfate (Na 2 SO 4 ) activator on the compressive creep of PC concrete blended with 50 and 70 wt% slag. Four concrete mixes (with and without 2.5% Na 2 SO 4 activator) containing 395 kg of cementitious material were prepared. The creep strain measurements were conducted on 150 × 300 mm cylindrical specimens for 140 days under sustained compressive load. The results showed that the 70% slag concrete had lower creep strain than 50% slag-blended cement concrete. The presence of Na 2 SO 4 helped reduce the creep strain of 50% slag concrete but slightly increased that of 70% slag-blended cement concrete. In addition, the applicability of the predictive model in AS3600:2018 for the creep behaviour of high slag content concrete was assessed.
Polycarboxylate superplasticizer is typically used to prepare a high-quality graphene oxide (GO) solution before mixing with cement grains. However, even if GO is well dispersed in water, they tend to re-agglomerate in the alkaline cement hydration environment, thus seriously decreasing the workability of the fresh mixture. In this study, we propose a more targeted method by synthesizing GO-coated silica fume (SF) to promote the utilization of GO in cement-based materials. Specifically, the surface of pristine SF was modified to convert their zeta potential (modified SF: MSF), then GO-coated SF (i.e., MSF@GO) was prepared via electrostatic adsorption of GO onto the MSF surface. The experimental results revealed that adding 5MSF@GO hybrid (0.04% GO and 5% MSF, by weight of binder) significantly reduced yield stress and plastic viscosity by 51.5% and 26.2%, respectively, relative to the 0.04% GO-modified sample. These findings indicated that application of GO-coated SF is an effective and environmentally friendly way to develop sustainable cementitious composites.
Nanocellulose (NC) is a promising reinforcing material for cementitious composites, but its effect on the mechanical properties of hybrid engineered cementitious composites (ECCs) has not been studied. In this paper, we investigated a hybrid polyethylene (PE)-steel fibre ECC reinforced with NC and the effect of NC dosages ranging from 0.1% to 0.4% on the compressive strength of the hybrid ECC. The optimum quantity of NC for the best mechanical property of ECC was determined. Enhancement of compressive strength was observed for all the mixes with NC compared with the reference mix, and the mix containing 0.2% NC showed the maximum improvement.
In real-life engineering, non-probabilistic structural information is very common in many and varied disciplines. This class of information is characterized by incompleteness and imprecision, such as interval, fuzzy sets, etc. Non-probabilistic structural information can be reflected in the structural performance and cause it to fluctuate within a specific range, instead of being deterministic. Thus, without appropriate consideration of non-probabilistic information, serious or even disastrous accidents may occur. Therefore, fully estimating the structural health status using non-probabilistic information, especially detecting the lower and upper bounds of the concerned structural response, is extremely significant in uncertainty-sensitive fields. To conquer this challenge, a virtual modeling technique underpinning a structural health assessment framework is introduced. The twin extended support vector regression (T-X-SVR) approach is embedded for virtual model construction. Continuous, differentiable expression of the established virtual model allows the optimal solutions for each interval analysis to be easily achieved. Information update is another inherent feature, which enables structural health assessment to be implemented with updated conditions without rebuilding the virtual model. To demonstrate the applicability of the proposed virtual modeling technique underpinned structural health assessment framework, the non-probabilistic informed elastoplastic nonlocal damage analysis was investigated for engineering structures.
The effective application of lightweight stay-in-place concrete forms for casting shear walls subjected to wind and seismic loading is of particular concern to practitioners. Insufficient technical data available for new kinds of wall systems, such as Polyvinyl Chloride (PVC) form walls, hinder their implementation in construction practice. To that end, an effective experimental and numerical campaign was launched at Western Sydney University to investigate the structural performance of PVC form walls when subjected to in-plane shear loading. A set of push-out specimens was designated to conduct monotonic in-plane shear tests until failure. All failure phenomena, capping strengths, and ductility capacities were monitored. Test results indicated that the embedded PVC latticed webs could efficiently protect the concrete web from sudden crushing and improve ductility capacity and failure pattern of the specimens. Nonlinear finite element analysis on test specimens was also conducted and good correlation with experiment results was achieved.
Sharer (referring to storyteller: Siyi Guan) has utilized autoethnography as a methodology to redact and share her own startup experience on the basis of personal business project. The first section comprises the narration of sharer’s personal startup experience, which is followed by the problem statement confronted during the project process, with the introduction of the research design of its methodology at the same time. There have been 5 interviewees participating in this research. Nvivo is utilized to extract the interview data along with its high-frequency words in written form after interviews. Ultimately, the overall project orientation process and future suggestions are elaborated. Keywords: Autoethnography; Startup experience; Environment; Face Masks
Determining the graphene oxide (GO) content is the key to applying GO to reinforce the mechanical performance and durability of cementitious composites. However, most of the previous studies are conducted from the perspective of experiments and lack elaboration on the mechanism of the GO-reinforced cementitious composite under different GO content. Hence, we investigated the effect of GO content on the reinforcing efficiency of calcium–silicate–hydrate (C–S–H) to trade off the enhancement of GO in cementitious composites and the corresponding economic benefits. The results demonstrated that an appropriate number of GO nanosheets can reinforce the cementitious composite with simultaneous high enhancing efficiency and economic benefits. The microdamage evolution of GO/C–S–H composites and the GO reinforcing mechanisms are reported. Our findings deepen the understanding of the enhancing mechanisms of GO embedded in C–S–H nanocomposites and help to determine the suitable GO content in practical engineering.
We report the outcomes of a study into the influence of alkali concentration on expansion induced by the alkali–silica reaction (ASR), a deleterious reaction that causes cracking and durability loss in concrete structures. We assessed the effect of alkali concentration on mortar bar expansion using a modified form of AS1141.60.1, the accelerated mortar bar test (AMBT). Mortar prisms were prepared with a reactive aggregate and immersed in alkali solutions of varying concentrations (from 0.4 to 1.0 M NaOH) and saturated limewater at 80 °C. Expansion was monitored for 28 days. The degree of expansion was observed to increase with increasing alkali concentration and an induction period prior to expansion was observed for the 0.4 M NaOH. No expansion was observed for mortar bars immersed in the control saturated lime water bath. Additionally, no expansion was observed for mortars using blended cements containing fly ash (FA) and ground granulated blast furnace slag, suggesting the AMBT is a viable technique for demonstrating the efficacy of mitigation strategies.
The COVID-19 pandemic not only has created a global health crisis but also has dramatic effects on the environment. To fight the spread of Coronavirus, governments imposed social distancing policies, which caused negative and positive impacts on the environment. Victoria, the second-most populated state in Australia, was hit by two waves of COVID-19. During the second wave of the pandemic, Victoria, especially Melbourne, experienced one of the most stringent and longest lockdowns globally. In this study, the changes in mobility trends, traffic, air pollution, noise pollution, and waste generation during the first and second waves of COVID-19 in Victoria are evaluated and compared. It was observed that the pandemic had both positive and negative impacts on the environment. During the second wave of the pandemic in Victoria, the mobility trends of public transport hubs, retail and recreation venues, and workplaces experienced a significant drop in movements at respective values of 85%, 83%, and 76% compared to the period of 5 weeks from 3 January to 6 February 2020. PM2.5 levels were lower by 23% at Alphington and 24% at Footscray from 16 March to 1 May 2020 compared with the average PM2.5 levels in the past 4 years. It was estimated that the respective daily generations of used face masks during the first wave and second wave of the pandemic in Victoria were approximately 104 and 160 tons.
Currently, there is no effective vaccine for tackling the ongoing COVID-19 pandemic caused by SARS-CoV-2 with the occurrence of repeat waves of infection frequently stretching hospital resources beyond capacity. Disease countermeasures rely upon preventing person-to-person transmission of SARS-CoV2 so as to protect front-line healthcare workers (HCWs). COVID-19 brings enormous challenges in terms of sustaining the supply chain for single-use-plastic personal and protective equipment (PPE). Post-COVID-19, the changes in medical practice will drive high demand for PPE. Important countermeasures for preventing COVID-19 transmission include mitigating potential high risk aerosol transmission in healthcare setting using medical PPE (such as filtering facepiece respirators (FFRs)) and the appropriate use of face coverings by the general public that carries a lower transmission risk. PPE reuse is a potential short term solution during COVID-19 pandemic where there is increased evidence for effective deployment of reprocessing methods such as vaporized hydrogen peroxide (30 to 35% VH2O2) used alone or combined with ozone, ultraviolet light at 254 nm (2000 mJ/cm²) and moist heat (60 °C at high humidity for 60 min). Barriers to PPE reuse include potentially trust and acceptance by HCWs. Efficacy of face coverings are influenced by the appropriate wearing to cover the nose and mouth, type of material used, number of layers, duration of wearing, and potentially superior use of ties over ear loops. Insertion of a nose clip into cloth coverings may help with maintaining fit. Use of 60 °C for 60 min (such as, use of domestic washing machine and spin dryer) has been advocated for face covering decontamination. Risk of virus infiltration in improvised face coverings is potentially increased by duration of wearing due to humidity, liquid diffusion and virus retention. Future sustained use of PPE will be influenced by the availability of recyclable PPE and by innovative biomedical waste management.
The origin of the novel human coronavirus (SARS-CoV-2) and its potential for harm increased face mask and medical waste in the environment, thereby necessitating the urgent prevention and control of the pandemic. The article estimates the face mask and medical waste generation in Asia during the pandemic to convince the waste management and scientific communities to find ways to address the negative impact that the waste disposal has on the environment. Standardisation, procedures, guidelines and strict implementation of medical waste management related to COVID-19, community habitats and public areas should be carefully considered to reduce pandemic risks in hospitals, as proper medical waste disposal effectively controls infection sources.
Introduction
One of the serious consequences of the SARS-CoV-2 pandemic is the shortage of protective equipment for health personnel. N95 masks are considered one of the essential protective equipment in the management of patients with COVID-19. The shortage of N95 masks implies potential health risks for health personnel and significant economic losses for the health institution. The objective of this work was to investigate the disinfection of N95 masks artificially contaminated with SARS-CoV-2 and ESKAPE bacteria by using hydrogen peroxide plasma.
Material and methods
We examined the disinfection capacity of hydrogen peroxide plasma against the SARS-CoV-2 and two members of the ESKAPE bacteria (Acinetobacter baumannii and Staphylococcus aureus) through a study of artificial contamination in situ of N95 masks. Amplification of specific genes by RT-PCR of SARS-CoV-2 and microbiological culture of ESKAPE bacteria was performed before and after the disinfection process.
Results
SARS-CoV-2 was not detected in all assays using five different concentrations of the virus, and A. baumannii and S. aureus were not cultivable with inoculums of 10² to 10⁶ CFU after disinfection tests of N95 masks with hydrogen peroxide plasma.
Conclusion
Disinfection of N95 masks by using the hydrogen peroxide plasma technology can be an alternative for their reuse in a shortage situation. Implications for the use of disinfection technologies of N95 masks and the safety of health personnel are discussed.
Plastics have been on top of the political agenda in Europe and across the world to reduce plastic leakage and pollution. However, the COVID-19 pandemic has severely disrupted plastic reduction policies at the regional and national levels and induced disruptive changes in plastic waste management with potential for negative impacts in the environment and human health. This paper provides an overview of plastic policies and discusses the readjustments of these policies during the COVID-19 pandemic along with their potential environmental implications.
The sudden increase in plastic waste and composition due to the COVID-19 pandemic underlines the crucial need to reinforce plastic reduction policies (and to implement them into action without delays), to scale up in innovation for sustainable and green plastics solutions, and to develop dynamic and responsive waste management systems immediately.. Policy recommendations and future research directions are discussed.
Plastics are essential in society as a widely available and inexpensive material. Mismanagement of personal protective equipment (PPE) during COVID-19 pandemic, with a monthly estimated use of 129 billion face masks and 65 billion gloves globally, is resulting in widespread environmental contamination. This poses a risk to public health as a vector for SARS-CoV-2 virus, which survives up to 3 days on plastics, as well as impacts to ecosystems and organisms more broadly functions. Concerns over the role of reusable plastics as vectors for SARS-CoV-2 virus contributed to the reversal of bans on single-use plastics, highly supported by the plastic industry. While not underestimating the importance of plastics in the prevention of COVID-19 transmission, it is imperative not to undermine recent progress made in the sustainable use of plastics. There is a need to assess alternatives that allow reductions of PPE and reinforce awareness on the proper public use and disposal. Finally, assessment of contamination and impacts of plastics driven by the pandemic will be required once the outbreak ends.
Background
The need for protective masks greatly exceeds their global supply during the current COVID-19 pandemic.
Methods
We optimized the temperature used in the dry heat pasteurization method to destroy pathogens and decontaminate masks while retaining their filtering capacity.
Results
The current study showed that dry heat at both 60°C and 70°C for one hour could successfully kill six species of respiratory bacteria and one fungi species, and inactivate the H1N1 indicator virus. After being heated at 70°C for 1 h, 2 h, and 3 h, the N95 respirators and surgical face masks showed no changes in their shape and components. The filtering efficiency of bacterial aerosol for N95 respirators were 98%, 98%, and 97% after being heated for 1 h, 2 h, and 3 h, respectively, all of which were over the 95% efficiency required and similar to the value before being heated (99%). The filtering efficiency for surgical face masks was 97%, 97%, and 96% for 1 h, 2 h, and 3 h of heating, respectively, all of which were also similar to the value before being heated (97%).
Conclusions
This method can be used at home and can resolve the current shortage of masks.
The outbreak of the coronavirus disease 2019 (COVID-19) pandemic not only has created a health crisis across the world but is also expected to impact negatively the global economy and societies at a scale that is maybe larger than that of the 2008 financial crisis. Simultaneously, it has inevitably exerted many negative consequences on the geoenvironment on which human beings depend. The current paper articulates the role of environmental
geotechnics in elucidating and mitigating the effects of the current pandemic. It is the belief of all authors that the COVID-19 pandemic presents not only significant challenges but also opportunities for the development of the environmental geotechnics field. This discipline should make full use of geoenvironmental researchers’ and engineers’ professional skills and expertise to look for development opportunities from this crisis, to highlight the
irreplaceable position of the discipline in the global fight against pandemics and to contribute to the health and prosperity of communities, to serve humankind better. In order to reach this goal while taking into account the specificity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the uncertainty of its environmental effects, it is believed that more emphasis should be placed on the following research directions: pathogen–soil
interactions; isolation and remediation technologies for pathogen-contaminated sites; new materials for pathogen contaminated
soil; recycling and safe disposal of medical wastes; quantification of uncertainty in geoenvironmental and epidemiological problems; emerging technologies and adaptation strategies in civil, geotechnical and geoenvironmental infrastructures; pandemic-induced environmental risk management; and modelling of pathogen transport and fate in geoenvironment, among others. Moreover, COVID-19 has made it clear to the environmental geotechnics community the importance of urgent international co-operation and of multidisciplinary research actions that must extend to a broad range of scientific fields, including medical and public health disciplines, in order to meet the complexities posed by the COVID-19 pandemic.
An appropriate amount of polypropylene fibre (PF) content is generally able to compensate for the low compressive strength of the recycled aggregate concrete. This mechanical strength is required to reliably estimate at the building site using partially and non-destructive testing methods. Therefore, in the present study, the compressive strength of concrete with PF at 0.1% by volume and different replacement levels of recycled coarse aggregate (RCA) was assessed using point load test (PLT) and Schmidt rebound hammer. According to the results, the sensitivity of the core specimens to the concentrated point load and the short size of PF in the failure zone of the PLT caused to appear a difference among the enhancement trends of PLI values by increasing the age. In addition, a two-variable equation between the rebound number and point load index (PLI) reliably predicted either strength of coarse natural concrete or recycled aggregate concrete or PRAC.
There are very limited researches carried out to investigate the influence of saturation degrees, freezing-thawing, and curing times on geotechnical properties of lime concrete (LC) and lime-cement concrete (LCC) due to the capillary action and changes in groundwater table. Subsequently, the primary goal of this research is to investigate the influence of these parameters on mechanical properties of LC and LCC using unconfined compression tests, namely uniaxial compressive strength (UCS), stress-strain behavior, deformability index (I D ), secant modulus (E S ), failure strain, bulk modulus (K), resilient modulus (M R ), brittleness index (I B ), and shear modulus (G). At first, the mechanical and chemical characteristics of the utilized materials were measured. Then, samples were made with an optimal amount of cement, lime, coarse-grained soil, fine-grained soil, and water. The samples were then exposed to saturation points extending from 0 to 100% after 14, 28, 45 and 60 curing days. Then, to consider the effect of amount of saturation on the mechanical properties, UCS tests were performed on some of the samples. Other LCC specimens were exposed to freezing-thawing conditions to consider the effect of this phenomenon on the mechanical properties as well. The results of more than 250 UCS tests demonstrated that the curing times significantly affected the strength of LC and LCC specimens. Moreover, it is not ideal and logical to utilize LC and LC columns at a profundity underneath or near the groundwater level, though it is reasonable to adopt LCC and LCC columns at a profundity beneath or near the groundwater level because of the immaterial effect of degrees of saturation on LCC. In addition, this study showed that extending the curing period and diminishing the saturation degree would increase the strength and mechanical properties of the LCC specimens. The results of freezing-thawing demonstrated a negligible increase in the strength of the LCC when the thawing process preceded the freezing process. However, the effect of freeze-thaw cycles on the strength properties of LCC may mostly be neglected.
Oil palm shell (OPS) is a biosolid waste in palm oil industry in the tropical countries which could be used as aggregate in concrete mixture. Since 1984, OPS has been experimented as natural lightweight aggregate in research studies to produce lightweight concrete (LWC). Medium and high-strength LWCs using OPS as coarse aggregate were successfully produced. However, higher drying shrinkage and lower mechanical properties for concretes containing higher volume of OPS are reported in previous studies. Therefore, OPS is not fit to be used as full coarse aggregate in concrete mixture and therefore, there should be an optimum OPS content in concrete. In this study, in a normal-weight concrete, normal coarse aggregate was replaced with OPS from zero to 100% with an interval of 20%. Tests such as slump, density, compressive strength in different curing conditions, splitting tensile strength, initial and final water absorptions, and drying shrinkage of cured and uncured specimens were conducted to find out optimum OPS content in concrete. From the test results, it could be summarized that OPS content should not exceed 60% of total volume of coarse aggregate.
A study was performed to assess the effects of magnetic water with different percentages of natural zeolite (NZ) on self-compacting concrete (SCC) mixes. Over the past decades, a limited number of studies were conducted by researches on the effects of magnetic water on SCC mixes. In addition, it seems that pozzolanic materials such as NZ can affect performance of magnetic water in SCC mixes. Following this, the present study was aimed to survey engineering properties of self-compacting concrete (SCC) containing magnetic water and NZ. To achieve this goal, slump flow, T50, V-funnel, L-box and visual stability index (VSI) were employed to evaluate the rheological properties of concrete mixes. Furthermore, hardened properties were investigated by means of compressive strength, splitting tensile strength, modulus of elasticity and water absorption tests. The concrete test results demonstrated that 20% NZ inclusion and magnetic water in SCC with the water–binder (W/B) ratio of 0.37 led to an optimum mix design and also this mixture could contribute to an increase in compressive strength, splitting tensile strength and modulus of elasticity up to 25%, 8% and 9%, respectively.
Although steel fibers have been used in cement and concrete composites for more than four decades, most of the steel fibers on the market today have been introduced prior to 1980. This is in sharp contract to the continuous progress and development in the cement matrix itself. Following a brief summary of the main properties and limitations of steel fi-bers used in cement based composites, this paper describes the rationale and technical background behind the develop-ment and design of a new generation of steel fibers for use in cement, ceramic and polymeric matrices. These fibers are engineered to achieve optimal properties in terms of shape, size, and mechanical properties, as well as compatibility with a given matrix. They are identified as Torex fibers. Typical tests results are provided and illustrate without any doubt the superior performance (2 to 3 times) of Torex fibers in comparison to other steel fibers on the market. The new fibers will advance the broader use of high performance fiber reinforced cement composites in structural applications such as in blast and seismic resistant structures, as well as in stand-alone applications such as in thin cement sheet products.
Coffee, the second most traded commodity and the second-largest beverage consumed around the world, is responsible for many environmental burdens in the form of spent coffee grounds (SCGs), a by-product from the brewing process of coffee. On the other hand, the carbon footprints and environmental impacts related to construction projects are very concerning. Therefore, researchers and industries have recently tried to move towards green construction practices. This paper presents an overview of utilisation of SCGs, as a promising green biowaste source, in the civil and construction industry. From the literature review conducted, it can be concluded that SCGs have potential use as aggregates in construction materials across a broad range of civil engineering applications. However, limited research and lack of evidence of successful practical applications in the field mean further comprehensive studies in this specific area is required.
One of the most practical ways to reduce the demand for natural aggregates in the construction industry and dispose of the construction and demolition (C&D) wastes in landfills is using recycled concrete aggregate (RCA) for pavement base and subbase applications. Previous researches have mainly concentrated on the engineering behavior of C&D aggregates under ambient temperature. Little research has been directed toward the possible impact of temperature on the performance of rubberized recycled concrete aggregate for pavement base/subbase applications. In this study, for the first time, the effects of freeze-thaw process on the engineering properties of RCA containing crumb rubber for pavement base and subbase applications were evaluated. The results show that the resilient modulus of the RCA/rubber blends subjected to freeze-thaw cycles was higher than that of the control samples (prepared and tested at constant room temperature of 25 o C). The unconfined compressive strength (UCS) of F-T samples (subjected to one-day freezing, followed by one-day thawing) was slightly lower than that of the control samples. It was found that the UCS value of T-F samples (subjected to one-day thawing, followed by one-day freezing) was remarkably higher than that of the control samples. Based on the preliminary experimental results, the blends of RCA and crumb rubber, as a low carbon concept and an economically viable option, can be used for pavement base/subbase subjected to freeze-thaw cycles.
Hydrocarbon contamination has been a challenging area of study in engineering geology (for example geotechnical, geo-environmental, and geological practices). Despite the relatively large number of investigations on the geotechnical and geological characteristics of hydrocarbon-contaminated soils, the improvement of these soils by fiber-reinforcement and interactions between contaminated soil and fibers have not been yet studied. In order to fill this scientific fact, standard compaction, direct shear, Unconfined Compressive Strength (UCS), and falling-head permeability tests were conducted on unreinforced and polypropylene (PP) fiber-reinforced Used Motor Oil (UMO)-contaminated sand bentonite mixtures. Accordingly, the shear strength is found to increase upon UMO contamination, while ductility is drastically decreased. UCS is impaired due to contamination and hydraulic conductivity is decreased. Results also reveal that despite the detrimental influence of UMO on the geotechnical properties of the soil, fiber reinforcement can contribute to direct shear, UCS, and ductility improvement. Hydraulic conductivity is found to slightly decrease initially and increase at high fiber contents.
Background
In the context of the ongoing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, the supply of personal protective equipment remains under severe strain. To address this issue, re-use of surgical face masks and filtering facepiece respirators has been recommended; prior decontamination is paramount to their re-use.
Aim
We aim to provide information on the effects of three decontamination procedures on porcine respiratory coronavirus (PRCV)-contaminated masks and respirators, presenting a stable model for infectious coronavirus decontamination of these typically single-use-only products.
Methods
Surgical masks and filtering facepiece respirator coupons and straps were inoculated with infectious PRCV and submitted to three decontamination treatments, UV irradiation, vaporised H2O2, and dry heat treatment. Viruses were recovered from sample materials and viral titres were measured in swine testicle cells.
Findings
UV irradiation, vaporised H2O2 and dry heat reduced infectious PRCV by more than three orders of magnitude on mask and respirator coupons and rendered it undetectable in all decontamination assays.
Conclusion
This is the first description of stable disinfection of face masks and filtering facepiece respirators contaminated with an infectious SARS-CoV-2 surrogate using UV irradiation, vaporised H2O2 and dry heat treatment. The three methods permit demonstration of a loss of infectivity by more than three orders of magnitude of an infectious coronavirus in line with the FDA policy regarding face masks and respirators. It presents advantages of uncomplicated manipulation and utilisation in a BSL2 facility, therefore being easily adaptable to other respirator and mask types.
The isolation wards, institutional quarantine centers, and home quarantine are generating a huge amount of bio-medical waste (BMW) worldwide since the outbreak of novel coronavirus disease-2019 (COVID-19). The personal protective equipment, testing kits, surgical facemasks, and nitrile gloves are the major contributors to waste volume. Discharge of a new category of BMW (COVID-waste) is of great global concern to public health and environmental sustainability if handled inappropriately. It may cause exponential spreading of this fatal disease as waste acts as a vector for SARS-CoV-2, which survives up to 7 days on COVID-waste (like facemasks). Proper disposal of COVID-waste is therefore immediately requires to lower the threat of pandemic spread and for sustainable management of the environmental hazards. Henceforth, in the present article, disinfection technologies for handling COVID-waste from its separate collection to various physical and chemical treatment steps have been reviewed. Furthermore, policy briefs on the global initiatives for COVID-waste management including the applications of different disinfection techniques have also been discussed with some potential examples effectively applied to reduce both health and environmental risks. This article can be of great significance to the strategy development for preventing/controlling the pandemic of similar episodes in the future.
Very limited research has been conducted to examine the shear behaviour of blended recycled waste materials using the large direct shear testing apparatus. In this study, a series of large-scale direct shear test (LDST) was undertaken to evaluate the effect of different sizes and different amounts of recycled tyre waste on the shear strength properties of recycled concrete aggregate (RCA) mixed with crumb rubber as pavement base/subbase application. The results of LDST indicated that RCA mixed with two different sizes (i.e., fine and coarse rubber) and three different percentages (i.e., 0.5%, 1% and 2%) of crumb rubber satisfied the shear strength requirements for use in pavement base/subbase applications. The introduction of both fine and coarse crumb rubber led to an increase in the apparent cohesion of RCA/rubber blends. However, beyond 0.5%, increasing the content of crumb rubber resulted in a decrease in the apparent cohesion. Based on the results of the laboratory testing undertaken in this research, a rational and useful model was proposed to estimate the shear strength parameters of RCA incorporating crumb rubber.
•New challenges in MSW management in Tehran after the COVID-19 pandemic was studied.•Over 5.5 millions of PPEs are being daily discarded in Tehran during COVID-19.•Hospital wastes are being disposed of without undergoing any treatment in Tehran.•Landfilling of MSW has increased by 34.7% after the outbreak of COVID-19.•Secondary contagion from improper management of MSW is probable in Tehran.
This Opinion Paper wishes to provide a summary of recent findings and solutions for a better understanding of the environmental and health problems associated with COVID-19. The list of topics covered is large: meteorology and air quality factors with correlation number of infections, sewage waters as a way to reveal the scale of COVID-19 outbreak, current hospital disinfection procedures and new eco-friendly technologies and list of drug therapies recommend waiting for the desired vaccine to come. During the last two months we did notice an increase in the scientific literature regarding COVID-19 with a partial vision of this problem. The current Opinion Paper is one of the first attempts, to my understanding, to summarize and integrate environmental and human health aspects related to the monitoring, fate and treatment solutions for COVID-19. That being said I believe that this Opinion Paper can serve as multipurpose document, not only for scientists of different disciplines but for social media and citizens in general.
The COVID-19 pandemic has had growing environmental consequences related to plastic use and follow-up waste, but more urgent health issues have far overshadowed the potential impacts. This paper gives a prospective outlook on how the disruption caused by COVID-19 can act as a catalyst for short-term and long-term changes in plastic waste management practices throughout the world. The impact of the pandemic and epidemic following through the life cycles of various plastic products, particularly those needed for personal protection and healthcare, is assessed. The energy and environmental footprints of these product systems have increased rapidly in response to the surge in the number of COVID-19 cases worldwide, while critical hazardous waste management issues are emerging due to the need to ensure destruction of residual pathogens in household and medical waste. The concept of Plastic Waste Footprint (PWF) is proposed to capture the environmental footprint of a plastic product throughout its entire life cycle. Emerging challenges in waste management during and after the pandemic are discussed from the perspective of novel research and environmental policies. The sudden shift in waste composition and quantity highlights the need for a dynamically reponsive waste management system. Six future research directions are suggested to mitigate the potential impacts of the pandemic on waste management systems.
This research aims to show the positive and negative indirect effects of COVID-19 on the environment, particularly in the most affected countries such as China, USA, Italy, and Spain. Our research shows that there is a significant association between contingency measures and improvement in air quality, clean beaches and environmental noise reduction. On the other hand, there are also negative secondary aspects such as the reduction in recycling and the increase in waste, further endangering the contamination of physical spaces (water and land), in addition to air. Global economic activity is expected to return in the coming months in most countries (even if slowly), so decreasing GHG concentrations during a short period is not a sustainable way to clean up our environment.
Recycling and the reuse of waste materials as a replacement for the traditional construction materials in building and civil infrastructure is a significant step to reduce greenhouse gas emissions and the use of natural resources. However, most studies have focused on the behaviour of construction and demolition (C&D) aggregates mixed with a single waste material. To the best of authors' knowledge, there is no previously published work on using C &D aggregates containing both crushed waste glass and crumb rubber for road base/subbase applications. In this study, a series of experiments were conducted to assess the dynamic behaviour of recycled concrete aggregate (RCA) and waste crushed rock (CR) blended with crumb rubber (R) and crushed glass (CG). Testing included permanent deformation, resilient modulus, Clegg impact hammer, dynamic lightweight cone penetration, aggregate crushing value, and Los Angeles Abrasion. The cyclic triaxial test is the most reliable test for the evaluation of the behaviour of unbound granular pavement materials under dynamic wheel loads. However, the test procedures are very time-consuming, complicated, and expensive. Therefore, it is highly desirable to have a simple and straightforward method to evaluate the dynamic behaviour of unbound waste aggregates. For the first time, a simple and quick method was proposed in this study for estimating the permanent deformation and resilient modulus properties of three combined waste aggregates by using two simple dynamic tests (i.e., Clegg impact hammer test and dynamic lightweight cone penetration test). The analytical results indicate that a strong correlation exists between the results of the cyclic triaxial test and simple-procedure dynamic properties.
This article examined the effect of recycled polypropylene fiber (PPF), which is generated during manufacturing of plastic chairs, in addition to Nano-Silica as a novel technique to enhance the mechanical characteristics of clay soil. The main motive of this research is to investigate the optimal combination of Nano-Silica and Polypropylene fiber with clay soil. The engineering properties such as liquid limit, plastic limit, maximum dry density and unconfined compressive Strength (UCS) are analyzed with virgin soil, the soil with Nano-Silica and combination of soil with Nano-Silica and polypropylene fiber. The Durability test is performed to understand the durability of stabilized soil by analyzing wetting–drying cycles Also, Scanning Electron Microscopy (SEM) test is carried out and images are obtained to understand micro-structural modification towards mixture of Nano-SiO2 and PPF. Four different combinations of Nano-Silica at different percentages 1%, 3%, 5% and 7% are used in integration with polypropylene fiber is used in different percentages such as, 0.1%, 0.4%, 0.7%, 1%, and 1.3%. From these experiments, it has been analyzed that with the increase of PPF content in addition to Nano-Silica, the UCS increases and maximum value of UCS is obtained at 7% of Nano-Silica with 0.7% of PPF. The intermixing of PP fiber with the soil acts as a reinforcing material in binding the soil particles and the ‘bridge effect’ of fiber reinforcement in soil impedes the further development of tension cracks.
The permanent deformation characteristic is an important material property in determining the traffic-induced load-carrying ability of unbound granular materials (UGM). Since the repeated load triaxial test (RLT) is time-consuming, complicated, and expensive, it is highly desirable that a relatively simple and quick test can be used for estimating the permanent deformation of pavement materials in the base and subbase layers. In practice, the design engineers usually rely on California bearing ratio and unconfined compression strength tests which are static tests and very much less reliable and accurate compared to dynamic tests such as the Clegg impact hammer and dynamic lightweight cone penetrometer tests. No attempt had been previously made to correlate Clegg impact value and dynamic lightweight penetration index with the permanent deformation of construction and demolition (C&D) aggregates containing crumb rubber. On the other hand, information about the dynamic behaviour of construction and demolition (C&D) materials together with waste crumb rubber, as a green and environmentally friendly pavement material, is very limited. In the current research, a serial of RLT, the Clegg impact hammer tests, and the new dynamic lightweight cone penetrometer tests were performed to evaluate the strength and stiffness of UGM incorporating different sizes/percentages of crumb rubber. The main aim of this study was to develop a simple and reliable indirect approach for estimating the permanent deformation of UGM containing crumb rubber. Based on the experimental results, it was concluded that rubber could be blended with C&D aggregates for base/subbase applications. Also, according to the analytical results, CIV and DLPI could be considered as reliable and acceptable testing methods for estimating the permanent deformation of the unbound granular materials incorporating crumb rubber for the design of flexible pavement since there was a good correlation between the testing results and the phenomenological models.
The rapid growth in plastic and demolition wastes generation by municipal and commercial industries is a significant challenge to developed and developing countries. The substitution of traditional construction materials with recycled materials is a sustainable solution which mitigates landfilling concerns and reduces the need for virgin quarry materials. In this research, an evaluation of the geotechnical and geo-environmental properties of Polyethylene terephthalate (PET) plastic waste and its blends, with two major constituents of construction and demolition (C&D) waste materials was undertaken. Recycled concrete aggregate (RCA) and crushed brick (CB) were blended with 3% and 5% of PET, and the geotechnical properties of six PET blends were evaluated in the laboratory. The experimental programme included particle size distribution, particle density, sieve analysis, flakiness index, Los Angeles abrasion, water absorption, modified Proctor compaction, hydraulic conductivity, and California bearing ratio (CBR) tests. In addition, the response of the PET blends under repeated dynamic loading conditions was investigated using repeated load triaxial (RLT) tests. CBR results of all six PET blends were higher than the minimum CBR requirements for usage as a subbase material. The RLT testing results indicated that PET blends with RCA and CB performed satisfactorily at 98% maximum dry density and at their optimum moisture contents under modified Proctor compaction effort. Furthermore, a geo-environmental evaluation of the PET blends was undertaken which consisted of determination of organic matter content, pH value, total/leachate concentration of the recycled materials for a range of contaminant constituents and the results were compared with requirements specified by environmental authorities. Control samples, 3% and 5% PET blends with RCA and CB satisfied the CBR requirements. Similarly, control samples, 3% and 5% PET blends with RCA were found to be satisfactory for RLT requirements for subbase applications.
The use of recycled concrete is a significant step to reduce the need for natural resources and the demand on landfill sites for disposing the waste. Previous studies have mainly focused on its behaviours under ambient temperature although the characteristics of recycled concrete after high temperature exposures is important in many practical applications such as fire resistance. Also, the effect of elevated temperature on the mechanical and porosity behaviours of recycled concrete aggregate (RCA) containing rubber for pavement base/subbase applications has never been studied. In this study, the effects of high-temperature environment on the mechanical properties of recycled concrete aggregate (RCA) mixed with crumb rubber (CR) in a range of 0.5–2% were investigated both experimentally and theoretically. Unconfined compression strength (UCS) and X-ray micro-tomograph tests were undertaken on the mixed samples which were heated to different temperatures ranging from 20 °C to 600 °C. It was observed from the experimental results that UCS increased under a higher temperature up to 300 °C. At an ambient temperature of 20 °C, RCA samples without any addition of CR exhibited the highest UCS value while under high temperature, RCA samples with 1% CR had the highest UCS value. The strength of RCA mixed with crumb rubber showed an increasing trend under a temperature higher than 150 °C, which can be attributed to the melting processes of the crumb rubber. According to the X-ray micro-tomograph tests, the inclusion of rubber led to a decreasing porosity. It is interesting to note that porosity rises when temperature increased from 20 °C to 150 °C. This may be due to the restructuring of the shape of rubber particles into spheres as well as the excessive pore water forces generated from water evaporation. Also, when the temperature increased from 150 °C to 450 °C, the porosity decreased since the melted rubber particles flowed into the voids and filled more pores. The outcomes of this study can provide practical guidance on the application of recycling concrete.
To avoid premature failures in pavement layers, strong aggregates must be selected for pavement constructions that can bear the accumulation of permanent deformations. Otherwise, rutting happens in the pavement layers due to the accumulation of permanent deformations. On the other hand, due to the extensive generation of construction and demolition
(C&D) materials around the world, the application of waste materials in civil engineering projects would be considered as an environmentally friendly and cost-effective solution. Although many studies have been performed to examine the performance of the crushed recycle pavement materials, the literature review shows that few studies have been conducted to examine the permanent deformation characteristic of recycled concrete aggregate (RCA) and crushed rock
(CR) containing both crumb rubber (R) and crushed glass (CG). In this study, a series of repeated load triaxial (RLT) tests were carried out to evaluate the permanent deformation (i.e. 100000loading cycles) of RCA and CR incorporating R and CG. The shakedown theory was used to characterize the permanent deformation behaviour of the samples. Also, Werkmeister’s criteria were applied to define the shakedown ranges of the samples. The results show that the RCA,RCA + 1% R + 5% CG, CR + 1% R + 3% CG and CR + 1% R+ 5% CG can be used as base and sub-base material in pavement.
One of the most destructive environmental issues around the world is the disposal of construction and demolition (C&D) wastes
such as recycled concrete aggregate (RCA), crushed rock (CR), waste glass, and scrap tire. Therefore, using the waste materials in civil
projects such as road pavement applications would significantly reduce the consumption of quarry-based virgin materials, alleviate landfill disposal, and minimize greenhouse emissions. Numerous studies have evaluated the effect of crushed glass (CG) for construction applications; however, the effect of CG on the behavior of the crushed recycled materials together with crumb rubber (R) have never been studied for road pavement applications. A series of geotechnical laboratory tests, including modified compaction, unconfined compression strength, California bearing ratio (CBR), and resilient modulus tests, have been done on the blends of different percentages of CG added to the RCA and CR aggregates, together with R for pavement base/subbase applications. The results indicated that the blends of the waste materials, as a low carbon concept, could be a viable and satisfactory alternative solution for future base/subbase applications.
The structural behaviour of pavements depends on the permanent and resilient deformations. These deformations are accumulated during the pavement lifetime. Although many studies have been done to explore the use of construction and demolition (C&D) waste materials in road pavement construction, the long-term permanent deformation behaviour (i.e., 100,000 loading cycles) of recycled concrete aggregate (RCA) with an addition of crumb rubber as base/subbase layers has not been studied yet. The aim of this study is to assess whether RCA combined with crumb rubber can be used as the base or sub-base materials or not. Two different crumb rubber sizes were used in this study: a fine type measuring 1-5 mm in diameter and a coarse type measuring 15-20 mm. 0.5, 1% and 2% crumb rubber by weight of the dry aggregate were added to the 20 mm RCA. A series of repeated load triaxial tests were performed to investigate the effects of the sizes and percentages of crumb rubber on the long-term permanent deformation characteristics of RCA incorporating rubber. The results show that only RCA and RCA containing 0.5% fine or coarse rubber can be used as base and sub-base material in pavement in terms of long-term permanent deformation.
This paper is focused on finding effective alternative for disposal of waste plastic bags by designing tiles with better mechanical strength, reduced flammability level, resistant against strong acids and bases and organic solvents, so that tiles can be used for designing structures for paver tiles for societal usage. In recent years the plastic consumption has increased manifolds leading to accumulation of plastic waste in large amount. Waste plastic bags being non-biodegradable and its extreme durability make its disposal process difficult. Plastic solid waste (PSW) present challenges and opportunities to the societies regardless of their technological advances and sustainability awareness. Traditional technologies for waste plastic disposal have failed to cope up with the increased generation of plastic waste. Also, the disposal of fly ash, waste by-product generated by combustion of coal in thermal power plants, is a serious problem both in terms of land use and environmental pollution. In this study, waste plastic matrix reinforced with fly ash (FA) and a flame retardant at different loadings (wt %) 5, 10, 15, 20 using twin screw extruder were molded into composite tiles and their characteristics were evaluated. Effect of different filler loading on waste plastic matrix was investigated. Composite (LFTP3) having appropriate ratios of fly ash and flame retardant showed reduced flammability with linear burning rate of 4.36 mm/minute and improved tensile strength of 9.68 MPa. Morphological and structural properties of all the composites were also investigated along with their flammability, resistance to different acids and bases and organic solvents, water absorption and mechanical strength.
The current paper aims to examine the effects of cement and zeolite contents on the strength of zeolite-cemented sand using the unconfined compressive strength (UCS) and splitting tensile strength (qt). First of all, the optimum content (i.e., the corresponding water content to the maximum UCS) was obtained from the response surface (RSM) and central composite design (CCD) methods. Then, unconfined compression and splitting tensile tests considering four distinct porosity percentages (η) related to Drsand = 35, 50, 70 and 85% (Dr = relative density), five cement contents (2, 4, 6, 8, and 10%), and six different percentages of zeolite replacement (0, 10, 30, 50, 70 and 90%) were performed. Then, the amounts of the improved UCS and qt of the specimens as a result of the porosity, zeolite and cement were measured. The results indicated that the 30% replacement of cement with zeolite (Z) was found the optimum amount of replacement. The strength improvement rate of the optimum zeolite-cemented sand (Z = 30%) compared to the mere cemented sand (Z = 0%) increased with the increase in the cement content as well as increase in the porosity of the compacted mixture. Based on the results of the zeolite-cement-sand mixtures, it has been shown that the UCS and qt improved by increasing the cement content (C). Also, the power function is well-matched to fit (UCS and qt)-C. The active composition parameter (AC) participate in the chemical reaction was introduced, as the minimum amount of either CaO or Al2O3 + SiO2. Afterward, the UCS and qt were plotted against the porosity/active composition parameter (η/AC), which is regarded as a controlling and key parameter of the UCS and qt. Also, the experimental results and the parameter of η−1.79AC1.43 introduce an acceptable description of the mechanical strength. Finally, the qt/UCS relationship is unique for the zeolite-cemented sand studied, being independent of the η/AC.
Since the determination of resilient modulus (Mr) from the repeated load triaxial test is rather complicated, due to the expensive procedure and time-consuming nature, attempts have been made to estimate it using other properties, such as the unconfined compressive strength and California bearing capacity based on empirical models. However, because of the dynamic nature of the Mr, it should be estimated by other simple-procedure dynamic properties. The Clegg hammer test has been considered as an alternative since it is not only dynamic in nature but also simple and quick. There has been no report of any previous study on correlating between CIV and Mr of construction and demolition (C&D) aggregates containing crumb rubber. In this research, a series of experiments were conducted to measure the Mr and CIV of the waste crushed rock (WCR) and recycled crushed concrete (RCC) mixed with the rubber of two different sizes and different contents (0, 0.5, 1, and 2%) for making a green pavement. The experimental results show that the CIV and Mr of both aggregates increased with the fine crumb rubber components but decreased with the coarse rubber content. The increase of CIV and Mr due to the increase of fine rubber percentage can be attributed to the filler effect of fine rubber particles that provides better interfacial bonding condition. The analytical results show that a strong correlation exists between the Mr, confining stress, deviator stress and the CIV with the R2 value ranging from 0.74 to 0.99.