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This paper presents an experimental study conducted to investigate the effect of fiber reinforcement on the mechanical properties and shrinkage cracking of recycled fine aggregate concrete (RFAC) with two types of fiber-polyvinyl alcohol (PVA) and nylon. A small fiber volume fraction, such as 0.05% or 0.1%, in RFAC with polyvinyl alcohol or nylon f...
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... can be explained by the higher air content of R-Ny01, which can have an effect on the compressive strength and modulus of elasticity of concrete. In addition, the modulus of elasticity was dependent on the density of concrete [31], which was also proved by the reduction in density of R-Ny01 as presented in Table 6. Additionally, the results exhibited that the relative strength of R-0 was lower than N-0 by 10.1%; further, in cases of fiber-reinforced RFAC, the relative strength of all specimens was lower than N-0, from 8.8% up to 17.5%. ...
Context 2
... can be explained by the higher air content of R-Ny01, which can have an effect on the compressive strength and modulus of elasticity of concrete. In addition, the modulus of elasticity was dependent on the density of concrete [31], which was also proved by the reduction in density of R-Ny01 as presented in Table 6. Table 7 lists the splitting tensile strength and the flexural strength for concrete specimens at 28 days. ...
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Citations
... Akono et al. [17] examined the microstructure of concrete with RFA and found that the porosity of C-S-H gel in RFAC accounts for 56% of the total porosity. Nam et al. [18] reported that RFAC exhibits 26% and 10% lower tensile and compressive strengths, respectively, compared to concrete with NFA. Hassan et al. [19] investigated the mechanical specifications of concrete incorporating RFA and NFA, highlighting higher reductions in compressive strength compared to tensile and flexural strengths. ...
The incorporation of waste materials in concrete is currently a practical solution to solve certain environmental concerns. Because of the property degradation of the produced concrete owing to the addition of waste materials, using pozzolans in the concrete mix can help improve the mechanical performance of recycled concrete. Therefore, in this research, the mechanical specifications of recycled concrete were evaluated at different volume fractions of recycled fine aggregates (RFA) replacing natural fine aggregates (NFA). In addition, the impact of adding colloidal nano-silica particles on the performance of conventional and recycled concretes was investigated. Various parameters comprising compressive strength, pulse velocity, splitting tensile strength, flexural strength, elastic modulus, and water absorption were carefully examined. The attained experimental results reveal that the mechanical and physical characteristics of concrete degrade with increasing the volume fraction of RFA replacing NFA. Also, increasing the weight percentage of nano-silica replacing cement up to 6% in conventional concrete and that containing RFA improves the mechanical and physical properties, the optimum percentage of which was determined as 4.5%. Furthermore, relationships were recommended for predicting the compressive, splitting tensile, and flexural strengths as well as the elastic modulus of concrete mixes by including the RFA and nano-silica replacement levels, which are in acceptable accordance with the experiments in the present study and those available in the technical literature. Finally, to investigate the environmental effects of recycled concrete with different RFA substitution levels and colloidal nano-silica incorporation, the problem-based CML 2000 and the damage-based IMPACT2002 + methods were applied using SimaPro9 software. Thus, environmental parameters such as acidification, global warming potential (GWP), eutrophication, natural resources, ecosystem quality, and human health were inspected. Subsequently, the GWP results were compared and presented using the CML 2000 and the Intergovernmental Panel on Climate Change (IPCC) approaches. To verify the estimates, all the attained results were examined against those captured from the Building for Environmental and Economic Sustainability (BEES) method. Findings show that despite the implementation of different unit measurements in different methods, the environmental effects in the CML 2000 and BEES meth-odologies are almost the same, suggesting that nano-silica is a raw material with the greatest environmental impact. Additionally, based on the life cycle comparison results of manufacturing one cubic meter of concrete with different mix designs using the damage evaluation approach, IMPACT 2002+, concrete with the RF0NS6 mix design triggered the highest damage extent in natural resource, climate change, ecosystem, and human health categories, respectively. This study fills a significant research gap from an environmental perspective by comprehensively investigating the durability and mechanical specifications of concrete containing RFA and nano-silica pozzolan. The findings presented in this research provide valuable insights into the realm of sustainable construction practices, paving the way for novel advancements in concrete technology.
... Also, according to the test results, the splitting tensile capacity of the samples declined by 19% at the RFA replacement percentage of 70%. Moreover, Nam, et al. [8] stated that the compressive and tensile capacities of RFAC were 10 and 26% less than concrete containing natural fine aggregate (NFA), respectively. Akono, et al. [9] studied the microstructure of concrete with RFA and reported that the porosity of C-S-H gel in RFA concrete was 56% of the total porosity. ...
... Several proposed factors influence the bleeding and plastic shrinkage cracking of concrete. A concise review of literature shows that a considerable number of studies investigated the effects of varying cement properties [23][24][25], addition of fibres [26][27][28][29], and inclusion of shrinkage reducing admixtures [30,31] on concrete bleeding and plastic induced cracking. However, another important factor is the presence of MFA in MS, which has not appeared in any published literature to date. ...
Construction industries have started to utilize manufactured sand (MS) as an effective alternative for river sand in concrete. High-grade parent rocks are crushed to obtain MS, which also produces a considerable amount of microfine aggregate (MFA). The higher percentage of MFA could lead to both positive and negative effects on the performance of cement-based mixes. This research was done to examine the influence of varying MFA levels, specifically 0%, 3%, 6%, 9%, and 12% (by weight) as the partial replacements of MS on bleeding and plastic shrinkage cracking of concrete. In addition to the varying MFA levels, some concrete mixes also included fly ash (FA) and superplasticizer to investigate the effect of free-water content in the mixes. The bleeding test data were taken as on-site measurements, while the cracks from the plastic shrinkage cracking test were evaluated using an image processing technique. The results concluded that the MFA replacements and the effective water-to-cement ratio have a significant effect on the selected concrete properties. With the increasing replacement levels, cumulative bleeding and crack initiation life gradually decreased, while a progressive increase was observed for crack width, crack length, and crack area.
... PVA fiber has been proved to restrain the free deformation of cementitious composite s [39,40]. Nevertheless, total shrinkage of PVA-ECC may reach triple that of ordinary concrete when identical water to cement ratio (w/c) is adopted [41]. ...
Engineered cementitious composite (ECC) enjoys huge potential in building structures thanks to its excellent tensile performance and energy absorption ability. However, free deformation of ECC deserves better understanding since large shrinkage strain usually induces internal tensile stress which would lead to cracking under constraint. Present study focuses on the full life-cycle shrinkage of polyvinyl alcohol (PVA) fiber reinforced ECC. Shrinkage and relative humidity (RH) at three water to cement (w/c) ratios were experimentally tested through novel integrated deformation measurement device. In contrast, plain mortars with the same w/c ratios were compared to evaluate the impact of PVA fiber on the over-time deformation and RH characteristics. Thereafter, shrinkage model considering fiber influence coefficient is established to simulate autogenous and drying shrinkage of PVA-ECC. Results show that full life-cycle shrinkage can be divided into two stages according to the internal RH measured. Distinct restraint effect of PVA fiber on both stages are observed. By comparing experimental and simulation results of PVA-ECC, the proposed fiber influence coefficient-based shrinkage model well illustrates the effect of PVA fiber, especially for high strength cementitious composites with relatively low w/c.
... The principal phenomenon for the cracking is the creation of negative tensile pressure at the surface, which pulls the particles and propagates the hairline cracks at the surface. [17][18][19] From the concise review of literature, effects of varying cement properties, [20][21][22] addition of fibers [23][24][25][26] and inclusion of shrinkage reducing admixtures 27,28 were proposed as the factors for bleeding and plastic shrinkage induced cracking of concrete. The presence of MFA could be also considered as a key factor, which is not appeared in any literature. ...
Manufactured sand (MS) has been started utilizing as an alternative in constructions due to the escalated demand for river sand (RS). The microfine aggregate (MFA) is a salient constituent in manufactured sand, which is a crushed reactive form of parent rocks having particles less than 0.075 mm. This paper presents the effects of varying microfine aggregate levels on bleeding , plastic shrinkage cracking (PSC) and compressive strength of MS made concrete. Two types of MS were utilized: MS from Hornblende-Gneiss rock (MH) and MS from Charnockite rock (MC) and the MFA level was ranged from 0% to 12% at 3% increments and the reference concrete was prepared with RS alone. With the MFA levels, the bleeding of MS concretes was reduced where, at 0% MFA level the maximum bleeding rates were observed for MC (1.63 kg/m 2) and MH (0.84 kg/m 2) concretes. PSC results were analyzed from an image processing technique, which revealed an increasing trend of mean and maximum crack widths, crack length and crack area with the MFA levels. At 0% MFA, the mean crack width of MC (0.19 mm) and MH (0.17 mm) con-cretes manifested marginally similar to RS concrete (0.17 mm). The decreasing bleeding with the MFA levels can be attributed to the increasing severity to PSC. Moreover, the optimum 28 days compressive strength of MC (57.5 MPa) and MH (56.1 MPa) concretes was achieved at 3% MFA level which are higher than RS concrete (51.5 MPa). Consequently, the MFA level should be limited to 3% for better plastic and hardened performance of MS made concrete.
... Furthermore, the addition of fibers, such as polypropylene, steel, glass, basalt and hybrid fibers, has been regarded as an alternative effective way to decrease the deformation of RAC (Behforouz et al., 2020;Mesbah and Buyle-Bodin, 1999;Nam et al., 2016;Saiz-Martinez et al., 2018;Tahmouresi et al., 2019). Based on the development of this technology, the addition of waste fiber is gradually becoming the next research hotspot owing to its higher environmental benefits. ...
Although recycled aggregate concrete (RAC) has been extensively studied, several critical problems about its fundamental behaviors are still urgent to be figured out. Therefore, this series of two reviews re-think fundamental behaviors of RAC based on the latest literature. In the last review (Part I), the mechanical and deformation behaviors of RAC have been intensively discussed. Here for Part II, the relationships between the replacement ratio of recycled aggregates (RA) and the durability of RAC are further presented. It is found that, due to the increase of total porosity, the resistance of RAC to freeze-thaw cycles, carbonation, and chloride ion penetration is usually decreased with the increasing replacement ratio of RA. As a result, the steel corrosion and corrosion-induced cracking in RAC are more serious than those in natural aggregate concrete (NAC). The prediction models for carbonation and chloride ion penetration of RAC and the corrosion-induced crack patterns are also presented. For addressing the degradation on the performance of RAC, several enhancement technologies such as the combined/optimization pre-treatment on RA and fiber reinforcement are put forward. Finally, the prospects of the high-performance/efficiency methodologies and applications of RAC are also shown.
... Wang et al. [65] expressed that the lime and ceramic content influenced the mechanical properties due to variation in w/c ratio while the inclusion of RFA. Another reason in mechanical properties decreased while RFA was the enhancement in porosity pointed out by Nam et al. [66]. After the methylene blue test, there has been no lime with the inclusion of RFA. ...
An experimental study has been conducted to investigate the effect of recycled fine aggregates (RFA) treated as washed (W-RFA), less washed (L-RFA) and unwashed (U-RFA) on the transport, mechanical and durability characteristics of concrete exposed to freeze-thaw cycles and MgSO4. Totally three groups of concrete mixtures were produced by replacing natural fine aggregates (NFA) with W-RFA, L-RFA and U-RFA at the percentages of 10, 20, 40 and 80% by weight of NFA. 12 mixtures incorporating RFA and reference mixture containing only NFA were fabricated. Mechanical performance was evaluated by compressive, splitting tensile strength at 7 and 28 days and Schmidt rebound hammer at 28 days. Dry bulk density, water absorption, porosity and sorptivity of concrete were also evaluated. Durability performance of concretes was evaluated by exposing to different freeze-thaw cycles and MgSO4 attacks. An abrasion test on the concretes was also performed. After performing durability tests, compressive, splitting tensile strength, relative dynamic elasticity modulus, microstructural observations and mass loss of the concretes were assessed. The results indicated that 80%W-RFA incorporated concrete improved the compressive strength considerably and achieved 28 day- compressive strength of 51 MPa. 10% L-RFA and 10% U-RFA incorporated concretes exhibited 28 day- compressive strength of above 52 MPa. The concrete with 40%W-RFA presented the best abrasion resistance after 7 and 28 days. 20%W-RFA incorporated concrete performed the best after 150 F-T cycles in terms of compressive strength.
... Shrinkage is defined as the volumetric contraction of concrete, especially at early ages, without applying any external force [1]. This property is of great importance for the durability performance of this material, due to the cracking that it may cause [2]. The appearance of cracks favours the attack of external agents that deteriorate concrete and corrode the reinforcements, thus reducing its service life [3][4][5]. ...
... MgO + H 2 O→Mg 2+ + 2Â⋅OH − →Mg(OH) 2 (1) So far, the use of reactive MgO has been validated exclusively regarding the production of cement pastes and mortars. Recent studies have shown that reactive MgO as cement replacement in relatively high quantities (10-20%) can be successfully used to produce mortars with improved shrinkage behaviour [37], reducing both autogenous [38] and total shrinkage [39]. ...
... On the other hand, the addition of MgO also increases the porosity of concrete, which in 1 Percentage loss of slump because of the addition of RA (compared to the reference mixes with the same binders, RHPC or RHPCMO). 2 Percentage variation caused by using early-age RA (compared to the mixes with the same composition but with matured RA). 3 Percentage decrease caused by MgO (regarding the mixes with the same composition and RA's maturity but with 100% OPC). turn compensates the increase of microstructural density caused by the higher real density of MgO [67]. ...
The high strength and durability of high-performance concrete (HPC) may be significantly reduced by shrinkage cracking. The use of reactive magnesium oxide (MgO) can reduce shrinkage of cement-based materials due to its expansive properties. This study intends to analyse the validity of MgO as shrinkage-reducing agent in recycled aggregate HPC. To do so, ten HPC mixes with 0%, 25%, and 100% of both early-age (7-days air curing) and matured (6-month air curing) RA were produced. In half of the mixes, 10% ordinary Portland cement was replaced with MgO. The use of MgO slightly worsened the mechanical behaviour of HPC, especially when combined with large amounts of RA. On the other hand, the expansion of MgO fully offset the autogenous shrinkage of HPC and reduced total shrinkage by around 20–40%. Water storage of RA, and its deferred release over time, produced a more efficient hydration of MgO, which in turn led to a further reduction of autogenous shrinkage. However, the increase of drying shrinkage caused by RA was greater than this decrease of autogenous shrinkage due to MgO, so the higher the RA content of HPC the lower the total shrinkage reduction when adding MgO. Thus, the decrease of total shrinkage caused by MgO was compensated by the shrinkage increase because of RA when adding amounts above 35% early-age RA and 42% matured RA. Therefore, despite the suitability of MgO as shrinkage-reducing agent in recycled aggregate HPC, its effectiveness was reduced with increasing amounts of RA.
... Like concrete-containing natural aggregates, recycled aggregate concrete also exhibits brittle behaviour in tension and flexure [31]. Therefore, various fibres are used to reinforce recycled aggregate concrete to improve its mechanical properties [32][33][34][35]. Among many fibres, steel fibre is one of the most effective materials to enhance the tensile strength of recycled aggregate concrete [36][37][38]. ...
In this study, the impact of steel fibres and Silica Fume (SF) on the mechanical properties of recycled aggregate concretes made of two different types of Recycled Coarse Aggregates (RCA) sourced from both low- and high-strength concretes were evaluated through conducting 60 compressive strength tests. The RCAs were used as replacement levels of 50% and 100% of Natural Coarse Aggregates (NCA). Hook-end steel fibres and SF were also used in the mixtures at the optimised replacement levels of 1% and 8%, respectively. The results showed that the addition of both types of RCA adversely affected the compressive strength of concrete. However, the incorporation of SF led to compressive strength development in both types of concretes. The most significant improvement in terms of comparable concrete strength and peak strain with ordinary concrete at 28 days was observed in the case of using a combination of steel fibres and SF in both recycled aggregate concretes, especially with RCA sourced from high strength concrete. Although using SF slightly increased the elastic modulus of both recycled aggregate concretes, a substantial improvement in strength was observed due to the reinforcement with steel fibre and the coexistence of steel fibre and SF. Moreover, existing models to predict the elastic modulus of both non-fibrous and fibrous concretes are found to underestimate the elastic modulus values. The incorporation of SF changed the compressive stress-strain curves for both types of RCA. The addition of steel fibre and SF remarkably improved the post-peak ductility of recycled aggregates concretes of both types, with the most significant improvement observed in the case of RCA sourced from a low-strength parent concrete. The existing model to estimate the compressive stress-strain curve for steel fibre-reinforced concrete with natural aggregates was found to reasonably predict the compressive stress-strain behaviour for steel fibres-reinforced concrete with recycled aggregate.
... This resulted in higher cement content and resulted in high drying shrinkage strains during the setting and hardening stages of ECC compared to NC [1,[9][10]. Although the use of a reasonable amount of PVA fibers was effective in reducing the generated volumetric change [11][12][13][14], the average drying shrinkage strain in ECC was 1200 µε -1800 µε, which is about two to three times that of shrinkage strain in NC (400 µε -800 µε) at equivalent age of 28 days [15]. Higher fiber content than the optimum 2% has shown to reduce shrinkage strain in ECC [16]. ...
The application of engineered cementitious composite (ECC) in liquid containing structures (LCS) may help to improve the cracking performance of these structures. This study investigates the hydration temperature, shrinkage, cracking and self-healing behaviors of 10 m length ECC and normal concrete (NC) panels under real field conditions of volumetric strains. The restrained panels of NC and ECCs, with different compositions of fly ash (ECC/FF) and slag (ECC/SL), were designed to represent a segment of LCS and were cast and monitored on site for seven months under natural temperature changes of wet/dry and freeze/thaw cycles. A detailed microstructural analysis was completed on full depth drilled cores to explore the self-healing efficiency of different crack layers. At 28 days, only ECC/SL exceeded the ACI 224R limit for crack width of concretes to be used safely in LCS. However, at longer ages, unlike ECC/FF and ECC/SL panels which showed significant healing of their volumetric strain cracks, the NC panel experienced a sharp increase in crack widths up to seven months of monitoring. Different concentrations of CaCO3 and C-S-H/CH products were characterized at the top, core and bottom layers of crack lines, confirming higher self-healing performance of the volumetric strain cracking in ECC/FF compared to ECC/SL and NC segments.
