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A general and simple method to disperse 2D nanomaterials for promoting cement hydration
... The electrochemical method is easy to operate and environmentally friendly, capable of producing uniformly sized, highly crystalline, water-soluble CDs, primarily GQDs. In 2024, He's group improved upon the method of Han et al. to prepare GQDs via electrochemical etching of graphite, which were then used to aid in dispersing two-dimensional (2D) nanomaterials [24,25]. Specifically, they used two graphite rods with a spacing of 6 cm (purity of 99.99%, length of 15 cm, diameter of 0.6 cm as the anode and cathode, which were then immersed parallelly in a beaker containing 800 mL of ultrapure water (Fig. 4a). ...
... and 25%/13.1%, respectively (Fig. 9d) [24]. These results demonstrate the great potential of these materials in enhancing the performance of cement-based materials. ...
... Enhancing mechanical properties is not only crucial for structural safety but also directly impacts the economic benefits and service life of the materials. As previously mentioned, the incorporation of J Mater Sci Figure 9 TEM images of 2D nanomaterials before and after dispersity and the effect enhancement: a g-C 3 N 4 [35]; b MK [41]; c CLDH [42]; and d GO, CLDH, and g-C 3 N 4 [24]. J Mater Sci two-dimensional nanomaterials has been proven to effectively enhance the mechanical properties of cement-based materials. ...
Carbon dots (CDs) are a new type of zero-dimensional fluorescent carbon nanomaterials. Due to their low toxicity, environmental friendliness, and excellent photostability, they show great potential in fields such as environmental monitoring, drug delivery, and catalysis. However, the practical application of CDs is still limited by the lack of large-scale application scenarios, posing a challenge for their industrial deployment. Civil engineering materials are the most widely used materials in the world, and the successful application of CDs in this field has excellently addressed this challenge. This review comprehensively summarizes the research progress of CDs as a novel material in civil engineering field, including synthesis methods of CDs, enhancement of mechanical properties and durability of cement-based materials, inhibition of metal corrosion, and the mechanisms involved in these aspects. This review aims to provide guidance for future research and practical applications, promoting the large-scale use and industrial production of CDs.
Graphical abstract
... Upon the addition of NS (N1.0), the microstructure showed more pores and generated a large amount of AFt and a small amount of C-S-H gel, and the formation of large-size CH crystals was inhibited because NS could react with CH to form C-S-H during hydration, but undispersed NS tended to agglomerate, and poor dispersion could not efficiently generate disordered CH and more C-S-H to fill the deleterious pores and cracks, which resulted in the inability to refine the microstructure of the cement matrix. [41][42][43] After ultrasonic dispersion for 40 min and mixing with 0.75 wt.% PCE (T40N1.0P0.75), The microstructure of the cement paste had been significantly improved. ...
... This condition suggested that the ultrasonic dispersion time was too short, the NS dispersion effect was not sufficient to make full use of its volcanic ash effect and filling effect, and a large number of harmful pores were not filled, resulting in unsatisfactory particle integration and hydration process, and the microstructure of the cement matrix could not be refined. 41 When the NS content was 0.5 wt.% (T40N0.5P0.75), although C-S-H gels were generated, CH crystals were clearly present, indicating that the NS content was insufficient to fully play its role in enhancing hydration and improving structure. ...
The dispersion of nano‐SiO2 (NS) in cement plays a critical role in enhancing the properties of cementitious materials. In this study, the combination of ultrasonic dispersion and polycarboxylic acid water reducing agent (PCE) was used to significantly improve the dispersion of NS. The effects of ultrasonic dispersion time, NS content, and PCE content on dispersion quality were investigated, alongside their impact on mechanical properties, electrical resistivity, and frost resistance. The results demonstrated that this synergistic method optimized the dispersion of NS, leading to superior mechanical properties and frost resistance. With an ultrasonic dispersion time of 40 min, NS content of 1.0 wt.%, and PCE content of 0.75 wt.%, the cement paste achieved its optimal performance. Compared to non‐dispersed samples, compressive strength increased by 33.7%. After 75 freeze–thaw cycles, the mass loss was 2%, the relative dynamic elastic modulus was 99.15%, and the strength loss was 13.74%.
... Rather, the algorithm gave a python code which was used to get Eq. (8). Also, the predictive abilities of this equation to forecast C-S for both datasets of training and testing has been given in scatter plots shown in Fig. 10b from which it is evident that the MEP predictions lie closer to the best fit line. ...
The use of naturally available materials such as metakaolin (MK) can greatly reduce the utilization of emission intensive materials like cement in the construction sector. This would reduce the stress on depleting natural resources and foster a sustainable construction industry. However, the laboratory determination of 28 day compressive strength (C-S) of MK-based mortar is associated with several time and resource constraints. Thus, this study was conducted to develop reliable empirical prediction models to assess CS of MK-based mortar from its mixture proportion using machine learning algorithms like gene expression programming (GEP), extreme gradient boosting (XGB), multi expression programming (MEP), bagging regressor (BR), and AdaBoost etc. A comprehensive dataset compiled from published literature having five input parameters including water-to-binder ratio, mortar age, and maximum aggregate diameter etc. was used for this purpose. The developed models were validated by means of error metrics, residual assessment, and external validation checks which revealed that XGB is the most accurate algorithm having testing of 0.998 followed by BR having values equal to 0.946 while MEP had the lowest testing of 0.893. However, MEP and GEP algorithms expressed their output in the form of empirical equations which other black-box algorithms couldn’t produce. Moreover, interpretable machine learning approaches including shapely additive explanatory analysis (SHAP), individual conditional expectation (ICE), and partial dependence plots (PDP) were conducted on the XGB model which highlighted that water-to-binder ratio and sample age are some of the most significant variables to predict the C-S of MK-based cement mortars. Finally, a graphical user interface (GUI) was made for implementation of findings of this study in the civil engineering industry.
Supplementary Information
The online version contains supplementary material available at 10.1038/s41598-025-01327-1.
... Therefore, 2D nanomaterials that can recognize target gas analytes at RT and have intrinsic flexibility are promising candidates for building integrated, flexible, and wearable gas sensors. [65][66][67][68][69][70][71][72] Second, electrons in 2D materials move freely in two dimensions, and the area over which gas molecules interact with the sensitive material is relatively large. [73][74][75][76][77][78][79] The electrons in 2D materials move freely in two dimensions, and the area over which gas molecules interact with sensitive materials is relatively large. ...
Gas detection has become a popular research topic in the field of environmental protection and disease detection because of the concerning increase in environmental pollution and human health problems. 2D MXenes are promising candidates for room‐temperature gas sensors because of their flexible and adjustable material compositions, high conductivities, high signal‐to‐noise ratios, and adjustable surface terminations. This paper presents the prospects of gas sensors, structure of MXenes, and potential sensing mechanisms of MXenes‐based gas sensors. Applications of Ti3C2Tx, V2CTx, Nb2CTx, and Mo2CTx MXenes in gas sensors for the detection of different gases are reviewed, and the challenges and potential research directions for applying MXenes in gas sensors are discussed. This review provides ideas for designing novel sensitive materials by analyzing the potential value of MXenes‐based gas sensors in the sensor field.
... The heat of hydration further increases, and it could also result in the formation of microcracks in the internal voids. Similar behaviors have also been reported in the literature [73][74][75][76]. Figure 5 depicts the relationship between CS and OPC/FA. Based on the experimental data, it can be concluded that the OPC/FA content to achieve optimum CS in GPC is 30%/70%. ...
Geopolymer concrete (GPC) has been developed using supplementary cementitious materials to reduce the carbon footprint associated with conventional concrete production. This study aimed to explore the production and simultaneous modeling of the properties of GPC using fly ash (FA) as the primary binder and ordinary Portland cement (OPC) as a partial replacement. Mechanical tests revealed that replacing FA with up to 30% OPC resulted in a 28-day compressive strength (CS) of 33.52 MPa and a flexural strength (FS) of 15.21 MPa. X-ray diffraction (XRD) analysis indicated the formation of nepheline and albite, which are associated with sodium aluminosilicate hydrate gel, a primary strength giving product in GPC. Additionally, gene expression programming (GEP), an artificial intelligence technique, was employed to predict the mechanical properties utilizing the experimental data. The prediction models demonstrated high accuracy, with a correlation coefficient greater than 0.90. The study’s results provide valuable insights into the performance of OPC-blended FA-based GPC and propose easy-to-use empirical formulations for standard mix design and proportioning of alternative blended GPC, promoting the application of sustainable concrete.
... Recent research continues to improve GO and other nanomaterial dispersion in cement-rich samples [29]. However, these studies do not present any practical advancement for nanoreinforcement in concrete. ...
... Zhu et al. (2022) examined soil water dynamics using stable isotopes, which provided essential insights into soilwater interactions critical for sulfate-bearing soils. He et al. (2024) introduced nanomaterials to enhance cement hydration, significantly improving strength and durability. Wei et al. (2023) focused on the seismic performance of composite columns, offering valuable data on ensuring resilience against dynamic loads. ...
Sulfate-bearing soils is widely distributed around the world, and this type of soil is prone to rock and soil disasters such as dissolution, corrosion of foundations, and swell when exposed to water. Cement is a frequently used stabilizer to treat sulfate-bearing soils. However, sulfate-bearing soils usually include various types of sulfates, such as, calcium sulfate (CaSO4), sodium sulfate (Na2SO4), potassium sulfate (K2SO4), and magnesium sulfate (MgSO4). So far, the effect of sulfate type on the strength and swelling properties of sulfate-bearing soil stabilized with cement has not been clarified. Therefore, in this study, the strength and swelling properties of four sulfate-bearing soils treated with cement were studied using unconfined compressive strength tests, and swelling tests. X-ray diffraction (XRD), scanning electron microscopy, and inductively coupled plasma spectroscopy were employed to study mineralogical, micro-structural properties, and concentrations of calcium ion of stabilized soils, to explore stabilization mechanisms. The results showed that the formation of magnesium silicate hydrate and highest concentration of free Ca²⁺ in the stabilized Mg-sulfate-soil caused its lowest strength. The reduction in free Ca²⁺ concentration was greater in the stabilized Na-sulfate-soil and K-sulfate-soil compared to stabilized Mg-sulfate-soil and Ca-sulfate-soil, contributing to the formation of more calcium silicate hydrate and ettringite. Therefore, the stabilized Na-sulfate-soil and K-sulfate-soil had greater swelling and strength compared to other soils. As the cement content increases, there are abundant in the sulfated cement stabilized soil observed in XRD and SEM photos. Overall, sulfates with monovalent cations increased the strength of cement-stabilized soils more than those with divalent cations, while sulfates with divalent cations improved the resistance to swelling of cement-stabilized soils. Before treating sulfate-bearing soils with cement, it is necessary to first determine the cations type in the soil. If the soil contains Mg²⁺, seek cement alternatives. If the other three cations are present, choose an appropriate cement content for stabilization. This study provides some references for the stabilization of sulfate-bearing soils with cement.
... Also in past, different analytical methods have been devised based on conditions of equilibrium and compatibility equations to estimate the CS. Eurocode 6 provides a mechanism to predict CS based on different input parameters such as compressive strength of mortar, blocks etc [11]. There have also been some experimental studies to determine CS [12][13][14][15]. ...
The design of masonry structures requires accurate estimation of compressive strength (CS) of hollow concrete masonry prisms. Generally, the CS of masonry prisms is determined by destructive laboratory testing which results in time and resource wastage. Thus, this study aims to provide machine learning-based predictive models for CS of hollow concrete masonry blocks using different algorithms including Multi Expression Programming (MEP), Random Forest Regression (RFR), and Extreme Gradient Boosting (XGB) etc. A dataset of 159 experimental results was collected from published literature for this purpose. The collected dataset consisted of four input parameters including strength of masonry units (fb), height-to-thickness ratio (h/t), strength of mortar (fm), and ratio of fm/fb and only one output parameter i.e., CS. Out of all the algorithms employed in current study, only MEP and GEP expressed their output in the form of an empirical equation. The accuracy of developed models was assessed using root mean squared error (RMSE), objective function (OF), and R2 etc. Among all algorithms assessed, XGB turned out to be the most accurate having R2 = 0.99 and least OF value of 0.0063 followed by AdaBoost, RFR, and other algorithms. The developed XGB model was also used to conduct different explainable artificial intelligence (XAI) analysis including sensitivity and shapley analysis and the results showed that strength of masonry unit (fb) is the most significant variable in predicting CS. Thus, the ML-based predictive models presented in this study can be utilized practically for determining CS of hollow concrete masonry prisms without requiring expensive and time-consuming laboratory testing.
... Determination of compressive strength of green concrete with blast furnace slag [27] Mechanical tests of the samples with different dosages of rice straw ash Evaluation of self-compacting concrete with rice straw ash as a partial replacement for cement at different time periods [28] Physical and mechanical testing of the samples containing different percentages of calcined sludge Study of cementitious materials with partial replacement of cement by sludge at different ages [29] A novel ultrasonic treatment using graphene quantum dots (GQDs) significantly improves the dispersion and exfoliation of 2D nanomaterials (GO, CLDH, CN), enhancing their ability to accelerate cement hydration and improve mechanical properties. This method increases the specific surface area and provides more nucleation sites, leading to better cement composite performance [30]. Additionally, research into ternary cementless composites using red mud (RM), ultra-fine fly ash (RUFA), and ground granulated blastfurnace slag (GGBS) reveals that while RM increases setting time and reduces fluidity and compressive strength, GGBS enhances compressive strength and alters hydration products, with optimal performance observed in a mix containing high GGBS content, achieving a compressive strength of 47.3 MPa [31]. ...
Using waste materials in the mixture of building materials is an approach aligned with the circular economy, a viewpoint that creates sustainable building industries, especially in developed countries. This study concentrated on the application of laponite (LAP), fly ash (FA), and bentonite (BENT) materials in the mixture of cement pastes. The first step used experimental practices to examine the metrics of toughness, three-point bending, and compressive strength with different percentages of added LAP, FA, and BENT after the characterization of samples by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The next step entailed assessment of cement paste specifications through some regressive equations obtained by the application of 2D curve fitting and sensitive analysis of additive (FA, LAP, and BENT) fluctuations in the structure of cement paste. The results show that linear polynomial equations are the best for the evaluation of cement paste terms as per different percentages of the additives. The environmental impact assessment (EIA) of nine prepared samples demonstrated that LAP created the safest condition in comparison to others. However, the ordered weighted averaging (OWA) computations applied for the sustainability assessment (SA) of the samples showed that the LAP is the most appropriate option for use in the structure of cement paste. Using experimental analysis and mathematical modeling, the behavior of cement paste interacting with mineral additives is evaluated. Sustainable mixtures are then presented based on EIA.
Carbon quantum dots (CQDs) have emerged as promising organic nanomaterials due to their unique physicochemical properties and versatile applications. In recent years, there has been a growing interest in exploring the role of CQDs in improving the performance of construction and building materials, including cement, concrete, and asphalt. This paper presents a comprehensive literature review of recent articles focusing on the synthesis methods of CQDs and graphene quantum dots (GQDs), their characteristics, and their effects on the mechanical, thermal, and durability properties of cement-based materials. Furthermore, the potential challenges and future research directions in this field towards carbon capture, utilization, and storage (CCUS) direction are also discussed. The mechanisms behind these improvements are analyzed, focusing on the interfacial bonding between CQDs, seeding nucleation of the cement hydration process, and filling effect. Additionally, the review addresses the challenges associated with CQD implementation, such as cost-effectiveness and large-scale implementation. Finally, a suggested outline for optimizing CQDs used in construction materials in many research directions is discussed, suggesting novel ways for high-performance, functional, and sustainable construction materials for smart applications.
Graphical Abstract
Graphene oxide (GO) has attracted significant attention as a nano-reinforcement for cement-based materials, owing to its exceptional mechanical properties and abundant surface functional groups. However, the precise mechanisms governing its effects in cement composites remain inadequately understood due to inconsistencies and gaps in the existing literature. This review conducts a comprehensive analysis of the dispersion and reinforcement effects of GO in cement materials, focusing on three key areas: (1) challenges associated with achieving uniform dispersion of GO in the high-pH environment of cement slurries and potential strategies to address them; (2) the influence of GO on the macroscopic properties of cementitious composites, including workability, load-bearing capacity, flexural strength, fracture resistance, and durability; and (3) the reinforcement mechanisms of GO, encompassing its role in hydration kinetics, alterations to the calcium-silicate-hydrate (C-S-H) structure, and bonding interactions at the cement matrix interface. Furthermore, recent advancements in optimizing the dispersion and reinforcement effects of GO, such as surface modification techniques, are explored, emphasizing its potential for multifunctional and intelligent applications. This review aims to provide engineering professionals with the latest insights into the application of graphene oxide as a nano-reinforcement in cement-based composites, while offering valuable guidance and direction for future research in this field.
In the process of developing coal chemical technologies, it is necessary to address environmental pollution and resource waste caused by the associated solid waste coal gasification slag (CGS). This study investigated the feasibility of using CGS as a substitute for fly ash (FA) in the preparation of paste casting bricks. The effects of curing conditions and CGS dosages on the physical properties of the specimens were investigated and related to the hydration behaviors through various microscopic techniques. The results showed that the occurrence of electrostatic flocculation and the enrichment of active substances increased the yield stress of the slurry as the CGS replacement rose, which manifested as decreased fluidity at the macroscopic level. The secondary hydration reaction was facilitated with the increased CGS replacement rate due to the desirable hydraulic activity of CGS. XRD, FTIR and TG results corroborated that the content of hydration products which contributed to strength development were enhanced with the addition of CGS under different curing conditions. XRD and SEM-EDS results indicated that the doping of elements such as Mg and Al under autoclaved condition led to a reduction in the grain size of tobermorite, and the micro-morphology tended to concentrate stresses under pressure. The results of this study promote the resourceful utilization of CGS in building materials and lay the foundation for further scale-up industrial application.
Engineered Cementitious Composites (ECC) are highly regarded in construction owing to their tensile ductility and crack control capabilities, making them suitable for various structural applications. The accumulation of multi-walled carbon nanotubes (MWCNTs) further enhances their mechanical properties. However, there’s a significant knowledge gap concerning MWCNTs-ECC impact resistance. The objective of this study is to tackle the challenges associated with evaluating, optimizing, and predicting MWCNTs-ECC impact resistance to ensure its safe and widespread use in critical infrastructure by applying response surface methodology (RSM). Moreover, the 13 mixtures of ECC combined with several quantities of PVA fiber and MWCNTs as input elements were utilized to calculate the first (E1) and final (E2) impact energies. The findings demonstrated that the MWCNTs-ECC combinations’ impact resistance improved as the input ingredient concentrations increased. Besides, the optimum E1 and E2 of ECC combined with 1% of PVA fiber were noted by 1398 Joules and 12,956 Joules at 0.065% of MWCNTs on 28 days respectively. Furthermore, Response prediction models for E1 and E2 were created, and after being validated with an analysis of variance (ANOVA), it was determined that they had high R² readings of 99.30% and 99.07%, correspondingly. The optimization process produced an ideal number of input variables for MWCNTs and PVA fiber, respectively, of 0.066% and 1%, with a desirability value of 100%. Moreover, it is recommended that the usage of 0.066% of MWCNTs in ECC combined with 1.0–1.50% PVA fiber provides optimum results for the construction industry.
The industrial production of cement contributes significantly to greenhouse gas emissions, making it crucial to address and reduce these emissions by using fly ash (FA) as a potential replacement. Besides, Graphene oxide (GO) was utilized as nanoparticle in concrete to augment its mechanical characteristics, deformation resistance, and drying shrinkage behaviours. However, the researchers used Response Surface Methodology (RSM) to evaluate the compressive strength (CS), tensile strength (TS), flexural strength (FS), modulus of elasticity (ME), and drying shrinkage (DS) of concrete that was mixed with 5–15% FA at a 5% increment, along with 0.05%, 0.065%, and 0.08% of GO as potential nanomaterials. The concrete samples were prepared by using mix proportions of design targeted CS of about 45 MPa at 28 days. From investigational outcomes, the concrete with 10% FA and 0.05% GO exhibited the greatest CS, TS, FS, and ME values of 62 MPa, 4.96 MPa, 6.82 MPa, and 39.37 GPa, on 28 days correspondingly. Besides, a reduction in the DS of concrete was found as the amounts of FA and GO increased. Moreover, the development and validation of response prediction models were conducted utilizing analysis of variance (ANOVA) at a significance level of 95%. The coefficient of determination (R²) values for the models varied from 94 to 99.90%. Research study indicated that including 10% fly ash (FA) as a substitute for cement, when combined with 0.05% GO, in concrete yields the best results. Therefore, this approach is an excellent option for the building sector.
Understanding how different hybrid composite designs under flexural, interlaminar shear and fracture is the objective of this study. The hybrid composite was manufactured utilizing the hand-layup process to produce three different laminate arrangements beside the neat composite. The effects of PC integration and position through the hybrid composites were evaluated, and an analysis of the damage mechanisms was performed. The results demonstrated that incorporating the PC sheet resulted in an improvement in overall performance. Additionally, delamination was determined to be the most prevalent type of failure, followed by fiber and matrix breakage and plastic deformation of PC sheet
The smooth surface of graphene oxide (GO) leads to limited interaction with hydrated cement paste, which severely compromises its benefits to improve the properties of cement composites. In this study, GO dispersion (GOD) and indium chloride were employed to prepare In(OH)3 loaded GO (In(OH)3@GO) with high surface roughness and large specific surface area. In(OH)3@GO obtained using indium chloride and GOD at a mass ratio of 4:100 (IG-4) exhibited increases in surface roughness and specific surface area of 67.6% and 49.9%, respectively, compared to GO without In(OH)3 (IG-0). In(OH)3@GOs were introduced into cement composites to analyse the impacts of varied In(OH)3 loading on mechanical properties, hydration performance and microstructure. Compared to IG-0, GO loaded with various amounts of In(OH)3 exhibited beneficial effects on the cement composites. In particular, cement composite with IG-4 exhibited a compressive strength improved by 26.4%, flexural strength improved by 38.1% and total pore volume reduced by 32.4%.
Herein, small‐sized fluorescent carbon nanoparticles (CNs) with tunable shapes ranging from spheres to various rods with aspect ratios (ARs) of 1.00, 1.51, 1.89, and 2.85 are prepared using a simple anion‐directed strategy for the first time. Based on comprehensive morphological and structural characteristics of CNs, along with theoretical calculations of density functional theory and molecular dynamics simulations, their shape‐control mechanism is attributed to interionic interactions‐induced self‐assembly, followed by carbonization. The endoplasmic reticulum‐targeting accuracy of CNs is gradually enhanced as their shape changes from spherical to higher‐AR rods, accompanied by a Pearson's correlation coefficient up to 0.90. This work presents a facile approach to control the shape of CNs and reveals the relationship between the shape and organelle‐targeting abilities of CNs, thereby providing a novel idea to synthesize CNs that serve as precise organelle‐targeted fluorescent probes.
Traditional room temperature phosphorescence (RTP) materials usually include organometallic composites and pure organic compounds, which generally possess the disadvantages of high toxicity, high cost and complicated preparation. Carbon dots (CDs) are a new kind of luminescent material and have attracted widespread attention due to their benefits of excellent tunable emission, nice biocompatibility, cost-effectiveness, facile preparation and environmental friendliness. Since photoluminescence is an important luminescent property of carbon-based fluorescent nanomaterials, CD-based RTP materials have sparked a new research wave due to the properties of extremely long phosphorescence lifetime, large Stokes shift and high environmental sensitivity. In order to construct excellent CD-based RTP materials, many attempts have been made, and the corresponding progress has been achieved. Herein, we summarize the progress in CD-based RTP materials in recent years, mainly focusing on the outstanding contributions over the years, phosphorescence emission, phosphorescence lifetime, preparation and application of CD-based RTP materials. In particular, this review provides a comprehensive summary and analyze the outstanding contributions in the fields of the phosphorescence emission and phosphorescence lifetime of CD-based RTP materials over the years. Finally, several existing challenges and the future outlook of RTP materials based on CDs have been put forward.
Nano-materials have various promising properties to concrete material. However, the poor dispersion of nano-materials remains to be a big challenge which impairs the target performances and thus increases the economic cost. In this study, we focused on one of the most widely used nano-materials, nano-SiO2 and investigated the influence of its dispersion on the early age hydration of cement pastes. A recently developed method was applied to chemically graft polycarboxylate superplasticizer onto nano-SiO2 particles to produce well dispersed particles with the shell core structure (nano-SiO2@PCE). Dispersity of nano-SiO2@PCE in deionized water (DI water) and in simulated pore solution of cement pastes was carefully characterized by Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), and Fourier Transform Infrared Spectrometer (FTIR) techniques. The effects of nano-SiO2 dispersion on the early age hydration of cement pastes were investigated. The results showed that with good dispersion only 0.5% by mass of nano-SiO2 can significantly accelerate hydration. The retarding effect unintentionally caused by PCE was observed to influence particularly on the length of induction period rather than other stages of hydration. BNG model was used in the end to quantitatively analyze and shed more lights on the influence of nano-SiO2 on the kinetics of C3S hydration. Keywords: Cement paste, Hydration, Nano-SiO2, Dispersion, PCE
The high water absorption and porosity of recycled concrete aggregates (RCA) typically result in a weak interface transition zone (ITZ), thus severely limiting the mechanical property and durability of the prepared concrete. This study proposes a targeted approach to improve the microstructure of ITZ through conformally coating graphene oxide (GO) on RCA (i.e., GO@RCA). The experimental results reveal that the 28-day compressive/ splitting tensile strength of concrete increases by 27%/40%, when GO@RCA replaces RCA. The GO coating significantly reduces the water absorption coefficient and the total charge passed by 15.1% and 63.4%, respectively. To further explore the practical application of such a strategy, instead of direct coating GO on RCA in the case of GO@RCA, RCA is pre-wetted with GO (termed WGO@RCA) before mixing with cement. Interestingly , the data show similar results as the case of concrete containing GO@RCA, strongly indicating the locality of GO at ITZ for WGO@RCA. The enhancement of concrete's mechanical and durability properties resulted from the sub-nanometer thickness of GO coating and the hydrophilic functional groups to promote cement hy-dration at ITZ locally.
Engineered cementitious composites (ECCs) are characterized by multiple cracking behaviors, high tensile-strain capacity, and excellent crack-control ability. Representative fine cracks are difficult to identify with available methods. This study presents a highly accurate and automatic semantic segmentation method for multiple cracks in ECCs using a dual pre-modification deep-learning strategy that considers its specific task scenario. The proposed strategy significantly improved the MIoU to 98.82 % and class accuracy of cracks from 92.28 % to 99.87 %. The generalizability of the model was verified by applying the method to images that were completely unrelated to the close-set. Overall, the proposed method has no requirements on the size of input images, and the entire processing is completely automatic and takes <5 s for a 4016 × 6016 image. Therefore, the proposed method is more intuitive than the traditional digital image correlation method, and the achieved results are also more informative and accurate.
Cement composites, including cement and mortar, are now the most commonly used building components, and thus an extreme and durable emphasis is being articulated. Unique nanoscale fibres, such as carbon nanotubes (CNTs) and graphene oxide (GO), have recently developed to open up new possibilities to boost cement composite performance. GO is a mono-atomically two-dimensional thick carbon allotropic structure that emerged as a 21st-century innovative material. It has been granted global attention owing to its extraordinary transport, thermal, optical, and mechanical properties. Tailoring the properties of cementitious composites with GO-nanomaterial regulates not only the secondary hydration mechanism but also boosts the mechanical performance, durable behaviour, self-healing, and other multifunctional properties. The influence of GO presents an astounding and distinctive performance such as enhancement of gel pores, reduction in larger capillary pores, bridging the microcracks and resisting its propagation, strengthening the overall cement composite performance. This article attempts to present a substantial review of the functioning of cement composites reinforced with GO nanomaterial.
Graphene materials have been extensively explored and successfully used to improve the properties of cement-based composites. However, current studies mainly focus on optimizing additional amounts and dispersion modes of graphene. The influence of other parameters, such as graphene crystallinity, size, and oxygen-containing functional group level, on the performance of cement mortar composite is not fully understood. Therefore, in this study, a series of reduced graphene oxides (rGO) with different oxygen concentrations were synthesized by controlling two parameters, namely, different concentrations of l-Vitamin C (10, 20, 50, and 70 wt%) and different reduction times (15, 30, 45, and 60 min), and added to the cement-mortar composite at the same dosage. The effect of rGO with different oxygen concentrations on the durability and microstructure of the composites was investigated. The durability results revealed that rGO with mild oxygen group level (i.e., prepared by 50 % l-Vitamin C reduction for 30 min) can remarkably enhance the durability of cement mortar composite material. Adding 0.1 wt% rGO with mild oxygen concentration to the cement mortar caused the initial water absorption and secondary water absorption to decrease by 44.75 % and 31.95 %, respectively, compared with ordinary cement mortar. This enables rGO/cement-mortar composites to have outstanding resistance in harsh erosive environments (i.e., high concentrations of CO2) because rGO promotes the cement hydration reaction and generates more hydration products. Meanwhile, the mild oxygen acid groups on the surface of the rGO act as a neutralizer in a strong alkaline medium, resulting in the formation of calcium carbonate precipitation, which further improves the compactness of the matrix.
Here, hydrophobic bulk molybdenum disulfide (MoS2) was efficiently exfoliated into two dimensional (2D) nanosheets assisted with amphiphilic carbon nanodots (CNDs) in pure water. The optimized concentration of obtained 2D-MoS2 is as high as 0.41 mg/mL, which is higher than that of reported literatures. The average lateral size and layer number of 2D-MoS2 is 142.6 (± 2.3) nm and 4, respectively. The characterizations and simulation demonstrated that CNDs can be instantly adsorbed on the surface of 2D-MoS2 and form 2D-MoS2/CNDs composite. Thus, after standing for 1000 h, the concentration of 2D-MoS2 still accounts for 90% of the initial concentration with the help of CNDs. Further, this technique can also be used to prepare graphene and 2D-WS2 nanosheets. 2D-MoS2/CNDs composite as adsorbent showed excellent adsorption capacity (1136.9 mg/g) and ultrafast adsorption rate (1 min) for methylene blue removal, which benefits from abundant adsorption sites and high dispersion. This work not only develops a facile and universal technique for green preparation of 2D nanomaterials in one pot, but also provides a promising adsorbent for removing organic pollutants from aqueous solution.
Nano-SiO2 is a brilliant candidate that endows cement-based materials excellent properties. However, its agglomeration in cement matrix is still an urgent problem. In order to address this issue, well-dispersed calcined stöber nano-SiO2 (CSNS) was prepared as modifier for Portland cement in this work. Monodisperse stöber nano-SiO2 (SNS) was firstly synthesized by using the traditional stöber method and then it was calcined to form CSNS. A series of properties including morphology and structure information of SNS and CSNS were obtained by using scanning electron microscope (SEM), particle size analyzer, X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FT-IR). Their potential pozzolanic activity was also evaluated by using a simulated pore solution method and the possible reaction products were analyzed by using SEM and thermogravimetric (TG) analysis. Finally, their effects on early hydration properties of Portland cement were preliminarily investigated by using isothermal calorimetry, XRD, TG and compressive strength tests. The experimental results showed that both SNS and CSNS with high dispersity and uniform size within 100 nm were successfully prepared. However, both of them present low pozzolanic activity within 3 days. When 2 wt.% SNS was added to cement, the occurrence of acceleration period was slightly delayed and the corresponding maximum heat flow was significantly reduced. Its addition also decreased both hydration degree of the cement paste and the compressive strength of the mortar at 1 day and 3 days. On the contrary, CSNS effectively overcame these negative effects of SNS on cement hydration, and further accelerated cement hydration. Compared with the Portland cement, the addition of 2 wt.% CSNS significantly increased the cumulative heat released with 72 h, and cement hydration degree and compressive strength at each curing age. This is because the hydroxyl (-OH) group was removed after calcination of SNS, which made the well-dispersed CSNS better accelerate cement hydration by effective nucleation sites and filler effects. The findings of this work can provide a guidance for the application of well-dispersed nano-materials prepared based on stöber method to effectively modify the performance of cement-based materials.
As a metal-free and visible-light-responsive photocatalyst, polymeric carbon nitride (PCN) is an ideal alternative to traditional titanium dioxide employed in photocatalytic cementitious materials (PCM) for environmental remediation. However, the interaction between the composition and microstructure of cementitious materials and PCN is far from clear. Herein, the hydration behavior, phase composition, microstructure, compressive strength and nitrogen oxides removal of the PCN-modified paste with different dosage of PCN at varying curing ages were investigated and the key factors governing the photocatalytic activity of the PCM were studied. The results show that the porosity of the PCN-modified pastes presented an increasing trend compared to the reference, but the micro-filler effect of PCN contributed to the varying reductions in the volume of harmful pores, which are mainly responsible for the highest compressive strength of 0.5% PCN-added pastes at 3 days and 28 days. Although the kinds of hydration products were not affected with the addition of PCN, the carbonates could be regulated to the well-crystallized and flower flaky calcites in the presence of PCN at 28 days. The well-crystallized calcite would be regarded as potential acceptors of photo-induced holes to promote the separation of electron-hole pairs on the PCN. The promoting effect of electron transfer could outperform the negative effect of the decreased porosity caused by ongoing hydration and carbonization, resulting in an enhanced photocatalysis of PCM with the increase of curing ages. The findings from this study would provide a novel understanding on the improvement of photocatalytic efficiency for PCM against the shielding effects of hydrates and carbonates.
Steel fiber reinforced concrete (SFRC) is a kind of modified concrete that has attracted much attention at present. Compared with ordinary concrete, SFRC has superior physical and mechanical properties, so it is widely used in railway sleeper prefabricated, highway pavement, and tunnel lining. However, the compressive strength, impermeability, and frost resistance of SFRC are not prominent compared with ordinary concrete. To optimize the performance of SFRC, different amounts of graphene oxide (GO) were added in this study. The results showed that the excellent properties of GO have a significant improvement effect on the mechanical and durability of SFRC. Among them, the compressive strength, flexural strength, and splitting tensile strength of the specimens were increased by 20.1%, 29.5%, and 26.2% compared with the reference group after 28 days of curing. At the same time, the penetration depth of chloride ion is reduced by 56.8% at most compared with the benchmark after adding GO, the mass loss and relative dynamic modulus loss were 4.5% and 32.6% after 100 freeze-thaw cycles respectively, which were much lower than those of the reference group. To explain this phenomenon, different microstructure characterization techniques including XRD, MIP, and SEM were used to study the composition, pore size distribution, and microstructure of concrete. The results showed that the main role of GO is to promote the early hydration reaction, repair the micro defects of the matrix, improve the density of the matrix and strengthen the bonding between steel fiber and the matrix. In this work, the strengthening mechanism of GO on the SFRC matrix has been discussed in detail.
Self-sensing cementitious composites (SSCCs) with carbon nanotubes (CNTs) have attracted extensive attention because of their excellent mechanical and durability properties combined with multifunctional benefits. However, their performance modulation, as well as scalable manufacturing and application, are limited by the uniform dispersion of CNTs inside them. Here, a straightforward approach to in-situ synthesizing CNTs on cement ([email protected]) toward alleviating the CNTs’ dispersion issue and enhancing their composite efficiency and effectiveness is explored. Due to the inherently containing silicate and ferrite phases, microscale cement particles act as effective substrate-bound catalysts, facilitating high-yield and strongly anchored CNTs growth. The hierarchically structured [email protected] integrates the dual functions of reinforcement and conduction, significantly affecting early-age hydration, mechanical, electrical, and self-sensing properties of the final SSCCs with [email protected] The [email protected] structure can promote early-age hydration while slowing the later hydration rate and hindering the strength development of the SSCCs. The addition of [email protected] can be effective in tailoring the electrical microstructures to enhance the electrical conductivity and self-sensing sensitivity of the SSCCs. The SSCCs with [email protected] achieved a maximum stress sensitivity of 2.87%/MPa with a gauge factor of 748. They demonstrated excellent repeatability and stability, outstanding adaptability to various applied conditions, and fast response and recovery. The developed SSCCs-engineered smart track slab is competent in axle counting and speed detection. It opens up a new territory to develop high-performance and versatile SSCCs-engineered smart components/structures for long-term, wide distribution, and low-cost monitoring of high-speed rail (HSR) infrastructures.
Photocatalysis can be an effective technique for eliminating organic contaminants from water. In this study, BiOBr flower-spheres coupled with porous graphite carbon nitride (g-C3N4) were synthesized by controlling the dosage of cetyltrimethylammonium bromide (CTAB). Various characterization techniques were then applied to elucidate the structure-performance relationships of the resulting heterojunction photocatalysts in degrading organic dyes. Experimental results established an optimal molar ratio for KBr to CTAB of 5:1. Benefiting from a remarkable porous structure and tight coupling between porous g-C3N4 and BiOBr, the optimal BiOBr-g-C3N4(2%) exhibited enhanced visible light absorption capability and promoted the separation of photoinduced carriers. Total removal efficiency for rhodamine B (RhB, 25.0 mL, 20.0 mg L⁻¹) reached 87% within 30 min in the presence of BiOBr-g-C3N4(2%) (20.0 mg) (i.e., 1.51 μmol (gphotocatalyst min)⁻¹), which is superior to the performance of BiOBr (72%) (i.e., 1.25 μmol (gphotocatalyst min)⁻¹), g-C3N4 (21%) (i.e., 0.37 μmol (gphotocatalyst min)⁻¹). Furthermore, the photocatalytic reaction rate constant over the optimal heterojunction was 0.034 min⁻¹, which is significantly larger than those of porous g-C3N4 (0.003 min⁻¹) and BiOBr (0.015 min⁻¹). Moreover, this type II heterojunction showed good universality for other organic dyes (such as methyl violet, methylene blue, and crystal violet), highlighting a promising potential role in the elimination of environmental pollutants.
Owing to their remarkable properties, graphene-based nanosheets (GNS) can enable the fabrication of high-performance and sustainable cement composites. Here we review recent advances in GNS-reinforced cementitious composites, focused on the novel strategies (i.e., dispersion, hybridization, coating, and dry mixing approaches) to effectively incorporate GNS into cement/concrete mixes. Furthermore, the impacts of GNS-reinforcement on the mechanical, durability and functional performance of cementitious materials were analytically covered. Lastly, we highlighted the increasing understanding of the fundamentals of the distribution and interplay of GNS within the complex cement microstructure – towards scientific principles to confidently translate GNS to the construction industry.
The mechanical and structural properties of cemented rockfill produced by mineral wastes as recycled aggregates limit its application. In this paper, the macroscopic mechanical and microscopic scanning tests were carried out to study the mechanical property and microstructure of cemented rockfill reinforced by carbon nanotubes (CNTs) and fractal aggregates. The strengthening and deterioration mechanisms of CNT dosage on cemented rockfill were revealed for systematically evaluating its engineering availability. The influencing mechanism of aggregate size distribution on cemented rockfill was clarified to analyze the contribution of optimizing aggregate size distribution. The results show that the strengthening of cemented rockfill by appropriate CNTs includes bridging microcracks, compacting micropores and reinforcing cemented matrix, while the deterioration by excessive CNTs is attributed to form the agglomerative clusters and hollow cemented matrices. The cemented rockfill with superior aggregate size distribution has uniform and dense microstructure with relatively few defects, which is conducive to CNT reinforcement.
Alternative current impedance spectroscopy (ACIS) is a promising non-destructive testing method to monitor long-term change and assess the durability of concrete. This study investigates the influences of Ethylene Diamine Tetraacetic Acid (EDTA) on the hydration of hardening cement by ACIS. It is found that EDTA retards the early-age hydration of cement but can facilitate the later age reaction. Pastes with EDTA show comparable or higher compressive strength than Control at 28 d, especially when the dosage is higher than 0.4%. Microstructural characterization results reveal the working mechanism of EDTA originating from its complexing effect on free ions. The resistivity evolution of the pastes detected by ACIS can well reflect the effects of EDTA on the cement hydration in different ages. Proportional relations are identified between the resistivity and other hydration parameters, such as reaction degree, chemical shrinkage, compressive strength. The results of this study indicate a wider prospect of ACIS in monitoring the microstructure evolution and macro-properties of cementitious materials.
The performance of cement composites was significantly affected by clinker mineral component and nanomaterials. In this work, the effect of clinker mineral component and nanomaterials (nano-SiO2, nano-CaCO3, and nano-TiO2) on cement composites were investigated. Results illustrated that the optimal mineral compositions of C3S, C2S, C4AF, and C3A were 60.23%, 20.01%, 9.74%, and 10.02%, respectively. With the incorporation of nano-particles, the setting time of HCSC was shortened and strength was significantly enhanced, due to acceleration on hydration and optimization on microstructure. The CH content of HCSC containing nano-SiO2 was lower than that of reference due to pozzolanic activity at 28d, whereas the reversed results were found in the HCSC containing nano-CaCO3 and nano-TiO2 due to the nucleation effect promoting hydration. In addition, nano-particles increased mean silicate chain and Al/Si ratio of calcium-silicate-hydrate.
This study developed a facile methodology for preparation of nanoscale dispersion of cellulose nanofibers (CNFs). A suite of methodologies was proposed for the first time to gauge the dispersion quality of CNFs, which was crucial to the subsequent compounding with cement to prepare nanocomposites. Being compatible with cement through interfacial bonding between –COO⁻ of CNFs and Ca²⁺ of cement, CNFs improved the compressive strength of cement by 18% at 0.096 wt% and flexural strength by 21% at 0.480 wt%. Reinforcing mechanisms were explained in terms of the hydration, pore structure and morphologies of the nanocomposites. CNFs at 0.096 wt% significantly decreased the pore volume of cement from 72.66 mm³/g to 51.39 mm³/g and reduced the cement water absorption from 17.23% to 10.60%, which was attributed to the enhanced microstructural densification and pore-size refinement.
Atomically-thin 2D materials have changed the landscapes of many fields. Their applications however are limited by lack of methods for readily and scalable production with high quality. Herein, a simple strategy is reported to exfoliate pristine single or few-layered 2D materials (MoS2, h-BN, WS2, g-C3N4 microsheets) using bottom-up grown amphiphilic graphene quantum dots (GQDs) as both the intercalation agent and dispersant. Further, it is shown that the as-formed GQD/MoS2 van der Waals heterojunctions (vdWHs) give enhanced performance for electrocatalysis of hydrogen evolution reaction owing to the synergistic coupling at the 0D/2D heterojunction, delivering a current density of 10 mA cm⁻² at a low overpotential of 160 mV with a small Tafel slope of 56.9 mV dec⁻¹. In addition to providing a new method for preparing ultrathin 2D microsheets, this study unleashes the application potential of 2D materials and GQD-based 0D/2D vdWHs as non-precious electrocatalysts.
Graphene oxide (GO) as a nano-reinforcing filler has great potential to improve the performance of cement-based composites, however, many challenges must be solved. Recent research has shown that GO tends to coagulate in the alkaline cement pore solution, limiting its reinforcement efficiency to improve the properties of cement composites. In this study, with polycarboxylic ether superplasticizer (PCE) as the main dispersant, methyl orange (MO) was further added to improve the dispersity of GO. The effect of MO on the dispersion of GO in saturated Ca(OH)2 solution was investigated by UV-Vis spectrophotometer, Zeta potentiometer and atomic force microscope. Very low content of MO could significantly improve the colloidal stability of GO in CH solution and the optimal dispersion of GO was achieved when the mass ratio of GO to MO was 1:1. The effect of MO-dispersed GO on cement composites was investigated through mechanical strength analysis, microscopic analysis and chloride ion permeation analysis. The results showed that when the mass ratio was 1:1 and the content of GO was 0.03%, the 3d and 28d flexural strengths of cement mortar (0.03%[email protected]) were increased by 27.4% and 15.4%, and the compressive strengths were increased by 21.8% and 15.3%, respectively, compared with the 0.03% GO-reinforced cement mortar(0.03%-GO). The chloride ion migration coefficient of 0.03%[email protected] was 8.18%, lower than that of 0.03%-GO, which was caused by the denser internal structure of the former. Microscopic tests showed that the addition of MO could promote the dispersion of GO in cement pore solution, regulate the growth of cement hydration crystal and make the cement slurry structure denser. The addition of MO could reduce the loss of fluidity of the fresh slurry caused by GO. This study might provide a low-cost method to simultaneously improve the dispersion of GO in cement pore solution and the workability of GO-blended cement mortar and had many potential practical applications.
This work aims to propose a novel method to treat the defects of delayed hydration and low early-age strength of cementitious composites blended with high-volume fly ash (HVFA). The influence of calcined layered double hydroxide (CLDH) on mechanical properties, hydration process and microstructure of HVFA cementitious composites have been explored. Assessed properties of HVFA cementious composites incorporated various contents of CLDH included compressive strength, flowability, pore size distribution and the alkalinity of pore solution. The hydration process and microstructure were detected by XRD, TGA, Barrett-Joyner-Halenda Analysis (BJH), and SEM-EDS. This work revealed the promising potential of using CLDH as the hardening accelerator for HVFA composites. Results indicated that 0.5–2 wt% CLDH addition can play an important role in early-age strength increment and the HVFA mixture with 0.5 % CLDH addition performed better than other contents. In addition, microstructural analyses demonstrated an acceleration in the hydration of HVFA mortars after CLDH added, thereby higher contents of hydrated products can be observed. Meanwhile, less than 1 % CLDH addition is shown to change the morphology and composition of C-(A)-S-H to be slenderer and with higher Ca/Si ratio. Increasing the pore alkalinity by hydrolysis process and the seeding effect are the main enhancement mechanisms of CLDH.
There is a growing interest in research on application of carbon nanotube (CNT) for development of high-performance cementitious composites. However, most of the research works on cementitious composites were focused on utilization of multi-walled carbon nanotube (MWCNT) which is cheaper and more readily available in the market. Since single-walled carbon nanotube (SWCNT) has superior mechanical properties to MWCNT, it is necessary to investigate the effect of SWCNT on properties of cement paste. In this study, SWCNT was dispersed in water using commercial air entraining agent (AEA). Sodium deoxycholate (DOC) was also used as a dispersing agent for comparison purposes. Cement paste samples containing SWCNT solutions were prepared, and rheological behavior, mechanical strengths and microstructural observation were investigated. According to the results, the addition of SWCNT solutions decreased plastic viscosity, but increased yield stress of cement paste. It was also found that addition of SWCNT increased both compressive and flexural strength of cement paste regardless of the type of dispersing agent used. Although cement paste with SWCNT dispersed by AEA showed less mechanical strength than that dispersed by DOC, it is still possible to be used as a dispersing agent for SWCNT because of its higher mechanical strength than plain cement paste as well as better economic efficiency and readiness of AEA toward construction business.
Chloride permeability and chloride binding capacity are two important factors for assessment of the rebar corrosion risk in reinforced concrete structures. In this work, the chloride permeability and chloride binding capacity of concrete modified with nano-SiO2 (NS), nano-CaCO3 (NC), multi-walled carbon nanotubes (CNT) were evaluated. The results demonstrate that incorporation of nanomaterials significantly decreases the chloride diffusion coefficients by refining the pore structure and reducing the pore volume. The experimental data strongly suggest the existence of a percolation threshold (critical porosity), below which the chloride permeability decreases dramatically. Addition of NS compromises the chloride binding capacity due to decreased pH value of pore solution, which results in dissolution of Friedel's salt. XRD suggests that adding NC restrains the formation of AFm phase, which is mainly responsible for the chemical binding. TG/DTG analyses confirm that adding CNT facilitates the formation of more amount of hydrates, thus enhancing the chloride binding. Addition of NS and NC leads to a decreased amount of Friedel's salt and thereby weakens the chemical binding.
Carbon dots (CDs) have opened up a new field of carbon nanomaterials and successively attracted increasing attention since their discovery in 2004. Owing to their ultrasmall size, tunable surface functional groups, excellent dispersibility, attractive stability, low toxicity, environmental friendliness, facile synthesis and low-cost precursors, CDs have been developed as green and promising friction-reducing and anti-wear materials in lubrication science, applied to energy conservation and extension of mechanical service life in recent years. However, there are few reviews focusing on the application of CDs in the important field of lubrication. In this review, we comprehensively summarize the development of CDs in lubrication for the first time. Firstly, three strategies for structural engineering design of CDs to improve their tribological characteristics are fully analyzed, in terms of size and shape control, surface modification and heteroatom doping. Secondly, the advance in lubrication application of CDs, including CDs as additives for lubricants, greases, gel and magnetorheological fluids as well as CDs as lubricating coatings, is systematically highlighted. Thirdly, the lubricating mechanisms of CDs as additives are introduced in detail. Furthermore, the remaining major challenges and opportunities for CDs in lubrication field are discussed and outlined.
It has been well recognized that the benefits and effectiveness of nanoparticles in cement-based materials could not be maximized if these are not well dispersed. To address this issue, in this study, different anionic (SDS and PCE) and nonionic surfactants (Tweens and Tritons) were used to disperse nanosilica (NS) in aqueous solution and cement pore solution. The results show that the dispersibility of NS in cement pore solution was improved, and the compressive strength of the cement-NS pastes increased linearly with critical micelle concentration (CMC) of nonionic surfactants. Among all surfactants studied, Triton X-405 led the paste to the highest increase in strength (33% at 1-day and 41% at 3-days) since it had the highest CMC. TEM and EDS analysis evidenced that this strength increase might be attributed to the nucleation of outer product CSH gel and its densification with calcite nanocrystals, attributed to Triton X-405 addition.
The unique physical and chemical properties of nano-particles can enhance the nature of cement-based materials at the micro-scale and nano-scale levels, leading to improved properties. To uncover the strengthening mechanism associated with various types of nano-particles, a laboratory investigation was undertaken to evaluate and compare the influence of nano-SiO2 and nano-CaCO3 on mechanical properties of ultra-high performance concrete (UHPC) made with 2% steel fibers. Each type of nano-particle was incorporated at four contents, and the mini-slump flow of the UHPC was maintained at 240–260 mm. The microstructure of the matrix and the fiber-matrix interface of UHPC, as well as the features of hydration products were characterized using advanced techniques, such as electron microscopy (SEM), X-ray diffraction (XRD), differential thermal gravimetric (DTG) analyses, 3D micro-tomography, and mercury intrusion porosimetry (MIP). Test results indicate that both the fiber-matrix strength and mechanical strength of UHPC increased with the increase of nano-SiO2 and nano-CaCO3 until threshold limits of 1% and 3.2%, respectively. The 28-d fiber-matrix bond, compressive and flexural strengths of the optimal UHPC mixtures made with 3.2% nano-CaCO3 were approximately 40%, 10%, and 20%, respectively, greater than those of the reference mixture. These strength values were higher than UHPC made with 1% nano-SiO2. When used below these optimal nano-material contents, the filler and nucleation effects related of the nano-SiO2 and nano-CaCO3 promoted the strength development through improved density and homogeneity with optimized structure of hydration products, as indicated by SEM observation and DTG analysis. Beyond these limits, additional use of nano-materials resulted in increased volume of air voids and capillary pores and weak interfacial zones due to the agglomeration of nano-particles, which hindered strength development.
Nowadays, many nanomaterials such as graphene oxide (GO), carbon nanotubes (CNTs), nano silica (NS) etc. have been introduced to improve the microstructures and performances of cement-based materials (CBM). Compared with other nanomaterials, NS has attracted much attention because of its pozzolanic reaction with calcium hydroxide (CH) to form calcium-silicate-hydrate (C-S-H) gel. Although several review papers have been published, the breadth and depth of literature coverage on NS and its effects on CBM is insufficient. This paper is aimed to keep researchers abreast of the latest research in the field. In particular, the influence of NS on CBM properties including workability, setting time, hydration characteristic, calcium leaching, porosity, mechanical strengths, and durability is critically reviewed. It is believed that this review paper will not only arouse new ideas to promote practical application of NS in construction materials but also provide some constructive guidance for similar research in the future.
Bisphenol A-type epoxy resin reinforced by TiO2 with different dosages (0, 1%, 3%, 5%) was for the first time used as a polymeric admixture to prepare ordinary Portland cement (OPC) mortars in this study. Tensile strength of the TiO2/epoxy resin composite, and flowability, compressive strength and flexural strength as well as the bonding strength of OPC mortars were measured. Scanning electron microscopy (SEM) was also carried out to observe the interfacial transition zone (ITZ) between sand and OPC paste, and the bonding interfacial transition zone (BITZ) between OPC mortar (either modified by the epoxy resin or not) and a substrate material. Results showed the tensile strength of the TiO2/epoxy resin composite was enhanced to a greater extent with a higher content of TiO2 nanoparticles. A lower flowability of mortar samples when modified by the epoxy resin was observed compared to the pure OPC counterpart. The compressive, flexural strength, flexural toughness indicated by the flexural-to-compressive strength ratio and bonding strengths of TiO2/epoxy resin-modified mortars quantified by the interface tensile strength were noted to be the highest for mortars modified by the epoxy resin containing 5% TiO2. For interface tensile strength, it was found that the increment was 7.3% and 14.6% for the mortar specimen modified by the epoxy resin with 5% TiO2 compared to the mortar modified by the same amount of epoxy resin but without TiO2 and the control with no epoxy resin respectively. SEM results showed that both ITZ and BITZ were denser when epoxy resin was added into the OPC mortar systems, leading to an improved flexural toughness and bonding strength. Several enhancing mechanisms are proposed including epoxy resin bridging effect, pore-filling effect, claw-like adhesion and delayed water loss and rigid TiO2 particles with good adhesion towards epoxy resin polymer molecules.
The extensive research on Liquid-Phase Exfoliation (LPE) performed in the last 10 years has enabled a low cost and mass scalable approach to the successful production of a range of solution-processed 2-dimensional (2D) materials suitable for many applications, ranging from composites to energy storage and printed electronics. However, direct LPE requires the use of specific solvents, which are typically toxic and expensive. Dispersant-assisted LPE allows us to overcome this problem by enabling production of solution processed 2D materials in a wider range of solvents, including water. This approach is based on the inclusion of an additive, typically an amphiphilic molecule, designed to interact with both the nanosheet and the solvent, enabling exfoliation and stabilization at the same time. This method has been extensively used for the LPE of graphene and has been discussed in many reviews, whilst little attention has been given to dispersant-assisted LPE of 2D materials beyond graphene. Considering the increasing number of 2D materials and their potential in many applications, from nanomedicine to energy storage and catalysis, this review focuses on the dispersant-assisted LPE of transition metal dichalcogenides (TMDs), hexagonal Boron Nitride (h-BN) and less studied 2D materials. We first provide an introduction to the fundamentals of LPE and the type of dispersants that have been used for the production of graphene, we then discuss each class of 2D material, providing an overview on the concentration and properties of the nanosheets obtained. Finally, a perspective is given on some of the challenges that need to be addressed in this field of research.
We employed Ti-bearing blast furnace slag (Ti-BFS) as raw material to prepare calcined TiO2-loaded layered double hydroxides (TiO2-CLDHs) through acidolysis-alkali precipitation coupled with pyrolysis strategy. During the pyrolysis process, the involvement of TiO2 and LDHs made the TiO2-CLDHs composites have superior photocatalytic ability and abundant porosities, resulting in highly-efficient removal of arsenic (As) from groundwater. Meanwhile, ·OH played crucial role in the As(III) oxidation process through the results of Electron-spin resonance spectroscopy (ESR) and X-ray photoelectron spectroscopy (XPS) measurements. In addition, the co-existing of humic acid in groundwater was found to compete for ·OH and adsorption sites of TiO2-CLDHs, leading to a decrease in As removal. This study not only provided a novel strategy for Ti-BFS disposal, but also evaluated the application of TiO2-CLDHs in the treatment of As contaminants in groundwater environment.
In order to understand the fundamental mechanisms beneath the aggregation of Graphene Oxide (GO) in cement pore solution, deep research about the differences in the dispersion behavior of GO in Ca(OH)2, CaCl2, and NaOH solutions has been done. The results showed that the prime factor responsible for the immediate aggregation of GO in cement paste is the complexation of Ca²⁺, rather than the deoxygenation of GO in the alkaline environment. GO could disperse uniformly in NaOH solution (pH = 12.9) for a few hours. However, with the gradual deoxygenation of GO, small agglomerates formed after 6 h due to the weak electrostatic repulsion and less hydrophilic nature. The analysis of X-ray photoelectron spectroscopy (XPS) and hydration heat measurement showed that GO maintained a large number of functional groups (especially carboxyl groups), which could act as growth sites for hydration products and interact with them. Moreover, the dispersion capacity of GO in the alkaline environment with the presence of polycarboxylate superplasticizer (PC) was also studied and the results revealed that PC could adsorb on GO surface due to the entropy gain and delay the aggregation of GO through steric hindrance effect.
The objective of this study is to assess and compare the effects of different nanoparticles, namely nano-TiO2, nano-Al2O3 and nano-Fe2O3, on the performance of self-consolidating concrete (SCC) in terms of fresh, mechanical, and durability properties through performing different experiments. TiO2, Al2O3, and Fe2O3 nanoparticles with the average diameter of 18, 15, and 14 nm were used with two different contents of 3% and 5% by weight of cement. For assessing the fresh properties of SCC, slump flow, V-funnel, L-box, and column segregation tests were conducted. For the mechanical properties, compressive strength of concrete was investigated, and for the durability properties rapid chloride migration (RCM), electrical resistivity, rapid chloride penetration (RCP), and water penetration depth tests were carried out. The result showed that the workability properties of the mixes slightly improved by 3% addition of nanoparticles while increasing this value to 5% decreased the workability. For higher content of nanoparticles, the incorporation of nanoparticles in the mixes increased the water demand and consequently caused a reduction of workability.
For compressive strength, nano-Fe2O3 showed a superior effect on the enhancement of strength in comparison to nano-Al2O3 and nano-TiO2. This observation was attributed to the formation of calcium ferric hydrate (C-F-H) gel in the microstructure. Moreover, the addition of all the nanoparticles resulted in an improvement of durability properties. High surface area of nanoparticles provided nucleation sites for cement particles and expedited the hydration process development. The formation of a higher content of hydration products helped the densification of microstructure. Moreover, nanoparticles controled the growth pattern of C-S-H gel, which led to the formation of a homogenous microstructure with smaller pore sizes and consequently to lower permeability against penetration of aggressive ions i.e., chloride. It is concluded that partial replacement of cement with nanoparticles on average improved the compressive strength and durability properties of SCC, but resulted in a reduction of workability.
Growing concerns of water pollution by dye pollutants from the textile industry has led to vast research interest to find green solutions to address this issue. In recent years, heterogeneous photocatalysis has harvested tremendous attention from researchers due to its powerful potential applications in tackling many important energy and environmental challenges at a global level. To fully utilise the broad spectrum of solar energy has been a common aim in the photocatalyst industry. This study focuses on the development of an efficient, highly thermal and chemical stable, environmentally friendly and metal-free graphitic carbon nitride (g-C3N4) to overcome the problem of fast charge recombination which hinders photocatalytic performances. Nitrogen-doped carbon quantum dots (NCQDs) known for its high electronic and optical functionality properties is believed to achieve photocatalytic enhancement by efficient charge separation through forming heterogeneous interfaces. Hence, the current work focuses on the hybridisation of NCQDs and g-C3N4 to produce a composite photocatalyst for methylene blue (MB) degradation under LED light irradiation. The optimal hybridisation method and the mass loading required for maximum attainable MB degradation were systematically investigated. The optimum photocatalyst, 1 wt% NCQD/g-C3N4 composite was shown to exhibit a 2.6-fold increase in photocatalytic activity over bare g-C3N4. Moreover, the optimum sample displayed excellent stability and durability after three consecutive degradation cycles, retaining 91.2% of its original efficiency. Scavenging tests were also performed where reactive species, photon-hole (h+) was identified as the primary active species initiating the pollutant degradation mechanism. The findings of this study successfully shed light on the hybridisation methods of NCQDs which improve existing g-C3N4 photocatalyst systems for environmental remediation by utilising solar energy.
Van der Waals heterojunctions (vdWHs) formed between 2D materials have attracted tremendous attention recently due to their extraordinary properties which cannot be offered by their individual components or other heterojunctions. Intriguing electronic coupling, lowered energy barrier, intimate charge transfer, efficient exciton separation occurring at the atomically sharp interface promise their applications in catalysis which, however, are largely unexplored. Herein, we demonstrate a 0D/2D vdWH between 0D graphene quantum dots (GQDs) and 2D pristine graphene sheets, simply prepared by ultrasonication of graphite powder using GQDs as intercalation surfactant. And such all-carbon Schottky-diode-like 0D/2D vdWH is employed for the emerging photoelectrochemical catalysis (water splitting) with high performance. The demonstrated low-cost and scalable bottom-up growth of heteroatom-doped GQDs shall greatly promote their widespread applications. Moreover, the mechanisms underlying GQD growth and heterojunction mediated catalysis are revealed both experimentally and theoretically.
The unique attractive properties that make graphene nanoplatelets (GNPs) effective nano-reinforcer for cement composites. Dispersion of GNPs with dispersant is a conventional method. In order to avoid the introduction of dispersant left in cement-based materials, water reducing agent was directly used to disperse GNPs. This article investigated GNPs were dispersed using different water reduced agents, the mechanical properties and toughening mechanism of modified GNPs reinforced cement composites. In this research, GNPs were dispersed well in aqueous solution using polycarboxylate superplasticizer (PS), naphthalene superplasticizer (NS) and melamine superplasticizer (MS) as dispersants with ultrasonication. Results showed that water reducers can improve the influence of GNPs on cement-based materials and a GNPs dosage of 0.06 wt% could make the GNPs/cement composites as flowable as the plain sample. The flexural strength of cement paste increased up to 16%, 13% and 20% with 0.06 wt% PS, NS and MS modified GNPs at 28d, it increased the compressive strength of the GNPs/cement composites by 8%, 5% and 11.2%. The ratio of compressive-bend strength of decline rates of PS and NS modified GNPs/cement composites were 7.4% and 8.2% at 0.06 wt% GNPs at 28d, while the ratio of compressive-bend strength of decline rates of MS modified GNPs/cement composites were 10.9% with 0.09 wt% GNPs at 28d. It found that GNPs could accelerate hydration process of cement composite, leading to more hydration products, finer CH crystals, longer mean chain length of CSH gel and lower porosity, and thus the propagation of cracks of the cement composites was inhibited.