Supplementary Cementitious Materials Research Articles

Valorization of industrial wastes for sustainable cement-based materials with enhanced chloride binding

Improving the chloride binding capacity of cement-based material can effectively slow down the corrosion of steel bars in concrete. This study investigated the valorization of two industrial wastes, carbonated sintering red mud (CSRM) and bauxite tailings (BT), as supplementary cementitious materials (SCMs) to enhance the chloride binding capacity of cement-based materials. CSRM and BT were incorporated separately and in combination to prepare cement paste mixtures, replacing 10–30 % of ordinary Portland cement. The bound chloride contents were determined, and the hydration products were characterized using X-ray diffraction and thermogravimetric analysis. Both CSRM and BT promoted the formation of Friedel's salt (FS) through increased aluminum dissolution and conversion of monocarbonate/monosulfate phases. In the early ages, the synergistic effect of CSRM and BT resulted in the highest FS content. At later ages, BT demonstrated superior chloride binding due to its high alumina content facilitating continued FS formation. Furthermore, the adverse effect of CSRM on the composite system was less than that of BT. At 28d age, when the SCMs content was 30 %, the compressive strength of cement-BT system was 34.5 % lower than the control, while the compressive strength of cement-CSRM system was only 20.9 % lower than the control. The findings highlight the potential of valorizing CSRM and BT as sustainable SCMs for developing chloride-resistant cement-based materials.

Development of hybrid gradient boosting models for predicting the compressive strength of high-volume fly ash self-compacting concrete with silica fume

In an effort to extend the service life of structures under harsh exposure conditions and reduce the carbon dioxide emissions from cement production, researchers are examining the performance of cement concretes with different mineral admixtures. This study focuses on self-compacting concrete (SCC) incorporating high-volume fly ash (HVFA) and silica fume (SF) as supplementary cementitious materials (SCMs). The aim is to investigate the fresh and hardened properties, particularly the compressive strength, of these combinations. SCMs were used to replace varying amounts of cement, with SF showing the greatest improvement in mechanical characteristics across all age groups. Advanced modelling techniques, including Gradient Boosting (GB), Gradient Boosting-Particle Swarm Optimization, Gradient Boosting-Bayesian Optimization, and Gradient Boosting-Differential Evolution (GB-DE), were employed to analyse the strength characteristics of HVFA-SCC. The GB-DE model emerged as the most accurate, with an R² value of 0.995029 and an RMSE of 0.023862. Additionally, an open-source GUI based on GB-DE is introduced to provide engineers with a transparent tool for optimizing concrete mix designs, addressing the opacity of traditional machine learning models.

ANN‐based analysis of the effect of SCM on recycled aggregate concrete

AbstractRising environmental awareness has prompted in‐depth studies on how the concrete industry affects the environment. Using recycled concrete aggregates (RCAs) and supplementary cementitious materials (SCMs) in concrete manufacturing provides advantages for sustainability. However, the broader chemical composition of SCMs and the inferior qualities of RCAs compared with natural aggregates (NAs) often lead to a decrease in concrete mechanical strength. The difficulty lies in foreseeing how the inclusion of SCMs and RCAs will affect the concrete compressive strength. The artificial neural network (ANN) approach presented herein can precisely forecast the recycled aggregate concrete (RAC) compressive strength, even when incorporates SCMs. The analysis employing the connection weight approach (CWA) determines how input variables influence compressive strength. Results indicate silica fume contributes most to compressive strength, followed by cement content, silica modulus, fine natural aggregate dosage, and coarse natural aggregate. Additionally, the amount of water utilized, the water/cement ratio, and the presence of RCA are all detrimental to compressive strength. The adverse effect of the cementitious materials' alumina modulus can be attributed to increased water demand during their reaction. Performance metrics of the final ANN model on the testing data subset include R2 = 0.94, and RMSE = 3.11, utilizing 834 data observations after outlier treatment for training and validation purposes. In summary, the ANN‐based approach demonstrates its efficacy in predicting concrete compressive strength when incorporating SCMs and RCAs, shedding light on the influential factors in concrete performance.

Integrated approach to assess the environmental suitability of red ceramic waste as a supplementary cementitious material in structural concrete

Integrated approach to assess the environmental suitability of red ceramic waste as a supplementary cementitious material in structural concrete

Experimental investigation of the temperature-dependent dissolution process of aluminosilicate glass and low-calcium supplementary cementitious materials under alkaline conditions

High-temperature curing is commonly employed to promote the pozzolanic activity of supplementary cementitious materials (SCMs) in cementitious systems. Herein, the temperature-dependent dissolution processes of low-calcium SCMs and synthesised aluminosilicate glass were examined at pH 13 for cementitious systems. The dissolution rate and thermal activation energy (TAE) were estimated using nonlinear fitting and the Arrhenius equation. Experimental and analytical findings demonstrated that the TAEs of investigated SCMs and aluminosilicate glasses were temperature-dependent, decreasing with increasing temperature. Moreover, the TAE of aluminosilicate glasses increased with increasing Al/Si ratio, mainly due to the higher TAE of Al2O3 compared to SiO2. In addition, the TAE of fly ash was higher than that of investigated glass, largely because the Si and Al coordination numbers increased with decreasing cooling rates, according to molecular dynamics analysis. The topological TAE derived from molecular dynamics analysis is a promising parameter for estimating the TAE of aluminosilicate glass.

Optimization and Modeling of 7-Day Ultra-High-Performance Concrete Comprising Desert Sand and Supplementary Cementitious Materials Using Response Surface Methodology

Optimization and Modeling of 7-Day Ultra-High-Performance Concrete Comprising Desert Sand and Supplementary Cementitious Materials Using Response Surface Methodology

Analyzing the Impact of Supplementary Cementitious Material and Polypropylene Fiber on the Fresh, Mechanical Properties, and Acid Attack of Quaternary Blended Self Compacting Concrete

Analyzing the Impact of Supplementary Cementitious Material and Polypropylene Fiber on the Fresh, Mechanical Properties, and Acid Attack of Quaternary Blended Self Compacting Concrete

Mix and measure II: joint high-energy laboratory powder diffraction and microtomography for cement hydration studies.

Portland cements (PCs) and cement blends are multiphase materials of different fineness, and quantitatively analysing their hydration pathways is very challenging. The dissolution (hydration) of the initial crystalline and amorphous phases must be determined, as well as the formation of labile (such as ettringite), reactive (such as portlandite) and amorphous (such as calcium silicate hydrate gel) components. The microstructural changes with hydration time must also be mapped out. To address this robustly and accurately, an innovative approach is being developed based on in situ measurements of pastes without any sample conditioning. Data are sequentially acquired by Mo Kα1 laboratory X-ray powder diffraction (LXRPD) and microtomography (µCT), where the same volume is scanned with time to reduce variability. Wide capillaries (2 mm in diameter) are key to avoid artefacts, e.g. self-desiccation, and to have excellent particle averaging. This methodology is tested in three cement paste samples: (i) a commercial PC 52.5 R, (ii) a blend of 80 wt% of this PC and 20 wt% quartz, to simulate an addition of supplementary cementitious materials, and (iii) a blend of 80 wt% PC and 20 wt% limestone, to simulate a limestone Portland cement. LXRPD data are acquired at 3 h and 1, 3, 7 and 28 days, and µCT data are collected at 12 h and 1, 3, 7 and 28 days. Later age data can also be easily acquired. In this methodology, the amounts of the crystalline phases are directly obtained from Rietveld analysis and the amorphous phase contents are obtained from mass-balance calculations. From the µCT study, and within the attained spatial resolution, three components (porosity, hydrated products and unhydrated cement particles) are determined. The analyses quantitatively demonstrate the filler effect of quartz and limestone in the hydration of alite and the calcium aluminate phases. Further hydration details are discussed.

Eco-friendly mix design of slag-ash-based geopolymer concrete using explainable deep learning

Geopolymer concrete is a sustainable and eco-friendly substitute for traditional OPC (Ordinary Portland Cement) based concrete, as it reduces greenhouse gas emissions. With various supplementary cementitious materials, the compressive strength of geopolymer concrete should be accurately predicted. Recent studies have applied deep learning techniques to predict the compressive strength of geopolymer concrete yet its hidden decision-making criteria diminish the end-users’ trust in predictions. To bridge this gap, the authors first developed three deep learning models: an artificial neural network (ANN), a deep neural network (DNN), and a 1D convolution neural network (CNN) to predict the compressive strength of slag ash-based geopolymer concrete. The performance indices for accuracy revealed that the DNN model outperforms the other two models. Subsequently, Shapley additive explanations (SHAP) were used to explain the best-performed deep learning model, DNN, and its compressive strength predictions. SHAP exhibited how the importance of each feature and its relationship contributes to the compressive strength prediction of the DNN model. Finally, the authors developed a novel DNN-based open-source software interface to predict the mix design proportions for a given target compressive strength (using inverse modeling technique) for slag ash-based geopolymer concrete. Additionally, the software calculates the Global Warming Potential (kg CO2 equivalent) for each mix design to select the mix designs with low greenhouse emissions.

Probabilistic Corrosion-free Service Life of the RCC Structures Made with OPC and Ultra-fine Slag-based Binders

The primary factor in the deterioration of reinforced concrete is chloride-induced corrosion. It has a direct impact on the service life of the structure and has been the subject of much research over the past 5 decades. One of the most cost-effective ways to lessen chloride-induced corrosion was identified to be the use of more supplementary cementitious material (SCM). Moreover, when SCMs are ground down to a smaller size, the resulting particles serve as microfillers, which have a significant impact on the improvement of mechanical properties and durability. This paper highlights the influence of grinding slag into an Ultra Fine Slag (UFS) on chloride ion penetration in the mortar specimen. A bulk diffusion test was performed on a mortar replaced with UFS which show a synergic reduction in chloride diffusivity in comparison with control mixes. In addition, an attempt is made on prediction of probabilistic service life estimation by Error function model.

Engineering properties as a supplement cementitious material of ground copper reduction slag extracted valuable metal from Cu slag

We have examined whether the copper reduction slag (CRS) generated after recovering valuable metals from copper slag (CS) by reduction process can be used as supplementary cementitious materials (SCMs). According to the test results, the Cu secondary slag with low Fe, Cu, and heavy metal contents had a suitable oxide composition for using as a SCM. CRS showed better grinding efficiency than that of ground blast furnace slag (GGBS). Ground CRS contributed to the formation of tobermorite under autoclaved curing conditions. The compressive strength of CRS mortar replacing 50 % of OPC generated 93 % of that of the OPC mortar. Based on the results of this study, we found that the CRS has highly appropriate engineering characteristics for using as SCMs for concrete. In addition, it is judged that the method of using secondary slag as a material for precast concrete produced under hydrothermal conditions can greatly contribute to the construction process of buildings by securing mechanical performance.

Low-carbon microwave curing of limestone calcined clay cement (LC3): Performance and mechanism

Limestone calcined clay cement (LC3) incorporates calcined clay and limestone as supplementary cementitious materials that can replace up to 50 % of conventional cement, significantly reducing the carbon emissions associated with cement production. However, challenges remain, including the inefficiencies of traditional curing methods and suboptimal early strength properties. Consequently, this study presents the low-carbon microwave curing approach for LC3 mortar. A comparative analysis of 15 different microwave curing systems was carried out. The results show that the optimum microwave curing efficiency is 300 W of heating power, 5 minutes of heating, 25 minutes of rest, and eight cycles. Three curing methods, including microwave curing, standard curing, and steam curing, were also compared. Microwave curing significantly increased the early strength of LC3 mortar, with 1-day compressive strength 1.78 times greater than standard curing and 1.26 times greater than steam curing. Microscopic studies show that the “thermal effect” of microwaving increases the internal Hc content of LC3, promotes the secondary hydration reaction of Ca(OH)2 within the LC3 material, and reduces the porosity of LC3, achieving reductions of 37.8 % and 8.9 % compared to standard and steam curing, respectively. This helps to improve the efficiency of the curing process. The results of this research will advance the use of low-carbon LC3 in building structures.

Optimization of Pre-Treatment Process in Spent Bleaching Earth (SBE) on The Characteristics of Pre-Treated SBE as Supplementary Cementitious Material

Optimization of Pre-Treatment Process in Spent Bleaching Earth (SBE) on The Characteristics of Pre-Treated SBE as Supplementary Cementitious Material

Mechanical performance and permeability of low-carbon printable concrete

Common issues in 3D printed concrete arise due to its high cement content, processing requirements, and the lack of extensive research into its long-term performance. To this end, this study explores using supplementary cementitious materials from local regions to partially replace cement, aiming at reducing the carbon footprint. Various printable mixtures with different substitution rates are formulated, and corresponding mechanical and permeability tests are conducted. It is revealed that the compressive and flexural strengths of 3D printed concrete with low cement content were lower than the strength of cast concrete due to the construction process of printed concrete; the mechanical strength of 3D printed concrete showed prominent anisotropic characteristics. It was found that, compared with the other two sets of ratios, the higher contents of FA and GGBFS could effectively fill the pores of the printed concrete. Both the capillary water absorption and the content of chloride ions of the low-carbon mixture were significantly lower than that of the pure cement-printed specimens.

Experimental investigation on properties of gold tailings recycled brick-concrete aggregate concrete under microwave curing

Tailings are the low-value solid waste by-products, which can be expected to serve as sustainable material through activation. In this study, activated gold tailings (GT) were utilized as supplementary cementitious materials to produce GT-cement slurry and gold tailings recycled brick-concrete aggregate (GT-RBCA) concrete. By varying curing methods including microwave curing and steam curing, the effects of resting time and curing temperature on compressive strength of GT-cement slurry specimens were experimentally analyzed. Also, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to analyze the hydration products and microstructure. Additionally, the compressive strength of GT concrete including GT-RBCA concrete under these curing methods were explored, followed by an assessment of environmental and economic benefits. The results demonstrated that a curing temperature around 40 °C with microwave method and 10%–20 % GT will benefit the strength development of GT-cement slurry specimens, reach the highest 28-day compressive strength of 42.6 MPa compared with steam curing and standard curing. This could be attributed to the “hot spot" effect of GT under microwave curing, leading to effective promotion of the pozzolanic reaction and subsequent enhancement of the hydration reaction. For GT-RBCA concrete, microwave curing exhibited the best effect on early compressive strength of GT-RBCA concrete compared with other curing methods. Particularly, whether the standard water-cement ratio condition (w/c = 0.42) or the low water-cement ratio condition (w/c = 0.35), GT-RBCA concrete under microwave curing at 40 °C and 10 % gold tailings substitution rate, achieved a maximum 12.3 % increase in 28-day compressive strength compared to steam curing and standard curing conditions. In addition, the GT-RBCA concrete under microwave curing obtained 11.7 % CO2 emissions reduction compared with steam curing.

Data-Driven Insights into Controlling the Reactivity of Supplementary Cementitious Materials in Hydrated Cement

Supplementary cementitious materials (SCMs) play an essential role in sustainable construction due to their potential to reduce carbon emissions, promote circular economy principles, and enhance the properties of concrete. However, the inherent diversity of SCMs makes it challenging to predict their degree of reaction (DOR). This study applies machine learning techniques to predict DOR while exploring key parameters affecting it. Five machine learning models are utilized: linear regression, Gaussian process regression (GPR), decision tree regression, support vector machine and extreme gradient boosting, with GPR providing the most accurate and adaptable prediction. The study delves into the impact of various parameters on DOR, revealing their significance. Silica content emerges as the most critical, followed by particle size distribution, specific gravity, and water-to-cement (W/C) ratio. Optimizing DOR requires extending curing time, reducing particle size distribution, and considering optimal silica content and W/C ratio. This research emphasizes the importance of understanding the relationships between parameters and the DOR of SCMs, providing insights to enhance the efficiency of SCMs in cementitious systems through machine learning and data-driven analysis.

Using ensemble machine learning and metaheuristic optimization for modelling the elastic modulus of geopolymer concrete

Geopolymer concrete emerges as a sustainable and durable alternative to conventional concrete, addressing its high carbon footprint and enhanced durability. The distinct properties of geopolymer concrete, governed by supplementary cementitious materials and alkaline activators, promise reduced environmental impact and improved structural resilience. However, its complex composition complicates the prediction of mechanical properties such as the elastic modulus, crucial for structural applications. This study introduces an innovative approach using the eXtreme Gradient Boosting (XGBoost) technique integrated with the multi-objective grey wolf optimizer to model the elastic modulus of geopolymer concrete. By dynamically selecting influential features and optimizing model accuracy, this methodology advances beyond traditional empirical models, which fail to capture the nonlinear interactions intrinsic to geopolymer concrete. Utilizing a comprehensive database gathered from extensive literature, 22 potential variables were examined that influence geopolymer concrete’s elastic modulus. After mitigating multicollinearity and optimizing hyperparameters via Bayesian optimization, six XGBoost models were developed with different combinations of input variables, revealing compressive strength and total water content as pivotal predictors. The findings illustrate the models’ precision, with the trade-off between prediction accuracy and model simplicity visualized through the relationship between the number of input variables and prediction error. The study culminates in a user-friendly graphical user interface that enables easy prediction of geopolymer concrete’s elastic modulus and fosters educational engagement. This interface, available online, underscores the practicality and accessibility of advanced machine learning predictions. Overall, this research not only provides a robust predictive framework for geopolymer concrete’s elastic modulus using optimized input variables but also enhances the understanding of its underlying determinants, contributing to the advancement of sustainable construction materials.

Influence of processing methods on the strength activity index for sludge as a supplementary cementitious material

Utilizing activated sludge as a partial substitute for cement can both curb cement consumption and address sludge reuse in an economically and environmentally-friendly manner. This study delves into the pozzolanic activity of mechanically-thermal (MT) activated sludge and alkali-mechanical-thermal (AMT) activated sludge, employing the strength activity index (SAI) method. Microscopic insights provided by X-ray diffraction (XRD), scanning electron microscopy (SEM), and laser particle size analysis aid in the interpretation of observed phenomena. The findings underscore the superiority of MT activation over AMT activation, with an SAI of 97 %. Optimal pozzolanic activity is achieved through a 2-hours holding time, slow heating at 10 °C/min, and rapid cooling. A calcination temperature of 800 °C effectively promotes the decomposition of active minerals and enhances the sludge's pozzolanic activity. Additionally, a ball milling time of 2 minutes proves sufficient to meet practical demands, as prolonged ball milling has a limited impact on sludge pozzolanic activity.

Effect of expanded perlite aggregates and temperature on the strength and dynamic elastic properties of cement mortar

The residential market consumes nearly half of the world’s concrete production, and it is anticipated that 68 % of the global population will reside in urban areas by 2050. Researchers have focused their efforts on exploring alternative options to natural aggregates in concrete and mortar. In line with the principles of circular economy, construction and demolition waste has been repurposed for the manufacture of cement-based materials. Volcanic products, which are abundant but underutilized, have been identified as an alternative to recycled aggregates. They offer several advantages over natural river aggregates, including reduced weight, enhanced thermal and acoustic insulation, improved fire resistance and pozzolanic characteristics. While there has been a significant amount of research on the use of expanded perlite as a supplementary cementitious material, studies involving the use of expanded perlite aggregates (EPA) in cement-based construction materials are relatively limited. This paper seeks to address this knowledge gap by investigating the use of EPA in cement-based mortar at both room and elevated temperatures. The study examines the impact of varying replacement percentages (10 %, 20 % and 30 % - by volume) of natural sand with EPA having a maximum grain size of 4 mm, and the exposure temperature of mortar prisms at the age of 28 days. Specifically, temperatures of 100ºC, 150ºC and 200ºC were selected for analysis. The impact of these parameters on the flexural and compressive strength of mortar, as well as its dynamic elastic properties, was experimentally determined. The findings indicate that, at room temperature, higher replacement percentages of natural sand by EPA result in decreased flexural and compressive strengths, by as much as 50 % and 30.71 %, respectively. However, the dynamic moduli values for replacement percentages up to 20 % are similar to those of the reference mix. Conversely, when subjected to temperatures up to 200ºC, significant improvements were observed in the flexural strength values, e.g. over 20 % for temperatures of 150°C and 200°C, with only marginal improvements in compressive strength, 3 % ÷ 20 % for temperatures of 150°C and 200°C, compared to values obtained at room temperature.

Enhancement of phosphogypsum-based solid waste cementitious materials via seawater and metakaolin synergy: Strength, microstructure, and environmental benefits

Phosphogypsum-based cementitious materials (PGCM) possess the potential to solidify corrosive ions in seawater and may serve as a viable alternative to Ordinary Portland Cement (OPC). However, despite this potential, limited research has explored the use of seawater as mixing water in PGCM, and the hydration mechanism underlying their interaction remains unclear. This study aimed to examine the impact of seawater on the macroscopic and microscopic characteristics of PGCM, as well as the underlying mechanisms and the evolution of PGCM properties in the presence of a synergistic effect between seawater and supplementary cementitious material, metakaolin (MK). The results demonstrate that using seawater as mixing water for PGCM mortars reduces workability. Conversely, sulphate ions in seawater shortened the induction period of PGCM, accelerated ettringite formation, shortened the setting time of PGCM, and enhanced the early strength of PGCM. However, the enhancement of the late strength of PGCM by seawater was limited. The synergistic effect of seawater and MK significantly increased the compressive strength of PGCM, with an enhancement of 45.31% and 20.48% at 28 and 90 days, respectively. This enhancement was linked to the hydration reaction of Na+ ions in seawater and MK, forming N-A-S-H gel network structure that influenced the microstructure of PGCM. Moreover, the incorporation of seawater and MK in PGCM offers both economic and environmental sustainability benefits.