Supplementary Cementitious Materials Research Articles

Understanding the utilization potential of lepidolite slag in cementitious materials: Composition characteristics, hydration properties, and high value-added cementitious system design

Lepidolite slag (LES) is a kind of solid waste produced by extracting lithium from lepidolite, but researches focused on it are still limited. This paper works on understanding the utilization potential of LES in cementitious materials from its composition characteristics, hydration properties, and high value-added cementitious system design. Results show that the reactivity of LES is notably low in both water and alkaline solution. As a supplementary cementitious material (SCM), LES exhibits several drawbacks, including prolonging setting time, reducing compressive strength, and deteriorating pore structure. With addition of 30 % LES, the compressive strength at 28 d decreased by 63.3 %. Considering the high gypsum content within LES, an all-solid waste cementitious system was designed using high-volume LES combined with blast furnace slag (BS) and a small amount of lime. System with 40 % LES presents similar compressive strength with system composed entirely of BS at both 7 d and 28 d. The mechanism is that the excellent compound activation effect of gypsum in LES and lime on BS promoted the transformation of hydrotalcite to ettringite in the system. Even when LES content reached 70 %, compressive strength at 28 d surpassed 15 MPa. This study proposes a novel high value-added utilization way for LES in cementitious materials.

Preparation of aragonite-rich whisker materials from magnesium slag and salt lake bischofite and its effects on cement properties

This study develops an innovative wet carbonation process utilizing Magnesium Slag (MS), Salt Lake Bischofite (SLB), and CO2 to prepare carbonized materials mainly composed of aragonite and active silica gel, all raw materials were solid wastes. Subsequently, it was employed as Supplementary Cementitious Materials (SCMs) additive in cement, with the goal of efficiently capturing carbon dioxide and transforming aragonite whiskers into high-value products. Investigated the parameters influencing the formation of aragonite, including temperature and the concentration of the SLB solution, while exploring the nucleation and growth mechanisms of aragonite. The findings reveal that under 80 °C, the suspension of MS with 0.83 % SLB solution swiftly produces needle-like aragonite whiskers with single crystal lengths ranging from 10-20 μm and diameters of 0.3–0.5 μm. With the increase in SLB concentration, the aspect ratio of aragonite whiskers decreases. Additionally, highly polymerized amorphous silica gel was also detected. Therefore, Carbonated Aragonite-type Magnesium Slag (CAMS) (34.0901 m2/g) exhibits a significantly larger specific surface area compared to MS (0.9877 m2/g), representing an enhancement factor of 34.5 times, which concurrently bolsters its capability to adsorb reactive ions. During the carbonation process, 1 g of MS can sequester and solidify 0.403 g of CO2. Furthermore, incorporating CAMS as SCMs into cement mixtures notably enhances both the compressive and flexural strengths of cement mortar. These findings offer a sustainable approach to the recycling of solid waste, CO2 sequestration, and the improvement of cement-based material properties.

Assessment of Various Mitigation Strategies of Alkali-Silica Reactions in Concrete Using Accelerated Mortar Test.

The widespread use of reinforced concrete continues to face challenges, particularly in mitigating alkali-silica reaction (ASR), due to its detrimental effects on concrete strength and durability. This paper investigates the effectiveness of using binary supplementary cementitious materials (SCMs) in mitigating ASR by incorporating metakaolin (MK) and waste glass powder (GP) as partial replacements for cement. Additionally, the potential of a new cement product, "NewCem Plus" (NCM), along with the use of basalt fibers and lithium, was evaluated through a 14-day accelerated mortar bar test following the ASTM C1260. This study also assessed concrete's properties such as its compressive strength and workability using the flow test. The results indicated that MK was effective, reducing expansion by 79%, 84%, and 88% with 10%, 20%, and 30% cement replacement, respectively, compared to the control mixture. On the other hand, GP showed a more modest reduction in expansion, with 10%, 20%, and 30% replacement levels reducing expansion by 20%, 43%, and 75%, respectively. Furthermore, the addition of lithium to MK significantly mitigated ASR, reducing expansion below the ASTM threshold. However, mixtures containing NewCem Plus, lithium, and basalt fibers showed minimal impact on ASR reduction. These findings underscore the viability of using binary or ternary blends of SCMs to mitigate ASR in concrete, encouraging their adoption in future concrete applications.

The effect of water absorption and specific gravity of supplementary cementitious materials on required water

The use of supplementary cementitious materials (SCM) is projected to increase because they reduce the global warming potential of concrete. When cement is replaced with SCM, the flow of the mixture may change. The porosity of the paste may also change as the liquid-to-solid volumes change when mass replacement is used. This paper discusses the role of water absorption and the specific gravity of the SCM on the water requirements of a mixture. Over thirty SCMs were tested, including sixteen natural pozzolans, ten coal ashes, three blended pozzolans, and one ground glass. The porosity of the SCM was measured using a drying rate test. The water absorbed by the natural pozzolans ranged from 3.25 to 17.25 %, 5.55–9.25 % for blended pozzolans, 4.10–18.95 % for coal ashes, and 4.20 % for ground glass. The water requirement measured using ASTM C311 ranged from −4.25 to 46.2 %. The specific gravity of the SCM is particularly important when it is significantly different from the specific gravity of the OPC, as this can change the liquid-to-solid volume ratio. Accounting for the absorption of water by the SCM and the specific gravity of the SCM (via volume replacement) resulted in 55 % of the specimens having a water demand within ±5 % of the original mixture to achieve the same flow, and 94 % of the samples had a water demand within ±20 %. This was substantially less than mass replacement. Using volume replacement and accounting for SCM absorption would have water requirements more similar to the original mixtures.

Utilization of incense stick ash as a supplementary cementitious material: Effects on strength, cement chemistry, and sustainability

Incense stick ash (ISA), a by-product generated from the combustion of biomass during religious rituals, presents challenges regarding its high-volume disposal despite some emerging technologies offering avenues for its reuse. This study aims to investigate the feasibility of utilizing ISA as a supplementary cementitious material and its impact on fresh and hardened properties, hydration kinetics, microstructure, and environmental and economic aspects of Portland cement (PC) pastes. Results reveal that incorporating 5–20 % ISA increases the cumulative heat release per gram of PC. Specifically, replacing 5 % of PC with ISA enhances the 28-day compressive strength, with an increase of 19.78 % compared to plain cement paste. However, further elevation in ISA substitution leads to a decline in compressive strength. The utilization of 5 % ISA refines the pore structure of samples and elevates the content of calcium silicate hydrate (C-S-H), particularly the proportion of high-density C-S-H. Additionally, carbonates present in ISA react with AFm to form monocarbon calcium aluminate, which stabilizes AFt and enhances the microstructural compactness of cement paste. Compared to plain cement paste, the paste with 5 % ISA exhibits lower coefficients for the cost of pastes per cubic meter, CO2 emission of pastes per cubic meter, and non-renewable energy consumption, underscoring the effective utilization of ISA and its role in promoting sustainability. This study will facilitate the application of ISA in cement-based materials and provide technical guidance for subsequent research.

Effect of costus lucanius bagasse fibre on fresh and hardened concrete using RSM modelling

This investigation purposes to use the recycling waste materials in concrete to produce a sustainable environment for construction. The Costus lucanius bagasse fiber (CLBF) was utilized as supplementary cementitious material (SCM) to analyse the workability and mechanical properties of blended cement concrete. The concrete samples were made with the inclusion of 5–20% of CLBF at several w/c ratio by applying RSM modelling and optimization. Moreover, the cubical specimens were cast to study the compressive strength (CS), while beams were used to investigate the flexural strength (FS) on 28th days correspondingly. The outcomes show that the compressive and flexural strengths were decreased with rise in proportion replacement in concrete at various w/c ratio. The highest flexural and compressive strengths was attained at 5% of CLBF at 28 days respectively. Across the tested specimens, the values of compressive strength and flexural strength ranged from 30.20 to 53.92 N/mm2 and 2.15–8.81 N/mm2 for CLBF correspondingly. Besides, the workability and water absorption of concrete is getting decreased as the content of CLBF increases while it is recorded increasing as w/c ratio increases from 0.20 to 0.40. Furthermore, response model predictions were constructed and verified applying ANOVA at an acceptable level of significance of 95%. The coefficients of R2 for the mathematical models ranged from 98 to 99.99%. The research study also indicated that cement can be substituted by CLBF in the production of concrete for various construction purposes.

A Comparative Evaluation of Embodied Environmental Impacts of Channel Stabilisation Using Concrete Lining and Alternative Pozzolanic Materials

Channel stabilisation with the lining of bed/ banks using cement-concrete (with/ without steel reinforcement as per the size, depth, and capacity), geomembrane, polymers, canvas, ramped earth, vegetation, gravel/ stone pitching, and brick blast is a common practice worldwide to save the adjacent flood plain areas from bank overflowing, seepage, water logging/ salinity, loss of water in irrigation channels, maintaining required water levels and strengthening of channels to be used as transportation means. A trapezoidal channel of cross-section 165 m2 and a lined perimeter of 42m was proposed to accommodate a super flood of 360 m3/sec discharge for a catchment area of 1446 km2 and 118 km length, using a projected heavy flood event of 6 cm precipitation in 8 hours for Swale River to ascertain the material calculation and its environmental impact. This concrete lining would likely produce an equivalent global warming potential/ embodied carbon dioxide (CO2) of 284 million kgCO2eq (kilogram CO2 equivalent) with the projected use of around 271 million kg of cement concrete and 78 million kg of steel. The enormous amount of embodied CO2 emissions from this projected lining project suggested using natural means of flood/ channel protection if feasible, or alternative supplementary cementitious materials with fibres should be used to minimise the environmental impacts.

Difficulties in Determining the Pozzolanic Activity of Thermally Activated Lower-Grade Clays.

Thermally activated clays (TACs) have been identified as possible supplementary cementitious materials (SCMs). To find a suitable clay and to optimise the activation process, it is necessary to determine its pozzolanic activity. However, the nature of clays is different from that of conventional SCMs. Therefore, the results of commonly used methods may differ; in some cases, they can even be misrepresented and misleading. This article aims to assess their applicability to TAC. Four direct and four indirect methods were compared by determination of the pozzolanic activity of three different clays calcined at varying temperatures. The isothermal calorimetry with lime combined with the mechanical strength's development was identified as an ideal combination. Contrarily, the lime saturation test was inapplicable. For the Frattini method, it was found to be beneficial to assess the change in activity due to the thermal treatment rather than the strict comparison with a calcium hydroxide saturation curve.

Innovative hybrid machine learning models for estimating the compressive strength of copper mine tailings concrete

The growing demand for copper and related materials in various industries is driving increased copper mining globally. This surge presents a substantial challenge in managing and responsibly disposing of large volumes of copper mine tailings (CMT). Incorporating CMT as supplementary cementitious materials (SCMs) in concrete addresses two significant environmental challenges simultaneously: reducing the accumulation of CMT waste in landfills and lowering the carbon footprint by reducing cement usage. The investigation into recycling CMT as a cement substitute involves a thorough assessment of its impact on the compressive strength (CS) of concrete. This research introduces innovative hybrid machine learning (ML) models for estimating the CS of CMT concrete, aiming to streamline strength assessment processes and save valuable resources. The method involves integrating features from large public datasets with the limited available data on the CS of CMT concrete. Support vector regression (SVR) was combined with advanced optimization techniques: firefly algorithm (FFA), grey wolf optimization (GWO) and particle swarm optimization (PSO) to create new hybrid models for forecasting the CS of CMT concrete. Additionally, traditional ML techniques like decision tree (DT) and random forest (RF) were used to compare with these SVR-based hybrids. All three hybrid models demonstrated strong performance, with SVR-FFA emerging as the most effective among them. Notably, SVR-FFA achieved the greatest R² score of 0.96, indicating superior predictive accuracy compared to SVR-PSO (0.92) and SVR-GWO (0.90). Additionally, the DT model attained an R² score of 0.88, while the RF model achieved an R² score of 0.84. Moreover, the SHapley additive exPlanations (SHAP) and partial dependence plots (PDP) analyses underscore the positive effects of curing age, cement, blast furnace slag, and superplasticizer on the CS of CMT concrete. A graphical user interface was developed for predicting the CS of CMT concrete, allowing for instant predictions without the need for conducting experiments.

Development of New Method for Concrete Carbon Emission evaluation: The Anti-freezing durability-oriented Carbon Emission Indicator (CEI) System and its application in design of low carbon HPC with high durability

This research focuses on the development of the Anti-freezing Durability-Oriented Carbon Emission Indicator (CEI) system for assessing concrete's carbon footprint with an emphasis on durability, particularly in freeze-thaw conditions. This novel approach reduces the environmental impact of concrete by integrating durability metrics into carbon emission evaluations. The paper presents experimental findings on mix designs for high-strength, low-carbon concrete, which demonstrate improved freeze-thaw durability. And found out that concrete mixes using sulfate-resistant cement with GGBS outperform those with FA and OPC in terms of low-carbon performance, in the newly developed 19 mixes, concrete mix incorporating air-entraining agents with sulfate-resistant cement and 40% GGBS as a supplementary cementitious material, namely the HPC1-P•HSRF-S group, demonstrates a distinct low-carbon advantage across various indicators.Overall, the inclusion of fibers is shown to improve freeze-thaw durability, though with limited impact on compressive strength. The research underlines the importance of optimizing concrete mix designs for both environmental and durability considerations, presenting a significant step towards more sustainable construction practices.

Assessing the impact of recycled concrete aggregates and metakaolin on the mechanical properties of pervious concrete

Population growth and urban expansion have increased impervious surfaces, leading to environmental issues such as stormwater runoff and groundwater depletion. Traditional concrete, while durable, contributes to these problems. There is a need for sustainable construction materials that can address environmental challenges and reduce the consumption of natural resources. Pervious concrete, enhanced with recycled aggregates (RCA) and supplementary cementitious materials (SCMs) like metakaolin (MK) present a potential solution. This study aims to improve the mechanical and durability properties of pervious concrete by incorporating RCA and MK, assessing their effects on workability, density, porosity, permeability, compressive strength and flexural strength. The incorporation of RCA resulted in increased aggregate porosity compared to natural aggregates. Workability was assessed using the slump test, density was measured, and porosity and permeability were evaluated. The results showed that incorporation of RCA generally decreased workability, density and strength, while the addition of MK improved these properties by refining the microstructure. Specifically, mixes with 10% MK demonstrated better performance in terms of increased compressive and flexural strengths, improved density and reduced porosity. The ANN model showed high accuracy in predicting compressive and flexural strengths. The study concludes that RCA and MK can enhance the mechanical and durability properties of pervious concrete.

Effects of Typical Supplementary Cementitious Materials (SCMs) on the Bonding Property of Cement with Casing under Shallow Formation of Deep-Water Environment

Due to low temperature environments and other factors, the performance of cement slurry is affected by deep-water shallow formation cementing, which makes it difficult to ensure the interface bonding quality. The objective of this study is to investigate the effect of fly ash (FA), metakaolin (MK), and microsilica (MS) as supplementary cementitious materials (SCMs) by replacing 5–20% of the cement on the bonding property of cement with casing in the shallow formations of deep-water environments. This is based on the cementing conditions for the 20″ surface casing in the deep-water shallow formation of the LS18-1 well area. Under the 30 °C experimental conditions, the results showed that the compressive and bonding strength of cement with FA and MS decreased gradually as their dosage increased. In contrast, compared with the control group (BG0), the compressive strength of the MK group increased by 25.6%, 32.1%, and 24.2% under the optimal dosages (MK15, MK15, MK20) at 3, 7, and 14 days (d), and the bonding strength increased by 73.6% at 3 d (MK15) and 34.9% at 7 d (MK15). The test analysis showed that MK can promote cement hydration and generate more hydration products, which are conducive to cement-casing interface cementation. Additionally, it can improve the pore structure, reduce the fractal dimension of the pore volume, and ensure a more reasonable distribution of cement stone crack openings.

New Eco-Cements Made with Marabou Weed Biomass Ash

Biomass ash is currently attracting the attention of science and industry as an inexhaustible eco-friendly alternative to pozzolans traditionally used in commercial cement manufacture (fly ash, silica fume, natural/calcined pozzolan). This paper explores a new line of research into Marabou weed ash (MA), an alternative to better-known conventional agro-industry waste materials (rice husk, bagasse cane, bamboo, forest waste, etc.) produced in Cuba from an invasive plant harvested as biomass for bioenergy production. The study entailed full characterization of MA using a variety of instrumental techniques, analysis of pozzolanic reactivity in the pozzolan/lime system, and, finally its influence on the physical and mechanical properties of binary pastes and mortars containing 10% and 20% MA replacement content. The results indicate that MA has a very low acid oxide content and a high loss on ignition (30%) and K2O content (6.9%), which produces medium–low pozzolanic activity. Despite an observed increase in the blended mortars’ total and capillary water absorption capacity and electrical resistivity and a loss in mechanical strength approximately equivalent to the replacement percentage, the 10% and 20% MA blended cements meet the regulatory chemical, physical, and mechanical requirements specified. Marabou weed ash is therefore a viable future supplementary cementitious material.

Accelerated environmental conditions study on palm oil fuel ash-incorporated engineered cementitious composites: A durability assessment approach

This study investigated the durability performance of Engineered Cementitious Composites (ECC) containing varying amounts of palm oil fuel ash (POFA) under accelerated environmental conditions. The research employed three distinct water-binder (cement + POFA) ratios (w/b) of 0.33, 0.36, and 0.38, along with POFA proportions ranging from 0 % to 1.2 % by mass of cement (POFA/C). Furthermore, ECC bars were immersed in 1 M NaOH at 80°C, with expansion and alkali-silica reaction monitored for 30 days. To examine the NaCl effect, ECC coupon specimens were first preloaded under four-point bending at 1.5 mm displacement, then exposed to a 3 % NaCl solution for 30 and 60 days, and then reloaded up to failure. The RCPT was performed at 28, and 90 days, per ASTM C1202 standard, by measuring the electrical current through a 50 mm thick, 100 mm diameter sample over 6 hrs. The results show that higher w/b ratios increased ASR-induced expansion in ECC bars, but higher POFA content mitigated this. ECC with 1.2 POFA/C at 0.33 w/b had the highest 0.1 % expansion at 30 days, within ASTM limits. The POFA-ECC specimens also exhibited enhanced chloride penetration resistance as POFA content increased, with the 1.2 POFA/C and w/b 0.33 specimens showing 61–71 % reductions in total charge passed at 28–90 days. Mechanically pre-loaded POFA-ECC remained durable when exposed to chloride. Additionally, POFA-ECC demonstrated self-healing of micro-cracks, allowing them to sustain significant flexural load capacity. These findings highlight the potential of POFA as a supplementary cementitious material in ECC, providing improved chloride resistance while preserving structural integrity.

A method of pretreating incineration ashes containing metallic aluminium using NaOH to mitigate volume expansion under highly alkaline conditions

Globally, millions of tonnes of incineration ashes are produced with a substantial portion remaining underutilized in low-value applications or disposed in landfills. Many types of fly ashes and bottom ashes contain metallic aluminium (Al0), which causes volume expansion when the ashes are used in alkali-activated materials and as a supplementary cementitious material due to the generation of hydrogen gas at high-pH conditions. This phenomenon significantly restricts the potential applications of these ashes. To address this issue, ashes can be pretreated with NaOH to oxidize the metallic aluminium (Al0) before their utilization. This study focuses on investigating the effect of the NaOH pre-treatment duration on fly ashes from the co-combustion of recovered solid fuel, peat, and wood. A pre-treatment process was conducted using 8 mol/L aqueous NaOH solution to treat the fly ash for up to 60 minutes. The formed slurry was subsequently used to prepare alkali-activated material by mixing it with bottom ash and employing either sodium silicate or sodium carbonate as an alkali activator. The NaOH pre-treatment demonstrated a 100 % metallic aluminium conversion into oxidized form resulting enhancement in mechanical performance, microstructure, and water absorption properties. The proposed method offers a highly efficient and rapid solution for eliminating the drawbacks caused by the presence of metallic aluminium and it can be conveniently implemented on construction sites. Concurrently, this study also explores the leaching behaviour of heavy metals during alkali-activation. Significant reductions in the leaching of Ba, Cr, Cu, Mo, and Pb were observed, highlighting the environmental remediation potential of alkali-activation methods.

Strength, durability, and heat development characteristics of high-performance concrete containing ground coal bottom ash with low and high calcium

Currently, the availability of fly ash has reduced continuously due to the shutdowns of coal-fired power generating plant as climate change concerns have increased. Therefore, the aim of this paper is to find an alternative pozzolan by examining the employment of low- and high-calcium oxide (CaO) ground bottom ash which has been abandoned rather using in concrete production. The bottom ashes were blended with fly ash as a partial substitution of cement (OPC) by observing their generic effects on the compressive strength, cumulative heat generation, chloride ion penetration, and water sorptivity of high-performance concrete. The samples of bottom ash were prepared by oven drying, particle size cutting, and grinding to enhance the reactivity and consistency. High-performance concretes were made at a water-to-binder (W/B) ratio of 0.27 and partial replacement of OPC up to 50 % by weight of the binder. The results indicated that the concretes with 28-day compressive strengths of 101.0 and 109.0 MPa (21.6 % and 28.2 % stronger than OPC concrete) were produced with 50 wt% OPC replacement with high- and low-calcium ground coal bottom ashes (HCBA and LCBA), respectively. These findings suggest that HCBA and LCBA have high pozzolanic reactivity and high possibility for utilization as pozzolan or supplementary cementitious materials in concrete. In addition, the binary blended binders (OPC-HCBA and OPC-LCBA) and ternary blended binders (OPC-HCBA-FA and OPC-LCBA-FA) produced had better chloride ion penetration resistance, less cumulative heat evolution, and lower water sorptivity than 100 % OPC as a cementitious material. Partial OPC replacement by HCBA and LCBA improved the chloride ion penetrability class of OPC concrete from “very low” to “negligible.” The cumulative heat generation due to the pozzolanic reaction of HCBA and LCBA from the partial replacement of OPC up to 50 % reduced 30–44 % relative to the OPC-based mixture throughout during 72 hours after mixing. The CaO content strongly influenced early compressive strength development and cumulative heat evolution but had less impact on chloride ion penetration resistance and water sorptivity.

Study on the Influence of Thermoplastic Microcapsules on the Sulfate Resistance and Self-Healing Performance of Limestone Calcined Clay Cement Concrete.

Limestone calcined clay cement (LC3), enhanced through reactions with volcanic ash and the interaction between limestone and clay, significantly improves the performance of cementitious materials. It has the potential to cut CO2 emissions by up to 30% and energy consumption in cement manufacture by 15% to 20%, providing a promising prospect for the large-scale production of low-carbon cement with a lower environmental effect. To effectively manufacture LC3 concrete, this study utilized limestone (15%), calcined clay (30%), and gypsum (5%) as supplementary cementitious materials (SCMs), replacing 50% of ordinary Portland cement (OPC). However, in regions abundant in sulfate, sulfate attack can cause interior cracking of concrete, reducing the longevity of the building. To address this issue, microcapsules containing microcrystalline wax, ceresine wax, and nano-CaCO3 encapsulated in epoxy resin were prepared and successfully incorporated into LC3 concrete. Sulfate resistance tests were conducted through sulfate dry-wet cycles, comparing samples with and without microcapsules. The findings revealed that the initial mechanical and permeability properties of LC3 concrete did not significantly differ from OPC concrete. LC3 concrete with added microcapsules (SP4) exhibited enhanced resistance to sulfate attack, reducing mass loss and compressive strength degradation. SEM images displayed a mesh-like structure of repair products in SP4. After 14 days of self-repair, SP4 exhibited a 44.2% harmful pore ratio, 98.1% compressive strength retention, 88.7% chloride ion diffusion coefficient retention, 91.12 mV maximum amplitude, and 9.14 mV maximum frequency amplitude. The experimental results indicate that the presence of microcapsules enhances the sulfate attack self-healing performance of LC3 concrete.

Exploring machine learning to study and predict the chloride threshold level for carbon steel reinforcement

Chloride-induced corrosion of steel reinforcing bar (rebar) is the primary cause of deterioration in reinforced concrete structures, posing a significant infrastructure challenge. The chloride threshold level (CTL) of rebar, which represents the critical amount of chloride needed to initiate active corrosion, is crucial in corrosion and service life prediction models. However, substantial uncertainties and a multitude of influencing factors, along with the absence of a universally accepted testing framework, hinder the achievement of a consistent CTL range for service life models and complicate comparisons of published values. This study addresses these challenges by developing multiple machine learning models to predict CTL, considering 21 carefully selected features. A comprehensive database of 423 data points was compiled from an exhaustive literature review. Seven machine learning models—linear regression, decision tree, random forest, K-nearest neighbors, support vector machine, artificial neural network, and an ensemble model—were developed and optimized. The ensemble model achieved superior prediction performance, with a mean absolute error of 0.218 % by weight of binder, root mean square error of 0.321 %, and a coefficient of determination of 0.751 on unseen CTL data. Partial dependence plots generated using the support vector machine model quantified the effect of each feature on CTL. The random forest model identified SiO₂ binder content and exposed rebar area to chlorides as the most influential factors. The study also examined the impact of supplementary cementitious materials (SCMs), finding that only blast furnace slag positively affected CTL.

Environmental and economic impacts of processing rice straw with water for energy and coproducts

Incorporating supplementary cementitious materials (SCM) such as rice straw ash (RSA) as cement replacement in concrete is a key path toward mitigating the contributions of cement to global climate change. A cost-benefit study and an environmental life cycle assessment (LCA) were performed to compute the impacts of water soaking, drying, and reverse osmosis (RO) of the leachate to factor in the use of rice straw as feedstock at biomass energy plants, RSA for concrete, and the RO-treated leachate as fertilizer and water for farms. The cost-benefit analysis showed that the sale of electrical energy from biomass, RSA, and fertilizer required further optimization of the processes to become profitable for the involved parties. The LCA showed a global warming avoidance equivalent to net -15kgCO2-eq per tonne of rice straw that could be achieved by substituting fossil fuel energy resources and cement avoidance in concrete.

Synergistic effects of waste coral powder and metakaolin in cement pastes: Hydration, pore structure, rheology, and strength

Coral reefs are abundant in waste coral powder, and how to utilize coral powder efficiently to construct far-sea projects has become a major focus of research and engineering field, which is conducive to the development of green economy. However, existing research lacks a comprehensive and systematic investigation of the cement-coral powder-metakaolin ternary system. In this study, the hydration and rheological behavior, micromechanical and mechanical properties, and pore structure evolution of the ternary system are systematically investigated to uncover the synergistic mechanism between metakaolin and coral powder. The results indicated that, based on hydration, rheology, and mechanical properties, the recommended proportions of cement, coral powder, and metakaolin are 75 %, 10 %, and 15 %, respectively. The combination of coral powder and metakaolin effectively promotes hydration. Furthermore, it accelerates the aluminate reaction, resulting in a stronger aluminate exothermic peak immediately. In addition, metakaolin reacts with coral powder to form carboaluminate, activating the activity of the coral powder, which in turn improves the mechanical properties and pore structure of the ternary system. Moreover, metakaolin undergoes a pozzolanic reaction with calcium hydroxide, which contributes to optimizing the pore structure of the ternary system and enhancing its mechanical properties. Additionally, coral powder promotes the conversion of monosulfate to carboaluminate while inhibiting the transformation of ettringite into monosulfate. The Herschel-Bulkley model accurately simulates the dynamic rheological behavior of the ternary system. This study is highly significant and practically valuable for transforming waste coral powder into a supplementary cementitious material for the construction of the far-sea projects, providing a scientific basis for future related studies.