Search Results (42)

The time-dependent structuration of cement pastes is a key parameter governing the fresh-state behavior of modern concretes. This study investigates the influence of four supplementary cementitious materials (SCMs): fly ash (FA), slag (S), limestone filler (LF), and metakaolin (MK) on both the total and irreversible structural build-up of cement pastes, under various temperatures (5, 20, 30 °C) and a constant replacement level of 30% at w/b = 0.45. Static yield stress was measured using a vane rheometer with or without re-shear to distinguish between the total (without re-shear) and irreversible (with re-shear) structural build-up. Complementary tests, including mini slump flow, isothermal calorimetry, and bleeding analysis, were conducted to assess the effect of SCMs on rheology, hydration and stability. Results show that all SCMs significantly reduced the rate and intensity of structural build-up compared with reference cement paste: after 90 min at 20 °C, the static yield stress (total structural build-up) was 1740 Pa for the reference mix and between 420 and 840 Pa for the blended systems. The irreversible fraction remained low (<10%) for all blended systems, confirming that early-age structuration is mainly governed by reversible flocculation rather than by hydration-driven bonding. Temperature significantly accelerated the total structural build-up in all mixtures; at 30 °C, the total build-up of slag-, LF-, and MK-blended pastes approached that of plain cement. However, while the reference cement paste exhibited a clear increase in irreversible structuration (from 25% at 20 °C to 35% at 30 °C), SCM-containing systems remained largely governed by reversible mechanisms, with the irreversible fraction consistently below 10%. These findings highlight the distinct roles of particle morphology, clinker dilution, and hydration kinetics in governing early structuration. Understanding these coupled mechanisms is essential for optimizing low-clinker binders used in self-compacting and 3D-printable concretes, where balancing flowability and early stability is critical. Full article

This study systematically investigates the utilization of marble industry waste—waste marble powder (WMP) as partial cement replacement and waste marble aggregates (WMA) as partial fine aggregate replacement—in self-compacting concrete (SCC). A detailed experimental program evaluated the effects of various replacement levels (5%, 10%, and 20% for WMP; 20%, 30%, and 40% for WMA) on compressive strength and durability, particularly resistance to aggressive sulfuric acid environments. Results indicated that a 5% WMP replacement increased compressive strength by 4.9%, attributed primarily to the filler effect, whereas higher levels (10–20%) led to strength reductions due to limited pozzolanic activity and cement dilution. In contrast, WMA replacement consistently enhanced strength (maximum increase of 11.5% at 30% substitution) due to improved particle packing and aggregate-paste interface densification. Durability tests revealed significantly reduced compressive strength losses and mass loss in marble-containing mixtures compared to control samples, with optimal acid resistance observed at 20% WMP and 40% WMA replacements. A comprehensive life cycle assessment demonstrated notable reductions in environmental impacts, including up to 20% decreases in Global Warming Potential (GWP) at 20% WMP replacement. A desirability-based eco-cost-mechanical optimization—simultaneously integrating mechanical strength, environmental indicators, and production cost—identified the 10% WMP substitution mix as the most sustainable option, achieving optimal balance among key performance criteria. These findings underscore the significant potential for marble waste reuse in SCC, promoting environmental sustainability, resource efficiency, and improved concrete durability in chemically aggressive environments. Full article

Alkali-activated binders (AAB) are a suitable and sustainable alternative to ordinary Portland cement (OPC), with reductions in natural resource usage and environmental emissions in regions where the necessary industrial residues are available. Despite its potential, the lack of mix design methods still limits its applications. This paper proposes a systematic parametric validation for AAB mix design applied to pastes and concretes, valorizing steel slag as precursors. The composed binders are based on coal fly ash (FA) and Basic Oxygen Furnace (BOF) steel slag. These precursors were activated with sodium silicate (Na₂SiO₃) and sodium hydroxide (NaOH) alkaline solutions. A parametric investigation was performed on the mix design parameters, sweeping the (i) alkali content from 6% to 10%, (ii) silica modulus (SiO₂/Na₂O) from 0.75 to 1.75, and (iii) ash-to-slag ratios in the proportions of 75:25 and 50:50, using parametric intervals retrieved from the literature. These variations were analyzed using response surface methodology (RSM) to develop a mechanical model of the compressive strength of the hardened paste. Flowability, yield stress, and setting time were evaluated. Statistical analyses, ANOVA and the Duncan test, validated the model and identified interactions between variables. The concrete formulation design was based on aggregates packing analysis with different paste contents (from 32% up to 38.4%), aiming at self-compacting concrete (SCC) with slump flow class 1 (SF1). The influence of the curing condition was evaluated, varying with ambient and thermal conditions, at 25 °C and 65 °C, respectively, for the initial 24 h. The results showed that lower silica modulus (0.75) achieved the highest compressive strength at 80.1 MPa (28 d) for pastes compressive strength, densifying the composite matrix. The concrete application of the binder achieved SF1 fluidity, with 575 mm spread, 64.1 MPa of compressive strength, and 26.2 GPa of Young’s modulus in thermal cure conditions. These findings demonstrate the potential for developing sustainable high-performance materials based on parametric design of AAB formulations and mix design. Full article

The dosage of mineral powder has a complex influence on the compressive strength of self-compacting concrete, among which the pore structure is a key determining factor. This study investigated the effects of different dosages of mineral powder (0%, 5%, 10%, 20%, and 30%) on the workability, mechanical properties, and pore distribution in C80 self-compacting concrete. The research results show that an appropriate dosage of mineral powder (0–20%) can significantly improve the spreadability and fluidity of C80 self-compacting concrete. This phenomenon is mainly attributed to the shape effect and micro-aggregate effect of mineral powder, which improve the fluidity of concrete, reduce the viscosity of the paste, and thereby increase the spreadability and gap-passing rate. By testing the BSD-PS1/2 series fully automatic specific surface area and pore size analyzer, we found that there are columnar pores and ink bottle-shaped pores in C80 self-compacting concrete, as well as a small amount of plate-like slit structures. Our observations with an SEM scanning electron microscope revealed that the width of micro-cracks and micro-holes is between 1 and 5 μm and the diameter is between 3 and 10 μm. These microstructures may have an impact on the mechanical properties of the structure. By applying fractal theory and low-temperature liquid nitrogen adsorption tests, this study revealed the relationship between the fractal characteristics of internal pores in C80 self-compacting concrete and the dosage of mineral powder. The results show that with the increase in mineral powder dosage, the fractal dimension first decreases and then increases, reflecting the change rule of the complexity of pore structure first decreasing and then increasing. When the dosage of mineral powder is about 20%, the compressive strength of SCC reaches the maximum value, and this dosage range should be considered in engineering design. Full article

Concrete structures are prone to cracking and seepage issues due to material degradation during long-term service. Ionic chelating agents (ICAs) can significantly enhance the durability and extend the service life of concrete structures by chelating metal ions in the cement matrix and promoting the formation of crystalline products within pores. The study selected commonly used ICAs, including sodium gluconate, sodium maleate, and sodium citrate, as well as a self-made high-efficiency ICA, to compare their chelating abilities for metal ions (such as Al³⁺, Mg²⁺, Fe³⁺, and Ca²⁺). Their effects on the performance and microstructure of cement-based materials were evaluated through tests on hydration heat, mechanical strength, the chloride ion diffusion coefficient, pore size distribution, and microstructural analysis. The results showed that the stronger the chelating ability of the ICA, the more significant its improvement on the performance and microstructure of cement-based materials. Cement paste incorporating the high-efficiency ICA exhibited significantly accelerated hydration kinetics, with the hydration rate markedly increasing and the peak heat release rising from 0.0012 W/g to 0.0016 W/g, thereby effectively enhancing the early-age properties of the cement-based materials. After 28 days, compared to ordinary mortar, the flexural and compressive strengths of mortar containing the high-efficiency ICA increased by 17.1% and 11.6%, respectively, while the chloride ion diffusion coefficient decreased by 37.4%. Pore size distribution and microstructural analyses indicated that mortar incorporating the high-efficiency ICA exhibited the most compact internal structure, with abundant crystalline products such as CaSiO₃ and 3CaO·Al₂O₃·3CaSO₄·32H₂O (AFt) forming within the pores. These findings suggest that optimizing the ion-chelating capacity of ICA provides a feasible strategy to enhance the compactness, durability, and mechanical performance of cement-based materials in practical engineering applications. Full article

Cemented paste backfill (CPB) improves underground stability by filling mine voids, but the high cost of cement presents economic challenges for miners. While alternative binders and admixtures have been explored, the combined impact of slag substitution and alkali-free (AF) accelerators on CPB performance is not yet fully understood. This study investigates the influences of slag substitution and AF accelerators on the performance of CPB through a comprehensive experimental approach. CPB samples were prepared with slag substitution ratios of 25%, 50%, and 75%, maintaining a fixed AF accelerator content of 0.4%. Various test techniques, including unconfined comprehensive strength (UCS), mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and thermal analysis (TG/DTA), were employed to study their mechanical and microstructural properties. Monitoring tests were also conducted to thoroughly assess the performance of CPB, including suction (self-desiccation), electrical conductivity (EC), and volumetric water content (VWC) tests. The results showed that the PCI50–SL50–0.4AF sample exhibited 2.3 times higher strength than the control sample for 28 days, with this improvement attributed to enhanced pozzolanic reactions contributing to better microstructural compactness. Monitoring tests revealed accelerated hydration kinetics and reduced water content in slag-reinforced CPB, highlighting the significant role of AF accelerator in facilitating rapid setting and improving early-age mechanical strength. Microstructural findings revealed that porosity decreased and C–S–H gel formation increased in the specimen containing slag and AF accelerators, contributing to increased strength and durability. These findings highlight the potential usage of slag and AF accelerators to enhance CPB’s mechanical, microstructural, and hydration properties, offering significant benefits for mining operations by improving backfill performance, while contributing to environmental sustainability through reduced cement consumption and associated CO₂ emissions. Full article

In the modern era of superplasticizer-based concrete technology, water demand (or specific surface) of aggregate is a significantly underestimated factor influencing cement paste demand in the self-compacting concrete (SCC) design process. The presented data show that it is the key factor for optimization criterion of SCC cement paste demand. Four models were taken into consideration (Bolomey, Stern, modified Loudon, and Relative Specific Surface), and all of them fit linearly very well (R² ≥ 0.95) to the relative thickness of coating aggregate with cement paste (t_rel). This means that all of these models may be used interchangeably in the process of SCC design without any alteration (so there is no need to develop a new model). Including the water demand of aggregate in the design procedure in its proposed version sets the bottom limit of superplasticizer dose for laboratory trials, leaving only small gap for eventual minor adjustments. Full article

The use of superplasticizers in a self-compacting concrete mix without the addition of a foaming agent in practice leads to a well-known problem associated with increased air entrainment and promotes the formation of harmful large bubbles, high-void content, and ununiform appearance. This paper presents research on the properties of cement paste consisting of Ordinary Portland Cement (OPC), powder based on ground granulated blast furnace slag (GBBS), and superplasticizer. The methodology of this study was the estimation of flow diameter and flow time, as well as the evaluation of the rheological characteristics. The influence of ground granulated blast furnace slag and polycarboxylate plasticizer on the flowability and viscosity of cement paste was studied. The effect of superplasticizer (SP) based on polycarboxylate esters (PCE) anti-foaming agent (AFA) based on a glycol ester and air-entraining admixture (AEA) based on an amphoteric surfactant on flowability, viscosity, rheological properties and the strength of the cement paste was evaluated. It was found that the increase of slag content in cement paste (25%) with the presence of superplasticizer (0.64%) significantly changes the flowability and viscosity. It was stated that the addition of 0.04% anti-foaming agents increases flowability (20%) and reduces viscosity (44%) of cement paste. It was stated that the addition of small dosages of glycol ester-based anti-foaming agent (0.02 and 0.04%) significantly changes the rheological properties, decreases the shear yield stress by 2.1–2.8 times, the plastic viscosity by 2.4–2.6 times and apparent viscosity 1.6–2.5 times, improves the compressive strength at the age of 1 and 7 days by 2.5 and 1.4 times, respectively. The addition of air-entraining admixture led to a decrease in the plastic viscosity by 1.2–1.4 times. It was stated that the presence of air-entraining admixture assists in increasing the apparent viscosity by 1.7–2.4 times. It was shown that the presence of complex admixtures of various origins, purposes, and mechanisms of action would assist in predicting the behavior of concrete mixtures under the conditions of the building site and reduce the consumption of polycarboxylate esters due to the enhancing plasticizing effect of anti-foaming agent and air-entraining admixture. Full article

Self-compacting concrete (SCC), known for its excellent fluidity and self-compacting ability, is widely used in civil engineering. To enhance the comprehensive performance of SCC, dolomite powder (DP) is integrated as a substitute for cement. This study aims to analyze the impact of DP on the yield stress relationship between self-compacting mortar (SCM) and self-compacting paste (SCP) from a multi-scale perspective. A new predictive model for the yield stress relationship between SCM and SCP incorporating DP is established by improving the $n$ value in the existing ${\varphi }_{\mathrm{e}}$ model, which characterizes the sensitivity of the mortar yield stress relative to changes in the paste yield stress. By conducting mini-slump flow tests on nine sets of cement–DP mixtures, it is found that DP impacts the yield stress relationship between SCM and SCP mainly through changes in the inter-particle filling effect, and the $n$ value in the predictive model is roughly between 2.4 and 3.6. When the DP content is kept constant and the particle size is changed, the $n$ value shows a strong positive linear relationship with the packing density of the paste (${\varphi }_{\mathrm{e},\mathrm{p}}$). The relationship between $n$ and ${\varphi }_{\mathrm{e},\mathrm{p}}$ is derived using the linear fitting method, which improves the model’s predictive accuracy by 95.2%. Full article

Biochar, the solid sub-product of biomass pyrolysis, is widely considered an effective water retention material thanks to its porous microstructure and high specific surface area. This study investigates the possibility of improving both mechanical and rheological properties of cement pastes on a micro-scale. The results show that using biochar as a reinforcement at low percentages (1% to 5% by weight of cement) results in an increase in compressive strength of 13% and the flexural strength of 30%. A high fracture energy was demonstrated by the tortuous crack path of the sample at an early age of curing. A preliminary study on the rheological properties has indicated that the yield stress value is in line with that of self-compacting concrete. Full article

The disposal of marine sediments poses a significant economic and environmental challenge on a global scale. To address this issue and promote resource optimization within a circular-economy paradigm, this research investigates the viability of incorporating untreated fine marine sediments as a partial replacement for sand in self-compacting concrete (SCC) designed especially for application in marine environments (an exposure class of XS2 and a resistance class of C30/37 according to standard NF EN 206). The concretes mis-design incorporating 30% by weight of sediment as a sand substitute was initially designed with the modified Dreux–Gorisse method. The findings indicate that it is feasible to design an SCC suitable for marine environments, incorporating 30% sediment replacement content and without significantly compromising concrete properties, durability, or the estimated lifespan of the formulated concretes. The integration of marine sediment as a sand substitute into the SCC mix design reduces the amount of binder and limestone filler without compromising the paste volume. This results in a significant saving of natural sand resources and a reduction in CO₂ emissions for SCC made with marine sediment. Full article

This research presented, for the first time, the results of the successful application of the waste press sludges, WSLP (plant for lacquer and paint) and WSEP (powdery enamel plant), from a wastewater treatment plant generated during heating device production in the construction industry. The results of WSEP characterization and its influence on cement paste, mortar, and concrete properties showed that this material could be used as a cement replacement (with a maximum replacement amount of 20%) in producing mortar and concrete. Although waste WSLP sludge does not possess pozzolanic properties and does not meet the criteria prescribed by the standards for application in mortar and concrete due to its chemical inertness and fineness, as well as its extended setting time, it can be used as a replacement for stone filler or other powdered mineral admixture in the production of self-compacting concrete (SCC) in amounts up to 100%, with a maximum quantity of up to 100 kg/m³. The obtained results indicate that with the appropriate conversion, waste sludges, despite representing hazardous waste, can be used as safe products in the construction industry; i.e., the waste material can become a useful and valuable raw material by applying (respecting) all of the principles of the green economy. Full article

This research aimed to determine how a super absorbent polymer affects the microstructural characteristics and water retention kinetics of a new composite made by substituting granite pulver (GP) and fly ash (FA) for cement. Understanding the mechanics of water movement is crucial for comprehending the effectiveness of autogenous curing. Several experiments were conducted to analyze the water mitigation kinetics of super absorbent polymer (SAP) in the hydrating cement paste of autogenous cured self-compacting concrete (GP-ACSSC) mixtures. In the first hours following casting, water sorptivity, water retention, and hydration tests were carried out. The effects of various concentrations of SAP and GP, which was utilized as an alternative cement for the production of sustainable concrete that leads to reduction in carbon footprint, on the autogenous cured self-compacting concrete with reference to the abovementioned properties were explored. The investigation showed that releasing the curing water at a young age, even around the beginning of hydration, allowed homogenous and almost immediate distribution of water across the full cured paste volume, which improved the water retention kinetics. Compared to the control mixtures, the addition of SAP up to 0.6% and the substitution of cement with GP up to 15% had favorable impacts on all water kinetics parameters. Full article

Self-compacted concrete (SCC) is a special type of concrete; it is a liquid mixture appropriate for structural elements with excessive reinforcement without vibration. SCC is commonly produced by increasing the paste volume and cement content. As cement production is one of the huge factors in releasing CO₂ gas into the atmosphere, by-product materials such as fly ash are utilized as a cement replacement in concrete. In addition to the positive environmental impact, fly ash can maintain an excellent fresh and mechanical property. Incorporating fly ash into self-compacted concrete is widely applied in practice. However, its application is frequently limited by a lack of knowledge about the mixed material gained from laboratory tests. The most significant mechanical property for all concrete types is compressive strength (CS); also, the slump flow diameter (SL) in the fresh state is a crucial property for SCC. Hence, developing an accurate and reliable model for predicting the CS and SL is very important for saving time and energy, as well as lowering the cost. This research study proposed a projection of both the CS and SL of SCC modified with fly ash by three different model approaches: Nonlinear regression (NLR), Multi-Linear regression (MLR), and Artificial Neural Networks (ANN). In this regard, two different datasets were collected and analyzed for developing models: 308 data samples were used for predicting the CS, and 86 data samples for the SL. Each database included the same five independent parameters. The ranges for CS prediction were: cement (134.7–583 kg/m³), water-to-binder ratio (0.27–0.9), fly ash (0–525 kg/m³), sand (478–1180 kg/m³), coarse aggregate (578–1125 kg/m³), and superplasticizer (0–1.4%). The dependent parameter (CS) ranged from 9.7 to 81.3 MPa. On the other hand, the data ranges for the SL prediction included independent parameters such as cement (83–733 kg/m³), water-to-binder ratio (0.26–0.58), fly ash (0–468 kg/m³), sand (624–1038 kg/m³), coarse aggregate (590–966 kg/m³), and superplasticizer (0.087–21.84%). Also, the dependent parameter (SL) ranged from 615 to 800 m. Various statistical assessment tools, such as the coefficient of determination (R²), Root Mean Squared Error (RMSE), Mean Absolute Error (MAE), Objective value (OBJ), and Scatter Index (SI), were used to evaluate the performance of the developed models. The results showed that the ANN model best predicted the CS and SL of SCC mixtures modified with fly ash. Furthermore, the sensitivity analysis demonstrated that the cement content is the most effective factor in predicting the CS and SL of SCC mixtures. Full article

With the interest aroused by the development of modern concretes such as printable or self-compacting concretes, a better understanding of the rheological behavior, directly linked to fresh state properties, seems essential. This paper aims to provide a phenomenological description of the rheological behavior of cement paste. The first part is devoted to the most common testing procedures that can be performed to characterize the rheological properties of cement suspensions. The second one deals with the complexities of the rheological behavior of cement paste including the non-linearity of flow behavior, the viscoelasticity and yielding, and the structural build-up over time. Full article