Search Results (765)

Foamed concrete is susceptible to drying shrinkage and environmental deterioration because of its porous structure. This study evaluated the effects of fly ash–ground granulated blast-furnace slag blends and polyvinyl alcohol fibres on the dimensional stability and durability of FC. Sixteen mixtures with SCM replacement levels of 0–35% and PVA fibre contents of 0–0.3 vol.% were tested for accelerated drying shrinkage, freeze–thaw resistance, sulfate wet–dry resistance, chloride penetration, and visible pore structure. A normalised multi-criteria evaluation was used to compare the mixtures across five performance indicators, with sensitivity analysis performed for six weighting schemes. Increasing SCM replacement generally increased the drying shrinkage but reduced the chloride penetration depth by 26.7%, 33.3%, and 56.7% at 15%, 25%, and 35% replacement, respectively. At 25% SCM replacement, PVA fibres reduced freeze–thaw-induced compressive strength loss by 62.12–98.48% relative to the corresponding fibre-free mixture. Optical microscopy identified a local stratified region in one of three C0.3 specimens, which was not considered a systematic feature. C0.3 achieved the highest overall score under equal weighting and remained among the top three mixtures under all six weighting schemes. Within the investigated mixture range, C0.3 showed consistently high overall performance, although longer-term durability assessment is required. Full article

Early-age cracking severely limits concrete durability in hot, arid environments due to rapid plastic and drying shrinkage. This study evaluates the cracking sensitivity of cement-based materials incorporating four local supplementary cementitious materials (SCMs): limestone filler from Djebel Béchar, natural pozzolan, silica fume, and gypsum under simulated arid conditions (55 °C, 12% relative humidity, 10 km/h wind). Using a custom climatic chamber, prismatic cement-grout specimens with internal restraints were tested. SCMs were evaluated at substitution rates of 2% to 8%. Limestone was further tested at higher rates (up to 40%) and in binary combinations. Findings were validated using micro-concrete with limestone substitutions (0–35%) combined with 4% natural pozzolan. Cracking sensitivity was assessed using maximum crack width and a cracking index, along with setting times and mechanical strengths. Results indicate that limestone filler demonstrated the most favourable performance. A 4% limestone substitution yielded a single crack with a maximum width of 0.1 mm, while an 8% substitution resulted in five cracks of about 0.2 mm. The optimal cracking index was achieved at a 35% limestone substitution rate, which also successfully extended initial and final setting times. While binary SCM combinations significantly reduced cracking compared to the unsubstituted reference, they did not outperform the optimal 35% single limestone substitution. Furthermore, the 28-day compressive and flexural tensile strengths of the micro-concrete were effectively maintained at up to 35% limestone combined with 4% pozzolan. Overall, these preliminary findings demonstrate that crushed limestone fines from Djebel Béchar are highly promising as partial cement replacements to improve concrete durability in arid climates. Further durability assessments and statistical validation are recommended to confirm these benefits for practical field applications. Full article

To promote the high-value utilization of coal gasification slag (CGS) resources and mitigate the environmental issues caused by its accumulation, CGS was separated into five fractions by particle size (2.36–4.75 mm, 1.18–2.36 mm, 0.60–1.18 mm, 0.30–0.60 mm, and 0.15–0.30 mm) and subsequently ground into CGS powders (CGSPs). The physicochemical properties of both CGS and the obtained CGSP were systematically characterized, and the effects of CGSP on the hydration behavior and engineering performance of ordinary Portland cement (OPC) were investigated. The results revealed significant differences in physical properties and composition among the various particle-size fractions of CGS and their corresponding CGSP. When 40 wt.% CGSP was used to replace Portland cement, the C2.36 fraction exhibited the highest early-age compressive strength (16.91 MPa and 25.3 MPa at 3 d and 7 d, respectively), which is attributed to its favorable chemical composition and abundant glassy components. In contrast, the C0.6 fraction achieved the highest 28 d compressive strength (50.0 MPa). The C0.15 fraction showed the lowest strength at all ages, may be mainly due to its high residual carbon content and low reactivity. Overall, the compositional differences among CGS fractions of different particle sizes govern the formation and evolution of hydration products, and the proposed strategy of “classified grinding and quality-oriented utilization” provides an effective approach for the high-value application of CGS in cement-based materials. Full article

This study presents an extensive investigation on the rheological and mechanical performance of cementitious mortars incorporating fines derived from recycled construction and demolition waste (CDW), including masonry units (bricks and ceiling blocks), autoclaved aerated concrete (AAC) units, and mixed demolition residues obtained during the renovation of a pre-war tenement house located in Warsaw, Poland. The CDW fines were assessed for their potential as secondary cementitious materials, SCMs. The proposed material concept aimed to integrate CDW into sustainable binder systems and reduce Portland clinker consumption, thereby lowering CO₂ emissions of the concrete industry. Binder blends were produced by replacing 25 wt%. of Portland cement with recycled fines, achieving a 33–36% fines/clinker mass ratio. Recycled fines obtained by grinding CDW materials were characterized in terms of morphology, specific gravity, PSD, specific surface area, pozzolanic activity, pH and—in the case of recycled AAC—also carbonation. Mortars mixes were tested for consistency directly after mix preparation, while hardened composites were tested for density, compressive strength and flexural strength after 28 and 90 days of water curing. Statistical analysis showed that the origin of recycled fines affected mortar performance, with pozzolanic activity identified as the key factor. However, all analyzed composites were characterized with good mechanical strength. Overall, the performed investigation confirmed the suitability of analyzed CDW fines for clinker-reduced, low-carbon binders and highlighted their potential (especially in the case of ceramic fines) to support circularity in construction. Full article

This study investigates the feasibility of utilizing stone dust waste, an industrial by-product generated during ornamental-stone quarrying processing, as a raw material for 3D-printing mortar. This approach reduces waste disposal and promotes a circular economy. Several high-strength cementitious mixtures were screened and optimized by varying raw materials as a function of slump flow evolution over time, which served as indirect assessment of open time and extrudability. Following the identification of the most suitable mixture for 3D printing, one of the raw materials (an ultrafine limestone filler) was subsequently replaced on a 1:1 mass basis with stone waste, selected due to its comparable particle-size distribution, to assess its feasibility as an alternative filler. Fresh-state properties were evaluated based on flowability, with slump values ranging from 16 cm to 13 cm over time, and extrusion tests on a screw pump, used to validate extrusion stability and shape retention. Hardened-state properties were determined at different curing ages. The incorporation of Apricena stone waste resulted in similar fresh-state and extrusion behaviour of mortar, without additional changes to the mix design, and the intended 30 min qualitative extrusion window was met. At 28 days, the mixture incorporating stone dust waste achieved flexural and compressive strength of 12.51 MPa and 79.72 MPa. The incorporation of stone dust waste resulted in an extrudable mixture for 3D printing, with the intended open time and fresh-state behaviour, as well as mechanical properties complying with high-strength applications. However, the full replacement of one of the limestone fillers led to an 8% reduction in 28-day compressive strength. Overall, the findings demonstrate that the recovery of stone dust slurry as viable supplementary cementitious material for 3D-printed concrete is viable. The data support the use of this stone waste as a raw material for 3D printing, and specific mortar development and mix optimization for different applications are recommended, including the quantitative assessment of buildability, printed mechanical properties, durability, and leaching and life-cycle assessment. Full article

Trenchless technologies are essential for urban sewerage infrastructure; however, standard Life Cycle Assessment (LCA) boundaries often overlook the upfront carbon footprint of vertical nodes (working shafts and precast manholes), particularly under deep excavation and difficult geological conditions. To bridge this research gap, this study establishes a comprehensive upfront carbon (Stages A1–A5) assessment model based on the EN 15804 standard, calibrated against empirical microtunneling inventory data from Hualien, Taiwan, characterized by deep excavations (10–12 m) and hard gravel strata (SPT N > 50). The empirical results reveal a dual carbon challenge: a geologically induced energy surge during construction (Stage A5, contributing 42.5% of total assessed upfront emissions) and an embodied carbon lock-in within high-strength permanent structures (Stages A1–A3, contributing 51.1%). To isolate these effects, a progressive four-scenario matrix was evaluated. Scenario simulations demonstrate that adopting high-volume supplementary cementitious materials (SCM) concrete manholes (50% cement replacement: 37.5% GGBS and 12.5% fly ash) achieves a material reduction factor (R_mat) of 15.0% in Stages A1–A3, fully offsetting the isolated 3539 kgCO₂e construction-energy increment imposed by the hard gravel strata, although total upfront emissions in Scenario IV remain slightly higher than the baseline Scenario I when evaluated across the complete A1–A5 boundary. This study provides an expanded LCA framework and empirical evidence for integrating geological constraints and low-carbon material specifications into underground infrastructure procurement and engineering design. Full article

The environmental impact of cement production has become a growing global concern due to its substantial contribution to CO₂ emissions. Sugarcane bagasse ash (SCBA), as a supplementary cementitious material, offers a sustainable alternative by partially replacing cement and reducing the carbon footprint of concrete. However, determining optimal mix proportions that balance mechanical strength, cost efficiency, and environmental benefits remains a complex challenge. In this study, a multi-objective optimization framework was developed by integrating automated machine learning (Auto-ML) with the NSGA-III algorithm. A surrogate model for predicting compressive strength was constructed using the TPOT-based Auto-ML tool, achieving high predictive accuracy with R² values of 0.993 and 0.908 for the training and test datasets, respectively. NSGA-III was then employed to derive Pareto-optimal mix designs, enabling simultaneous optimization of strength, cost, and CO₂ emissions. To validate the proposed multi-objective optimization framework, SCBA concrete specimens were prepared using the optimized mix proportions and tested under uniaxial compression. The experimental results exhibited good agreement with the predicted values, with deviations within an acceptable margin, thereby confirming the accuracy and reliability of the framework. This study provides a practical approach for the intelligent design of low-carbon SCBA concrete, contributing to the advancement of sustainable construction practices. Full article

The growing use of 3D concrete printing has increased the need for cementitious mixtures that combine adequate mechanical performance with lower environmental impacts and production costs. However, these requirements may conflict, making mixture selection a multi-criteria problem. This study assessed nine cementitious mixtures for 3D concrete printing by integrating Life Cycle Assessment (LCA) with the MARS-SC multi-criteria decision-making method. We adopted a cradle-to-gate system boundary and conducted the environmental assessment according to ISO 14040 and ISO 14044 using SimaPro and the Ecoinvent database. We integrated environmental, functional, and economic indicators using the Methodology for the Relative Sustainability Assessment of Building Technologies (MARS-SC) to obtain an overall sustainability score. The mixture containing 40% limestone filler and 10% metakaolin showed the best environmental performance, with a global warming potential of 358 kg CO₂ eq/m³. The mixture reduced the GWP by 45.01% and 54.28% compared with two mixtures with higher cement contents and without partial cement replacement. However, this environmental advantage did not result in the highest overall sustainability score because of lower functional and economic performance. When the three dimensions were considered together, Blf30 and Blf40 achieved the highest sustainability scores (NS = 0.66). Although both mixtures had lower mechanical performance than the cement-rich mixtures, their environmental and economic results led to a more favorable overall assessment. The integrated analysis therefore shows that reducing environmental impacts does not, by itself, necessarily produce the most sustainable mix. Full article

The increasing generation of construction and demolition waste, along with the depletion of natural aggregates, has driven growing interest in recycled concrete aggregate (RCA) and reclaimed asphalt pavement (RAP) as sustainable alternatives in concrete production. However, a direct and systematic comparison between the two materials remains limited. This review addresses this gap by applying PRISMA guidelines to analyze 82 peer-reviewed studies published between 2010 and 2026. Both materials are evaluated across three key domains: physical properties, mechanical performance, and microstructural characteristics. The findings indicate that RCA can reduce compressive strength by up to 26%, mainly due to the presence of porous adhered mortar and a complex interfacial transition zone (ITZ). In contrast, RAP weakens bonding with cement paste because of its hydrophobic bituminous coating, leading to adhesive failure at the mortar asphalt interface. Despite these limitations, RCA and RAP exhibit distinct behaviors in terms of shear capacity, ductility, energy absorption, and durability. Enhancement techniques such as surface treatment, carbonation, supplementary cementitious materials, and fiber reinforcement show potential in improving performance. Additionally, life cycle and economic analyses reveal that RAP can reduce total costs and carbon emissions when efficiently processed. This study provides a unified comparative framework to support sustainable material selection and design optimization. Full article

Concrete is the most used construction material, but its long-term performance depends on durability. Although fly ash has been used as a supplementary cementitious material, the effects of its mechanical activation on the concrete durability require further investigation. This study evaluated the influence of replacing 30% of cement with natural Class F fly ash (NFA) and ground fly ash (GFA) in concrete with a water-to-binder ratio (w/b) of 0.62, using a mixture without fly ash (WFA) as reference. Mechanical activation was performed by milling the fly ash, followed by characterization through particle size analysis and X-ray diffraction. Concrete durability was assessed using electrical resistivity, ultrasonic pulse velocity (UPV), water absorption, porosity, rapid chloride permeability (RCPT), carbonation resistance, and compressive strength tests. Mechanical milling reduced and transformed the ash morphology from spherical to amorphous, while quartz and mullite remained the main crystalline phases. Compared with CNFA, CGFA exhibited up to 101% higher electrical resistivity, 39.6% greater resistance to chloride penetration, 10.8% improved carbonation resistance, 0.4% lower water absorption, and a 5.38% reduction in porosity, although compressive strength decreased by more than 20%. These results demonstrate that mechanically activated fly ash is a viable alternative for enhancing the concrete durability performance exposed to aggressive environments. Full article

Construction on very soft peaty clay remains a major geotechnical challenge due to its high compressibility and low-bearing capacity. The deep mixing method (DMM) is widely adopted for in situ stabilization using cement; however, environmental concerns associated with cement production have driven the search for sustainable alternatives such as geopolymers using low-carbon materials. Existing studies predominantly rely on dried peat, processed precursors such as fly ash or calcined ground rice husk ash (RHA), and high concentrations of alkali activators such as sodium silicate (Na₂SiO₃) and sodium hydroxide (NaOH), which increase both environmental and economic burdens. This study develops a novel waste-based geopolymer incorporating untreated brick kiln-derived RHA, activated solely with low-concentration NaOH, while completely eliminating Na₂SiO₃. The avoidance of precursor pre-treatment and Na₂SiO₃ significantly reduces processing energy, cost, and associated environmental emissions. A systematic investigation was conducted to determine the optimum mixing time for maximizing strength under field-relevant conditions. Mechanical performance was evaluated using unconfined compressive strength tests considering variations in binder content, curing duration (7, 28 days), alkali concentration (6, 3 M), and alkali-to-binder ratio (0.3, 0.5, 0.7). Failure characteristics were examined, and an integrated framework combining cost analysis, life cycle assessment, and grey relation analysis was employed to optimize mix design. The optimized geopolymer achieved 2.2 times higher strength than cement-treated soil, with 25% cost reduction and more than 85% reduction in environmental impact. These findings demonstrate a scalable and sustainable solution for stabilizing highly organic soils, while promoting the valorization of supplementary cementitious materials without energy-intensive preprocessing. Full article

Autogenous shrinkage is a key factor contributing to early-stage cracking in high-performance concrete (HPC), which significantly affects structural durability and service life. As core components of HPC, supplementary cementitious materials (SCMs) can significantly improve concrete workability, mechanical properties, and durability, as well as reduce the risk of shrinkage cracking in HPC, by regulating hydration kinetics, pore structure, and microstructural evolution. The primary objective of this review is to elucidate the differential mechanisms by which different active pozzolanic materials regulate the autogenous shrinkage of HPC. This paper elucidates the patterns and mechanisms by which typical SCMs in HPC (such as fly ash, slag, silica fume, limestone powder, and nano-silica) affect the autogenous shrinkage of HPC. It analyzes the influence of key factors—including the type of SCMs, dosage, particle characteristics, water-to-binder (w/b) ratio, and composite blending on the autogenous shrinkage of HPC. Research indicates that highly reactive SCMs (such as silica fume and nano-silica) accelerate the self-drying process and increase autogenous shrinkage, whereas low-reactivity SCMs (such as fly ash) suppress autogenous shrinkage through dilution effects and by prolonging the hydration cycle. The combined use of multiple SCMs can achieve synergistic control of autogenous shrinkage and mechanical properties. Furthermore, this paper reviews existing autogenous shrinkage prediction models that account for the influence of SCMs and outlines future research directions. At the same time, this review identifies the limitations that currently exist in the research: there is a lack of a unified quantitative theoretical framework for the synergistic effects of multicomponent admixtures. The applicability of prediction models under multi-field coupling of temperature, humidity, and corrosive media is limited. And there is insufficient experimental data on the long-term shrinkage behavior of new low-carbon admixtures such as rice husk ash and calcined clay, which requires further dedicated research. Full article

Lithium slag powder (LSP), a by-product of lithium extraction, has attracted increasing interest as a supplementary cementitious material (SCM) due to its aluminosilicate-rich composition and growing availability. However, its limited intrinsic reactivity constrains direct use in cementitious systems. This study systematically investigates the effect of calcination temperature on the physicochemical properties, pozzolanic reactivity, and cement hydration performance of LSP. LSP was thermally treated at 300–900 °C, and structural and morphological changes were characterized using X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The reactivity of calcined LSP was quantitatively assessed through isothermal calorimetry (R3 test), thermogravimetric and derivative thermogravimetric analysis. Chapelle testing, leaching tests, and compressive strength measurements of cement mortars. Controlled calcination was found to enhance the intrinsic reactivity and pozzolanic activity of LSP, resulting in improved long-term mechanical performance. The findings provide mechanistic insights and practical guidance for the sustainable use of lithium slag as an SCM in cement-based materials. Full article

The transition to lower-clinker binders in heavy precast concrete is constrained by the need to combine rapid production cycles, high early-age strength, self-compacting performance, durability and measurable environmental benefits. The scientific gap addressed in this study is the limited integrated evidence comparing these criteria under conditions that are representative of industrial heavy precast production, particularly for CEM II/A-S 52.5 R and CEM II/B-V 42.5 R. Four concretes were assessed: CEM I 52.5 R, CEM II/A-S 52.5 R, CEM II/B-V 42.5 R, and a 50:50 CEM I/CEM II/B-V binder. The experimental programme included slump-flow, a plant-specific 600 mm flow-time indicator, compressive strength development, hardened density, water absorption, water penetration under pressure and freeze–thaw resistance. Environmental performance was evaluated using the manufacturers Environmental Product Declarations (EPDs) for the cement component within a cradle-to-gate boundary. All mixtures corresponded to at least strength class C50/60 at 28 days, while CEM I, CEM II/A-S and the 50:50 blend corresponded to C55/67. CEM II/A-S reduced water absorption from 5.49% to 4.29% and water penetration from approximately 61 to 23 mm relative to CEM I, but its freeze–thaw strength loss was 26.80% compared with 4.50% for CEM I. CEM II/B-V provided the lowest cement-related GWP, approximately 154 kg CO₂-eq/m³, about 25% below CEM I, whereas the 50:50 blend reduced this indicator by approximately 12% while achieving the highest 28-day compressive strength (approximately 78 MPa). The results show that cement selection for heavy precast concrete cannot be based on clinker content or strength alone. CEM II/A-S offered the most balanced technological and transport-property performance, whereas CEM II/B-V offered the greatest GWP reduction but requires consideration of its lower strength class and slower early-age development. Long-term durability and full life-cycle impacts remain to be verified. Full article

The maturity method (ASTM C1074) predicts in situ concrete strength from a recorded temperature history but assumes a constant apparent activation energy, contradicting the experimental evidence that the activation energy falls as hydration shifts from kinetics control to diffusion control—an effect that differs between binder chemistries when supplementary cementitious materials (SCMs) are used. This study develops a physics-based maturity model in which the apparent activation energy varies linearly with temperature, Q(T) = Q₀ + β_Q(T − T_ref), coupling a variable-energy Arrhenius equivalent age to a hyperbolic strength–maturity relationship. The model was calibrated on 196 mean-strength observations (588 cube tests) from seven self-compacting concrete mixtures cured isothermally at 10, 20, 35 and 50 °C and tested at seven ages (1–90 days). All four SCM systems (fly ash, GGBS, silica fume and rice husk ash) returned a negative coefficient (−210 to −974), enclosing the temperature sensitivity implied by independent calorimetric measurements on Portland cement paste (≈−580 J/(mol·K)), whereas the ordinary Portland cement control returned a positive point estimate (+101) that is not statistically distinguishable from zero. The model achieved R² = 0.929 (RMSE = 4.74 MPa), outperforming the constant-energy ASTM C1074 baseline in both accuracy and the Akaike Information Criterion while eliminating its systematic bias at the temperature extremes. Five-fold cross-validation confirms the out-of-sample accuracy (R² = 0.901, RMSE = 5.59 MPa), and bootstrap analysis shows the negative coefficients of the fly ash, GGBS and rice husk ash systems to be statistically significant. External validation on 120 independent literature observations gave R² = 0.881. Full article