Search Results (842)

This study evaluated the potential use of waste mineral wool recovered from heating pipe insulation as a functional additive in cement concrete. The research aimed to determine the effect of this fibrous recycled material on the mechanical, physical, durability, thermal, and microstructural properties of concrete. One reference mix and three modified mixes were prepared, incorporating waste mineral wool at 12%, 16%, and 20% by cement mass. All mixes were prepared using CEM I 32.5R cement, 0/2 mm basalt aggregate, 2/8 mm granite aggregate, and a superplasticizer. After 28 days of sample curing, compressive strength, splitting tensile strength, density, water absorption, frost resistance, and thermal parameters were determined. Microstructural observations were also performed on concrete fracture surfaces. The results showed that the addition of mineral wool reduced the compressive strength from 84.9 MPa for the reference concrete to 63.8–53.3 MPa for the modified concretes. At the same time, moderate dosing improved the splitting tensile strength, reaching a maximum of 3.93 MPa with a 16% addition. The most favorable thermal effect was achieved with a 12% addition, for which the thermal conductivity coefficient decreased from 1.3461 to 1.1988 W/(m·K). The results indicate that waste mineral wool can be used in concretes with limited structural function; however, its dosage requires optimization due to increased water absorption and decreased compressive strength. Full article

Growing environmental concerns associated with Portland cement production, along with the continuous accumulation of construction and demolition waste, have intensified the need for sustainable construction materials and effective recycling strategies. This study experimentally investigates the performance of fly ash-based geopolymer concrete (GPC) incorporating recycled concrete aggregate (RCA) as a partial replacement for natural coarse aggregate, compared to conventional ordinary Portland cement concrete (OPC), with a particular focus on integrated durability performance. Ten mixtures were prepared, including five GPC and five OPC mixes with RCA replacement levels of 0–100% by volume. Mechanical properties were evaluated through compressive, splitting tensile, and flexural strength tests, while durability performance was assessed using water permeability, chloride penetration, acid resistance, elevated temperature exposure up to 1000 °C, and accelerated corrosion tests, supported by SEM–EDX analysis. Results show that GPC outperforms OPC across all replacement levels. Optimal performance was achieved at 20–40% RCA, while at 60% RCA a slight reduction in strength was observed; however, the values remained relatively high, particularly for GPC mixtures, indicating stable performance. A significant reduction occurred only at full replacement. GPC also exhibited lower permeability, enhanced corrosion resistance, improved thermal stability, and better resistance to acid attack. This study provides strong evidence that GPC can effectively compensate for the inherent limitations of RCA, offering a durable and eco-efficient alternative for structural and infrastructure applications. Full article

The whole pavement life cycle is divided into five phases: raw material production, construction, service use, maintenance and rehabilitation, and end-of-life (EOL). Distinct system boundary definitions (cradle to gate, cradle to site, cradle to grave) are clearly distinguished, and two categories of vehicle-related emissions are strictly differentiated: baseline vehicle operation emissions (excluded) and pavement-induced incremental emissions (included only for full cradle-to-grave accounting). According to cited highway pavement inventory data (functional unit: 1 m² full cross-section composite pavement, cradle-to-gate material-only boundary), cement-related materials account for merely 4.7% of total structural material mass yet contribute over 84.5% of material-phase carbon emissions, while asphalt mixture construction emissions generally make up less than 10% of mixing-stage outputs. In the use phase, pavement deformation, rolling resistance elevation and surface texture loss trigger extra vehicle fuel consumption and associated greenhouse gas increments. Maintenance-stage emissions stem from repair material manufacturing, on-site machinery operation and traffic congestion delays during lane closure; milling, transportation and recycling dominate EOL carbon outputs. This review further classifies all emissions into direct engineering emissions and pavement-derived indirect emissions, compares carbon performance and service-life extension effects of eight mainstream maintenance strategies, and thoroughly decomposes milling, stockpiling, haulage and recycling links of waste asphalt, alongside multiple environmental burden allocation methods for reclaimed asphalt pavement (RAP). A full spectrum of green low-carbon technologies is summarized, including biochar bio-materials, RAP, crumb rubber, industrial byproducts, warm-mix asphalt (WMA), cold recycling and CCUS negative-carbon materials. We also balance their emission reduction benefits against potential deterioration risks to rutting resistance, fatigue life and moisture stability. Combined with a life-cycle cost assessment (LCCA), this study analyzes cost-emission trade-offs of all technical routes, and deeply discusses multi-source uncertainty, sensitive input parameters and universal methodological limitations of pavement LCA. Core takeaways indicate that raw material production and long-term service use are the two dominant carbon emission stages; a medium RAP-WMA combination and cold in-place recycling represent the most economically and environmentally balanced mitigation solutions. Major research gaps and targeted future research directions are proposed, providing standardized theoretical support and dual environmental–economic decision references for low-carbon asphalt pavement design and full-life carbon accounting. Full article

The fine powder fraction generated during concrete recycling is often regarded as a low-value by-product or used as a filler in cement-based materials. This study investigates recycled concrete powder (RCP) as the main component of pressed cement-free and low-cement mineral composites. The <0.14 mm fraction was obtained by crushing and sieving concrete waste. Cylindrical specimens were produced by semi-dry pressing at 20 MPa with a forming moisture content of 12–13% and cured under humid-air conditions. Four systems were studied: untreated RCP, thermally activated RCP, RCP with 2.5 wt.% Portland cement, and RCP with 5 wt.% Portland cement. Thermal activation was performed at 600 °C for 2 h. Compressive strength, bulk density, and water resistance coefficient were determined at 3, 7, and 28 days. At 28 days, compressive strength increased from 6.9 MPa for untreated RCP to 11.4 MPa for thermally activated RCP and 12.8 MPa for RCP with 5 wt.% cement, while the water resistance coefficient increased from 0.61 to 0.86. DTA/TGA analysis revealed thermal effects and mass-loss patterns consistent with the presence and evolution of hydrated and carbonate-containing phases. The results demonstrate that RCP can serve as a structure-forming component in pressed cement-free and low-cement materials. Full article

The current reuse of blast furnace slag is limited, and the products made from it have low added value and minimal pricing potential. The primary objective of this research is to develop new eco-friendly 3D printing materials using blast furnace slag as the main raw material, simultaneously achieving combined optimization of color appearance and material performance, to increase the reutilization value of slag and address environmental problems caused by slag. Existing studies on slag-based 3D printing materials mainly focus on improving material performance, often neglecting the combined optimization of color and material performance. This study proposes a solution to create colored slag-based 3D printing materials, aiming to break the conventional view of slag waste as simply “black or gray.” This study optimized the particle size distribution of slag-based 3D printing materials using the Andreasen model. The CIELAB color difference formula was applied to reveal how color difference values varied under different mix ratios. Digital image analysis was conducted to evaluate the color characteristics of the specimens and the uniformity of the pigmentation. After 28 days of natural air curing, the color difference ΔE at various measurement points on each colored specimen remained below 3.0, indicating that iron oxide pigments exhibit satisfactory color stability within the slag matrix. To ensure high-quality 3D printing, this study examined the effect of water temperature on the curing time of colored slag-based 3D printing materials. Range analysis results showed that water temperature exerted the most significant influence on setting time (range = 255 s), substantially greater than that of pigment dosage (range = 15 s) and pigment type (range = 5 s). The Herschel–Bulkley constitutive model was used to calculate the flow index of the material. Printing tests confirmed that colored slag 3D printing materials are suitable for extrusion-based 3D printing. The 28-day compressive test results showed that the average fracture load of the three pigmented specimen groups ranged from 23.30 to 24.58 N. Cost analysis further indicated that the comprehensive material cost is approximately 467 RMB/ton, which is lower than that of commercially available colored cement, demonstrating favorable economic competitiveness. The development of colored materials for 3D printing based on blast furnace slag can expand their applications and market potential. It also improves material performance and market acceptance, and its cost advantage over commercial colored cement further enhances its viability for practical applications, promoting high-value recycling and reuse of slag waste. Full article

Waste rock wool (WRW) has attracted increasing attention as a supplementary cementitious material (SCM) because of its mineral composition and its potential for reducing industrial waste. Although thermal treatment is commonly applied during WRW recycling, the practical necessity of additional low-temperature thermal treatment after mechanical activation remains unclear. This study evaluated the feasibility of mechanically activated WRW as an SCM by comparing materials with and without subsequent thermal treatment at 250 °C. Cement paste containing 15 wt.% WRW was prepared, and the effects of thermal treatment were evaluated through X-ray fluorescence (XRF), scanning electron microscopy (SEM), compressive strength testing, and thermogravimetric analysis (TGA). The XRF and SEM results revealed only negligible differences in chemical composition and particle morphology between the thermally treated and non-thermally treated WRW. Although both WRW mixtures exhibited lower early-age compressive strengths than the Plain mixture, comparable or higher long-term strengths were achieved. The TGA results also showed only minor differences in calcium hydroxide content and degree of hydration between the two WRW mixtures. Overall, additional low-temperature thermal treatment provided limited practical benefits beyond mechanical activation alone. These findings demonstrate that mechanically activated WRW without subsequent thermal treatment is a feasible supplementary cementitious material, offering a simplified and more energy-efficient recycling strategy for cementitious applications. Full article

Water treatment sludge (WTS) is a by-product of water treatment plants, which is often landfilled and risks contaminant leakage into the environment. However, it is rich in aluminosilicate content, which suggests potential suitability as a supplementary cementitious material (SCM), offering a sustainable approach for waste recycling and carbon emission reduction in cement production. While prior reviews have broadly addressed WTS reuse across construction materials, the mechanisms governing its pozzolanic performance as a cement replacement remain insufficiently synthesized, including its emerging use in alternative binders. This systematic review addresses this gap by synthesizing literature from 2010 to 2026 on WTS as a partial cement replacement in cement-based materials (CBMs), in both binary and ternary blends. Findings show that WTS can exhibit high pozzolanic reactivity after grinding and calcination at 600–800 °C, though performance varies depending on source and composition and processing. Partial replacement of cement with 10% calcined WTS was most frequently identified as the optimal substitution level, improving mechanical properties by promoting C-S-H and C-A-S-H formation, although some studies report favourable long-term strength at higher substitution. However, most studies reported that further increasing WTS content in the mix (beyond 10%) leads to a decrease in performance due to the dilution effect, which limits the formation of C-S-H. This review further discusses the durability aspects and environmental impact of using WTS, which remain underexplored in the literature, and highlights areas for future investigations. Full article

Electromagnetic wave absorption ability and mechanical strength are critical performance metrics for cement-based microwave-absorbing materials. Enhancing electromagnetic wave absorption efficiency typically involves the incorporation of functional phases and optimization of pore structures. However, these modifications often introduce challenges, such as interfacial incompatibility between the functional phase and cement matrix, and reduced material density, which can compromise mechanical integrity. This study presents a structurally engineered, high-performance cement-based microwave-absorbing material fabricated from solid waste materials. By leveraging the poor interfacial compatibility between rubber powder and cement paste, the material achieves increased porosity, thereby improving impedance matching. Additionally, the presence of abundant dielectric and magnetic components in slag significantly enhances electromagnetic wave dissipation. Through the synergistic tuning of impedance matching and dissipation capacity, the cement-based microwave-absorbing material demonstrates a substantial improvement in electromagnetic wave absorption, with the absolute value of its reflection loss increasing by 2.8 times after CO₂ curing. Furthermore, the application of CO₂ curing technology facilitates the transformation of alkaline compounds such as Ca(OH)₂ into CaCO₃, resulting in notable gains in mechanical performance—compressive strength and flexural strength are elevated by 38% and 23%, respectively. This work not only achieves a balanced optimization of electromagnetic wave absorption and mechanical robustness in cement-based materials but also offers a sustainable pathway for the high-value utilization of industrial solid waste. Full article

Residual mortar on recycled fine aggregate contains pores and microcracks that weaken mortar strength and resistance to water ingress. This study treated recycled fine aggregate with 5 wt.% KH570 silane and used waste ceramic micropowder, at 4–12% of the total recycled fine aggregate mass, to replace an equal mass of the fraction not exceeding 0.6 mm. At a constant water-to-cement ratio and comparable flowability, compressive strength, flexural strength, 28 d water absorption, and maximum water pressure without visible leakage were evaluated, together with SEM, XRD, and MIP analyses. Mortar strength first increased and then decreased with increasing ceramic micropowder content, whereas water absorption showed the opposite trend. Among the tested replacement levels, SCR8 achieved the most favorable mean performance, with 28 d compressive and flexural strengths of 42.4 and 6.0 MPa, respectively, 38.6% and 25.0% higher than those of the unmodified recycled mortar. Its water absorption decreased by 36.4% to 7.48%, and it sustained 0.6 MPa without visible leakage. Microstructural results indicated fewer local defects, improved interfacial continuity, lower cumulative mercury intrusion, and a shift toward smaller pore throats. These improvements could be associated with combined regulation of aggregate wettability and pore-throat structure. Full article

To promote construction waste recycling and develop sustainable pavement materials, this study utilized recycled aggregates (crushing value 7.8%) obtained from bridge demolition as a 100% replacement for natural aggregates in recycled pervious concrete. The research focused on investigating the influence of different aggregate gradations (single-sized 4.75–9.5 mm and binary-graded combinations: 4.75–9.5 + 16–31.5 mm, 2–5 + 13–26.5 mm) and different water-to-cement ratios (0.26, 0.27, 0.30) on the concrete properties. Tests on compressive strength, splitting tensile strength, and connected porosity revealed the following results: The strength of recycled pervious concrete was comparable to that of natural aggregate concrete, and strength decreased with increasing aggregate size. The optimal water-to-cement ratio varied with gradation: 0.27 for the single-sized 4.75–9.5 mm aggregate and 0.30 for the binary-graded combinations. Splitting tensile strength was generally low, showed insignificant growth from 7 d to 28 d, was sensitive to interfacial defects, and exhibited high data variability. Connected porosity was inversely proportional to compressive strength and decreased with increasing water-to-cement ratio. This study provides experimental evidence for optimizing the preparation of high-performance recycled pervious concrete using recycled aggregates. In addition, the influence of fiber type, dosage, and length was preliminarily examined through an orthogonal design. Full article

This investigation evaluated the suitability of solar waste sand (SWS), derived from recycled photovoltaic panels, as a raw material in clinker production. Raw materials were prepared, analysed, and used to design reference and SWS raw mix kneaded balls. The balls were subjected to sintering tests with varying peak temperatures; the clinker mineralogy was analysed using X-ray diffraction (XRD). The SWS raw mix contained 13.14% SWS with 78.31% and 8.55% of limestone and clay, respectively. The SWS clinker had 55.64 ± 2.26% C₃S, 18.67 ± 1.27% β-C₂S, 1.57 ± 0.35% CaO_f, and 3.70 ± 1.41% MgO_f at 1350 °C, all within recommended ranges. Minor oxides, including Na₂O, K₂O, and MgO, reduced the required sintering temperature relative to the typical 1450 °C, as expected. The presence of an amorphous layer suggested the optimal temperature may be around 1350 °C. Furthermore, the high Na₂O content in the SWS clinker is believed to have helped stabilise β-C₂S. Low C₄AF and the absence of C₃A might indicate its suitability as a clinker for sulfate-resistant cements. Incorporating SWS directly into the raw mix for clinker production is an innovative approach to both diverting solar waste from landfills and partially supplementing sand and limestone. Full article

The transition toward low-carbon cement production requires alternative fuels with improved environmental performance and resource efficiency. Refuse-Derived Fuel (RDF), produced from pre-treated non-recyclable waste streams, represents a promising alternative fuel; however, its heterogeneous and varying composition presents challenges for stable combustion and process optimization. In this study, a comprehensive physicochemical characterization of RDF was performed and compared with pet coke, a conventional, fossil cement kiln fuel. The analysis included manual sorting, particle size distribution, elemental characterization, Scanning Electron Microscopy coupled with Energy dispersive X-ray spectroscopy (SEM/EDS), X-ray Diffraction (XRD), thermogravimetric and differential scanning calorimetry (TGA/DSC), and Higher Heating Value (HHV) determination. The RDF sample exhibited a heterogeneous polymeric-mineral composition dominated by plastics, paper, textiles, and inorganic fractions. TGA revealed a broad multi-stage thermal degradation profile, while calorimetry indicated HHV of 19.2 ± 0.3 MJ/kg and ash content of 11.6 wt.%, compared with 34.57 ± 0.11 MJ/kg and 1.97 wt.% for pet coke, respectively. SEM/EDS and XRD analyses confirmed the coexistence of polymeric and mineral phases in RDF, whereas pet coke exhibited a predominantly carbonaceous and homogeneous composition. The generated dataset supports computational fluid dynamics (CFD)-based cement kiln combustion models and RDF utilization for fossil fuel substitution in the cement industry. Full article

This study investigates the feasibility of using recycled sand derived from excavation waste as a sustainable alternative to natural sand in mortar production. The novelty of this work lies in the comprehensive evaluation of mortar performance using 100% recycled sand across a wide range of sand-to-cement (S/C) ratios, combined with microstructural and economic analyses. Six mortar mixes with S/C ratios ranging from 0.50 to 2.75 were prepared at a constant water-to-cement ratio. The experimental program assessed fresh and hardened properties, including flow, density, water absorption, compressive strength, and microstructural characteristics. The results demonstrate that excavation waste sand possesses suitable properties for mortar applications. An optimal mix with an S/C ratio of 0.7 achieved superior performance, with a 28-day compressive strength of 48.8 MPa, a density of 2.147 g/cm³, and a flow value of 108%, satisfying both strength and workability requirements. Increasing the S/C ratio resulted in reduced strength and increased water absorption, indicating a clear performance trend governed by paste content and porosity. Furthermore, the study provides practical insights into material efficiency and cost implications, showing that recycled sand mortar can reduce material costs by approximately USD 2.4 per ton compared to natural sand mortar. Overall, the findings support the potential of excavation waste sand as a viable and sustainable construction material, contributing to resource conservation and circular economy practices in the construction industry. Full article

Ultra-high-performance concrete (UHPC) typically contains high cement and steel-fiber contents, leading to high cost and carbon emissions. This study developed a low-carbon UHPC by partially replacing cement with industrial solid waste (ISW) composed of ground granulated blast-furnace slag and calcium carbide slag, and by partially replacing steel fibers with recycled plastic fibers (RPF). The effects of ISW and RPF on flowability, mechanical properties, hydration behavior, microstructure, carbon emissions, and raw-material cost were investigated. ISW had a limited influence on flowability, whereas RPF markedly reduced flowability. Appropriate ISW and RPF contents increased flexural and compressive strengths by up to 41.02% and 14.93%, respectively. The 30% ISW-50% RPF mixture provided the highest flexural strength, while 30% ISW-30% RPF achieved the highest compressive strength with acceptable flowability. Hydration heat, XRD, SEM, and FTIR analyses showed that moderate ISW promoted early hydration and C-S-H/C-A-S-H gel formation, whereas excessive ISW caused dilution and reduced matrix compactness. Therefore, 30% ISW-30% RPF is recommended as the balanced formulation, whereas 50% ISW-50% RPF is more suitable for carbon- and cost-sensitive applications and maintains approximately 150 MPa compressive strength. Full article

Although low-carbon geopolymers incorporating construction and demolition waste (CDW) offer a promising circular economy pathway, the synergistic mechanisms between pretreated recycled fine aggregates (RFA) and geopolymer binders have not been systematically elucidated. This study investigated the comprehensive performance of geopolymer mortar containing recycled powder (RP) incorporating RFA; 50% Fly ash, 25% slag, and 25% RP were incorporated as precursor for the production of geopolymer binders, while the replacement ratios (0%, 20%, 40%, 60%, 80%, 100%) and the pretreatment methods (carbonation and prewetting) of RFA were taken as experimental parameters. The effect of these parameters on the fluidity, setting time, water absorption, compressive strength, and microstructure of recycled geopolymer mortar (RGM) and recycled cement mortar (RCM) was analyzed. Results showed that as the RFA replacement ratio increases, the measured properties generally decline. However, pretreating the RFA, particularly through carbonation, effectively mitigates these drawbacks. The use of 60% carbonated RFA enhanced the compressive strength of RGM by 12% compared to untreated RFA at equivalent replacement ratio. A comparative evaluation of the performance variations between RGM and RCM revealed that geopolymer mortar exhibited lower fluidity, faster setting time, and higher compressive strength. The microstructure analysis by SEM showed that the geopolymerization reaction between adherent cement paste in RFA and geopolymer binders significantly enhanced the microstructural compactness compared to RCM. Furthermore, carbonation and prewetting treatments can mitigate cracks and pores in the mortar. The results demonstrate that RGM prepared with carbonated RFA offer an estimated 76% reduction in net CO₂ emission and 14.3% reduction in total cost relative to conventional cement mortar. This study established a framework that compares the mechanisms of RFA pretreatment and equip engineers with validated pretreatment strategies for upcycling CDW into construction materials. Full article