Search Results (68)

Foamed asphalt cold recycling technology is one of the key engineering approaches to address the accumulation of large quantities of reclaimed asphalt pavement (RAP) in road maintenance and rehabilitation. However, a systematic design methodology that simultaneously accounts for long-term fatigue resistance and toughness has not yet reached a unified consensus or widespread application. Existing studies have investigated the effects of fine aggregate gradation or cement content on individual performance aspects of mixtures, but studies incorporating both factors into a unified experimental framework for parallel comparison of multiple performance indicators remain limited. To this end, this study designed three mineral aggregate gradations with significantly different fine aggregate contents and systematically evaluated the effects of gradation composition, foamed asphalt content, and cement dosage on the mechanical properties, moisture stability, high-temperature stability, and fatigue performance of the mixtures. Indirect tensile fatigue tests under a stress-controlled mode were conducted to determine the fatigue life of different gradations at four stress ratio levels. The results indicate that sufficient fine aggregate content, particularly particles smaller than 0.075 mm, is a key factor in enhancing mixture compactness, indirect tensile strength, and resistance to moisture damage. The effect of cement on fatigue performance exhibits stress-level dependency: at low stress ratios, the addition of cement improves fatigue life, whereas at high stress ratios, the increased brittleness of the material reduces fatigue resistance, which is consistent with findings reported in previous studies. Furthermore, this study provides comparative experimental data for different fine aggregate gradations. The optimal gradation scheme demonstrated superior overall performance across all evaluated indicators, verifying the feasibility of achieving a balance between strength and toughness through gradation optimization. Compared with conventional design methods guided by a single strength index, this study offers a more comprehensive basis for mix design optimization of foamed asphalt cold recycled mixtures and provides engineering references for their application in long-life pavement maintenance. Full article

This study presents a novel, rapidly synthesized geopolymer foam fabricated from granite industrial waste using microwave sintering, reducing the demolding time from 7 days to 3 min and the overall processing time to 24 h, while enhancing mechanical performance. Five sample compositions (G1–G5) were prepared with varying granite powder and alkaline solution ratios, cured in a microwave for 3 min, and sintered for an additional 3 min. X-ray fluorescence (XRF), compressive strength tests, water absorption, thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Fourier transform infrared spectroscopy (FTIR) were used for thorough characterization. The compressive strength increased progressively from 13 MPa (G1) to 20 MPa (G5), the total porosity decreased from 33.33% to 18.58%, the water absorption reached a minimum of 2.02% (G5), and the bulk density rose from 1.143 to 1.49 g/cm³. XRF analysis confirmed Si/Al molar ratios of 6.5–11.4, indicating enhanced aluminosilicate network development. FTIR confirmed progressive geopolymerization, with integrated Si-O-T band areas increasing from 41,900 a.u. (G1) to 44,680 a.u. (G5). The microwave sintering approach consumed over 90% less active energy than conventional thermal curing, significantly reducing associated CO₂ emissions and thereby supporting SDG 7, SDG 12, and SDG 13. These results position granite-waste-derived geopolymer foam as a high-performance, energy-efficient alternative to conventional fired bricks and cement-based construction materials. Full article

Foam concrete and fiber-reinforced foam concrete are promising building materials for sustainable and energy-efficient construction. Improving the environmental performance of cellular composites through the use of industrial waste and additives based on them is highly relevant. This study intends to create a novel complex nanomodifying additive (CNA) from industrial waste and nanomaterials, alongside new eco-friendly foam concrete (FC) and fiber-reinforced foam concrete (FFC) mixes incorporating CNA and polypropylene fiber (PF). Experimental studies yielded the optimal CNA formulation and described a method for its preparation. The test results indicate that FC’s properties are enhanced by CNA. The properties were best in the FC that was modified with 10% CNA. The FC control composition was surpassed by a 25.5% increase in compressive strength and a 23.1% increase in flexural strength, with a 9.5% reduction in thermal conductivity. Dispersed PF reinforcement also positively impacts the properties of FFCs with CNA, and the combined modification of 10% CNA and 1.2% PF provides maximum increases in compressive and flexural strength, amounting to 43.1% and 102.2%, respectively, and a 16.9% reduction in thermal conductivity. A microstructural analysis of the cellular composites confirms the feasibility of the tested formulation solutions. The FFCs, when modified by CNA and PF, display a homogeneous cellular structure, and the interpore zones contain multiple clusters of calcium silicate hydrate. Using CNA in the production of FC and FFCs will reduce cement consumption and improve their environmental friendliness. Full article

Municipal solid waste incineration (MSWI) fly ash is classified as hazardous waste due to its enrichment of heavy metals and dioxins. This article systematically reviews its generation pathways, physicochemical characteristics, and potential environmental risks, based on the literature from 2010 to 2025 sourced from Web of Science, Scopus, ScienceDirect and China National Knowledge Infrastructure. Emphasis is placed on heavy metal stabilization, dioxin degradation and resource recovery from MSWI fly ash. The mechanisms, technical advantages, and application limitations of three mainstream detoxification, including solidification/stabilization, extraction and thermal treatment, were emphasized. For instance, geopolymer achieves >99.6% Pb immobilization and electrodialytic removal rates of Cd up to 98%, while vitrification reduces the MSWI fly ash volume by >50%. A comprehensive exploration of MSWI fly ash resource utilization was conducted, covering the preparation of ceramic tiles, synthesis of glass ceramic and glass ceramic foams, processing of road substrates, and modification of cement-based composite materials. The current technological system still faces challenges such as high costs, excessive energy consumption, and secondary pollution. Future research should focus on developing green, low-carbon, and low-cost processes, improving long-term environmental stability of products and strengthening pollution source reduction control. Full article

In order to better understand the mechanical properties of lightweight cement-based composite concrete (LWC), expanded polystyrene (EPS) beads are used as lightweight aggregate (LWA) in this paper. 50%, 70%, and 90% of EPS foam beads by volume are used to partially replace normal fine aggregate in different EPS concrete compositions. In addition, Ordinary Portland cement (OPC) was substituted with silica fume (SF) in EPS concrete at varying weight percentages of 15%. Nine mixes are made in order to examine the properties of EPS concrete. In the testing program, fresh density, slump, compressive strength, splitting tensile strength, flexural strength, thermal conductivity, and absorption are all determined. Although workability is improved, the mechanical properties of concrete are generally decreased when EPS beads are used. The addition of silica fume (SF) successfully counteracted the mixture’s overall decline in mechanical properties across all the mixtures that have been used. More solid material can be found per square inch of surface area in materials with a higher density, which results in more continuous heat-conduction pathways. In comparison to the control mix, the compressive strength of the polystyrene modified mixes showed a noticeable decline, falling by roughly 62% for P-50%, 69% for P-70%, and 71% for P-90%. In contrast, mixes P-90%-1.2, P-90%-1.4, and P-90%-1.6 reduced absolute strength compared to P-90%; their performance is nonetheless noteworthy because of their extraordinarily high EPS content. Despite having lesser absolute strengths than P-90%, mixes of P-90%-1.2, P-90%-1.4, and P-90%-1.6 nevertheless performed admirably considering their remarkably high EPS content. Full article

Large-scale mining of graphite, a crucial strategic mineral, generates substantial amounts of graphite tailings (GT). The stockpiling of this solid waste occupies vast land resources and poses persistent environmental risks due to potential heavy metal leaching. Repurposing GT into construction materials presents a promising solution, with its use as a partial replacement for fine aggregates in cementitious composites being one of the most effective methods. This review systematically consolidates current research on graphite tailings cement mortar (GTCM) and graphite tailings concrete (GTC). Due to its physicochemical properties comparable to natural sand, GT is suitable for producing building materials. Studies consistently demonstrate that a substitution level of 10% to 20% optimizes overall performance. This optimal range enhances particle packing, promotes cement hydration via pozzolanic activity, and refines the microstructure, leading to improved workability, superior mechanical strength, and enhanced durability, including resistance to permeability, freeze–thaw cycles, and chemical attacks. Moreover, the inherent carbon content imparts electrical conductivity to GTC, enabling functional applications like de-icing and structural health monitoring. The successful utilization of GT also extends to lightweight foamed and autoclaved aerated concrete. However, research on the structural behavior of GTC components remains limited. Preliminary findings on beams and columns are encouraging, but comprehensive studies on their seismic performance and design methodologies are urgently needed to facilitate the widespread engineering application of this sustainable material and mitigate the environmental impact of tailings accumulation. Full article

In the era of growing demand for sustainable solutions in construction, increasing attention is being paid to the potential use of waste materials as components of building composites. This article presents the results of a study on the impact of ground polyurethane foam waste on the mechanical properties and durability of cement mortars. The waste, derived from industrial production processes, was used as a partial replacement for fine aggregates in various proportions. The analysis included bulk density, compressive and flexural strengths, water absorption, and resistance to freeze–thaw cycles. The results indicate that adding waste reduces the density of the mortar, which can be advantageous in applications requiring lightweight materials. The most favourable balance of strength retention, density reduction, and frost resistance was observed with a 1% addition, as the mortar maintained good mechanical performance and freeze–thaw durability while achieving reduced weight. Higher waste content (2–3%) led to significant deterioration of the mechanical properties due to increased porosity. All samples exhibited increased strength after 25 freeze–thaw cycles, possibly due to continued hydration under moist low-temperature conditions. The analysis of the microstructure of cement coatings with the addition of polyurethane foam enabled the explanation of the causes of the observed changes in physico-mechanical properties resulting from ageing factors. This study suggests that small amounts of waste can be effectively used to produce lightweight and environmentally friendly construction materials, supporting circular economy practices. Full article

The recycling of ultralight foam concrete (ULFC), both with and without phase-change material (PCM), involves crushing it and using the resulting recycled foam concrete powder (RFCP) as a partial substitute for cement or sand in cement composites. These recycling paths remain insufficiently explored in the literature regarding practical feasibility. Since both RFCP and PCM reduce the flowability of fresh mortars, incorporating RFCP with PCM is, in practice, only feasible with the addition of a superplasticizer (SP). The primary objectives of this study were to determine: (1) the effect of RFCP with PCM, when used to replace cement or sand, on mortar properties, and (2) its influence on the performance of the superplasticizer (SP), to assess the feasibility of using RFCP with PCM in cement composites. The addition of RFCP, both without PCM (RFCP_0) and with PCM (RFCP_PCM), deteriorates the properties of fresh and hardened mortars compared to reference mortars. The negative impact of RFCP is less pronounced when it replaces sand rather than cement. Compared to RFCP_0 mortars, RFCP_PCM mortars exhibit reduced flowability. PCM delays setting and reduces heat evolution during the first 48 h of hardening. PCM does not significantly affect strength or water absorption but increases shrinkage and lowers thermal conductivity. While RFCP_PCM does not impair SP efficiency, PCM causes SP to significantly retard setting and hardening. Full article

The growing energy demand in the residential sector, driven by the extensive use of air conditioning systems, poses serious environmental and economic challenges. A sustainable alternative is the use of efficient insulating materials derived from waste resources. This study presents the synthesis of glass–ceramic foams produced from recycled glass (90 wt%), pumice (5 wt%), and limestone (5 wt%), sintered at 800 °C for 10 min. The resulting foams exhibited a low apparent density of 684 kg/${\mathrm{m}}^3$ and thermal conductivity of 0.09 W/m·K. These were incorporated into composite insulating panels composed of 70 wt% ceramic pellets and 30 wt% Portland cement, achieving a thermal conductivity of 0.18 W/m·K. The panels were evaluated in a 64.8 ${\mathrm{m}}^2$ social housing model located in Chihuahua, Mexico, using TRNSYS v.17 to simulate annual energy performance. Results showed that applying a 1.5-inch ceramic foam panel reduced the annual energy demand by 16.9% and the total energy cost by 14.7%, while increasing the panel thickness to 2 in improved savings to 18.4%. Compared with expanded polystyrene (EPS), which achieved 24.9% savings, the proposed ceramic panels offer advantages in fire resistance, durability, local availability, and environmental sustainability. This work demonstrates an effective, low-cost, and circular-economy-based solution for improving thermal comfort and energy efficiency in social housing. Full article

The preparation of construction waste into eco-friendly recycled powder (RP), partially replacing cement to produce foam concrete with thermal insulation properties, provides a new approach for the resource utilization of RP. In this study, different components of construction waste were used to prepare recycled paste powder (RPP), recycled brick powder (RBP), and recycled concrete powder (RCP). The effects of RP on the microstructural and macroscopic properties of foam concrete were investigated at replacement rates ranging from 0% to 30%. The research results indicate that the microstructure of all three types of RP exhibits irregular shapes, and their chemical compositions show significant differences. Partial replacement of cement with these RP leads to the deterioration of the matrix microstructure, which negatively affects the workability and mechanical properties of the foam concrete. However, the addition of RP effectively mitigates the drying shrinkage of the foam concrete, with RBP showing particularly outstanding performance in this regard. Specifically, the maximum drying shrinkage rate of F-30RBP is 9.33% and 11.31% lower than that of F-30RPP and F-30RCP, respectively. Furthermore, the incorporation of RP has a minimal effect on the thermal conductivity of the foam concrete, indicating that RP is well-suited for use in foam concrete. Full article

Global urbanization has led to massive generation of high-water-content waste slurry, creating serious environmental challenges. Conventional treatment methods are costly and unsustainable, while cement-based foamed lightweight soils typically exhibit low strength and limited CO₂ sequestration. To address this issue, this study proposes a novel stabilization pathway by integrating a MgO–mineral powder–carbide slag composite binder with CO₂ foaming–carbonation. The approach enables simultaneous slurry lightweighting, strength enhancement, and CO₂ fixation. A series of laboratory tests were conducted to evaluate flowability, density, compressive strength, and deformation characteristics of the carbonated lightweight stabilized slurry. Microstructural analyses, including SEM and XRD, were used to reveal the formation of carbonate phases and pore structures. The results showed that MgO content strongly promoted carbonation, leading to denser microstructures and higher strength, while mineral powder and carbide slag optimized workability and pore stability. Orthogonal testing indicated that a mix with 25% mineral powder, 12.5% MgO, and 7.5% carbide slag achieved the best performance, with unconfined compressive strength up to 0.48 MPa after carbonation. Compared with conventional cement- or GGBS-based foamed lightweight soils, the proposed system exhibits superior strength development, improved pore stability, and enhanced CO₂ sequestration potential. These findings demonstrate the feasibility of recycling high-water-content waste slurry into value-added construction materials while contributing to carbon reduction targets. This study not only provides a sustainable solution for waste slurry management but also offers new insights into the integration of CO₂ mineralization into geotechnical engineering practice. Full article

Wet–dry cycles are a key factor aggravating the durability degradation of foam concrete. To address this issue, this study prepared bentonite slurry–steel slag foam concrete (with steel slag and cement as main raw materials, and bentonite slurry as admixture) using the physical foaming method. Based on 7-day unconfined compressive strength tests with different mix proportions, the optimal mix proportion was determined as follows: mass ratio of bentonite to water 1:15, steel slag content 10%, and mass fraction of bentonite slurry 5%. Based on this optimal mix proportion, dry–wet cycle tests were carried out in both water and salt solution environments to systematically analyze the improvement effect of steel slag and bentonite slurry on the durability of foam concrete. The results show the following: steel slag can act as fine aggregate to play a skeleton role; after fully mixing with cement paste, it wraps the outer wall of foam, which not only reduces foam breakage but also inhibits the formation of large pores inside the specimen; bentonite slurry can densify the interface transition zone, improve the toughness of foam concrete, and inhibit the initiation and propagation of matrix cracks during the dry–wet cycle process; the composite addition of the two can significantly enhance the water erosion resistance and salt solution erosion resistance of foam concrete. The dry–wet cycle in the salt solution environment causes more severe erosion damage to foam concrete. The main reason is that, after chloride ions invade the cement matrix, they erode hydration products and generate expansive substances, thereby aggravating the matrix damage. Scanning Electron Microscopy (SEM) analysis shows that, whether in water environment or salt solution environment, the fractal dimension of foam concrete decreased slightly with an increasing number of wet–dry cycle times. Based on fractal theory, this study established a compressive strength–porosity prediction model and a dense concrete compressive strength–dry–wet cycle times prediction model, and both models were validated against experimental data from other researchers. The research results can provide technical support for the development of durable foam concrete in harsh environments and the high-value utilization of steel slag solid waste, and are applicable to civil engineering lightweight porous material application scenarios requiring resistance to dry–wet cycle erosion, such as wall bodies and subgrade filling. Full article

Foamed concrete has been widely applied in construction engineering; however, the performance requirements vary across different structural components. Its production typically involves a substantial consumption of cement, which imposes both environmental and economic burdens. Therefore, this study examined foamed concrete with dry apparent densities of 500–1000 kg/m³, in which cement was partially replaced (0–30%) by recycled powder from construction and demolition waste. Macroscopic performance was evaluated through drying shrinkage, compressive strength, softening coefficient, carbonation coefficient, and thermal conductivity, while microstructural analysis was conducted to clarify the underlying mechanisms. The results indicate that the internal composition of the recycled powder primarily consists of SiO₂, CaCO₃, and C-S-H gel. When recycled powder is used to replace cement, the microstructure of the resulting paste gradually deteriorates compared to that of the control group without recycled powder, and a significant amount of inert SiO₂ is introduced. As the replacement ratio of recycled powder increases, the compressive strength of foamed concrete across various density grades exhibits a gradual decline. Notably, when the replacement ratio reaches 30%, the reduction in mechanical performance becomes more substantial. However, the incorporation of recycled powder can effectively mitigate the drying shrinkage of foamed concrete. Moreover, the incorporation of recycled powder exerts minimal influence on the thermal conductivity and porosity of foamed concrete, demonstrating its favorable compatibility and potential for application in foamed concrete systems. Full article

The environmental impact of traditional construction materials has led to increasing interest in developing more sustainable alternatives. This study addresses the development of low-carbon autoclaved aerated concrete (AAC) through the complete replacement of ordinary Portland cement (OPC) with ground granulated blast furnace slag (BFS), activated with lime and, in some formulations, supplemented with calcium carbide slag (CCS). Five different AAC mixtures were prepared and evaluated in terms of workability, foaming behavior, compressive strength, phase composition, density, thermal conductivity, and life cycle assessment (LCA). The BFS-based mixtures activated with lime exhibited good workability and foaming stability. After pre-curing, the addition of CCS significantly improved the formation of tobermorite during autoclaving. As a result, the BFS–CCS formulations achieved compressive strengths comparable to the reference OPC-based mix while maintaining low densities (420–441 kg/m³) and thermal conductivities in the range of 0.111–0.119 W/(m·K). These results confirm the technical feasibility of producing structural-grade AAC with a lower environmental footprint. Full article

Foam cement, as a building insulation material, encounters a major problem in practical application, which is the difficulty in achieving a balance between its strength and insulation performance. To achieve multi-objective optimization of foamed cement mix design, this study first determined the optimal ranges of nano-silica aerogel (NSA), foaming agent, and polypropylene (PP) fiber dosage through single-factor experiments. Then, response surface methodology (RSM) was employed to construct a quadratic polynomial regression model, systematically investigating the influence of different NSA contents, foaming agent contents, and PP fibers contents on the thermal conductivity and compressive strength of foamed cement. Finally, the optimal mix ratio was further predicted and experimentally validated. The results demonstrate that the regression model developed using RSM exhibits high accuracy and reliability. The correlation coefficients R² of the regression models established by the response surface method are 0.9756 and 0.9684, respectively, indicating good prediction accuracy. The optimized mix ratio was determined as follows: NSA content, 9.548%; foaming agent content, 0.533%; and PP fiber content, 0.1%. Under this mix, the model predicted a thermal conductivity of 0.123 W/(m·K) and a 28-day compressive strength of 1.081 MPa. Experimental verification confirmed that the errors between predicted and measured values for all performance indicators were within 5%, demonstrating the high reliability of the predictive model. This study provides support for the practical application of foam cement as a thermal insulation material in construction projects and offers guidance for optimizing its mixture composition. Full article