Search Results (125)

In this study, three types of industrial solid waste—granulated blast furnace slag (GBFS), fly ash, and desulfurization gypsum (DG)—are utilized to collaboratively prepare low-carbon cementitious materials. The effects of steam curing temperature, constant temperature time, and fly ash content on the mechanical properties of multi-source solid waste cementitious materials are systematically investigated, and the optimal mix proportion ratio for low-carbon cementitious materials is determined. The results indicate that as steam curing temperature and constant temperature time increase, the compressive strength of the ternary cementitious material generally shows an upward trend, while the fly ash content exhibits a negative correlation. When the steam curing temperature is 70 °C, the constant temperature time is 10 h, the fly ash content is 20%, and the strength can reach 24 MPa, with both its engineering performance and economic benefits meeting the requirements of practical applications. Meanwhile, the steam curing temperature shows a tendency of first decreasing and then increasing shrinkage rate after 28 d, with the lowest shrinkage rate at 70 °C. Extending the constant temperature time can slightly reduce shrinkage, and the addition of 20–30% fly ash can optimize shrinkage performance. Moreover, the TG/DTG and SEM-EDS microscopic testing demonstrates that the ternary system achieves synergistic activation by accelerated mineral dissolution, ion release and enhanced alkalinity under steam curing, which jointly promotes the formation of AFt and C-A-S-H gel to refine microstructure and improve compactness. This study can not only reduce the consumption of cement, but also facilitate the recycling of industrial waste, providing theoretical support for the application of multi-source solid waste low-carbon materials in practical engineering. Full article

This research investigates the formation and behavior of sustainable crumb rubber-modified gypsum–cement–pozzolan (GCP) composites, with a view to their use in a broad concept for construction. GCP binders are gaining attention as a low-carbon replacement for Portland cement, and the addition of recycled rubber helps the achievement of circular economy goals and potentially increases durability. The present research evaluates the impact of crumb rubber (CR) on the mechanical strength, water absorption, dimensional stability, and freeze–thaw resistance of 3D-printed GCP-rubber composites. Composite blends of variable proportions of crumb rubber were prepared at constant binder ratios. Mechanical properties were defined by prism specimens (40 × 40 × 160 mm) by the flexural and compressive strengths, and deformation was determined by micrometers to measure longitudinal strain as a function of curing. Water absorption was determined prior to freeze–thaw cycling to define pore saturation. Durability was investigated using two approaches: (1) controlled freeze–thaw experiments on cube specimens, with XF1 grade performance achieved, and (2) ultrasonic pulse velocity (UPV) testing of specimens 3D-printed for assessing internal structural change after long-term frost exposure. Results showed that compressive strength decreased moderately (10–20%) with increasing rubber content from 17% up to 50%, while flexural strength improved up to 15%, showing the elastomeric action of CR. Water absorption was reduced by 5–8% in the rubber-modified blends due to the hydrophobic character of rubber. Deformation tests also confirmed minimum length variation (<0.02%) during curing. Freeze–thaw durability was enormously improved, and test specimens retained more than 95% of initial strength. UPV measurements detected only a relatively modest velocity drop (~50 m/s) after 36 days cycling with subsequent stabilization up to 200 days, demonstrating long-term internal structure with minimal progressive damage. In summary, the findings demonstrate that GCP composites with crumb rubber incorporated are printable, dimensionally stable, and capable of freeze–thaw degradation resistance. Despite a moderate loss of compressive strength, the balance of introduced durability and sustainability suggests their competence as viable materials for additive manufacturing in construction. Full article

Cadmium (Cd) and lead (Pb) co-contamination in construction and demolition waste landfill soils presents a significant challenge to ecosystem health, necessitating effective remediation strategies. This study investigated a synergistic approach combining a composite amendment (compost, superphosphate, desulfurized gypsum) with seven plant species to elucidate the interactions driving metal immobilization and phytoextraction. The amendment significantly altered soil properties: it reduced total Cd while increasing its bioavailability, and enhanced soil fertility (e.g., elevated organic matter and total nitrogen). Plant responses varied: Solanum americanum Mill. and Tagetes patula L. exhibited high Cd phytoextraction capacity, whereas Lolium perenne L. sequestered Cd/Pb primarily in roots. The bacterial community shifted from an oligotrophic, stress-tolerant state (e.g., Sphingomonas-dominated) in contaminated soil to a copiotrophic, functionally active state (e.g., Streptomyces-enriched) in amended soil. Community structure was strongly correlated with available Cd, pH, and nutrient levels. Key microbial biomarkers were specifically enriched in different plant rhizospheres. In contrast, the fungal community exhibited minimal responsiveness. These findings demonstrate that remediation efficiency is governed by an integrated “amendment–plant–microbe” framework: amendments regulate metal bioavailability, plants execute extraction or stabilization, and the restructured microbiome supports nutrient cycling and plant health. This integrated remediation strategy directly supports the Sustainable Development Goals of the 2030 Agenda, especially on environmentally sound management of chemicals and wastes and land degradation neutrality. This mechanistic understanding underscores the necessity of combined biological and chemical strategies for sustainable remediation of co-contaminated soils, ultimately enabling ecological reclamation and safe recycling of such urban marginal lands into productive uses. Full article

The stability of upstream tailings remains a critical geotechnical challenge due to the inherently weak mechanical properties of fine-grained mine tailings. This study investigated a tailing improvement method using (i) emulsified polymer and (ii) combinations of recycled gypsum and cement kiln dust (CKD). A comprehensive experimental program—including unconfined compressive strength (UCS) analysis, direct shear tests (DSTs), and oedometer consolidation tests—was conducted to assess the performance of various treatment mixtures. The results showed that blends of CKD and gypsum, particularly at a 1:2 ratio and a 10% dosage, significantly improved shear strength, reduced compressibility, and lowered hydraulic conductivity by over an order of magnitude. The inclusion of plaster (commercial gypsum) further enhanced the UCS by more than 100% compared to recycled gypsum and increased the cohesion (c’) values from 0 to 32.8–47.2 kPa. The compression index (c_c) decreased from 0.15 to 0.05, and the maximum volumetric strain (ε_v) at an applied effective stress of 800 kPa decreased from 17% to 5%. Emulsified polymer treatments also enhanced the mechanical and hydraulic properties of the clayey tailings; however, the overall improvements were lower than those achieved with CKD–gypsum blends, suggesting that further optimization of the polymer concentration or its combination with mineral additives may yield better results. These findings offer a foundation for further research into the use of polymers in geoenvironmental applications, particularly for erosion control, contaminant encapsulation, and hydraulic barrier development. Overall, this study highlights the potential of using industrial by-products, such as CKD and gypsum, as sustainable, cost-effective materials to improve tailing performance, while identifying promising directions for polymer-based solutions in geotechnical engineering. Full article

Construction and demolition waste (CDW) poses a significant environmental challenge, and the efficient recovery of high-quality recycled aggregates (RA) is vital for sustainable resource use. This study assesses how water jigging functions as a gravimetric separation method for ceramics, bricks, gypsum, and concrete, emulating the composition of inert CDW components. Material parameters, including bulk density, specific gravity, and shape factor, were initially measured to evaluate their effect on separation performance. Laboratory jig tests employed various controlled feed combinations, and the material stratification was analyzed at different levels of the jigging bed. The results exhibited that separation performance is dependent strongly on mixture complexity and density contrast. In binary mixtures, the B3 mixture showed the sharpest separation, reaching ceramic recovery to 92.65% in dense layer and separation efficiency of 90.59%. The materials with similar properties, particularly ceramics and bricks, showed greater overlap in layers and weaker stratification. In ternary systems the ceramics recovered mainly in intermediate layer with recovery range 46.8–49.6% and the maximum separation efficiency was 19.21%. Results indicating that addition of third component reduces the separation sharpness due to differences in particle morphology and overlapping density ranges. This investigation shows that water jigging has potential for ceramic-rich fractions upgrading in CDW, especially if differences between density of components are significant. Full article

Since 2007, the porosity–to–cement relationship has been widely used as a unified parameter to predict mechanical strength, durability, expansion, and stiffness of stabilized soils. In this formulation, the volumetric binder content is adjusted by an internal exponent x, typically ranging between 0 and 1, to balance the relative contributions of porosity and cementation. Traditionally, the parameters of this relationship have been obtained using manual regression procedures. This study proposes an automated calibration methodology for the porosity–binder index, where the parameters A, B, and x are determined through an iterative optimization framework based on minimization of the sum of absolute errors (SAE) combined with a Monte Carlo search algorithm. The methodology is applied to a cement-stabilized clay blended with ground glass (GG), recycled gypsum (GY), and limestone residues (CLW). The predictive capability of the calibrated model is evaluated using unconfined compressive strength (q_u) and initial shear stiffness (Go) datasets. Two calibration strategies are considered: Calibration Process No. 1, based on CLW mixtures and q_u values only, and Calibration Process No. 2, incorporating all mixtures (CLW, GG, and GY) and both q_u and Go responses. The results indicate that Calibration Process No. 2 provides a more robust and physically consistent parameter set, yielding coefficients of determination of 0.9318 and 0.9412 for q_u and Go, respectively. The proposed algorithm-driven calibration framework improves predictive capability and provides a systematic approach for determining the parameters of the porosity–binder relationship. Full article

The building sector is a major source of CO₂ emissions and construction waste, motivating the development of sustainable materials and end-of-life recycling strategies. Bio-concretes, combining mineral binders with plant-based aggregates, offer low density and favorable hygrothermal performance but remain insufficiently studied with respect to recyclability, particularly for gypsum-based materials. This study experimentally investigates the thermal recycling of gypsum–hemp bio-concrete, in which gypsum acts as the binder and hemp shiv as the aggregate. Thermogravimetric analysis of individual constituents and the bio-concrete was conducted to identify a temperature range enabling gypsum dehydration without hemp degradation. Controlled oven treatments at selected temperature–time couples were then applied to determine optimal recycling conditions, followed by the bio-concrete remanufacturing using 100% recycled constituents. Physical, thermal, and mechanical properties were evaluated before and after recycling under controlled conditions. Results show that a treatment at 180 °C for 60 min enables effective gypsum dehydration (18–20% mass loss) while preserving hemp integrity. Recycled gypsum–hemp bio-concrete exhibits increased density (368 to 587 kg·m⁻³) and compressive strength (0.05 to 0.52 MPa), accompanied by a moderate increase in thermal conductivity (0.081 to 0.096 W·m⁻¹·K⁻¹). These findings demonstrate the feasibility of 100% thermal recycling of gypsum–hemp bio-concrete without constituent separation. Full article

The large-scale dredging activities in port areas generate substantial quantities of dredged soil, leading to land occupation and disposal challenges, while industrial wastes such as fly ash and desulfurization gypsum remain underutilized. In this study, industrial wastes were employed as a curing agent to stabilize dredged soil, aiming to achieve both mechanical performance improvement and cost-effective recycling. In total, 100 g of curing agent was added to 1 kg of sludge. The optimal strength-maximizing formulation comprised 4.5% activator 1 #, 4.5% fly ash, 4.5% mineral powder, and 0.5% desulfurization gypsum. It achieved an unconfined compressive strength of 0.794 MPa. For enhanced cost-effectiveness, a modified binder blend (1.88% activator 1 #, 4.5% fly ash, 4.5% mineral powder, and 0.5% desulfurization gypsum) delivered 0.63 MPa at 28 days, satisfying mechanical construction specifications. Results demonstrate that unconfined compressive strength increases with solid wastes; however, with the extension of solidification time, the unconfined compressive strength of dredged soil gradually slows down. Full article

Phosphogypsum is one of the most widely produced gypsum-containing wastes. Therefore, researchers worldwide are exploring ways to recycle them. It is most often considered as an alternative to natural gypsum in the production of calcium sulfate hemihydrate. There are also isolated studies aimed at producing insoluble anhydrite (CaSO₄ II) from phosphogypsum. Compared to hemihydrate, anhydrite is characterized by greater strength and water resistance, and compared to Portland cement, it demonstrates lower energy consumption and CO₂ emissions during production. This study examined the possibility of phosphoanhydrite binder (CaSO₄ II) synthesis by calcination at 600, 800, and 1000 °C of phosphogypsum from four different industrial plants. Phosphoanhydrite binders capable of self-hardening, without the use of special additives, were synthesized. Their maximum strength at 28 days reached 57 MPa, and 69 MPa at 90 days. New data have been obtained regarding the influence of initial phosphogypsum characteristics and calcination temperature on the properties of CaSO₄ II and the hardened phosphoanhydrite paste. Full article

Concrete poses many environmental and economic problems due to its heavy reliance on natural resources. The objective of this study was to explore the potential of utilizing recycled materials, specifically waste glass powder and demolition sand, to assess their effectiveness in reducing the formation of delayed ettringite and consequently enhancing the strength of sustainable concrete. This study assesses the combined effects of waste glass powder and demolition sand on stable, sustainable concrete under sulfate exposure. A comprehensive experimental program included 23 mixes using different types of fine aggregate in concrete: standard sand, demolition sand, and mixes with 10–30% ground glass fines replacing Portland cement (PC). Also, the effects of added sodium sulfate and gypsum (1%, 3%, and 5%) on compressive, tensile, and flexural strengths were analyzed by conducting mechanical tests at 7, 28, and 56 days. Finally, SEM, EDS, and XRD were conducted to analyze the microstructures of the concrete mixes. Using gypsum and sodium sulfate provides sulfate ions to study their effects on Delayed Ettringite Formation and mechanical performance. The results of the present work showed that the optimal mix (20% glass powder with 1–3% gypsum) achieved a 21% increase in 28-day compressive strength and a denser microstructure with reduced microcracking. Gypsum showed more stable behavior under the tested conditions compared with sodium sulfate. The microstructure studies supported this conclusion and further demonstrate that optimal amounts of glass result in a denser concrete matrix with less cracking, which is used much more effectively. Full article

Gypsum is a widely used building material because of its good non-structural performance and low cost. However, when exposed to moisture and other harsh environments, it may lose its strength. In this study, gypsum composites (GCs) reinforced with recycled polyethylene (PE) fibers from bird nets (BNs) were developed, exposed to wet–dry cycles and fire, and then mechanically tested to verify the influence of these exposures on their properties. The main highlights include: at 40% replacement of gypsum with BN fibers, surface hardness increased by 5%, and with a fiber content of 10%, the compressive strength showed a slight increase of 3%, and flexural strength decreased by only 9%. The 10 wet–dry cycles did not have much influence on the mechanical performance, unlike exposure to fire, which drastically reduced it. Moreover, open porosity was reduced by 19% and total water absorption by 17% with 40% BN fiber content, making them suitable as additives in GCs for application in humid environments. Full article

Gypsum has been used as a building material for a long time due to its environmental friendliness, exceptional fire performance, and ease of use. However, it is also known to have poor moisture resistance and lower mechanical performance. Construction and demolition wastes, which can cause many environmental issues if not properly managed, are increasingly recycled as reinforcement materials in gypsum mortar. This study aims to assess the effect of incorporating fine glass waste aggregates into gypsum mortars on their physical, mechanical, and adhesive properties. The effect of replacing sand from 0% to 100% by glass waste in gypsum mortar was investigated using various tests and analyses including scanning electron microscopy (SEM), X-ray diffraction (XRD), thermal analysis (DTA and TGA), setting time, flexural and compressive strengths, adhesive, surface hardness, water absorption, thermal conductivity, and ultrasonic pulse velocity. The results obtained emphasize that glass waste can substitute sand in gypsum mortar, even when used at high replacement levels. Replacing all the sand in mortar with glass waste results in a 11% increase in porosity, a 9% decrease in density, and a 53% decrease in thermal conductivity, while still maintaining acceptable mechanical performances. The adhesive strength shows a great dependence on the nature of the substrate. Full article

The Muji carbonic springs on the northeastern margin of the Pamir Plateau provide a natural window into tectonically controlled CO₂ degassing within a continental collision zone. Through mineralogical and geochemical analyses, this study constrains the formation mechanisms and regional geological significance of carbonic spring systems. The formed deposits are dominated by calcite and aragonite, with minor dolomite, quartz, and gypsum. The compositions of major elements are consistent with the observed mineral assemblages, reflecting that the carbonate deposition was mainly governed by CO₂ degassing intensity and associated kinetic effects under cold-spring conditions. Carbon isotopes of the deposits are consistently enriched in heavy carbon with δ¹³C values of +3.5‰ to +9.1‰, indicating a persistent contribution of deep-sourced CO₂, most likely derived from metamorphic decarbonation of the crustal carbonates. Calcite exhibits moderate δ¹³C values due to rapid precipitation limiting isotope enrichment, whereas aragonite records higher δ¹³C signatures under subdued degassing and stable hydrodynamic regimes. The narrow δ¹⁸O range (−10.7‰ to −12.6‰), closely matching that of the spring waters, indicates that the tufas record the δ¹⁸O of the spring waters through DIC-water oxygen exchange. Trace element distributions (Sr–Ba–U) reveal systematic enrichment in deep-sourced fluids and progressive downstream geochemical alteration driven by spring–river mixing. The HD springs show high Sr and δ¹³C values, indicating minimal dilution of ascending CO₂-rich fluids, while MJX and MJXSP groups record variable degrees of shallow mixing. Collectively, the Muji system exemplifies a coupled process of “deep fluid input–shallow mixing–precipitation kinetics.” Its persistent heavy δ¹³C and trace-element enrichments demonstrate persistent metamorphic CO₂ release through fault conduits under ongoing compression. These findings establish the Muji springs as a key non-volcanic analogue for deep CO₂ degassing in continental collision zones and provides new insights into crustal carbon recycling and tectonic–hydrochemical coupling at plateau margins. Full article

The intensification of agricultural practices and the consequent dramatic decrease in soil organic matter has increased the use of organic fertilizer to recover soil fertility and plant productivity. The aim of this study was to compare the effect of three amendments obtained from the recycling of urban and agri-food wastes on rhizosphere microbial community, soil, and plant nutrient status. The experiment was carried out on rhizobox-grown, 1-year-old vines of Sangiovese (Vitis vinifera L.), grafted onto 110 Richter (V. berlandieri × V. rupestris) planted in April 2023. Twenty-four rhizoboxes were filled with soil collected from a field trial in which three types of amendments had been applied since 2019. In detail, the complete randomized experimental design (with four replications) compared the following treatments: (1) municipal organic waste compost (ACM), (2) agri-food organic waste compost (ACF), (3) defecation gypsum (GDD), and (4) a control that received 60 kg of N ha⁻¹ year⁻¹ (CK). The application of the amendments increased the soil concentration of total C, total N, and pH. The application of ACM increases soil K and Zn and the concentration of N and K in plant roots. The application of all the amendments increased leaf N concentration in comparison with CK, but only ACF increased leaf P. ACM was the most effective in promoting microbial biodiversity, increasing phyla like Bacillota, Pseudomonata, and Bacteroidota, including genra like Bacillus, Neobacillus, Paenibacillus, and Pseudomonas. ACF promoted Nitrosospherota and Chitinophaga, and GDD promoted Chloroflexota and Agrobacterium. Full article

The aquaculture industry generates large amounts of shell waste, with limited recycling options at the industrial scale. This study explores the feasibility of substituting 20% of gypsum with seashell waste to produce sustainable, fire-resistant panels for non-load-bearing walls on a semi-industrial scale (2.4 × 2.2 × 0.1 m). The new composite exhibits high density (≈1500 kg/m³) and mechanical performance comparable to commercial gypsum. Thermal and fire tests confirmed its excellent insulation and stability: after 4 h of standard fire exposure, the non-exposed surface temperature remained below 80 °C, meeting European fire-resistance criteria. The incorporation of shell waste slightly reduced density and thermal conductivity (0.23 W/mK at 500 °C) without affecting strength or surface hardness. Environmental characterization revealed leaching and radionuclide levels well below regulatory limits, confirming its safety for building use. Overall, this work demonstrates, for the first time at a semi-industrial scale, the technical and environmental feasibility of reusing seashell waste as a gypsum substitute for fireproof materials. The proposed approach advances circular-economy strategies for aquaculture residues, providing an innovative pathway toward sustainable and low-impact construction products. Full article