Search Results (80)

Vegetation concrete is a composite material integrating plant growth and concrete technology. In this study, solid waste materials (phosphogypsum and recycled aggregates) were utilized to prepare vegetation concrete. Semi-hydrated phosphogypsum (HPG) was used to replace ordinary Portland cement as a cementitious material in a gradient manner, while recycled coarse aggregates (RCAs) fully replaced natural crushed stone. The basic properties of phosphogypsum–recycled aggregate-based vegetation concrete were analyzed, and X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the hydration products of vegetation concrete with different mix ratios. The results indicated that replacing cement with HPG exerted a significant alkali-reducing effect and provided favorable cementitious strength. When the porosity was 24% and the HPG content was 50%, the vegetation concrete exhibited optimal performance: the 28-day compressive strength reached 12.3 MPa, and the pH value was 9.7. Recycled aggregates had a minimal impact on strength. When 0.5% sodium gluconate was added as a retarder, the initial setting time was 97 min and the final setting time was 192 min, which met construction requirements with little influence on later-stage strength. Microscopic analysis revealed that the early strength (3d–7d) of vegetation concrete was primarily contributed by CaSO₄·2H₂O crystals (the hydration product of HPG), while the later-stage strength was supplemented by C-S-H (the hydration product of cement). Planting tests showed that Tall Fescue formed a lawn within 30 days; at 60 days, the plant height was 18 cm and the root length was 6–8 cm. Some roots grew along the sidewalls of concrete pores and penetrated the 5 cm thick vegetation concrete slab, demonstrating good growth status. Full article

This paper focuses on the resource utilization of phosphogypsum, a major industrial by-product from phosphate fertilizer production, in highway engineering materials, exploring its performance optimization and collaborative modification mechanisms. Phosphogypsum, primarily composed of CaSO₄·2H₂O, faces challenges such as acidity (pH ≈ 3.56), poor water resistance, and strength limitations, which hinder its engineering application. This study investigates pretreatment methods (e.g., lime neutralization, physical grinding) and the synergistic effects of additives like metakaolin, steel slag, slag powder, and stone powder. The results show that adjusting phosphogypsum’s pH to 10 via lime neutralization significantly improves its mechanical properties, with its 28-day compressive strength increasing by 21%. The optimal dosage of cement as an alkaline activator is 4%, while steel slag performs best at 10%. Metakaolin (11% dosage) enhances the 28-day strength of 30% phosphogypsum-containing systems by 89–114% through pozzolanic reactions, forming a high-strength aluminosilicate network, enabling the preparation of C35 concrete with a 28-day strength of 44.5 MPa. Additionally, stone powder exhibits the most effective strength improvement, with the 56-day strength increasing by 12.5 MPa compared with the reference group. Economically, utilizing 30% phosphogypsum and 11% metakaolin reduces C35 concrete costs by 15–20%. This research provides theoretical and technical support for the large-scale application of phosphogypsum in highway engineering, addressing environmental and economic challenges. Full article

At present, phosphogypsum, as an industrial by-product, is a solid waste in phosphoric acid production, and its accumulation has caused serious environmental pollution. Furthermore, due to the insufficient insulation properties of traditional wall materials, the issue of a rising proportion of building energy consumption in total social energy consumption has become increasingly pressing. The study investigated vitrified beads as a light aggregate and phosphogypsum, mineral powder, and quicklime as an inorganic composite cementitious system to prepare the phosphogypsum-based lightweight thermal insulation material. The effect mechanism of the initial material ratio on the mechanical properties and micro-morphology of insulation materials was studied by macroscale mechanical property testing, X-ray diffraction, and scanning electron microscopy. Meanwhile, in order to meet the performance indexes specified in relevant standards, insulation materials were modified by adding sulfate aluminate cement, basalt fibers, and a waterproof agent to improve the strength, toughness, and water resistance. Based on the single-factor experimental design, the optimal dosage of various admixtures was obtained. The results indicated that the optimal properties of the sample were achieved when the binder–bead ratio was 1:4, the water–binder ratio was 1.6, the dosage of hydroxypropyl methylcellulose was 0.1%, and the solid content of waterborne acrylic emulsion was 24%. The optimal dosages of cement and fibers were 8% and 0.9%, respectively. The cement hydration products and gypsum crystals lapped through each other, filling the pores in the matrix and increasing the strength of the sample. In addition, the fibers could form a disordered network structure inside the matrix, disperse external force, weaken the stress concentration at the tip of internal cracks, and significantly improve the toughness of the modified sample. By incorporating 2.0% paraffin emulsion in the mortar and spraying 5 dilutions of sodium methyl silicate on the external surface, dense protective layers were formed both inside and outside the modified sample. The water absorption rate reduced from 30.27% to 23.30%, and the water resistance was increased to satisfy the specified requirement for the insulation material. Full article

The large-scale and high-value utilization of industrial solid waste has become a key research area in sustainable building materials. However, ensuring effective backfilling quality in narrow or irregular spaces remains challenging in civil engineering. Developing flowable solidification materials from industrial solid waste not only resolves issues inherent in traditional backfilling techniques but also enhances efficient resource utilization. In this study, phosphogypsum was used to prepare geopolymers, which served as binders replacing cement in producing phosphogypsum-based fluidized solidified soil (PFSS). The workability, mechanical strength, and toxic substance leaching of PFSS were evaluated. Moreover, the underlying mechanisms of strength formation and toxic substance immobilization were investigated. The optimal PFSS composition was determined to have a water-to-solid ratio of 0.48–0.50 and a geopolymer content of 12–18% (by mass). Under these conditions, the material exhibited fluidity ranging from 160 to 220 mm, a 28-day compressive strength of 0.86 MPa, a California Bearing Ratio (CBR) of 8%, and a resilient modulus of 40 MPa. These parameters satisfy the performance standards required for backfilling in high-grade highways. The leaching concentrations of heavy metals (As, Pb, and Cr) complied with China’s Class III groundwater quality standards. Microstructural analyses indicated the occurrence of hydration, pozzolanic reactions, geopolymerization, and carbonation. Microstructural analyses indicated the formation of an interlocking three-dimensional network, composed of C-S-H, C-A-S-H gels, and ettringite (AFt), which contributes significantly to the strength development and immobilization of heavy metals. These products collectively formed an interlocking three-dimensional network structure, significantly contributing to PFSS strength development. Heavy metals were effectively immobilized within the matrix due to the combined effects of physical adsorption and chemical bonding. Full article

Grouting materials are essential for trenchless road repair. However, conventional cement-based grouting materials suffer from considerable shrinkage and low early-age strength. To address these challenges, this study utilizes industrial solid wastes (phosphogypsum and slag) for the synergistic synthesis of a phosphogypsum–slag-based geopolymer (PBG). Using PBG as a binder and fine sand as an aggregate, a sustainable grouting material was developed. The influence of binder-to-sand and water-to-solid ratios on PBG workability was systematically evaluated, identifying the optimal water-to-solid ratio. Based on this, the effects of the binder-to-sand ratio on mechanical strength at various curing ages, durability, and leaching of toxic substances were analyzed. The mechanism of strength development mechanism and immobilization behavior of toxic substances were revealed through SEM. The results indicate that the material exhibits excellent performance when the water-to-solid ratio is 0.28 and the binder-to-sand ratio ranges from 0.70 to 0.75. The material exhibits fluidity of 160–240 mm, initial setting time > 30 min, and final setting time < 400 min, a bleeding rate < 0.4%, and 28-day compressive strength ≥ 9.0 MPa. Both the impermeability and freeze–thaw resistance of PBG grouting material improve with a higher binder-to-sand ratio. Toxic substance leaching complies with Class III groundwater quality standards. Carbon footprint analysis indicates that the material significantly reduces carbon emissions. Full article

In this article, composite binders based on industrial waste—phosphogypsum, granular phosphoric slag, and burnt barium carbonate tailings––are investigated. It was found that the optimal composition (65% slag, 20% phosphogypsum, 15% tailings) provides compressive strength up to 31.1 MPa after steaming, which corresponds to grade M300 cement. Replacing natural gypsum with phosphogypsum increases strength by 5–10%, and using waste reduces cost by 20–25% compared to traditional binders. This technology eliminates the need for high-temperature firing, reducing energy consumption by 40–50%. Neutralization of harmful impurities of phosphogypsum with oxides of MgO and CaO reduces the ecotoxicity of the material by 70–80%. It is shown that hydrothermal treatment accelerates hardening, providing 90% of brand strength in 28 days. The developed binders are promising for the production of building blocks, road surfaces, and land reclamation. Full article

The durability of construction and building materials under sulphate environments is an important indicator to evaluate their service life. In this study, the physical and mechanical behaviours of wood-ash-based alkali-activated materials (AAMs) incorporating coal fly ash, metakaolin, natural zeolite, and calcined phosphogypsum were assessed before and after being subjected to sodium sulphate corrosion cycles via the compressive strength, mass, and volume changes. The microstructure, elemental composition, and phase identification were further analysed using X-Ray Diffraction(XRD) and scanning electron microscope(SEM). The results show that the exposure to sulphate solution caused decalcification and dealumination of hydrates, releasing calcium and aluminium to react with sulphate and forming expansive erosion products, ettringite and gypsum. This contributed to the microstructural damage, leading to mass change, volume expansion, and compressive strength loss of 7.33, 1.29, and 60.42%. The introduction of binary aluminosilicate precursors enhanced the sulphate resistance by forming a well-bonded microstructure consisting of calcium (aluminate) silicate hydrate and sodium aluminate silicate hydrate, with the compressive strength loss decreasing up to 18.60%. The co-usage of calcined phosphogypsum deteriorated the mechanical properties of AAMs but significantly improved the sulphate resistance. The sodium sulphate environment facilitated anhydrate hydration, generating more sulphate hydrates and hemigypsums that co-existed with erosion products, forming a compact microstructure and improving the compressive strength by twofold. Full article

Phosphogypsum represents a gypsum-based solid waste originating from phosphoric acid production, which can be exploited for road filling after cement modification. This study delved into the composition design of high-volume phosphogypsum road base materials, aiming to ascertain their feasibility for subgrade filling, and refine the mix ratio. The main content of phosphogypsum was set at three high-proportion intervals of 86%, 88% and 90%, while the total content of inorganic curing agent was fixed at 0.5% of the total material. Within such a total amount, the proportion of bentonite was preserved at 20%, whereas the proportion of waterproofing agent was configured at three gradients of 20%, 25% and 30%, with the remaining part supplemented by powdered sodium silicate. Merged with trace amounts of inorganic curing agents, particularly the waterproofing agent component, the composite cementitious system comprising cement and ground granulated blast-furnace slag (GGBS) was leveraged to augment the key road performance and water stability of high-volume phosphogypsum-based materials. Material strengths were observed to be distinguishable under an array of phosphogypsum contents, which could be explained by the varying proportions of cement, GGBS and waterproofing agent. The test samples and microscopic products were dissected via XRD and SEM, demonstrating that the hydration products of the materials were predominantly C-S-H gel and ettringite crystals. Full article

Current research on foamed lightweight soil primarily focuses on mechanical properties and durability, with few studies addressing its hydraulic characteristics and internal pore structure in road reconstruction applications. However, the material’s high porosity and low bulk density may significantly alter its mechanical properties and durability under prolonged rainwater exposure, highlighting the importance of investigating its hydraulic characteristics and internal foam structure. Based on the analysis of water absorption and bulk density in phosphogypsum-based foamed lightweight soil, this study further discusses the material’s softening coefficient and internal pore structure through systematic data comparison. Experimental results demonstrate that the unconfined compressive strength (UCS) of both dry and water-soaked specimens increases linearly with dry density. Notably, soaked specimens with 0.5 g/cm³ dry density achieve compliant 7-day UCS values while displaying a steeper strength increase compared to dry specimens. A dry density of 0.64 g/cm³ ensures a softening coefficient exceeding 0.75, confirming the material’s suitability for humid environments. The material contains predominantly small pores (90% ≤ 0.2 mm diameter), with improved bubble distribution at the edges and higher upper porosity. Spherical pores (roundness 0.5–1) enhance mechanical properties, while phosphogypsum (optimal 10% dosage) effectively improves both strength and workability but requires corrosion control due to its hydration products. Full article

Accurate determination of sulfate content in phosphogypsum (PG) and cement-based materials is crucial for understanding the corrosion mechanisms of cement-based materials, developing corrosion models, establishing durability design methods, and implementing maintenance strategies. To overcome the limitations of traditional gravimetric and EDTA titration methods in accurately quantifying low-concentration SO₄²⁻ in PG and cement-based materials, an IoT-enabled conductometric titration system was developed to improve precision and automation. First, the principle of conductivity titration is introduced, in which Ba(NO₃)₂ is used as the titrant. Second, a method for eliminating the effects of H⁺, Cl⁻, and Ca²⁺ ions is proposed. The impact of the titration rate, volume of liquid to be measured, titrant concentration, and other interfering ions on the results is discussed. Finally, the conductivity titration method was successfully applied to determine sulfate content in PG and cement-based materials. The results demonstrate that the self-developed conductivity titrator exhibits high testing accuracy, with a standard deviation of 0.013 for 15 repeated titrations, a coefficient of variation of 0.52%, and a recovery rate between 103.2% and 103.9%. The optimal solution volume to be determined was 5 mL. Ba(NO₃)₂, at approximately twice the sulfate concentration, enhances endpoint sensitivity and minimizes precipitation interference. Ag₂O and CO₂ significantly reduce the interference from H⁺, Cl⁻, and Ca²⁺ ions by generating weakly conductive substances, such as H₂O, AgCl, Ag₃PO₄, CaF₂, and CaCO₃. Conductometric titration demonstrated accurate SO₄²⁻ quantification in PG and cement-based materials, enabling standardized protocols. This approach provides both theoretical and technical support for rapid sulfate detection in complex systems, with significant implications for both industry and academia. For the industry, it offers a reliable and standardized method for sulfate detection, enhancing quality control and process efficiency. For academia, it establishes a foundation for further research in civil engineering and environmental material analysis, contributing to both practical applications and theoretical advancements. Full article

Phosphogypsum, a byproduct of orthophosphoric acid production, is one of the large-tonnage wastes. Since phosphogypsum mainly consists of CaSO₄ 2H₂O, it can be considered as an alternative gypsum-bearing raw material in the production of gypsum binders. However, its features, such as particle morphology and the presence of impurities, can negatively affect the characteristics of phosphogypsum-based binders. Identification of these factors will allow us to develop methods for their minimization and increasing the efficiency of phosphogypsum use from the required source as a raw material for the production of phosphogypsum-based binders. In this regard, the manuscript contains a comprehensive and comparative analysis of phosphogypsum and natural gypsum, which makes it possible to establish their differences in chemical composition and structural and morphological features, which subsequently affect the properties of the phosphogypsum-based binder. It has been established that the key factor negatively affecting the strength of phosphogypsum-based paste (2.58 MPa) is its high water demand (0.89), which is due to the high values of the specific surface area of the particles and the presence of a large number of conglomerates with significant porosity in phosphogypsum. It has been suggested that preliminary grinding of phosphogypsum can help reduce the amount of water required to obtain fresh phosphogypsum-based paste with a standard consistency and improve its physical and mechanical properties. Full article

Phosphogypsum, a by-product of phosphate fertilizer production, was predominantly used as a supplementary additive in recycled construction materials. However, there are few detailed studies on utilizing phosphogypsum as the primary component in inorganic cementing materials while achieving cost-effective detoxification. This study aimed to develop a harmless phosphogypsum-based inorganic cementing material (PICM) mainly based on phosphogypsum, in which cement, quicklime, and a stabilizer were used as additives. Harmful ions and acidity were first detected through X-ray fluorescence and ion chromatography and then harmlessly treated with quicklime. Compaction parameters, mechanical performance, X-ray diffraction analysis, moisture, and freezing resistance were characterized successively. The results illustrated that fluoride and phosphate ions were the primary soluble contaminants, whose leaching solution concentration can be reduced to 15.31 mg/L and undetectable with 2% quicklime through the mass proportion of phosphogypsum added and mixed. Meanwhile, the corresponding pH value was also raised to over 8. Cement content and quicklime were positively correlated with PICM’s maximum dry density. PICM with 25% cement and 2.5% stabilizer presented the highest unconfined compression strength, and flexural strength did not show significant regularity. PICM was mainly composed of quartz, gypsum, ettringite, and calcite, whose content decreased as cement content and quicklime content increased. Stabilizer, quicklime and cement content were positively correlated with PICM’s freezing and moisture resistance. Full article

The paper presents a comprehensive study of the processing possibilities for phosphogypsum, a large-tonnage chemical industry waste, into highly sought-after products, such as ultraviolet pigments, and alkalizing reagents for the preparation of organomineral fertilizers. The materials obtained were characterized by X-ray diffraction (XRD), transmission electron microscopy, and thermogravimetric analysis (TGA). It was found that the phosphogypsum thermal treatment process in the presence of a reducing agent (charcoal, sunflower husk) allowed us to obtain new products with a high added value. For the first time, the possibility of obtaining various products by varying process conditions was established. The process of thermal reduction of phosphogypsum in the presence of charcoal at temperatures of 800–900 °C and an isothermal holding time of 60 min resulted in us obtaining samples capable of glowing when irradiated with ultraviolet light. This effect is due to the formation of a composite material based on calcium sulfide and calcium sulfate in the system. The process of the regenerative heat treatment of phosphogypsum at temperatures of 1000–1200 °C resulted in us obtaining a composite material consisting of calcium oxide and sulfate, which can be used for fractionating liquid waste from livestock farming and to obtain organomineral fertilizer. The technological methods developed allow the usage of chemical industrial waste and agricultural waste in secondary processing to produce highly innovative products that will contribute to the achievement of the sustainable development goals, in particular, “Ensuring rational consumption and production patterns”. Full article

Phosphogypsum, a byproduct of phosphate fertilizer production, represents a significant environmental concern due to its large-scale production and low utilization rates. Although preparing phosphogypsum-based cementitious materials offers a potential solution to these issues, high-content phosphogypsum cementitious systems encounter significant technical barriers, including long setting durations and insufficient early-age strength development, thereby restricting their practical implementation. Hence, this research developed innovative modifiers through an environmentally friendly low-temperature thermal activation process (100–160 °C) utilizing recycled phosphogypsum aggregates and circumventing the substantial carbon emissions associated with conventional modification approaches. Systematic characterization demonstrated that the dehydration phase modifier synthesized at 120 °C (DH120) exhibited optimal phase composition, resulting in a 35.7% enhancement in its 14-d compressive strength (9.8 MPa vs. 7.2 MPa for the control) and an 11.3% reduction in its initial setting time (27.5 vs. 31.0 h for the control). Microstructural characterization by low-field nuclear magnetic resonance and X-ray diffractometry revealed that DH120 effectively enhanced refinement of the pore structure (37.7% mesopore volume reduction) and promoted the ettringite crystallization kinetics. This work establishes a sustainable framework for utilizing industrial byproducts in cementitious material systems. Full article

Phosphogypsum (PG) is used to prepare eco-friendly cementitious materials, representing a high-value resource utilization approach. However, there are some shortcomings, such as a long setting time and low early strength in phosphogypsum-based cementitious materials (PBCMs), which limit their engineering applications. This work aimed to improve their early performance by adding sodium aluminate. In particular, the effects on the compressive strength, setting time, and fluidity of PBCMs were investigated. Additionally, the effect of sodium aluminate on hydration was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that the addition of sodium aluminate results in a significant enhancement in 3 d compressive strength and an obvious procoagulant effect on setting time in PBCMs. When the content of sodium aluminate reaches 1 wt.%, the 3 d compressive strength of PBCMs can reach 10.72 MPa. Compared with the control group (A0, without sodium aluminate), the 3 d compressive strength is improved by 587.39%, and the final setting time is shortened by 4 h 4 min. The microscopic test results show that sodium aluminate can provide sufficient aluminum components at the early stage of hydration, which could effectively enable more phosphogypsum to participate in hydration and accelerate the early part of the process of the hydration reaction. This is conducive to increasing the number of early hydration products of ettringite (AFt) and C-A-S-H gel to improve the early compressive strength and shorten the setting time. Full article