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The direct discharge of boron mud poses significant environmental hazards to soil and groundwater. Despite extensive research efforts, the reprocessing of boron mud has not yielded significant advancements. Recently, the development of magnesium cement has spurred interest in the reutilization of boron mud. However, the direct treatment of boron mud remains challenging, necessitating pre-treatment in most studies to achieve substantial results. Consequently, research on the direct incorporation of untreated boron mud is scarce. This study explores the feasibility of using uncalcined boron mud as a base material in basic magnesium sulfate cement (BMSC), composed of lightly calcined magnesia and magnesium sulfate heptahydrate. The effects of varying boron mud content on the compressive strength of the BMSC system were investigated. The results indicate that the 5·1·7 phase is the primary strength phase of BMSC. When the boron mud content is 30%, the uncalcined boron mud has a minimal impact on the formation of the 5·1·7 phase. Additionally, the 28 days compressive strength of BMSC-B30 showed a slight difference compared to the control group BMSC-C, registering at 66.7 MPa. TG-DSC analysis revealed that the presence of a small amount of boron mud inhibits the micro-expansion trend of the BMSC structure. Furthermore, XRD and SEM analyses confirmed that the addition of uncalcined boron mud does not significantly alter the phase structure of the 5·1·7 phase in BMSC. This study provides a foundational basis for the long-term development of direct boron mud treatment. [ABSTRACT FROM AUTHOR]

Exposure of concrete to acidic environments can cause the degradation of concrete elements and seriously affect the durability of concrete. As solid wastes are produced during industrial activity, ITP (iron tailing powder), FA (fly ash), and LS (lithium slag) can be used as admixtures to produce concrete and improve its workability. This paper focuses on the preparation of concrete using a ternary mineral admixture system consisting of ITP, FA, and LS to investigate the acid erosion resistance of concrete in acetic acid solution at different cement replacement rates and different water–binder ratios. The tests were performed by compressive strength analysis, mass analysis, apparent deterioration analysis, and microstructure analysis by mercury intrusion porosimetry and scanning electron microscopy. The results show that when the water–binder ratio is certain and the cement replacement rate is greater than 16%; especially at 20%, the concrete shows strong resistance to acid erosion; when the cement replacement rate is certain and the water–binder ratio is less than 0.47; especially at 0.42, the concrete shows strong resistance to acid erosion. Microstructural analysis shows that the ternary mineral admixture system composed of ITP, FA, and LS promotes the formation of hydration products such as C-S-H and AFt, improves the compactness and compressive strength of concrete, and reduces the connected porosity of concrete, which can obtain good overall performance. In general, concrete prepared with a ternary mineral admixture system consisting of ITP, FA, and LS has better acid erosion resistance than ordinary concrete. The use of different kinds of solid waste powder to replace cement can effectively reduce carbon emissions and protect the environment. [ABSTRACT FROM AUTHOR]

Supplementary cementitious material (SCM) plays an important role in blended cement, and the effect of the particle size and morphology of siliceous supplementary cementitious material on hydration should not be ignored. In this study, 0.5 h and 1 h of wet grinding was applied to pretreat iron ore tailing powder (TP), and the divergence in pozzolanic behavior and morphology were investigated. Then, the treated TPs were used to replace the 30% cement contents in preparing blended cementitious paste, and the impact mechanism of morphology on performance was studied emphatically. M, the autogenous shrinkages of pastes were tested. Finally, hydration reaction kinetics was carried out to explore the hydration behavior, while X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used to characterize the hydration product properties, respectively. Meanwhile, microscopy intrusion porosimetry (MIP) was also carried out to characterize the pore structures of hardened specimens. Results indicated that wet grinding has a dramatic effect on particle size and morphology, but hardly affects the phase assemblages and pozzolanic reactivity of TP, while the particle shape of TP changes from sub-circular to clavate and, finally, back to sub-circular. The results of hydration reaction kinetics, representing the morphology of particles, had a significant effect on hydration rate and total heat, and compared with the sub-circle one, the clavated particle could inhibit the hydration procedure. With the increasing grinding time, the compressive strength of cementitious paste was increased from 17.37% to 55.73%, and the micro-pore structure became denser; however, the autogenous shrinkage increased. [ABSTRACT FROM AUTHOR]

How to treat the iron tailings of mining solid waste with high value is an urgent problem on a global scale. In recent years, the application of iron tailings in the building materials industry has attracted the attention of many scholars. The conversion of iron tailings into green building materials helps achieve carbon neutrality and high-value utilization of solid waste, and promotes sustainable development. Although iron tailings have been extensively studied as supplementary cementitious materials, the performance of concrete is not ideal due to its low activity. In this study, the hybrid supplementary cementitious materials system was prepared by iron tailings, phosphorus slag, and steel slag, and the effects of supplementary cementitious materials type, iron tailings content, iron tailings grinding time, and supplementary cementitious materials content on concrete performance were studied. The compressive properties, iron tailings properties, pore structure, interfacial transition zone, and element distribution of hydration products of concrete were tested by compressive strength tests, X-ray Diffractometer (XRD), X-ray Photoelectron Spectroscopy (XPS), Mercury Intrusion Porosimetry (MIP), Backscattering Electron Tests (BSE), and Energy Dispersive Spectrometer (EDS). The results show that further grinding improves the iron tailings activity. There is a synergistic mechanism between steel slag and phosphorus slag in the composite supplementary cementitious materials, which overcomes the low activity defect of iron tailings and produces concrete with a compressive strength exceeding 40 MPa. The composite supplementary cementitious materials can optimize the interfacial transition zone of the concrete interface and reduce the calcium–silicon ratio of the hydration products. However, it will deteriorate the pore structure of the concrete matrix, cause part of the concrete matrix to be damaged and lead to a loss of compressive strength, and the loss is acceptable. This work broadens the methods of comprehensive utilization of iron tailings and also provides a reference for a more detailed understanding of the properties of iron tailings-based concrete. [ABSTRACT FROM AUTHOR]

In order to control energy consumption and reduce pollution, the use of supplementary cementitious materials (SCMs) instead of cement to produce green cementitious materials can save energy, reduce emissions and achieve sustainable development. This study demonstrates the possibility of developing SCMs with iron tailings (IOTs), fly ash (FA) and ceramic powder (CP) ternary system, as well as the optimization and improvement scheme of gelation activation. The effects of activator dosage, mix ratio and substitution rate on mechanical properties of ternary SCMs system were investigated. The formation and evolution of hydration products were analyzed by differential thermogravimetric analysis (DTA) and scanning electron microscopy (SEM). The results of the study show that there is synergy in the system. The results show that there is synergy in the system and the hydration reaction is sufficient. At the substitution rate of 30%, the doping ratio of IOTs, CP and FA is 1:2:2 and the Ca(OH)2 is 0.6%, the strength reaches 39.9 MPa and the activity index is 91.5%, which can provide a basis for the application and more in-depth study of IOTs multi SCMs. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the coupling effect of cement and organosilicon hydrophobic agents on the water resistance of phosphogypsum. Different weight ratios of Portland cement were added to adjust the alkalinity of this system and further improve the work efficiency of the organosilicon hydrophobic agents. Some macroscopic performances, such as the water absorption, the compressive strength, the flexural strength, and the softening coefficient, were measured to characterize the water-resistance of phosphogypsum. The microscopic characteristics were analyzed via contact angle tests, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) to understand the mechanism of organosilicon hydrophobicity. The results indicated that both the compressive and flexural strengths of phosphogypsum first increased and then decreased with the increase of organosilicon hydrophobic agents. Meanwhile, the surface contact angle continued to increase and the softening coefficient exhibited an obvious increase. When the hydrophobic agent was combined with Portland cement, the softening coefficient of phosphogypsum further increased from 0.80 to 0.99, while the water absorption rate was significantly reduced from 16.0% to 0.8%. Microscopic tests proved that the hydrophobic organic molecules can be polymerized under the high alkalinity, and promote the formation of a hydrophobic film, thus significantly improving the water-resistance of phosphogypsum. [ABSTRACT FROM AUTHOR]

Iron ore tailings (IOTs) are gradually used as building materials to solve the severe ecological and environmental problems caused by their massive accumulation. However, the bulk density of IOT as aggregate is too large, which seriously affects the concrete properties. Therefore, in this paper, the effect of hydroxypropyl methylcellulose (HPMC) on the workability, mechanical properties, and durability of concrete prepared from IOT recycled aggregate was studied. The action mechanism of HPMC on the workability and the mechanical properties of the IOT concrete was analyzed by mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM). The results show that HPMC can effectively improve the segregation problem caused by the sinking and air entrainment of IOT aggregate and improve the crack resistance of concrete with little effect on its compressive strength and electric flux. These results are due to the air-entraining thickening effect of HPMC, which improves the slurry viscosity, hinders the sinking of aggregate, and improves the workability. At the same time, HPMC film, after concrete hardening, will bridge the slurry and aggregate through physical and chemical effects, hinder the propagation of microcracks, and improve the crack resistance. [ABSTRACT FROM AUTHOR]

In this paper iron tailing sand (TS) are used as aggerate to develop ultra high-performance concrete (UHPC). The mix proportion of UHPC is designed and TS were added by 25%, 50%, 75% and 100% (wt.%, i.e., weight percentage) to replace natural river sand. Firstly, the influence of TS on the slurry behavior was carried out. The experimental result indicates that with the continuously increasing content of TS, the workability of slurry decreases, while the air content increases. Considering the workability, the optimal replacing dosage of TS should be less than 50%. Then, tests for the hardened specimens were taken. The compressive behavior and micro-porosity deteriorate with increasing content of TS, and the compressive strength had a positive linear relationship with the workability, which indicated that the decline the compressive behavior is mainly due to the loss of flowability. Finally, autogenous shrinkages of UHPC with different TS dosage were also tested. At the same time, the micro-structure of specimens was discussed, which was deteriorate with the increasing dosage of TS. Therefore, comprehensively considering the compressive behavior, micro-structure and shrinkage behavior, as much as 50% of the aggregate could be replaced by TS when developing UHPC. [ABSTRACT FROM AUTHOR]