Sustainable assessment and synergism of ceramic powder and steel slag in iron ore tailings-based concrete.

Solid waste management is a critical issue worldwide. Effectively utilizing these solid waste resources presents a viable solution. This study focuses on Iron ore tailings (IOTs), a solid waste generated during iron ore processing, which can be used as supplementary cementitious materials (SCMs) but have low reactivity, hindering their large-scale application in concrete production. To address this, ternary SCMs were prepared using ceramic powder (CP) and steel slag (SS) to enhance the performance of concrete incorporating IOTs. The study found that the synergistic effect of CP and SS significantly improved the compressive strength of concrete, with a notable increase of up to 21% compared to concrete with IOTs alone. Mercury intrusion porosimetry (MIP) and backscattering electron (BSE) analyses revealed that the ternary SCMs significantly optimized the characteristics of the interfacial transition zone (ITZ), which in turn enhanced the compressive properties of the concrete. This contributed to maintaining the structural integrity of the concrete, even amidst variations in the pore structure. Importantly, the incorporation of ternary SCMs led to a 23% reduction in carbon emissions, from 400.01 kg CO2/m3 to 307.48 kg CO2/m3, and elevated eco-strength efficiency from 0.1 to 0.14. The study highlights the role of multi-material synergy in developing composite SCMs systems, fostering the sustainable advancement of green building materials.

Strength and Microscopic Mechanism of Cement-Fly Ash-Slag-Desulfurization Gypsum Solidified Mica Schist Weathered Soil.

Mica schist weathered soil possesses a number of poor engineering characteristics, which make it difficult to use as a subgrade material for resource utilization. Therefore, in this study, a new type of curing agent, CFSD (cement-fly ash-slag-desulfurized gypsum), is proposed for this soil. The effects of different curing agent dosages, age of preservation, and confining pressure on the stress-strain curves were analyzed via the uniaxial compression test and triaxial compression test, while the micromorphological characteristics of cured soil were analyzed via X-ray diffraction analysis and the SEM test combined with Image J software. In this paper, we also establish a microscopic mechanism model to determine how curing agents increase the strength of mica schists. The results reveal that the compressive strength of solidified soil increases rapidly within 28 days; the CFSD dosage of 4% at 7 d increased by 103.23% by 28 d. After 28 d, the trend of compressive strength growth was flat. The CFSD dosage of 4% at 7 d increased by 128.34% by 90 d; with the increase in the dosage, the curve transformed from flat to steep. These results suggest that the CFSD dosage is positively correlated with the damage strain and damage bias stress of solidified soil. The curves for the strain softening type with a 4% dosage as the initial effective confining pressure increased from 50 kPa to 300 kPa; the failure stress and failure strain increased by 202.09% and 90.85%, respectively. With the increase in curing agent dosage and maintenance age, the pore size of 2~5 µm, >5 µm interval decreased from 56.46% to 27.92%, the porosity decreased from 12.51% to 4.6%, and the hydrate produced by the curing agent cemented and filled up the pore space between the loose particles of the soil body. Thus, the large pore space became microporous, and the pore structure densification was greatly improved.

Effect of Iron Tailing Powder-Based Ternary Admixture on Acid Corrosion Resistance of Concrete.

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.

Sustainable Use of Waste Oyster Shell Powders in a Ternary Supplementary Cementitious Material System for Green Concrete.

The increasing concern for decarbonization and sustainability in construction materials is calling for green binders to partially replace cement since its production is responsible for approximately 8% of global anthropogenic greenhouse gas emissions. Supplementary cementitious materials (SCMs), including fly ash, slag, silica fume, etc., can be used as a partial replacement for ordinary Portland cement (OPC) owing to reduced carbon dioxide emissions associated with OPC production. This study aims to investigate the sustainable use of waste oyster shell powder (OSP)-lithium slag (LS)-ground granulated blast furnace slag (GGBFS) ternary SCM system in green concrete. The effect of ternary SCMs to OPC ratio (0%, 10%, 20%, and 30%) on compressive strength and permeability of the green concrete were studied. The reaction products of the concrete containing OSP-LS-GGBFS SCM system were characterized by SEM and thermogravimetric analyses. The results obtained from this study revealed that the compressive strength of concrete mixed with ternary SCMs are improved compared with the reference specimens. The OSP-LS-GGBFS ternary SCMs-based mortars exhibited a lower porosity and permeability compared to the control specimens. However, when the substitution rate was 30%, the two parameters showed a decline. In addition, the samples incorporating ternary SCMs had a more refined pore structure and lower permeability than that of specimens adding OSP alone. This work expands the possibility of valorization of OSP for sustainable construction materials.

Preparation of Mineral Admixture from Iron Tailings with Steel Slag-Desulfurization Ash and Its Application to Concrete.

Iron tailing solid waste not only has a high annual output but also has a low comprehensive utilization rate. Low utilization rate of iron tailings seriously restricts the development of comprehensive utilization of solid waste. In order to prepare an iron tailings-based ternary solid waste admixture and to verify its application to concrete, first, the effect of solid waste synergy on the strength of an iron tailings-steel slag-desulfurization ash admixture (ISD) system was investigated. Second, the effect of chemical activator dosing on the strength of an ISD system was studied and the mechanism of chemical activator action on the ISD system was investigated by thermogravimetric analysis (TG-DTA) Then, the effect of this admixture on the strength of concrete was studied. Finally, the mechanism of the effect of this admixture on the strength of concrete was clarified by mercury intrusion porosimetry (MIP) and backscattering electron tests (BSE). The results showed that the 7 d and 28 d compressive strengths of the ISD admixture were significantly higher than those of iron tailings single admixture. The 7 d and 28 d compressive strengths of the ISD system reached 24.9 MPa and 36.1 Mpa, respectively, when the ratio of iron tailings:steel slag:desulfurization ash = 1:1:1. Na2SiO3 is suitable for the early strength agent of the ISD admixture, but the amount of admixture should not exceed 0.6% of the admixture. TG-DTA shows that Na2SiO3 is enhancing the early strength of the ISD system by promoting the consumption of Ca(OH)2 in the ISD system to produce C-S-H. However, in the late reaction of the ISD system, Na2SiO3 inhibits the late strength development of the ISD system by suppressing Ca(OH)2 production. Concrete with ISD dosing of 30% or less meets the C40 requirement. MIP and BSE show that ISD provides a filling effect to concrete, but also causes a reduction in the active reactants of concrete and the combined effect of microfilling and active effects affects the strength development of ISD concrete. This study provides a theoretical and scientific basis for the preparation of iron tailings-based ternary solid waste dopants, and, in addition, the study promotes the consumption of iron tailings solid waste and the development of multiple solid waste dopants.

Study on Properties and Optimization of Ternary Auxiliary Cementing Materials for IOTs.

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.

Application of Iron Tailings-Based Composite Supplementary Cementitious Materials (SCMs) in Green Concrete.

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.