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This study investigated the effects of lithium slag and iron tailings on the hydration mechanism of Basic Oxygen Furnace (BOF) slag cement paste with the addition of 0.06% diethanol-isopropanolamine (DEIPA). This study examined the fluidity, compressive strength, pore solution pH, and hydration products of BOF slag-based composite cementitious materials. The results showed that DEIPA facilitated the conversion from ettringite (AFt) to monosulphate (AFm) and improved the early compressive strength of the BOF slag–cement mortar. Incorporating lithium slag into the DEIPA-containing BOF slag–cement system promoted AFt formation, increased calcium-silicate-hydrate production, and enhanced the microstructure. BOF slag, lithium slag, and iron tailings exhibit synergistic effects in cement pastes. BOF slag and lithium slag provided the reactive components SiO2 and Al2O3. In the early hydration stages, the iron tailings primarily served as fillers, accelerating the system's reactions. [ABSTRACT FROM AUTHOR]

Alkali-activated cementitious materials, as an environmentally friendly cementitious material, can effectively reduce carbon emissions and improve the utilisation of solid wastes. However, traditional strong alkali activators have limitations such as high carbon emissions and poor safety. In order to overcome the defects of traditional strong alkaline activators and realise the high value-added use of calcium carbide residue (CCR), this paper adopts CCR as an alkaline activator to activate granulated blast furnace slag (GBFS)-steel slag (SS) cementitious systems for the preparation of alkaline-activated cementitious materials. The effects of CCR content and SS content on the compressive strength and working performance of CCR-GBFS-SS cementitious systems are analysed, along with the hydration process of CCR-GBFS-SS cementitious systems and the mechanism of action through the hydration products, their chemical structure and their microscopic morphology. The research results show that CCR-GBFS-SS cementitious systems have a 28-day compressive strength of 41.5 MPa and they can be controlled by the setting time; however, the flow performance is poor. The SS content can be increased to improve the flow performance; however, this will reduce the compressive strength. In CCR-GBFS-SS cementitious systems, CCR is the main driving force of hydration reactions, GBFS mainly provides active silica and aluminium and the amorphous C-(A)-S-H gel and ettringite formed by the synergistic action of multiple solid wastes are the main sources of compressive strength. With the extension of the curing time, the amount of hydration products in the cementitious systems gradually increases and the matrix of the cementitious systems gradually becomes denser. This study will provide a reference for the consumption of low-value solid waste such as CCR and the preparation of low-carbon cementitious materials from multi-component solid wastes. [ABSTRACT FROM AUTHOR]

The preparation of iron ore tailings (IOTs) into supplementary cementitious materials (SCMs) is an effective approach to achieve value-added utilization of industrial solid waste. This study systematically investigates the hydration pattern and strength development of Portland cement systems with the incorporation of IOTs, steel slag (SS), granulated blast-furnace slag (GBFS), and fly ash (FA) under the action of different chemical additives. The hydration products, and microstructure and pore structure of the SCMs are analyzed using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and mercury intrusion porosimetry. The findings of this study demonstrate that chemical activation plays a significant role in the strength development of SCMs. Among the five chemical activators tested, Triethanolamine (TEA) had the greatest influence on mechanical properties. The maximum compressive strength of the SCMs at 28 days was 42.9 MPa at a dosage of 1%. Specifically, the addition of TEA promotes volcanic ash reactions, and the high fineness of SCM provides nucleation sites for hydration products. Interactions between the volcanic ash reaction and the complexation reaction of TEA have a positive effect on compressive strength development. This research expands the potential for IOTs SCMs through chemical activation methods for value-added applications. [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]

In this study, a type of fly ash and iron tailing powder were used as a binary supplementary cementitious material (SCM) and two different mechanically activated procedures, named coalescent activation and separated activation, were carried out to improve the pozzolanic reactivity. Then, three binary supplementary cementitious materials were used to replace 30 wt% of ordinary Portland cement to develop cemented mortars, and the compressive strength, hydration products, and micro-structure were studied. The experimental results indicated that the activated supplementary cementitious materials increased the compressive strengths of the mortars by 5.4% and 13.2%, negligibly changed the hydration product types, and impacted the quantity only. The application of SCMs also prolonged the setting time and decreased the hydration rate, profiting the application. Simultaneously, the micro-pore structure was ameliorated, and the porosity decreased. Therefore, comprehensively considering the improved mechanical behavior and inexpensive cost, the activated binary SCM can be considered an ecological and economical admixture, especially for the coalescent activation procedure. [ABSTRACT FROM AUTHOR]

Recently, the increasing of ultrafine-tailings increases the amount of ordinary Portland cement (OPC) in cemented paste backfill (CPB), which leads to the rise of CPB cost and carbon emission. As a result, it is necessary to develop alternative binders. The present work focuses on the preparation of a new binder, which is activated by a mixture of calcined quarry dust (CQD) and NaOH at a mass ratio of 1:1. The results indicated that CQD/NaOH was more effective than using NaOH or CQD alone in activating blast furnace slag (BFS) and also showed better performance than OPC. The compressive strength of the CPB samples using 10% CQD/NaOH was around 3.78 MPa after curing for 90 days, around 42% higher than the OPC-based CPB samples. The reaction products of CQD/NaOH-activated BFS consisted mainly of C-(A)-S–H, hydrotalcite like phases (Ht), and M-S–H. The generation of Ht phases lowered the Al incorporation into the structure of C-S–H, resulting in lower average Al/Si ratio and mean chain length. [ABSTRACT FROM AUTHOR]

This study investigates the synergistic effect of steel slag (SS) and metakaolin (MK) on cementitious systems. The compressive strength, flowability, packing properties, hydration products, and microstructure of composite cementitious materials containing SS and MK are investigated using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope with energy-dispersive X-ray spectroscopy, mercury intrusion porosimetry, and surface fractal analysis. The results show that the incorporation of MK into the SS-cement system increases the wet packing density and generates calcium silicate hydrate with low Ca/Si and high Al/Ca ratios, thus increasing the compressive strength. In addition, the pore structure is refined. This study facilitates the sustainable and high-value utilization of SS and MK. • The packing density and PSD were used to evaluate physical synergies. • The synergistic effect of SS and MK can produce produced C-S-H with low Ca/Si. • SS and MK replacement cement can reduce costs and carbon emissions. [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]

Steel slag is a solid waste during steel production, which poses substantial environmental impacts. The present work explored the feasibility of preparing an eco-friendly binder for cemented paste backfill (CPB) using steel slag after being thermal treated. Steel slag was calcined at 600, 800 and 1000 °C. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) were performed to study the structure modification on steel slag after thermal treatment. Steel slag calcined at 1000 °C (SS100) showed the highest pozzolanic reactivity due to the formation of dicalcium silicate (C 2 S). SS1000 was then used to prepare binders for CPB supplemented by metakaolin (MK) and silica fume (SF). The results showed that samples with 15 wt% MK and 5 wt% SF addition (P3) demonstrated the optimal performances. After curing for 28 days, the CPB samples (CPB3) using P3 as a binder showed the highest compressive strength (2.88 MPa) at a binder/tailings ratio of 1/4, reaching around 88.7% of that of the CPB samples made using ordinary Portland cement (OPC). Leaching tests showed that all the toxic metals were stabilized in CPB3, which posed no environmental risk. [Display omitted] • Reactivity of steel slag was highly enhanced after calcination at 1000 °C. • C 2 S was detected after calcination at 800 °C. • An eco-friendly binder was prepared using calcined steel slag. • CPB samples showed superior performance using calcined steel slag based binder. [ABSTRACT FROM AUTHOR]

Based on the characteristics of alkali-activated materials (AAMs) in energy saving and emission reduction, as well as giving full play to the complementary advantages of multi-component solid waste. In this study, a new type of AAMs was prepared from oil shale residue (OSR), ground granulated blast furnace slag (GGBFS), and fly ash (FA). Compressive and flexural strength tests, fluidity experiments, setting time, heat of hydration, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), and Thermo-gravimetric analysis (DTG-TG) were used to analyse the mechanical properties, workability, mineral composition, microstructure, and hydration products of the AAMs. The results showed that the microstructure of AAMs was dense, with high early strength, good mechanical and working properties, and no tendency for retrogressive strength with an increase in the age of maintenance. Under the action of NaOH/Na 2 SiO 3 , there is a synergistic hydration of the water-hard and volcanic ash materials, and the three raw materials have synergistic hydration properties and indispensable coupling mechanisms. Meanwhile, the effect of the activator content on AAMs is bidirectional. The OSR, GGBFS, and FA in the AAMs exhibited faster hydration reactions under the action of NaOH/Na 2 SiO 3 and abundant hydration products, which mainly included C-S-H, C-A-S-H, N-A-S-H, and small amounts of CaCO 3 , hydrotalcite (HT), and Ettringite (AFt). The specimens all met the requirements of the 42.5-grade composite silicate cement, and some specimens reached the strength requirements of the 62.5-grade silicate cement or above. OSR has great potential as a silicate-aluminate material, and this study provides a solid foundation for its further development and utilisation. • Oil shale residue was added into to blended slag/fly ash alkali activated binder system. • There is a synergistic effect of OSR-GGBFS-FA. • All specimens are comparable with Portland cement 42.5, even to Portland cement 62.5. • The hydration products are C-S-H, C-A-S-H, N-A-S-H gels, calcite, hydrotalcite, and AFt. [ABSTRACT FROM AUTHOR]

Arsenic-containing biohydrometallurgy waste (BW) is used to prepare a cementitious material, on the one hand, to solve the problem of lack of cheaper and greener binder for cemented paste backfill (CPB), on the other hand, to alleviate the arsenic pollution caused by BW. The binders were prepared by mixing blast furnace slag (BFS), BW, and ordinary Portland cement (OPC). The influence of mix proportions on the binder properties was investigated, including reaction kinetics, strength development, phase assembles of hydration products and arsenic (As) immobilization effects. Isothermal calorimeter analysis suggests that the binder reaction kinetics were highly determined by the mix proportions, and more BW addition decreased the reaction rate according to the Krstulovic-Dabic model. The optimal mix proportion of binder is 65–30-5, i.e., 65 wt% blast furnace slag, 30 wt% BW, and 5 wt% OPC. The compressive strength of this sample after curing for 3 days and 60 days is about 9.25 MPa and 40.88 MPa, respectively, and the hydration products mainly consist of ettringite and calcium silicate aluminate hydrate (C-(A)-S-H). Additionally, arsenic can be effectively immobilized in the binder, resulting from the denser structure (physical encapsulation) and ion exchange between arsenate and sulfate in ettringite. [Display omitted] • BW was used to prepare a cementitious material for CPB. • Binder 65–30-5 showed the highest compressive strength. • The hydration products mainly consisted of ettringite and C-(A)-S-H. • As could be effectively immobilized in the binder. [ABSTRACT FROM AUTHOR]

Cemented paste backfill (CPB) favors the sustainable development of mine industry. However, as the primary cementitious binders in CPB, the high cost of ordinary Portland cement (OPC) discourages CPB utilization. In the present work, low-carbon and low-cost binders activated by Na 2 CO 3 supplemented by calcined quarry dust were used in CPB. The binder was prepared using a 'one-part' method. It was found that binders prepared using 8% Na 2 CO 3 and 5% CQD show the best performance. The superior properties of the binders were attributed to the promoted binder hydration and special phase assembles of the hydration products. Cost and carbon emission analysis showed that Na 2 CO 3 activated binder was cheaper and greener. The cost and CO 2 emission of binder B8Q5 were lower than OPC by around 34.16% and 87.76%, respectively. Besides, leaching tests showed that all the toxic metals were stabilized, which posed no environmental risk. • A novel 'one-part' sodium carbonate activated binders is proposed. • CQD modified 'one-part' sodium carbonate activated binders showed superior mechanical and environmental performance. • Ht and M-S-H gels intermixed with C-(A)-S-H gels. • The heavy metals leaching from the CPB samples with 5% CQD addition fulfilled the standard limit. [ABSTRACT FROM AUTHOR]