Compressive Strength and Microstructure Properties of Alkali-Activated Systems with Blast Furnace Slag, Desulfurization Slag, and Gypsum

Abstract

This study investigates the effect of desulfurization slag (DS) and gypsum (G) on the compressive strength and microstructure properties of blast furnace slag-(BFS-) based alkali-activated systems. DS is produced in a Kambara reactor process of molten iron produced in a steel production process. DS contains CaO, SiO2, Fe2O3, and SO3 and is composed of Ca(OH)2 and 2CaO·SiO2 as main compounds. In this investigation, the weight of BFS was replaced by DS at 5, 10, 15, 20, 25, and 30%. In addition, G was also applied at 9, 12, and 15% by weight of BFS to improve the compressive strength of the alkali-activated system with BFS and DS. According to this investigation, the compressive strength of the alkali-activated mixes with BFS and DS ranged from 14.9 MPa (B95D5) to 19.8 MPa (B90D10) after 91 days. However, the 28 days compressive strength of the alkali-activated mixes with BFS, DS, and G reached 39.1 MPa, 45.2 MPa, and 48.4 MPa, respectively, which were approximately 78.8 to 97.5% of that of O100 mix (49.6 MPa). The main hydrates of the BFS-DS (B80D20) binder sample were Ca(OH)2, CaCO3, and low-crystalline calcium silicate hydrates, while the main hydration product of BFS-DS-G (B75D10G15) binder was found as ettringite. The use of BFS-DS-G binders would result in the value-added utilization of steel slag and provide an environmentally friendly construction material, and contribute to a reduction of CO2 in the cement industry.

Establishment of the Controlled Low-Strength Desulfurization Slag Prediction Model for Compressive Strength and Surface Resistivity

“…Figure 9 shows the simulated results of the relationship between the hyperbolic function coefficients a and b and the DS replacement rate. The value of the coefficient a is distributed in the interval of 2.3-5.7, and the relationships between the parameters a 1 and a 2 and the DS can be approximately expressed as an increasing function, as shown in Figure 9a and Equation (2). Where a 1 and a 2 are the linear regression parameters of the hyperbolic function coefficient a.…”

“…After the torpedo car, the sulfur is removed by a desulfurizing agent, and the obtained slag body is discharged into the torpedo car and then slowly cooled to a fine granular shape, and because of the high content of SiO 2 in the components thereof, it is also called the sulfur residue. Since the desulfurized slag still contains a part of the slag, after subsequent processing, such as magnetic partition, crushing, and smashing, the slag can be recovered, which improves the purity and utilization value of the desulfurized slag [2]. In recent years, some studies have been carried out to replace part of the natural coarse aggregate and fine aggregate with desulfurized slag in the design of concrete mix ratio and applied to cement mortar [1][2][3][4][5][6][7].…”

“…Since the desulfurized slag still contains a part of the slag, after subsequent processing, such as magnetic partition, crushing, and smashing, the slag can be recovered, which improves the purity and utilization value of the desulfurized slag [2]. In recent years, some studies have been carried out to replace part of the natural coarse aggregate and fine aggregate with desulfurized slag in the design of concrete mix ratio and applied to cement mortar [1][2][3][4][5][6][7]. From the study of [2], it was found that desulfurized slag can be used to replace the natural sand in the cement mortar mixture, and it was pointed out that, if the mortar solidified at a high temperature and the desulfurized slag replacement rate increased, the mortar volumetric expansion tended to increase, and the rate of volumetric expansion increased.…”

“…In recent years, some studies have been carried out to replace part of the natural coarse aggregate and fine aggregate with desulfurized slag in the design of concrete mix ratio and applied to cement mortar [1][2][3][4][5][6][7]. From the study of [2], it was found that desulfurized slag can be used to replace the natural sand in the cement mortar mixture, and it was pointed out that, if the mortar solidified at a high temperature and the desulfurized slag replacement rate increased, the mortar volumetric expansion tended to increase, and the rate of volumetric expansion increased. Additionally, as the desulfurization slag replacement rate increases, the compressive strength tends to decrease [5][6][7][8].…”

Removal of Cd2+ and Pb2+ from Wastewater through Sequent Addition of KR-Slag, Ca(OH)2 Derived from Eggshells and CO2 Gas

“…23 The main constituents of KR-Slag are calcium oxide, iron oxide, and silicon oxide, in which calcium oxide is more than 45% depending on the amount of the desulfurizer (lime) used in the KR mechanical stirring process. 24 Due to the high content of calcium oxide, it has versatile applications such as a cement-free binder in concrete, 23,25,26 in acid mine drainage treatment, 22 for soil modification, 27 as an alkali activator of an alkali-activated system, 28 and backfill material. In contrast, solid wastes such as eggshells have valuable applications in versatile fields.…”