The Influence of CaO and MgO on the Mechanical Properties of Alkali-Activated Blast Furnace Slag Powder

Abstract

CaO and MgO are both reported as effective activators for blast furnace slag. However, the synergistic effect of these two components on the mechanical properties of alkali-activated blast furnace slag remains unclear. In this study, the flexural and compressive strengths of alkali-activated blast furnace slag powder with MgO and CaO range from 0% to 30% by the mass ratio of alkali-activated blast furnace slag powder are investigated. Moreover, the dry shrinkage rate of alkali-activated blast furnace slag powder is measured. One percent refractory fibers by volume of binder materials are added in the alkali-activated blast furnace slag. Some refractory fibers are treated with water flushing, meanwhile, some refractory fibers are directly used without any treatment. Finally, the scanning electron microscope, the thermogravimetric analysis curves and the XRD diffraction spectrums are obtained to reflect the inner mechanism of the alkali-activated blast furnace slag powder’s mechanical properties. The water-binder ratios of the alkali-activated blast furnace slag powder are 0.35 and 0.42. The curing ages are 3 d, 7 d and 28 d. The measuring temperature for the specimens ranges from 20 °C to 800 °C. Results show that the flexural and compressive strengths increase with the increased curing age, the decreased water-binder ratio and the addition of refractory fibers. The water-treated refractory fibers can improve the mechanical strengths. The mechanical strengths increase in the form of a quadratic function with the mass ratio of MgO and CaO, when the curing age is 3 d, the increasing effect is the most obvious. A higher water-binder ratio leads to an increasing the drying shrinkage rate. The activated blast furnace slag powder with CaO shows a higher drying shrinkage rate. The mechanical strengths decrease with the increasing testing temperature.

The Influence of CO2 Curing on the Mechanical Performance and the Corresponding Chloride Ion Resistance of Alkali-Activated Compound Mineral Admixtures

“…In addition, as illustrated in Figure 8, the second step can be observed, which is the temperature of 368.2 °C. In this step, the TG values decrease, which is ascribed to the decomposition of calcium silicate hydrate, the hydrated single sulfur calcium sulphoaluminate and hydrated polysulfur calcium sulphoaluminate [20,36]. As illustrated in Figure 8, the TG values are decreased by CO2 curing, due to the fact that CO2-cured alkali-activated compound mineral admixtures show less bound water than the alkali-activated compound mineral with standard curing, thus decreasing the reduction of TG values.…”

“…Additionally, the compressive strengths of alkaliactivated BFS and FA can reach values higher than 80 MPa and 100 MPa, respectively. Feng et al found that the assembly unit of CaO and MgO can improve the mechanical strengths, high temperature resistance and compactness of the microstructure [20]. The compressive strength of ordinary concrete is less than 60 MPa while high performance concrete shows a compressive strength of 60 MPa-100 MPa; therefore, the compressive strength of alkali-activated BFS is close to the compressive strength of ultra-high performance concrete.…”

Investigating Mechanical Properties of Alkali-Activated Slag Cementitious Material for Load-Bearing Layer of Sandwich Panels

“…The material combinations required per cubic meter of AASCMS are shown in Table 3. Previous studies had shown [18] that AASCM exhibits good performance when the modulus of potassium silicate is 1.0, the alkali content is 14% and the fiber content is 1% by mass. Thus, the fiber content in this study adopted 1% for all testing samples.…”

Durability and Sustainability of Cement and Concrete Composites

“…Ground-granulated blast-furnace slag (GGBS) is a kind of high-activity waste slag formed via the quenching and granulation of silicate and alumino-silicate as the main components in blast-furnace smelting pig iron. Feng et al [ 5 ] prepared an alkali-activated GGBS material with CaO and MgO as activators. It was reported that the addition of MgO and CaO helps to improve the mechanical strengths of alkali-activated GGBS.…”