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. 2022 Sep 3;15(17):6128.
doi: 10.3390/ma15176128.

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

Shihui Feng  1 , Jing Zhu  1 , Ruixuan Wang  1 , Zijian Qu  1 , Lizhuo Song  1 , Hui Wang  2
Affiliations

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

Shihui Feng et al. Materials (Basel). .

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.

Keywords: CaO; MgO; alkali-activated blast furnace slag powder; compressive strength; dry shrinkage rate; flexural strength.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Automatic universal testing machine equipped with a temperature controllable box.
Figure 2
Figure 2
The measurement of dry shrinkage rate.
Figure 3
Figure 3
The mechanical strengths with different curing age. (a) Flexural strength. (b) Compressive strength.
Figure 4
Figure 4
The mechanical strengths of activated blast furnace slag powder with MgO. (a) Flexural strength. (b) Compressive strength.
Figure 5
Figure 5
The mechanical strengths of activated blast furnace slag powder with CaO. (a) Flexural strength. (b) Compressive strength.
Figure 6
Figure 6
The shrinkage rate of reactive powder concrete.
Figure 7
Figure 7
The SEM morphology of alkali-activated blast furnace slag powder with MgO. (a) With 10% MgO-3 d. (b) With 10% MgO-28 d. (c) With 30% MgO-3 d. (d) With 30% MgO-28 d.
Figure 7
Figure 7
The SEM morphology of alkali-activated blast furnace slag powder with MgO. (a) With 10% MgO-3 d. (b) With 10% MgO-28 d. (c) With 30% MgO-3 d. (d) With 30% MgO-28 d.
Figure 8
Figure 8
Thermogravimetric analysis curves of specimens. (a) TG curves. (b) DSC curves.
Figure 9
Figure 9
The X-ray diffraction (XRD) spectra curves.
Figure 10
Figure 10
The mechanical strength with different testing temperature.
Figure 11
Figure 11
The SEM morphology of alkali-activated blast furnace slag powder measured at high temperature environment. (a) 200 °C. (b) 400 °C. (c) 600 °C. (d) 800 °C.
See this image and copyright information in PMC

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