3.2.1. Setting Time and Workability

Table 5 provides the setting time of the cement paste with BS and indicates that cement setting was delayed. BSC7 showed the most significant delay, at 64% later than the control. The slowest final setting occurred for BSC7, which was postponed by 230 min (~3.8 h). As mentioned in [39], all cement specimens with an initial setting time of less than 45 min or a final setting time of longer than 6.5 h should be considered as unqualified and sub-quality products. Hence, even though the final setting time was delayed, BSC pastes still achieved a satisfactory setting time.


**Table 5.** Evolution of setting time with different treatments.

\* Value compared with control cement paste.

The workability is an important parameter in concrete mixture design. Therefore, slump tests were performed for all BSC specimens, and the results are shown in Figure 8. A marked loss in workability resulted in an increase in the number of particles in the matrix. A higher replacement of BP with cement led to a weaker slump. Nearly zero slump was observed for BSC5 and BSC7 because the increasing content of BS may absorb additional water from the mixture, which requires further investigation.

**Figure 8.** Slump evolution of alkali-treated BSC.

3.2.2. Morphology and Physical Properties

An analysis of BSC at 28 days by SEM in Figure 9 showed a favorable interface between the BS and matrix. The particles were spherical or cylindrical, distributed nearly uniformly in the matrix, and no large pores were observed. Some microcracks were visible, which may be because of the dehydration of cement.

**Figure 9.** SEM analysis of alkali-treated BSC.

Figure 10 compares the density and porosity for different BSC contents. A correlation between the density and porosity showed that the specimens became lighter and more porous with an increase in BS proportion. The same observation is possible in Figure 3. BS addition to the mixture resulted in an increased void exposure at the specimen surface. The substitution of 7 wt.% cement by BS yielded a matrix that was 14.1% lighter and 6.1% more porous than the control mortar, which agrees with previous research [40].

**Figure 10.** Density and porosity of alkali-treated BSC.
