From the analysis of the results of this research, the following conclusions can be established:
The addition of SSA in concrete for the manufacture of blocks with very dry consistency provides densities and mechanical strengths similar to the control sample (without SSA), while the water absorption suffers a considerable decrease. It is important to highlight the behavior of the sample with a 10% replacement of sand by SSA, which shows the best performance in terms of density, absorption and capillarity. In this case, a matrix that fills the gaps in a better way is obtained, due to the increment of fine particles, and its mechanical evolution is far superior to the control sample and the other samples analyzed in this study. The use of this mixture could also represent significant environmental and economic benefits.
Note that there is a high correlation between density, absorption and capillary absorption in mortars and concretes (when dry mass density decreases, water absorption and capillary absorption increase); and between compressive strength and ultrasonic pulse velocity in mortars.
In conclusion, the results can be attributed to the combination of two features of the SSA. On one side, the fine materials that occupy the gaps between the coarse aggregate particles, with an increase in density. On the other side, it is a pozzolanic material with an identifiable reactivity, even at early ages, which effect is reflected in the different tests performed.