Fig. 4 shows the results of maturation influence on compressive strength in specimens where polymer contains 0.5% of montmorillonite. It is clear the difference in hardening process when the amount of polymer is increasing. In the first place for 1:1.7:0.4 samples, the 7-days compressive strength represents 68% of 28- days compressive strength, while 14-days compressive strength shows 96.6% of 28-days. On the opposite conditions for 1:0:2.1 samples, the 7-days compressive strength shows 58% of 28-days compressive strength and 14-days represents 61% of 28-days compressive strength. This is an interesting behavior because when the amount of polymer is greater the hardening of cement is slower. This is due to the poor interaction in cement matrix when major amounts of polymer are added to the mortar; this complicates the water transportation in capillary cement paste, by the tortuosity caused for polymer pellets. Additionally it is well known the reaction between alkali components of cement and siliceous aggregates, that causes ‘‘alkaline reaction’’ (alkali–aggregate reaction, AAR), making the reaction faster but causing failures in concrete [36]. In other hand, with respect to the control sample, for 1:1.7:0.4 samples, the 28-days compressive strength is 80%, relative to the control test, while 1:0:2.1 samples shows only 22% of the 28-days compressive strength of control sample. According to the obtained results, adding a large amount of polymer reduces gradually the material compression resistance. Finally, 28-days
compressive strength of 1:0:2.1 samples reaches 4.04 MPa. These results are above the strength required for construction bricks by the Complementary Technical Standards Regulations of Construction for Distrito Federal (Mexico) being of 3.92 MPa.