Volume Changes of Alkali-Activated Slag-Based Mortars and Concretes in Sealed and Free Conditions

The goal of this paper is to assess the evolution of the autogenous strains as well as the thermal strains (thanks to the assessment of the coefficient of thermal expansion) of alkali-activated slag-based materials at early age. The effect of the sand and the coarse aggregates on the paste and mortar scale to upscale to mortar and concrete, respectively, has been investigated as a function of the age of the material. The restraint imposed by the sand on the paste seemed more significant than that of the coarse aggregate on the mortar. In addition, the long-term autogenous strains have been monitored on the mortar scale. These results revealed a separation into groups based on the solution concentration. Different testing methods were also compared. Thermal and autogenous strains were monitored with a customized testing device where the thermal variations are controlled. These devices were the horizontal corrugated tubes method (for tests on paste and mortar scales) and the vertical corrugated tubes method (for tests on mortar and concrete scales). Depending on the compositions (lower concentration), good correlations can be obtained between the two testing methods. Moreover, the autogenous strain of two different specimen sizes was also assessed manually (initially for the long-term), but early-age comparison showed good correlation for lower solution-to-binder ratios. On the concrete scale, a correlation based on the modified equations from the standards was established between the compressive strength and the tensile strength, obtained from the splitting tensile test.