Despite the best efforts to avoid it, in practice, most concrete cracks. The cracking can be due to a variety of causes including thermal gradients, moisture gradients, and attack by the external or internal environment (sulfate attack, alkali-silica reaction, etc.). The failure of concrete due to cracking typically follows the classic bathtub service life function [1], with significant early age cracking. Concrete that survives this early age period in a crack-free condition may remain so for decades before cracking due to the above-mentioned degradation mechanisms. Clearly, avoiding early age cracking is critical to providing concrete that meets its intended design purpose and performs acceptably throughout its intended service life.
In low water-to-cement (w/c) ratio concretes, one significant contributor to early age cracking is the self-desiccation [2] and autogenous deformation that occurs during the early age period. As the cement hydrates, the reaction products occupy less space than the reactants (Le Chatelier contraction/chemical shrinkage). This chemical shrinkage results in a self-desiccation and the creation of empty porosity within the material (once set has occurred). The meniscii present at the interfaces between the water-filled and empty pores will result in the development of stresses within the liquid phase which will also, of course, result in autogenous stresses and strains within the solid framework of the hydrating cement paste. Because the stresses in the pore solution are directly proportional to its surface tension, it seems logical that shrinkage-reducing admixtures (SRA- conventionally used to control drying shrinkage [3]), which lower this surface tension, could also be used to mitigate autogenous shrinkage and early age cracking in low w/c ratio cement-based materials. In this paper, fundamental studies on the influence of SRAs on desiccation in cement pastes and mortars cured under sealed and drying conditions will be presented.