Evaluation of the Cracking Risk in Alkali Activated Materials by Means of Restrained Shrinkage

Abstract

Early age micro-cracks development is the source of many durability issues of concrete structures. Specifically, crack formation caused by restrained deformation takes place at a time when the properties of the material are still evolving and its deformation rate is high. The present study used the ring test to investigate the early age cracking sensitivity in restrained conditions of NaOH activated slag. In addition, several parameters were considered, such as the molarity of the activating solution, and the solution-to-binder ratio. An increase in the solution molarity leads to higher compressive strength, autogenous shrinkage, and internal stress, while increasing the solution quantity produces the opposite effect: compressive strength, autogenous shrinkage, and internal stress decrease. Moreover, the internal stress has been compared with the tensile strength of the material showing a good agreement between experimental and modelled results and the low influence of viscous properties of the material at early age. From a general perspective, it has been observed that autogenous shrinkage is the main phenomenon influencing the early age cracking behaviour of alkali-activated slag, whereas creep does not act significantly as a relaxation factor and reduces the internal stress and strain, and the cracking risk.