Activation of pozzolanic and latent-hydraulic reactions by Alkalis in order to repair concrete cracks

摘要

The low degree of hydration of fly ash (FA) and slag (BFS) particles in high-volume FA and BFS concrete offers the possibility to activate the unreacted particles upon crack formation to close the crack. In this paper, a preliminary study is performed to evaluate the use of alkaline activators to stimulate the formation of reaction products in the crack. First, the reaction rates of crushed pastes mixed with alkaline solutions or water were monitored by calorimetry. These tests showed that alkaline activators stimulate the reactions more than water. Secondly, cracked mortar beams were stored in different alkaline solutions or water and the crack self-closing ratio was calculated after microscopic investigation at different time intervals. The results indicated that reference mixes, containing only ordinary portland cement as binder, heal very well autogenously, while a solution of Ca(OH)2+Na2CO3 seems to be the most suitable activator to stimulate crack closing of BFS concrete. Thirdly, the regain in strength due to healing of the cracks was determined. Compared to other self-healing techniques, strength regain is limited (about 10-40%).