The early-age cracking sensitivity, shrinkage, hydration process, pore structure and micromechanics of cement-based materials containing alkalis with different metal ions

The early-age cracking sensitivity of cement-based materials containing alkalis with different metal ions (Na+ and K+) is investigated. The results indicate that alkalis containing both Na+ and K+ can promote the early cracking sensitivity of cement-based materials, in which K+ having a higher promoting effect than Na+. By exploring the shrinkage properties, hydration process, pore structure and micromechanics, the mechanism of the cracking performance of cement-based materials containing alkalis with different metal ions are revealed. According to the experimental results and the analysis of mechanism, alkali enhances the cracking sensitivity of cement-based materials by increasing their shrinkage rate, promoting hydration process, and refining pore structure. But the improvement of cracking sensitivity of cement-based materials containing alkalis with Na+ or K+ is related to cohesive force and structure of calcium silicate hydrates clusters.