Development of sustainable alkali-activated slag/fly ash mortars: An effective and eco-friendly approach to shrinkage mitigation

The utilization of alkali-activated fly ash/ground blast furnace slag (AAFS) in construction field presents both economic and environmental advantages. However, the widespread application of AAFS is impeded by its high drying shrinkage compared to ordinary Portland cement. This study explores the potential of recycled red brick aggregate (RRBA) as a substitute for natural sand to mitigate the drying shrinkage of AAFS mortars through internal curing. The experimental results indicate that the incorporation of RRBA can remarkably decrease drying shrinkage of AAFS mortars. The shrinkage compensation ratio of specimens with RRBA ranges from 4.8 % to 70.8 %, with a higher RRBA content resulting in higher shrinkage compensation ratio. The particle size, content, and pre-treatment method of RRBA exhibit significant influence on the shrinkage reduction efficiency of AAFS. RRBA facilitates the maintenance of a high IRH in specimens at 1-7 days and correspondingly reduces the drying shrinkage ratio of specimens during this period. The addition of RRBA provides a water-rich environment in matrix and increases the proportion of large pores in specimens, which are advantageous for reducing the drying shrinkage of the specimens. A model suitable for predicting the long-term drying shrinkage of AAFS mortars with RRBA is proposed in this study.