Shrinkage model for waste clay brick-based geopolymer concrete

This study investigated the shrinkage behaviour of geopolymer concrete (GPC) under various curing environments. One-part GPC was prepared by using waste clay bricks (WCB), fly ash and slag as precursors and anhydrous sodium silicate as the sole activator. The samples were subjected to initial curing in three different environments: standard curing in lime-saturated water, unsealed ambient curing, and sealed ambient curing. Irrespective of the curing environment, GPC showed a higher shrinkage than conventional concrete with ordinary Portland cement. Compared to sealed and unsealed curing, standard curing was able to reduce the shrinkage in GPC by more than 22%, considering the 28-day shrinkage strain. However, this curing environment was not suitable in terms of strength development. For WCB-based GPC, the sealed curing improved the strength gain, and also reduced the shrinkage compared to unsealed curing by more than 50%. The existing standard prediction models for Portland cement concrete significantly underestimated the shrinkage of GPC. This study proposed a new model with higher accuracy to predict the shrinkage of GPC. The model used a 28-day shrinkage value to estimate the long-term behaviour, and has the flexibility to adjust its coefficient based on the exposure environment.