Autogenous shrinkage model for concrete accounting for compounding effects of mineral admixtures

The inclusion of mineral admixtures, such as ground granulated Blast Furnace Slag (BFS), silica fume, and fly ash, is gaining popularity in both normal and high-strength concrete in current structural applications to enhance concrete performance at both fresh and hardened states. The double- or triple-adding of mineral admixtures leads to a significant impact on the mixture's time-dependent behavior, in particular on the autogenous shrinkage. However, a generally applicable prediction model is still not available either in the literature or in the standard codes. This is particularly important for high-strength sealed concrete as the autogenous shrinkage significantly influences the long-term responses, for example, in concrete-filled steel tubular (CFST) columns. To address this issue, a new autogenous shrinkage database concerning the mineral admixture influence on the autogenous shrinkage of sealed cementitious composites, including concrete, mortar, and cement paste, was first set up, which includes a total of 739 shrinkage tests. Next, a new autogenous shrinkage model was then proposed, considering the mineral admixture influence by using the equivalent water-to-binder ratio. This research showed that: (1) the mineral admixture influence on autogenous shrinkage would be more significant for mixes with a lower water-to-binder ratio. This applies to the silica fume, fly ash, and BFS with a specific surface area larger than 400 m2/kg; (2) the BFS or fly ash influence on autogenous shrinkage would be less for mixes with larger silica fume replacement ratio; (3) the opposing effect of BFSs with coarse and fine particles is more pronounced in concrete that has lower water-to-binder ratios. The proposed model offers accurate predictions regarding the autogenous shrinkage of concrete, incorporating all aforementioned features.