Optimal adjustment of ACI formula for shrinkage of concrete containing pozzolans

Very few models have been developed to estimate shrinkage of concrete containing pozzolans, and most existing models (particularly the ACI model) are not calibrated with pozzolanic concrete. This paper presents an improvement of the ACI model for shrinkage of concrete containing three types of pozzolans including silica fume (SF), fly ash (FA), and slag (SL). A comprehensive database is collected from the literature to cover a wide range of mixture components and mix proportions. In particular, to capture the effect of the dosage and type of each pozzolan, the time function in the ACI model is modified and a new correction factor associated with compressive strength is added. The model parameters in the modified time function and the new correction factor are assessed using a computational intelligence method called particle swarm optimization. The results of several statistical indicators show better prediction performance for the modified ACI model (M-ACI) than the original ACI formula.