Extension of Powers-Brownyard Model to Pastes Containing Supplementary Cementitious Materials

The properties of cementitious materials depend on the proportions of unhydrated phases, hydrated phases, and pore volumes in the paste. The Powers-Brownyard model (PB model) has been used to estimate these volumes for ordinary portland cement (OPC) as a function of degree of hydration. However, the PB model was not developed for systems containing supplementary cementitious materials (SCMs). This work combines the PB model and thermodynamic calculations to predict capillary and gel porosity, chemical shrinkage, and the volumes of all hydrated and unhydrated phases for OPC-SCM pastes. SCM reactivity is a dominant factor in predicting the hydrated paste phase and pore volumes in OPC-SCM systems. Pore refinement occurs with increasing SCM reactivity, and the proportion of gel pores relative to solids increases from Powers-Brownyard assumptions when SCM is used. The proposed model provides additional information on unreacted and reacted phase volumes. Keywords: porosity; Powers-Brownyard model; supplementary cementitious material (SCM); thermodynamic modeling.