Calcium sulfoaluminate (CSA) cements have been shown to have lower carbon footprint than that of Portland cement. In addition, the expansive nature of CSA-based cement can be utilized to enhance the resistance against shrinkage cracking by inducing compressive stress in concrete. The current paper reports the hydration and early-age volume changes of three OPC-CSA binary cement systems with varying CSA content. Hydration and phase development was monitored through calorimetry and quantitative X-ray diffraction. Expansion characteristics of OPC-CSA blends were monitored in saturated lime water. A geochemical modeling program (GEMS-PSI) was used to estimate the saturation levels of ettringite which had strong correlation with 1 day-expansion. The volume fraction of ettringite in a given pore volume was found to have a stronger correlation with expansion of OPC-CSA blends than the ettringite content. Furthermore, a poromechanical model was used for estimating the tensile stress in OPC-CSA blends.