By modelling pore cross-sections as ellipses, this paper advances a recent model for predicted unsaturated water flow within concrete (Collins and Sanjayan, J Porous Mater doi:10.1007/s10934-008-9245-4, 2008). Predicted and measured unsaturated flow within concretes composed of two different cementitious binders, namely alkali activated slag (AAS) and ordinary Portland cement (OPC), are contrasted. AAS has environmental benefit due to significantly less energy required (than OPC) during manufacture, however predictive modelling of unsaturated flow of water within AAS concrete has had no prior investigation. Factors that significantly affect unsaturated flow within concrete, including age of sample and the type of sample conditioning (curing) prior to testing, are analysed. The prediction model, incorporating elliptical cross-sectional pore shape, shows reasonable agreement with sorptivity test data for AAS, however the circular cross-section better predicts unsaturated flow within OPC concrete. Although, the actual pore cross-sections are neither truly circular nor elliptical, adoption of an equivalent ellipse for AAS significantly reduces the margin between the predicted and measured water uptake.