Sulfate Ion Diffusion Assessment of Blended Cement Concrete with Fly Ash and Limestone Powder

Limited data are available on the measurement of sulfate diffusivity in blended cement-based materials. An experimental study of the diffusion of magnesium sulfate ions in blended cement concrete was performed using different blending materials: fly ash, and lime powder. Different values of cement blending ratio, water–binder ratio, and binder content were studied. Compressive strength loss and weight loss tests were performed to assess the sulfate resistance of the studied mixes. The diffused amount of magnesium sulfate ions was measured using a titration test at different depths from the concrete surface and at different ages up to 12 months of sulfate attack. Fick’s second law of nonlinear diffusion was solved using the error function method to develop a simplified model to estimate the sulfate ions diffusion coefficient with different blending materials. These simplified models are a function of the cement blending ratio, water–binder ratio, and binder content. The initial compressive strength decreased by 15.8% and 31.6% for blended cement concretes with 40% fly ash and lime powder, respectively. The weight loss of concrete decreased by 16% at a 40% fly ash blending ratio, whereas it increased by 33.3% at a 40% lime powder blending ratio. The blended cement with fly ash and lime powder had a greatly reduced concrete diffusion coefficient, by 38% and 14% for fly ash and limestone powder, respectively, despite its lower initial compressive strength. The proposed model performed well in simulating sulfate ion ingress in concrete compared with previously published models; it had the best mean value (0.958) and the lowest standard deviation (0.122).