External Sulfate Attack

In external sulfate attack, sulfate ions diffuse into the concrete and react to form expansive products, and the resulting internal pressure cracks the matrix. The cracking then makes diffusion easier, so the process accelerates itself.

The group treated this as a coupled diffusion and damage problem rather than a durability index. The 2003 formulation with Raphael Tixier in the ASCE Journal of Materials in Civil Engineering couples sulfate transport to an expansion model and a damage law, so that the strain, the stiffness loss, and the time to cracking come out of the same calculation. It remains among the most cited work from the group.

Later work extended the approach to blended cements, where fly ash and slag change both the diffusion rate and the amount of reactive aluminate available, and studied the parameters that govern how long a material survives exposure.