A Novel Uniaxial Penetration Approach to Investigate External Sulfate Attack on Blended Cement Pastes

The main problem of the sulfate attack topic is the understanding of the so-called physical sulfate attack. However, the current existing testing methods are not suitable for sulfate attacks under arid conditions. A new uniaxial approach is established to investigate sulfate attack by combining these two aspects into one single sample. The different behaviours after sulfate exposure with this uniaxial penetration approach are compared with various cement materials. Portland Cement (PC), Sulfate-Resisting Cement (HS), and Limestone Calcined Clay Cement (LC3) show different levels of sulfate resistance: PC is quite susceptible to ettringite-type attack and causes expansion and cracking LC3 cement show negligible expansion and cracking but accordingly potential to salt crystallization attack due to the sulfate ingress from the capillary rise and crystallization from drying. The damage of spalling due to Na2SO4 salt crystallization is dependent on the exposure conditions (constant RH and temperature). Results show that expansive force is from the ettringite crystallization pressure in the confined space (radius < 50 nm) within C-S-H gel with a supersaturation, damage from salt crystallization pressure only happens potentially once the water evaporation rate is faster than the capillary rise.