Sulfate attack of deep foundation concrete: New testing method and influence of temperature on degradation mechanism

Thaumasite attack presents a significant concern within the domain of deep soil foundation construction. In these exposure conditions, concrete is exposed to sulfate-rich groundwater from the fresh state, hence the need for specific durability testing procedure. The use of supplementary cementitious materials (SCM) has long been a way to prevent external sulfate attack. The specific degradation due to thaumasite sulfate attack (TSA) at 5 °C mitigates the observations made for the use of SCM at 20 °C. In response to these challenges, a new testing method has been developed and 41 cement-based binder mixtures, encompassing diverse supplementary cementitious materials (SCM), fillers, and variable C 3 A contents, were tested at 5 °C and 23 °C. Their behavior at 5 °C was consistent with the phenomenology of TSA: visual deterioration , and significant mass loss of several specimens up to -9%. The presence of thaumasite at 5°C was substantiated through SEM and XRD analyses. The measurements at 5 °C indicate that length variations are not a fully reliable parameter to assess the resistance to TSA: a sample with low length variation (0.1%) had a mass variation of 6%, indicating a significant degradation. The joint use of mass and length variations as indicators thus offers valuable insights into the identification of optimal composition for cement-based materials regarding their resistance in deep foundation exposure conditions.