Development of accelerated test methods by electromigration to assess the risk of internal sulfate attack in heat-cured mortar and concrete

Internal sulfate attack induces the formation of delayed ettringite (DEF) in hardened cement-based materials. DEF is a complex phenomenon, detrimental to the durability of concrete and which develops in the long term, depending on the temperature history of the material at early age, its composition, its physicochemical and mechanical properties, and the environmental conditions. Today, the risk assessment and prediction of this pathology are still mainly based on laboratory tests which can extend over several months, or even several years. In this context, the objective of the present study is to develop two original experimental devices, making it possible to shorten the time needed to detect the risk of potential internal sulphate attack, using the application of an electric field on mortar and concrete specimens. The results obtained, coupled with microstructural observations carried out using scanning electronic microscopy, show that the two devices make it possible to both accelerate DEF, through electromigration, and measure simultaneously, continuously and automatically the longitudinal and lateral specimen deformations related to the formation of delayed ettringite. Using the devices developed, the time needed to observe the swelling threshold of 0.04 % is divided by a ratio of 2–2.5 and 1.7–1.9 between the mortar and concrete specimens subjected to electric field and the control mortar and concrete specimens, respectively.