AFt/AFm distribution and microstructural properties of thermally cured concretes containing rice husk ash

The behaviour of concretes with and without rice husk ash was experimentally investigated with respect to the susceptibility to delayed ettringite formation. Concrete specimens have previously undergone a specific initial thermal curing up to 85°C, which was designed to trigger delayed ettringite formation. Specimens were subsequently exposed to a specific exposure environment by water immersion at 38°C, over 1 year. Expansion measurements and microstructural analyses were performed to evaluate the level of attack, as well as the integrity of concretes and chemical characteristics of compounds by means of SEM-EDS. Mechanical properties were also assessed over one year to detect the level of damage from delayed ettringite formation. The data has indicated that the incorporation of 8% of rice husk ash could partially reduce the level of DEF expansion and damage. The microstructure of cement matrices from both the reference and RHA concrete indicated different features, sulfate phase compositions and degradation stages. The reference concrete contained radial cracking from filled pores and nearby interfacial transition zone, whereas RHA concrete presented denser features, with microcracking scattered at random across cement matrix and minor neoformations.