Consideration on the influence of deterioration on deformation velocity in mortar and cement past specimens subjected to external aggressive attacks

Concrete durability depends not only on the material composition and on the resulting porosity but also on the environmental conditions. In particular, when a concrete structure is in contact with sulfate-rich waters or soils, a series of complex chemical reactions can occur between the sulfates diffusing within the material and the aluminates of the cement paste, leading to leaching, secondary gypsum, and ettringite formation, overall expansion, and degradation of concrete. These phenomena are gathered within the general term of sulfate attack. To assess the behavior of the same cementitious material subject to different external aggressive attacks, prismatic specimens of cement paste and specimens of mortar and concrete produced with the same Portland cement, were immersed in demineralized water and in different solutions containing 5% and 10% sodium sulfates. The expansion was monitored in time by direct length measurements and the degradation of the stiffness was indirectly obtained through non-destructive ultrasound wave propagation tests. These experimental tests allowed studying the deformation behavior of prismatic cementitious specimens with and without aggregate. The first results obtained by this research suggest that the typical cyclical behavior of the deformation velocity could be influenced by the deterioration and or the detachment of surface layers due to salt crystallization. Therefore, in this paper, that aspect of the phenomenon will be investigated, and the previous results implemented with new laboratory monitoring of the same samples.