Permeability of cover concrete: Can choice of aggregate turn out to be more determinant than the W/C ratio

Based on research work carried out jointly at the laboratories of the Institut National des Sciences Appliquées (INSA) in Toulouse (France) and the University of Sherbrooke (Canada), it has been observed that the gas permeability of concretes produced in Toulouse always proves to be lower. A study performed on mortars has been devised to assess the importance of the mineralogical nature of the aggregate. The permeability of mortars with marble aggregate is consistently less than that of mortars with granite aggregate. By virtue of interaction with the hydrated cement paste, the mineralogical nature of the aggregate dictates, to a greater extent than the W/C ratio, the level of air permeability of the mortar subjected to drying. Results also reveal that gas permeability is dependent upon the paste/aggregate interaction of the smallest particles. The partial substitution of the tines portion of a concrete aggregate by a similarly-sized marble aggregate warrants further consideration, in the aim of optimizing the gas permeability of the concrete and thereby increasing durability of the cover concrete.