"The Quality of the Covercrete of Low-, Medium- and High-Strength Concretes"

Abstract

A comprehensive research program was carried out to evaluate the quality of the outer layer of concrete (the 'covercrete'), in terms of its durability and protective value to the underlying reinforcing bars. Part of the results of that investigation are presented in this paper, namely those dealing with the influence of the concrete grade and cement type on the permeability to oxygen and water obsorption properties of the 'covercrete' of concrete specimens subjected to 7 days moist + 21 days dry curing. The results obtained show that the permeability to oxygen is reduced 40 times when the concrete strength is raised from 25 to 85 MPa, whilst the rate of water obsorption is reduced by a factor of 4. In addition, the cement type (including Portland and blended cements) seems to play only a secondary role in the quality of the 'covercrete' of concretes of the same grade, especially above 25 MPa.