Influence of early curing on the sub-surface permeability and strength of silica fume concrete

Abstract

The difficulties of producing durable concrete in hot climates is widely appreciated, along with the potential benefits of using cement replacements. However, there is relatively little published data on the influence of curing methods or hot climate on the Permeability of condensed silica fume (CSF) concrete. This paper reports on part of a research programme on the performance of silica fume concretes cured in temperate and hot climates. More specifically, it describes the influence of early curing on the sub-surface air and water permeabilities of CSF concretes up to the age of 6 months and compares these with the development of surface permeability and compressive strength. The effect of curing duration, method (water and polyethylene) and environment (temperate and hot) on three strength grades (C25, C40 and C55 are reported, the conditioning involving appropriate diurnal temperature/humidity cycling. The work has demonstrated that curing duration, method and climate have a large impact on silica. fume concrete's permeability and hence its potential durability, in terms of resisting carbonation and ingress of other aggressive mediums such as chlorides. The silica fume concretes responded, favourably to the hot climate if at least two days moist curing was provided, the greatest improvements occurring with the lower strength grades. Good correlations were, found with surface air and water permeabilities; the surface tests have the advantage of being totally non-destructive and easier to perform in situ (although they are still sensitive to the moisture state of the concrete). Protective quality categories are proposed for each test method.