Influence of recycled coarse aggregates on permeability of fresh concrete

Abstract

The following work is an experimental study of the behaviour of very early-age concrete. Six different concretes, four of them containing recycled coarse aggregates were studied for the first 2.5 h. The studies were carried out in a ventilated tunnel in order to imitate severe desiccation conditions. In order to indirectly obtain the permeability coefficient, settlement, capillary depression and evaporation were measured for all six concretes. The initial permeability coefficient of each concrete is determined starting from initial bleeding rate. The use of recycled coarse aggregates leads to a high bleeding rate for high water to cement ratios. Permeability coefficients at air entry are then determined starting from capillary depression gradients. Recycled coarse aggregates do not seem to influence the air entry value which is highly dependent on the paste quality. At air entry, the permeability coefficient of recycled coarse aggregates concrete mixes is higher than that of natural aggregates concrete mixes. At high evaporation rates, in severe desiccation conditions, recycled coarse aggregates seem to reduce bleeding for mixture with low water cement ratios. Permeability coefficient is a key physical parameter to understand drying of fresh concrete.