Effect of aggregates and microcracks on the drying rate of cementitious composites

We investigated the effect of aggregate concentration on the drying rate of cementitious composites with glass beads, sand grains, or expanded polystyrene (EPS) beads as aggregates. The drying rate of composites with non-diffusive aggregates (glass beads and sand grains) decreased with aggregate concentration. Composites with 60% glass beads dried a factor 1.3 slower than plain cement paste with the same w/c-ratio. Composites with EPS-beads showed the opposite trend: an increased drying rate for composites with higher aggregate concentrations. However, the effective diffusion coefficients of the EPS-composites decreased with increasing aggregate concentration. A higher aggregate concentration means that less water needs to diffuse out of the material to reach a specific degree of drying, and this effect mainly determined the drying rate of the composites with EPS-beads. The development of drying shrinkage microcracks had a small effect on the drying rate of the studied composites.