Capillary absorption of structural lightweight aggregate concrete

The present study aims to characterize the capillary absorption of structural lightweight aggregate concrete (LWAC), taking into account different compositions with lightweight aggregates (LWA) of very distinct porosity. The influence of the following parameters is analysed: the volume and initial water content of LWA; the cement content and its replacement by fly ash or silica fume; the partial replacement of normal weight aggregate by lightweight coarse or fine aggregate; different curing conditions. It is shown that LWAC usually has higher initial and long-term absorption than normal weight concrete (NWC) of the same composition. However, the sorptivity tends to be similar in both concretes, regardless of the type and volume of aggregate and the water/cement of the surrounding paste. Moreover, the sorptivity is lower in LWAC than in NWC of the same strength. It is also shown that the coarser the porosity of the LWA the lower is the capillary action. The capillary absorption is higher in LWAC with pre-soaked LWA and increases as the percentage replacement of cement by fly ash increases and the percentage of silica fume decreases.