Absorption and sorptivity of cover concrete

The absorption characteristics and sorptivity of cover concrete obtained by the initial surface absorption test (ISAT), the covercrete absorption test (CAT), and the sorptivity test have been studied and compared. Two types of concrete, namely ordinary portland cement (OPC) control and low water concrete (LWC) of grade 35 have been tested. The laboratory work has shown close agreement between the ISAT and sorption results but the CAT yields higher results. An analytical model has been developed based on the mechanisms of capillary suction and pressure-driven flow, In this model water entering concrete during the tests is assumed to be concentrated in a well-defined volume. This volume is fully saturated and is separated from the surrounding concrete by a wetting front at which capillary suction occurs. By applying the physical equations for capillary suction pressures and permeability the experimental. results are explained in terms of the basic properties of the concrete. The model gives good agreement with the experimental results.