British Standard and RILEM water absorption tests: A critical evaluation

British Standard and RILEM capillary suction rate and water absorption tests used for clay bricks, stones and pre-cast concrete products are critically examined. Experimental data are reported comparing the initial rate of suction with the sorptivity, an analytically based method of measuring capillary suction rate. Experimental work is also reported comparing water contents attained as a result of vacuum saturation absorption and the British Standard 5 h boiling test. Results of 24 h and 30 min immersion tests are also reported. It is concluded that the initial rate of suction test is fundamentally flawed and may produce misleading results because of its use of only a single point measurement. It is further concluded that vacuum saturation provides the most accurate measurement of water absorption, and therefore porosity. The 5 h boiling test generally produces results significantly below those obtained by vacuum saturation with samples attaining approximately 90% of vacuum saturation. Immersion tests, used to provide comparative data on the rates of absorption of different materials, can only be valid if the specimens have identical dimensions.