A method to determine water retainability of porous fine aggregate for design and quality control of fresh concrete

Water retainability of a porous aggregate is defined, including absorption as well as adsorption. This moisture property is important for mix proportion and quality control of fresh concrete. An alternative test method to determine water retainability of porous fine aggregates is developed. By the conventional test method for obtaining absorption, it is not possible to reach the saturated surface dryness by collapsed-cone criterion due to the high inter-particle friction of the porous aggregate. The test method was designed, based on the concept of gravitational removal of excess water from the porous aggregate sample. Two procedures i.e. static and accelerated methods were studied to achieve the acceptable reliability within a reasonable time of testing. The comparison between test results of water absorption according to ASTM C 128 and those of water retainability by the proposed method indicated that this method had a better testing precision for all porous fine aggregates, as proved by the smaller standard deviations within the test results given by different individuals. Feasibility of the method was also validated by comparing the properties of conventional concrete (CVC) and self-compacting concrete (SCC) made of normal and porous fine aggregates. The water content of mixtures incorporating expanded clay and two types of bottom ash as river sand replacement of 0, 10, and 20% were adjusted, on the basis of the water absorption from the ASTM C 128 method and the water retainability from the proposed method. From the comparison, it was shown that the proposed test method was effectively applied as an alternative test for water retainability of porous fine aggregates in the quality control of fresh concrete.