Sorptivity of self-compacting concrete with high volume fly ash and its eco-mechanical-durability performance

Abstract

The durability of concrete is governed by the ability of the concrete to resist the penetration of aggressive agents from the environment. The capillary pores of concrete play an important role in the absorption of water, through which aggressive agents may enter into the body of concrete. The rate and amount of absorbed water can be measured by the sorptivity test. It is also recognised that the composition of concrete itself influences the pore structure of the concrete. Hence, in a non-conventional concrete with a very different mixture such as self-compacting concrete (SCC) incorporating a high volume of fly ash, the sorptivity is expected to be different from that of the concrete. This paper aims to determine the influence of high volume fly ash contents on the sorptivity of SCCs, as measured by the method of ASTM C1858. The balanced performance of the concrete – in terms of ecological, mechanical, and durability performance – is assessed using the eco-mechanical-durability index (EMDI). The index is developed as a combined value of eco-mechanical index (EMI) and eco-durability index (EDI). The sorptivity is adopted as the durability parameter in developing the EDI. The results confirm that an optimum value of sorptivity at an early age is obtained when about 55% of the OPC is replaced with fly ash. At a later age, however, the optimum value is changed to the 65% replacement level. A higher volume of fly ash tends to decrease the EMI but increase the EDI. Consequently, the effect of fly ash content on EMDI depends on the relative importance between EMI and EDI. Where EMI and EDI are considered to be equally important, the effect of fly ash content on EMDI is controlled by the greater sensitivity of the EDI to the fly ash. Thus, it is shown in this particular case that at later age i.e. when the effect of fly ash is maximal, the highest EMDI is found in the SCC with 70% of the cement replaced by fly ash.