Durability properties of micro-cracked ECC containing high volumes fly ash

Abstract

This paper presents the durability of Engineered Cementitious Composites (ECC) that contain high percentages of Class-F fly ash (FA). ECC is a newly developed high performance fiber reinforced cementitious composite with substantial benefit in both high ductility in excess of 3% under uniaxial tensile loading and improved durability due to intrinsically tight crack width. Composites containing two different contents of FA as a replacement of cement (55 and 70% by weight of total cementitious material) are examined after 28 days of curing. Accelerated aging (exposure to continuous sodium hydroxide at 38 °C and sodium chloride solutions at room temperature) and tests of transport properties (salt ponding, rapid chloride permeability and sorptivity tests) are used to study the effect of FA on the durability of the ECC. After accelerated aging, direct tensile tests are performed to evaluate the effect of deterioration on the tensile strength, tensile strain capacity and crack width of ECCs. In addition to virgin specimens, the durability performances of mechanically loaded specimens are also tested. Test results show that both mechanically pre-loaded and virgin (without pre-loading) ECC mixtures with high volumes of FA remain durable in terms of mechanical performances after accelerated aging period, and show a tensile strain capacity of more than 2%. In terms of transport properties, micro-cracks induced by mechanical pre-loading increase the chloride transport and the sorptivity values of ECC. Moreover, increasing FA content is shown to have a negative effect especially on the transport properties of ECC tested in this study. However, the risk of water transport by capillary suction and chloride transport by diffusion in ECC, cracked or uncracked, is found to be comparable with that in normal sound concrete.