Durability of mechanically loaded engineered cementitious composites under highly alkaline environments

Durability of mechanically loaded Engineered Cementitious Composites (ECC) is investigated in this paper. ECC offers significant potential for durable civil infrastructures, due to its high tensile strain capacity of more than 3%, and controlled micro-crack width of less than 80 μm. An experimental study was designed to investigate the durability of ECC material with regard to cracking and healing under combined mechanical loading and environmental loading conditions. ECC coupon specimens were firstly pre-loaded under uniaxial tension to different strain levels, and then exposed to an alkaline environment up to 3 months at 38 °C and reloaded up to failure. The reloaded specimens showed slight loss of ductility and tensile strength, but retained the multiple micro-cracking behavior and tensile strain capacity of more than 2% (about more than 200 times that of normal concrete and normal fiber reinforced concrete). The test results indicated strong evidence of self-healing of the micro-cracked ECC material, which can still carry considerable tensile stress and strain and restore nearly the original stiffness. The phenomenon of self-healing effectively closes the micro-cracks even after one month exposure period. In addition to coupon specimens, ECC bar specimens were also immersed in alkali solution at 80 °C in accordance to ASTM C 1260 to determine their length change due to alkali silica reaction (ASR). The ECC bar specimens did not show any expansion at the end of 30 days soaking period. Therefore, these test results indicated that ECC, both virgin and micro-cracked, remain durable despite exposure to a high alkaline environment. The risk of ASR in ECC is determined to be low.