Influence of microcracking on water absorption and sorptivity of ECC

This paper presents the results of an experimental investigation on the water absorption and sorptivity properties of mechanically loaded Engineered Cementitious Composites (ECC). ECC is a newly developed high performance fiber reinforced cementitious composite with substantial benefit in both high ductility and improved durability due to tight crack width. By employing micromechanics-based material design, ductility in excess of 3% under uniaxial tensile loading can be attained with only 2% fiber content by volume, and the typical single crack brittle fracture behavior commonly observed in normal concrete or mortar is converted to multiple microcracking ductile response in ECC. In this study, water absorption (ASTM C642) and sorptivity tests (ASTM C1585) were conducted to determine absorption capacity and sorptivity of microcracked ECC. The experimental program described in this paper indicated that microcracks induced by mechanical loading increases the sorptivity value of ECC without water repellent admixture. However, the use of water soluble silicone based water repellent admixture in the production of ECC could easily inhibit the sorptivity even for the mechanically loaded ECC specimens. Moreover, the incorporation of the water repellent admixture reduced the absorption capacity of the resulting ECC mixture. Based on this study, the risk of water transport by capillary suction in ECC, cracked or uncracked, is found to be low compared with that in normal sound concrete. The incorporation of water repellent admixture further lowers this risk.