Water transport in cracks controlled by digital image correlation in wet sprayed concrete with and without an EVA based co-polymer admixture

Abstract

Experiments were undertaken on wet sprayed concrete discs to investigate the effect of cracking on capillary suction and permeation through sprayed concrete for tunnel linings. The 98 mm diameter, 50 mm thick discs were cracked by tensile splitting, with the crack widths controlled and measured by digital image correlation and also checked by microscope measurements. Both a standard sprayed concrete mix and a mix containing an EVA (ethylene–vinyl-acetate) based co-polymer powder were tested. Cracks increased the rate of capillary suction compared to uncracked samples, due to rapid rise of water in the crack and absorption occurring over the surface area of the crack in addition to the area of the base of the disc. Discs with wider crack widths exhibited a higher rate of water permeation per area of crack. Inclusion of the EVA based co-polymer reduced the rate of capillary suction and the permeation flow rate coefficient (measured flow / theoretical viscous laminar flow) for a given crack width compared to the standard mix. Self-healing occurred both during water permeation and water storage of cracked discs. The use of CT scanning to measure the crack through the full thickness of a disc was explored and compared to crack width measurements made at one surface of the disc only.