PERMEABILITY STUDY OF CRACKED CONCRETE

Cracks in concrete generally interconnect flow paths and increase conc rete permeability. The increase in concrete permeability due to the pr ogression of cracks allows more water or aggressive chemical ions to p enetrate into the concrete, facilitating deterioration. The present wo rk studies the relationship between crack characteristics and concrete permeability. In this study, feedback controlled splitting tests are introduced to generate crack width-controlled concrete specimens. Sequ ential crack patterns with different crack widths are viewed under a m icroscope. The permeability of cracked concrete is evaluated by water permeability tests. The preliminary results indicate that crack openin gs generally accelerate water flow rate in concrete. When a specimen i s loaded to have a crack opening displacement smaller than 50 microns prior to unloading, the crack opening has little effect on concrete pe rmeability. When the crack opening displacement increases from 50 micr ons to about 200 microns, concrete permeability increases rapidly. Aft er the crack opening displacement reaches 200 microns, the rate of wat er permeability increases steadily. The present research may provide i nsight into developing design criteria for a durable concrete and in p redicting service life of a concrete structure. (C) 1997 Elsevier Scie nce Ltd.