Cracks―Concrete Repair's Life Threatening Wounds

摘要

Cracking in concrete repair systems is one of the truly critical phenomena of repair pathology responsible for corrosion, deterioration and failure. The problem of repair cracking has become widespread not only with respect to severe environments which are intensifying restrained volume change stresses but also with respect to repairs in relatively benign environments. Cracking accelerates the penetration of aggressive substances into the concrete and repair material from the exterior environment which in turn aggravates any one or a number of various mechanisms of deterioration. Moisture transport mechanism in the repaired structures is a tool for transferring an outer standard environment into an inner environment, and from one inner environment (existing substrate) into another (repair material). The crack resistance of concrete repair is bearing on three equally important "elephants": (1) design details and specifications; (2) repair materials; (3) in-situ workmanship and quality control This study demonstrates that the properties of cementitious repair materials have to be engineered for dimensional compatibility with existing concrete to improve their resistance to cracking. How good should the cementitious composite material used for repair of existing concrete structures be? How good is good enough? The paper summarized the factors involved and approaches taken when selecting cementitous repair materials. Performance criteria is presented for the selection of dimensionally compatible repair materials and standard material data sheet protocol. The recommended approach can enable material quality improvement, more accurate service life prediction, and satisfactory performance of repaired concrete structures during their intended service life.