Evaluation of bond strength between old and new concrete in structural repairs

Good bond between old and new concrete is indispensable for many repairs. Following an examination of the factors involved and the methods of testing bond, the results of an experimental programme of slant shear tests are presented. The programme comprised 223 tests designed to study test methods and the effects of bond coats, surface preparation and ageing of the base concrete. The results are analysed in terms of a Coulomb criterion and evidence is produced that good bond can be achieved by casting the repair against mature concrete with no bonding aids, provided the base surface is dry and reasonably rough.