Durability of bonded cement-based overlays: effect of metal fibre reinforcement

Abstract

Cement-based bonded overlay is a frequently used technique for smoothing a damaged surface and/or restoring or improving the mechanical capacity of a structure by increasing its thickness. It is well established that the durability of such a repair is limited by its debonding from the substrate. Whatever the original cause of this debonding, there is general agreement that cracks cutting the repair layer (or any discontinuity such as joints or boundaries) are systematically involved. In situ repairs have demonstrated that reinforcement with commonly used contents of fibres effectively improves the durability of the repair. However, numerous trials under conventional laboratory conditions have failed to confirm the beneficial effects of the fibre reinforcement and three times as much fibre has been required to produce laboratory effects similar to those found in the field. This paper aims to explain this discrepancy. One part of the explanation may be that cracking due to length change (pre-cracking) is not likely to affect small laboratory specimens. Also, most of the laboratory tests have used monotonic loading (or monotonic straining) cases while fatigue loading would constitute a more realistic test. When such corrections are taken into account, a better understanding is obtained of the actual role of fibre reinforcement on the durability of cement-based repairs, as shown by the results and analysis presented here.