The delamination of the surface layer of concrete floors during or after the surface finishing operations (floating, troweling, and polishing) is no new phenomenon. However increased numbers of cases have been reported these last years and unlike before, the delamination fracture can often be observed deeper in the concrete underneath the dense layer (mostly comprising embedded surface hardeners). These observations have prompted the BBRI to conduct a research project ('FloorCrete'), in order to determine the possible reasons for the increased occurrence of delamination. In currently encountered cases, two main causes for delamination can be observed: an excess of entrapped or entrained air in the concrete and late bleeding. The timing of the start of the finishing operation is also crucial (notion of "window of finishability"). A slow setting-time or crusting of the surface of the concrete can complicate the determination of the optimal finishing time. The influence on the air-content, the bleeding-rate and the hardening properties of concrete of different concreteconstituents is being investigated in this research project. The first results are presented and some provisional practical recommendations are given.
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