Mould release technologies with regard to concrete surface finish

Concrete durability is in part dependent upon the quality of the concrete cover zone. The type of mould release technology used has a direct effect on the surface finish of fair-faced concrete, and this in turn affects long-term durability. This work examined two mould release agents (MRAs), one permeable formwork liner and a type 1 polypropylene fibre concrete combined with a single MRA. Cubes were cast in film-faced plywood moulds using C40 concrete that enabled comparisons to be drawn between the MRAs. The pilot study examined a range of variables for two different reactive MRAs (FS (petroleum based) and CL (vegetable oil based)). The release agents used are commercially available as reactive-based MRAs. In addition, controlled permeability formwork (CPF) and a concrete mix with polypropylene fibre additions were used. The pilot study results showed that the CPF liner produced the least number of blowholes and, in that respect, was the best performing technology used. Consequently, the CPF provided the most likely finish that would provide long-term durability. None of the technologies employed produced a completely uniform colour throughout, but the CL MRA cubes and polypropylene fibre reinforced cubes produced the most consistent colouring. Two of the best performing mould release products (CPF and FS) were then tested using a high-resolution optical measurement system and the initial results were examined in much greater detail, taking account of surface roughness, pore volume and pore size. The CPF proved to produce a better finish than the FS release agent.