The effects of permeable formwork on the surface properties of concrete

The surface properties of concretes cast in both conventional (impermeable) formwork and in permeable formwork have been compared. The effect of subsequent curing after stripping the formwork has also been examined. Three grades of concrete (C20, C30 and C50) have been tested. The laboratory test programme has demonstrated that the use of permeable formwork reduces surface absorption, water permeability and chloride diffusion, while increasing surface hardness. The incidence of blowholes on the formed surfaces is greatly reduced even for high–strength concrete. Results from both laboratory and site trials show a reduced carbonation depth for concrete cast in permeable formwork. A reduction in the near surface water/cement ratio can also be demonstrated. The overall conclusion drawn from this work is that the surface properties of concrete can be considerably improved by the use of permeable formwork. A similar performance may be expected from a grade C30 concrete cast in permeable formwork relative to a grade C50 concrete cast in conventional formwork.