Effect of controlled permeability formwork (CPF) on white concrete

This paper reports results of a study comparing the same,white concrete cast with three different types of formworks: controlled permeability formwork (CPF); a high-density five-layer wood-based formwork; and conventional impermeable plywood formwork work (PERI). The CPF system used consisted of impermeable plywood formwork covered with a liner that needs no tensioning, classified ar Type III under a recent Concrete Society/CIRIA report. The research program consisted of carrying out a variety of test methods to assess the performance of concrete such as surface hardness, degree of whiteness, visual assessment of blowholes (blowhole ratio), absorption by capillarity, water permeability, mercury intrusion porosimetry (MIP), accelerated carbonation resistance to chloride penetration, and scanning electron microscopy (SEM). Results of this research program show that using the high-density five-layer wood-based formwork does not seem to be recommendable, as concrete cart with this formwork generally performed less well than the same concrete cast with the conventional formwork. On the contrary, except for the whiteness factor that was slightly reduced CPF seems to dramatically enhance the surface properties of concrete.