Specifying concrete for chloride environments using controlled permeability formwork

The paper describes a study carried out to explore how controlled permeability formwork (CPF) can be used within existing concrete durability specifications (mix limitations) for chloride environments. Tests were carried out to consider (i) chloride diffusion rates and, under wetting and drying conditions, (ii) rates of chloride contamination build up at cover depth and (iii) reinforcement corrosion. The effects of CPF were measured against design strength, cover depth and cement type of concrete cast against plywood formwork (impermeable formwork - IMF). The use of CPF liner on formwork was found to significantly enhance chloride and corrosion resistance of concrete. Moreover, the results demonstrated that CPF could be used within the BS 5328 durability framework for chloride environments to allow either a 20 mm cover reduction (50 to 30 mm) at fixed design strength (40 N/mm²), or a reduction in design strength of 10 N/mm² (50 to 40 N/mm²) at fixed cover depth (30 mm). It was additionally found for Portland cement (PC) concrete that the use of CPF gave equivalent performance to concretes containing PFA and GGBS as constituents of cement and a ternary cement comprising both materials, cast against plywood formwork. This suggests that the 'trade offs' within BS 8500 for PC/PFA and PC/GGBS cements in chloride environments, could also be permitted for CPF concrete containing PC.