This report describes an investigation and assessment of the four main types of permanent formwork. Steel formwork and `Omnia' precast concrete planks were load tested in the 1970s at Imperial College; glass reinforced cement (GRC) and glass reinforced plastic (GRP) panels were load tested at TRRL in the 1980s. All types were inspected on bridges built around 10 to 20 years ago. The results of these investigations suggest that profiled steel permanent formwork is generally strong and durable but is susceptible to corrosion at cut edges. Panels with shear connectors indented in the troughs are not recommended. Loading tests on `Omnia' planks generally gave satisfactory results though some fatigue failures of the welded lattic occurred. Cracks were observed in the `Omnia' planks on some of the bridges inspected. The reason for this cracking is unclear and further investiation is recommended. GRP formwork performed well in laboratory fatigue tests but modifications to the manufacturing process are needed to ensure the corrosion protection of the steel reinforcement in the panels. Single skin GRC formwork panels are considered to be safe to use but problems inherent in multi-skinned panel designs have proved difficult to correct. Hence the use of multi-skinned GRC formwork is not recommended.
Abstract