The Influence of Controlled Permeability Formwork on the Durability and Transport Properties of Near Surface Concrete


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Title: The Influence of Controlled Permeability Formwork on the Durability and Transport Properties of Near Surface Concrete

Author(s): A. E. Long, A. A. Sha'at, and P. A. M. Basheer

Publication: Special Publication

Volume: 154


Appears on pages(s): 41-54

Keywords: carbonation; chlorides; curing; diffusion; durability; formwork (construction); freeze thaw durability; permeability; tensile strength; Materials Research

Date: 5/1/1995

The durability of reinforced concrete structures can be improved by resorting to methods which insure a better resistance of concrete to various aggressive environments. Some commonly used methods include subjecting concrete to a better curing practice, the use of modified concretes, and the application of surface treatments on concrete surfaces. In addition to these, efforts have been made in the recent past to develop new techniques by which the water- cement ratio in the near surface region can be lowered and a dense matrix achieved. One way of achieving this is to use a controlled permeability formwork system (CPF), in which the surplus mixing water and entrapped air are removed from the fresh concrete via a fiber liner. This produces a surface layer of concrete with a very low permeability which is likely to be highly resistant to various forms of environmental attack. Relatively little information is available at present on the efficiency of CPF in improving the protection of the concrete against various mechanisms of deterioration and on how it compares with other techniques, such as the application of better curing practices. Therefore, an experimental investigation was carried out with three water-cement ratios, five different curing regimes (air curing, wet hessian curing, and the use of three different curing compounds), and the application of a CPF liner system. Measurements of gas permeability, sorptivity, chloride diffusivity, surface tensile strength, freezing and thawing resistance, and carbonation resistance have indicated that the use of CPF can enhance the durability of concrete and that the extent of this improvement is significantly more than that obtained for the various curing regimes. This paper details the experimental program and presents results which are used to evaluate critically the use of CPF for normal concrete.