INTERPRETATION OF HYDROPHOBICITY IN CONCRETE BY IMPREGNATION

The durability of reinforced concrete structures is greatly affected by corrosion of steel reinforcement through chloride attack. The use of impregnates is the most widely employed method to tackle chloride attack for structures in the UK. Impregnate manufacturers and DMRB standards stresses the use of impregnates on dry surfaces, achieving a dry surface is easy however moisture below the surface exists and this can affect the performance of the impregnates. The Concrete cubes were cast and cured, before being submerged in a water bath to determine their moisture content at various times. The cubes were surface dried, water and silane based impregnates were applied and then submerged in salt solution. The cubes were dry drilled at various depths of 5-20 mm for dust samples, which were used to obtain chloride concentrations by the method of Volhards titration. The performance of impregnates is dependent on the quality of concrete, as it directly influences the pore structure which in turn determines the rate of chloride ingress. Impregnate application on dry surface showed a chloride concentration of 0.029% at 20 mm. However impregnates applied to a dry surface, but with a moisture content of 1.88% showed a chloride concentration of 0.053%. This indicates the performance of impregnates is effected by moisture. Although solvent based impregnate performed better than the water based in dry condition, their performance are similar when applied in the moist concrete.