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.