Since the early 1990s there has been a requirement to utilise hydrophobic pore-lining impregnants to provide additional durability on Highways Agency structures subjected to aggressive conditions – primarily arising from the use of de-icing salts. The material that has generally been used as an impregnant is monomeric alkyl (isobutyl) – trialkoxy silane. More recently alternative materials have come onto the market and the Highways Agency (HA) has updated its requirements to include new test methods to assess the effectiveness and performance of pore-lining impregnants. The purpose of these tests is to facilitate the acceptance of these alternative materials.
A series of experiments was undertaken to assess the effectiveness of available impregnants for suppressing the ingress of chloride ions into concrete and their long term effectiveness in service. Laboratory tests demonstrated that the ingress of chloride ions by ponding and water uptake by sorptivity was significantly reduced by treatment with the pore-lining impregnants. By contrast, pore-blockers provided only very limited resistance to chloride ingress and virtually no resistance to water uptake. A limited number of tests were also undertaken on cores extracted from bridges.

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