Investigations into the Water Repellent Surface Near Layer in Concrete by Neutron Radiography

By impregnation of concrete with a water repellent compound such as silane, a water repellent surface layer can be established. Due to this surface impregnation capillary absorption of water and aqueous salt solutions can be significantly reduced. The aim of this protective surface treatment is in many cases to obtain better frost resistance and to reduce chloride penetration. Water vapor can still transgress the impregnated layer in and out of concrete. In the contribution experimental results to visualize the width and the water content within the water repellent surface layer are described. The water distribution was determined quantitatively by neutron radiography. The results obtained allow to explain earlier findings, which indicated that an efficient chloride barrier can be established by deep impregnation only. In a water repellent layer with a thickness lower than 6 mm there remains enough water which allows reduced migration of chloride into the pore space of the material. The requirements of published recommendations are herewith supported and justified. (A)