INTEGRAL WATER REPELLENT CONCRETE BY ADDITION OF SILANE EMULSION

摘要

Surface impregnation with water repellent agents such as silane gel is a reliable and advanced technology to protect concrete from ingress of aggressive solutions into the porous structure. An alternative method is to add silane emulsion to the fresh concrete in order to produce integral water repellent concrete. In this contribution, concretes containing different amounts (2 %, 3 %, 4 % and 6 %, related to the weight of cement) of silane emulsion have been prepared. Finally the mechanical properties, water capillary suction, siloxane distribution and chloride penetration of integral water repellent concrete are compared with properties of plain concrete. It has been found that addition of silane emulsion retards the hydration of cement and results in decrease of compressive strength and bending strength of concrete. A high percentage of silane migrates with the escaping water towards the exposed surface and forms a siloxane network there. Capillary suction of integral water repellent concrete is then significantly reduced by approximately 90 % compared with the neat concrete. If the dosage is higher than 3 % the additional silane emulsion will not reduce water absorption further. Chloride penetration is also reduced greatly by addition of silane emulsion, while it does not make more sense to add more than 4 %. Considering the influences of silane emulsion on all the properties studied in this project, it is proposed that the optimum amount to add in the fresh concrete is 2 % ～ 3 % related to the weight of cement. In this way the use of integral water repellent concrete can be considered to be a valid alternative.