Improvements Of Anti-freezing Performance Of Concrete By Hydrophobic Treatments

Air entraining agent can greatly improve the frost resistance of concrete,however,the use of air entraining agent will reduce concrete strength.In the northern regions of China,ordinary concrete is still widely utilized in most concrete road and bridge members.It is an urgent task to study how to improve the frost resistance of normal concrete against salt freezing and normal freezing performance,and to reduce concrete frost damages further.In this paper,by applying different silicone hydrophobic agents on ordinary concrete with different water-cement ratios,the improvements of anti-freezing performances of concrete were studied.Experiments of concrete water absorption,contact angle,accelerated freezing and thawing cycle in 5%MgCl₂ solution and tap water,and normal slow freezing and thawing cycle experiments were also conducted.The relationships between the concrete mass loss ratio,relative dynamic modulus of elasticity,water absorption and contact angle were studied,and it was found:the water absorption of silicone hydrophobic agent treated concrete decreased significantly,and the contact angles were mostly higher than 90°;The surface denudation of the hydrophobic agent treated concrete after salt and tap water freezing-thawing cycles decreased,however,the relative dynamic elastic modulus of concrete changed little.In addition,some conclusions are obtained as follow:1)After hydrophobic treatment,the surface wetting edge angle of concrete increases,and the water absorption rate decreases.The wetting edge angle of the concrete varies with the water repellents.2)The hydrophobic treatment has obvious improvement on the anti-salt performance of concrete,but the effect on ordinary freeze-thaw is not significant.3)Compared the quick-freezing test,the surface of the slow-frozen test concrete specimens is lighter denuded in the same freeze-thaw cycles,which is much smaller than that of quick-freezing test.4)The frost resistance of air-entrained concrete is much higher than that of ordinary concrete.After the air-entrained concrete is treated by water repellent,the concrete surface is denuded less than the concrete without hydrophobic treatment.However,when the surface of concrete is dented more than the depth of penetration of the with the increasing of freeze-thaw cycles,the hydrophobic agent loses its effect silicone,and the denudation rate of concrete with hydrophobic treatment may be higher than that of the concrete without hydrophobic treatment.