Influences Of TEOS Surface-treatment Agent On The Properties Of Cement-based Materials

Concrete is one kind of material that always used in construction industry.However,concrete is permeability because of being porous.So the Invasion of water,harmful ion and gas may lead to poor durability and short lifetime.The corrosion of concrete results in enormous economic loss and resource waste.And it has been a hot research that the effective methods to Improve the durability and service life of concrete.Harmful substance invades from outside,so it is a kind of research thinking to improve compactness of concrete surface.Nano-silica(CNS)is widely used in cement-based materials because of its excellent pozzolanic activity and nanoparticle characteristics.Some researchers put forward that brushing nano-silica sol or its precursor tetraethyl orthosilicate(TEOS)on surface of cement-based materials can fill the clearance and improve integrality.TEOS is precursor of CNS,which produces silicon by hydrolysis.The silicon can react with hydration products of cement-calcium hydroxide to produce C-S-H to improve surface density.TEOS is a kind of colourless liquid and easy for surface imprednation and chemical reaction,because of its monomer structure and low consistence.This thesis studied on TEOS surface-treatment agent for cement-based materials,which included mix proportion,impregnation process and performance influence on cement-based materials.First of all,this thesis studied on mix proportion and impregnation process of TEOS surface-treatment agent.This thesis researched decreasing effect of mortar surface water absorption rate of 7 kinds of mix proportion,9 kinds of impregnation process and impregnation time.Then it researched the effect on cement-based materials carbonation resistance and salt frost resistance by 3 kinds of mix proportion.Finally,this thesis used water vapor transmission test to research the effect of TEOS surface-treatment agent on cement paste moisture permeability by 2 kinds of water cement ratio.This thesis also used microhardness test and SEM test to research the difference of hardness,morphology and calcium-silicate ratio between ordinary mortar and TEOS surface-treatment agent dealt mortar,in order to explore micromechanism of TEOS surface-treatment agent.The results show that:several kinds of TEOS surface-treatment agent leads reduction of surface water absorption rate of mortar to 30%-70%.When the ratio of ethyl alcohol,water and TEOS is 4/1/3,the decreasing effect is optimum,which reaches 73%.TEOS surface-treatment agent brushing times has great influence on mortar surface water absorption rate.And the more times TEOS surface-treatment agent brushed,the more reduction of mortar surface water absorption rate.The dosage of every time has little influence on mortar surface water absorption rate.The surface sealed curing after brushing TEOS surface-treatment agent has positive effect on mortar surface water absorption rate,which is optimum when sealed curing time reaches 6h.But mortar surface water absorption rate reduces beyond 6h.All 3 kinds of TEOS surface-treatment agent can improve carbonation resistance and salt frost resistance.The optimum decreased ratio of carbonation depth reaches 60%,and the optimum decreased ratio of salt frost quality loss reached 80%.TEOS surface-treatment agent can improve surface hardness of mortar.The results of microhardness test and carbonization test show that effective depth of TEOS surface-treatment agent is 1-2mm.TEOS agent can also reduce the moisture permeability of cement paste,and moisture permeability reducing rate for cement paste with water cement ratio being 0.4 reaches 60.5%.The results of SEM test show that the part of mortar dealt with TEOS surface-treatment agent has fewer hole and calcium-silicate ratio.It is just because TEOS surface-treatment agent can react to produce C-S-H to fill pore and improve surface density.