Study On Organic Modification Of Ethyl Silicate In Weathering Layer Of Earthen Sites

Ethyl silicate has been widely studied and applied in the field of cultural relic building weathering layer reinforcement due to its superior permeability.However,as a lasting and effective surface protection material for cultural relics,the durability of ethyl silicate still needs to be further optimized and improved.In this study,ethyl silicate(TEOS)was modified by adding silicone modifiers(n-octyltriethoxysilane(OTES)and polymethylhydrosiloxane(PMHS)with different mass ratios(5%,10%,15 %,20%,25%).The results showed that TEOS modified by two silicone modifiers could obviously improve the basic properties and durability of soil.Good appearance compatibility could be obtained when the modifier content is less than 20%;when the addition amount of modifier was 15%,the maximum growth rates of compressive strength could reach 156% and 180%;the maximum decrease rate of hygroscopicity is about 90%;The contact angle between water droplets and soil increased with the increase of modifier content and was between42 °-80° and 121 °-131°,respectively.The modified reinforcement samples did not collapse after 15 days of water resistance and salt resistance immersion test,and the modified reinforcement samples with high addition amount remained intact after 10 wetting-drying and freezing-thawing cycles.In order to further improve the permeability of modified TEOS,this paper explored the effects of different mass ratios of Et OH(5%,10%,15%,20%,25%)+TEOS system and OTES,PMHS modified Et OH-TEOS system on TEOS permeability rate,soil mechanical properties and durability.The results showed that Et OH improved the permeation rate of TEOS up to 73% in different proportions of Et OH-TEOS system.When the content of Et OH was more than 15%,the cracking phenomenon could be obviously observed in the reinforced soil,and the compressive strength loss rate could reach 9%.At the same time,a large area of soil collapse occurred after two dry-wet or freeze-thaw cycles.The protective effect of Et OH(15%)+TEOS system modified by 15% OTES and PMHS on soil was equivalent to that of OTES(15%)+TEOS and PMHS(15%)+TEOS,and the presence of Et OH could further improve the permeability of single silicone modification.The improvement of soil properties was mainly attributed to the following three points:(1)The existence of Et OH mainly acted as a solvent to improve the permeability of reinforcement materials;(2)OTES,PMHS and TEOS could play the role of filling pores and connecting soil particles by hydrolysis and solidification,and the hydrolysis and solidification was the most sufficient when the addition of silicone modifier was 15%.(3)Both OTES and PMHS had good durability due to the hydrophobic groups in the structure.For the best modified TEOS ratio(15% PMHS+15% Et OH+70%TEOS),the applicable conditions of soil moisture content(0%,5%,10%,15%)and curing temperature(20 °C,40 °C,60 °C,80 °C)were explored and the durability was evaluated.It was found that a strong hydrophobic protective layer could be formed on the surface of the specimen after reinforcement and protection(contact angle was 106 °-132 °);the soil with moisture content of10% and below had strong rain erosion resistance and dry-wet cycle resistance,and the calcium sulfate coating formed on the surface could form a certain protective effect.The increase of curing temperature under the same moisture content was more conducive to the improvement of soil strength.This study concluded that under the condition of soil moisture content less than 10% and relatively high curing temperature(summer climate),this reinforcement material could obtain the best protection effect.At the same time,the best modified TEOS formula obtained in this study could provide certain reference and corresponding technical support for the reinforcement and repair of weathering layers of other similar soil,stone and brick sites.