Preparation And Performance Optimization Of Beijing Ming Dynasty Great Wall Mortar

The Great Wall is a world cultural heritage,but there is relatively little research on the Ming dynasty Great Wall mortar in Beijing,problems such as unstable material properties,lack of corresponding standard requirements in preparation process and mortar ratio limit the standardized use of lime mortar in renovation projects.Based on the above problems,the microstructures of the Ming dynasty great wall mortar samples from different regions and parts were analyzed by XRF,XRD,TG,SEM,FTIR and MIP;The effects of origin and aging mode on the composition,microstructure and macro-properties of lime were discussed;Finally,the effects of cellulose ether,metakaolin and silica fume on the macro-properties,micro-structure and durability of traditional waxy rice mortar were investigated.The main conclusions are as follows:The mortar from different parts of the Great Wall in Dazhuang section of Yanqing and Jiankou section of Huairou were compared and analyzed.The results show that the composition of the Great Wall masonry mortar in Yanqing and Huairou areas is quite different.The content of Mg,Si and organic matter in Huairou mortar is much higher than that in Yanqing mortar.This is because Huairou mortar stone material may contain more magnesite,and Huairou masonry mortar contains a small amount of sand.The masonry mortars in both places contain glutinous rice,which result in a smaller crystal grain size of CaCO₃ and a denser structure.There are also differences in the composition of mortar for different parts in the same area.The grouting mortar is quite different from other types of mortar,and contains more sand and stones.And the stone joint masonry mortar contains a small amount of fine sand.The pavement masonry mortar is not fully carbonized,and contains a small amount of Mg（OH）₂ and Ca（OH）₂.The presence of glutinous rice is detected in brick masonry,jointing,and pavement masonry mortar,but no glutinous rice is detected in grouting and stone joint mortar.The effects of origin and aging on the composition,microstructure and macro-properties of lime were studied.The results show that the contents of Ca and Mg in lime vary with different producing areas.During the aging process of lime,the aging mode,origin and aging time all affect the grain size and crystal structure of calcium hydroxide,and the grain size of calcium hydroxide decreases with the aging time.The immersion aging method is better than sealed aging and natural aging;for the lime produced in Nanshilou area,the lime prepared by immersion aging has smaller grain size,higher activity and higher content of calcium hydroxide.after forming,hardening and curing,it can form a denser microstructure and have better mechanical properties.The effects of cellulose ether,metakaolin and silica fume on the composition,microstructure,macro-properties and durability of traditional sticky rice-lime mortar were studied.The results showed that the addition of cellulose ether,metakaolin and silica fume improved the mechanical properties,shrinkage properties and freeze-thaw resistance of sticky rice-lime mortar to a certain extent.Cellulose ether stores a certain amount of free water in the early hardening process of sticky rice-lime mortar,and plays a role of"internal curing"inside,improving the carbonization degree of sticky rice-lime mortar at the same age,and making its structure more compact.Metakaolin and silica fume generate hydrated calcium silicate（C-S-H）through pozzolanic reaction,fill some pores,and significantly improve the mechanical properties and freeze-thaw resistance of sticky rice-lime mortar.