Investigation Of The Chemical Characteristics And Bonding Mechanism Of Chinese Traditional Lime Mortars

Lime mortar,which is composed of binding materials lime,aggregate,water and additives by proportionally,is mainly used in the construction of masonry,pointing rendering and beautifying.Conventionally,mortars used before the invention of Portland cement in the end of the 19th century are termed ancient,historical or traditional mortars.And then,the traditional lime mortar is referred to the mortar using slaked lime as adhesive in history.Lime mortar,which is employed till now in some areas all over the world,originated in the middle Neolithic age(5000a BP)in China according to many archaeological discoveries.The Chinese traditional lime mortar reached its culmination during the mid-19th century,especially the organic-inorganic lime mortars,playing a very important role on the preservation of ancient buildings.However,the understanding of the details of the Chinese traditional mortars,especially lime mortar during the Ming and Qing dynasties(1368-1911 AD),is still limited and rarely reported in the literature.The paper summarized the component of traditional lime mortar,the study progress of lime mortar in the domestic and foreign,as well as the major traditional organic-inorganic lime mortars in ancient China.In the present work,we investigate lots of ancient buildings in situ,and subsequent laboratory analysis and characterizations were performed on those collected mortar samples.The following are the main points:The rammed lime earth from the Zhengzhou Shang city was studied.The research suggests that:The rammed lime earth is made of binding material calcium carbonate and aggregate material sand.The binding/aggregate ratio is 1:2.68.These results show that the rammed earth were constructed based on artificial formula.The rammed lime earth is a tabia composed of calcium carbonate and quartz.The B/A ration near the optimal ration of tabia(lime/earth/sand 1:1:1).This is to say,craftsmen of the Shang Dynasty have rich experience on rammed earth and architectural technology.The traditional lime mortars from Zhejiang Province were studied.The experimental results showed that:the main component of masonry mortars is calcium carbonate,and they were made by pure lime mortar.The raw materials of mortar samples were mainly calcareous quick lime,and sample from Taizhou city also contained magnesium quick lime.There are four city walls were built by sticky-rice mortars.It suggests that the technology of adding the sticky rice soup into mortar was universal in the Ming Dynasties.We have also analyzed other chemical and physical characteristics of these masonry mortars.The results can afford the basic data for the future repairmen programs,development of new protective materials,and comparative study of mortars.The traditional masonry mortars from ancient city wall built during Ming and Qing dynasties were studied.The analytical results show that pure lime mortar was widely used in construction during the Ming and Qing dynasties,and it was also a common practice adding sticky rice soup into slaked lime to form sticky-rice lime mortar during preparations.This organic-inorganic composite material could effectively improve mechanical strength of the lime mortar.Moreover,it was firstly found that the sticky-rice lime mortar sample from Kaifeng ancient city wall contained very fine quartz aggregates,with an approximate binder/aggregate ratio of 1:1.The appearance of this type of mortar probably indicates a great development of Chinese traditional mortars during the mid-19th century.The binding mechanism within the brick-lime mortar composite structure from Kaifeng ancient wall was studied.The analytical results showed that a transitional zone was formed due to the gradual penetration of slaked lime putty into the bricks via capillary action and/or stresses.After the curing process of the lime within the brick,the mortar was tightly bonded to the brick to form a mechanical inter-locking structure.Meanwhile,the pozzolanic reaction happened between the amorphous alumniosilicates and the slaked lime putty to form hydraulic substances in the transitional zone,which in turn could yield a higher binding strength and thus improve the stability of the masonry structures.