| Earthen sites are the evidence of ancient human activities,which reflect the comprehensive conditions of people’s daily life and production at that time.It also indirectly reveals the ability of the ancient working people to adapt to nature and change nature.As a special form of architecture,cultural relics and historic sites occupy the extremely high values in terms of art,science,and history,with dual properties of substance and culture.Such complex properties make heritage relics “non-reconstruction”,in other words,once the cultural relics are destroyed,they are impossible to recover.As cultural relics preservation researchers,it is our duty to make these ancient buildings long term preserved as possible with maintain technical and scientific management methods,and also using the new technology to display valuable cultural relics.Weathering is one of the main diseases developed on earthen sites in arid and semi-arid environment of Northwest China.Under the impact of strong sandy wind and heavy rainfall,wind erosion and rain erosion have a great threat to the sites.If we do not take effective measures immediately,these precious cultural relics are likely to disappear permanently in deserts.According to current researches,chemical reinforcement is the main way to solve the problem of weathering,while the core content of chemical protection is to develop anti-weathering materials and scientific conservation technology.For a long time,the lack of anti-weathering materials is a major problem that restricts the development of heritage conservation.Most of the materials only stay in the laboratory testing stage.Only a very small part of products can be applied on the actual protection project,however,it also has the possibility to find that the material is not suitable for strengthening the earthen site many years later.At present,the research on the anti-weathering materials is generally focused on the organic materials.Organic consolidants have the advantages of easy modification,high consolidation strength and good tenacity,however,they also have the disadvantages of poor compatibility and aging resistance.Inorganic consolidants,in spite of their good compatibility and ageing resistance,are generally poor in permeability,weak consolidation effect,and excessive soluble salts.Lime,as a kind of traditional materials,more than one thousand years ago,has been widely used in various types of construction projects.In the early years of the last century,lime water was used to repair stone historical buildings.However,the low concentration of lime water greatly reduces the consolidation effectiveness.It often requires repeated spraying to obtain some degree of effect,and excess water causes some damage to cultural relics.In recent years,the rapid progress of nano technology has greatly promoted the development of materials science,and also provides a new research direction for the development of anti-weathering and strengthening consolidation products in the field of earthen site conservation.Some research groups successfully develop nano size calcium hydroxide materials,which overcome the disadvantages of traditional lime water,such as low concentration and poor permeability,and achieve good results in sculpture,wall paintings and other aspects of protection.Although the nano size calcium hydroxide with good reinforcement effect has attracted great attention in the field of cultural relics protection,but there is no systematic research for the reinforcement of earthen sites.According to the requirements for the appropriate protection,the use of new materials and construction technology must be fully tested,only when the material is proved to be effective and harmless to the long-term preservation of cultural relics,the new material can be put into use.In view of the above understanding,the main research content and results of this paper are summerised as follows:(1)Based on the requirement of in situ testings and laboratory strength testings,a kind of drilling resistance instrument is developed,including the principle of operation designment and data analysis.By testing the penetration resistance value of the soil samples treated by different concentration and different application amount of PS solution,good result of strength change is obtained,and the applicability of this drilling resistance instrument is preliminarily verified.(2)With the reinforcement effect of nano size calcium hydroxide obtained in the stone relics,we purchase some kinds of commercial nano calcium hydroxide reinforcing agents,and do a series of laboratory testings to evaluate the reinforcement effect on the mechanical strength,water resistance and compatibility.The results demonstrate that the concentration of the consolidant agent has a great influence on the reinforcement effect.Furthermore,the present results based on laboratory tests show that a high concentration product(E25-Grey)has a better performance than low concentration products such as E-5 and IP-5 in the aspect of mechanical strength and water resistance ability.All specimens treated with Ca LoSi L? products demonstrate a decrease in permeability and surface colour change to a certain degree compared with the reference group.(3)Based on the method of preparing nano calcium oxide particles from “secondary lime” method,5 groups of calcined temperature(600℃,650℃,700℃,800℃ and 1000℃)are set.The mineral composition and particle morphology of the product are compared by SEM,XRD and other methods.The results show that Ca(OH)2 powders are transformed into a kind of spherical CaO particles with diameter 150~300nm after being calcined at a temperature of 800 oC.Meanwhile,the Ca(OH)2 particle via inverse microemulsion has a smaller size of 30 nm in diameter and 100~150nm in length.The obtained nano calcium oxide powder and nano calcium hydroxide powder are dispersed in ethanol by ultrasonic machine,by adding the surface active agent,the nano calcium products can have a high concentration suspension with stable condition.(4)The soil samples are treated by nano calcium oxide and nano calcium hydroxide consolidants,and commercial calcium oxide is provided as the reference group.The mechanical properties and variation of water resistance after treatment are analysed by unconfined compressive strength,direct shear strength,drilling resistance test and disintegration test.The data of unconfined compressive strength shows that the soil samples which are reinforced by nano CaO consolidant,calcined at 800 oC,and nano Ca(OH)2 consolidant by inverse microemulsion increased by 13.5% and 25.9%,respectively.The cohesion of soil samples reinforced by nano CaO consolidant and nano Ca(OH)2 increases by 69.8% and 97.7% when compared with the unreinforced soil samples.Furthermore,water durability is greatly enhanced after treatment.(5)The consolidation mechanism of nano calcium based materials is studied by the combination of macroscopic and microscopic structure.The test results of soil water characteristic curve show that the pore diameter of the specimen after reinforcement becomes a little larger.The precipitated material is gradually converted to calcareous deposition through carbonation and pozzolanic reaction.The strength of the grain structure in a porous material is given by the cohesion due to mineral bridges,to the adhesive forces across the mineral surfaces and to mechanical interlocking effect of indentation.The cementation of calcareous deposition connected these loose soil particles in a way that greatly improved the mechanical properties and water resistance of samples. |
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