Research And Application Of Shrinkage Performance Of Natural Hydraulic Lime Grout Used In The Heritage Conservation

There are numerous brick and stone cultural relic buildings on the vast Chinese land that carry a wealth of precious cultural and historical information.They have been subject to the erosion of the natural environment and man-made destruction,which caused a variety of diseases and problems that need to be repair scientifically and effectively.As a very effective reinforcement method,grouting is widely used in geotechnical engineering.The cementitious grouts are the most applied materials because it's good grouting and bonding properties as we all known.But its strength is too high and contains a large amount of soluble salts,which is not suitable for the restoration of brick and stone cultural relics.Therefore,the development of new cultural relics to repair grouting materials has always been a hot topic in the field of cultural relic protection.Natural hydraulic lime is a kind of lime material with hydraulic characteristics.In recent years,it has gradually attracted the attention of cultural relics protectors because it has good compatibility and mechanical strength.It is often used as a grouting adhesive material for cultural heritage buildings to reinforce the structural parts.However,with the increasing of frequency,the shrinkage problem of lime based grouting material itself is becoming increasingly prominent,which seriously affects the quality of grouting reinforcement.Therefore,it is necessary to conduct research on the shrinkage of natural hydraulic lime grouting materials and find appropriate solutions to provide certain guidance for the correct use of natural hydraulic lime in the protection of cultural relics buildings in China.In this paper,in order to solve the problems such as large shrinkage and unsatisfactory bonding effect of the existing natural hydraulic lime grouting materials,a combination of indoor experiment,outdoor simulation and field test was used to explore the shrinkage characteristics of natural hydraulic lime grouting material,and then prepare a natural hydraulic lime grouting material with good performance.The main research contents and research results of the paper are as follows:(1)Study the influencing factors of shrinkage of natural hydraulic lime grouting material.Starting with the composition of natural hydraulic lime grouting materials,the effects of types of natural hydraulic lime,types and amounts of aggregates,active materials,water-reducing agents,and curing conditions on the shrinkage of natural hydraulic lime grouting materials were studied through experiments.law.The results show that when preserving the fluidity of the grouting material,adding calcium powder or quartz sand and appropriate water reducing agent can effectively reduce the shrinkage rate of the natural hydraulic lime grouting material.A small amount of active material has little effect on the shrinkage of the grouting material,but the excessive amount of the materials significantly increases the shrinkage.Water-reducing agent can reduce the water-cement ratio of the grouting material,thereby reducing the shrinkage rate of the stone body.The curing conditions mainly affect the rate of contraction and deformation of stones in the grouting material and have little effect on the final shrinkage.Increasing the temperature or reducing the humidity will cause the shrinkage deformation to accelerate.In addition,the shrinkage properties of grouting materials prepared from different types of natural hydraulic lime are basically equivalent.(2)To study the effect of expansion agent on the shrinkage of natural hydraulic lime grouting material.A certain amount of UEA expansive agent,calcium oxide expansive agent,magnesium oxide expansive agent,and plastic expansive agent were respectively mixed into the natural hydraulic lime grouting material to detect the change trend of the sample shrinkage rate during the curing period of 28 days.The results showed that except for the calcium oxide expansion agent,the remaining three expansion agents are not suitable for use in the natural hydraulic lime grouting material at the present stage.(3)Preparation of natural hydraulic lime grouting material with excellent comprehensive performance.Orthogonal test method was adopted to consider the fluidity,compressive and flexural strength,capillary water absorption coefficient and 28-day shrinkage rate of natural hydraulic lime grouting material.The optimal formula for the natural hydraulic lime grouting material in the present stage was: 53% of NHL2,30% of heavy calcium powder,6% of metakaolin,1.5% of wood fiber,9% of expansive agent and 0.5% of water reducer.(4)Wall grouting simulation test and field engineering application of the natural hydraulic lime grouting material formulated with the best formula.The results show that the natural hydraulic lime grouting material expansion and contraction performance is also related to the nature of the reinforcement of the body material,the better the water absorption of the substrate,the more easily the grouting material stone body shows the expansion.(5)In addition,after disassembling the grouting simulation test wall to observe changes in the interior of the wall,the results show that the natural hydraulic lime grouting material prepared in this experiment has good diffusion performance,and can be closely integrated with the masonry clay,thus effectively improving the strength and durability of bulk materials have important application value.