The Research Of Modification On The Replacement Of Mortar To Reinforce The Gulangyu Historical Buildings

According to incomplete statistics,there are nearly a thousand historical buildings on Gulangyu Island.Along with the success of application for Intangible Cultural Heritage,the protection and utilization of these historical buildings have received more and more attention.About one-quarter of the buildings in the current situation are worrying,especially the problem of wall damage is the most common,and the impact on the building’s appearance is also the most intuitive.Through field investigation and sampling analysis,it is found that the historical buildings of Gulangyu are mostly built with lime-based mortar,most of which are lime-clay mixed mortar,and a small part are lime mortar.Cracking,moldy blackness,water seepage and weathering are now common and other serious degradation phenomena.To the end,our team proposed the technology of mortar replacement to reinforce historical buildings’repairment and protection.Lime is one of the earliest inorganic gelling materials used by mankind.It has good compatibility with masonry,will not cause secondary damage to historical buildings,and has the irreplaceable advantages of other materials in the field of historical building repair.Lime mortar and masonry can be well matched,which not only avoids the problems of easy ageing and short service life of organic repair materials such as polymer grouting,grouting and polymer mortar,but also avoids the use of cement-based mortar for solving the problem of obvious color difference and high strength caused by the time is poor,and the match between the two types of mortar and masonry is poor.Limestone is usually used to burn lime in inland areas of China,and in the southeast coastal areas of Fujian,oyster shells are used everywhere to burn lime(referred to as shell ash).Adhering to the protection principle of "raw materials,original processes and minimal intervention",it is a wise choice to use mortar made by the shell ash as a replacement mortar when restoring buildings with a history of over one hundred years in Gulangyu.However,all the common problems of lime-based mortar with traditional shell mortar:slow coagulation and hardening,low hardening strength,especially low early strength,large shrinkage and deformation and resistance to water.Obviously,the traditional shell mortar cannot meet the requirements of rapid strengthening.So scientific methods are needed to improve its performance defects.This article uses traditional materials of clay,glutinous rice,fiber and so on,and silico-aluminum active materials to modify the shell gray mortar.Finally,by introducing two kinds of silico-aluminum modified materials,the gas-hard shell ash was successfully transformed into both modified shell ash with hydraulic and gas hardening properties,the modification effect is remarkable.Based on this,a series of investigations have been made on the mix design,performance indicators and micro-mechanism of the modified shell ash mortar,and the modified shell ash mortar has been used in the building repair and repair work of No.99 Lujiao Road,Gulangyu,Xiamen.It achieved good results.Through the above research and engineering applications,the following results have been obtained:1.Based on field investigations,four typical historical buildings on Gulangyu Island(around and in the middle of the island)were selected as representative.The composition and microstructure of the existing mortar were sampled and analyzed to evaluate the weathering degree of the existing mortar.The results show that most of the mortar of the buildings is mixed with lime-clay,and a small part is lime mortar.The building has suffered from sea breeze,salt mist erosion and high temperature,high humidity,and dry and wet damage for many years,resulting in severe weathering;2.The simulation test research of the traditional shell ash mortar was carried out,and the results confirmed that the hardened shell ash mortar only contains two crystalline components of calcium carbonate and calcium hydroxide,without any hydraulic components,and its microstructure is loose and porous,resulting in the very low strength of the mortar,the compressive strength at 28d is even less than 0.5 MPa;3.Clay,glutinous rice,fiber and other traditional materials were used to modify the shell ash mortar.The results show that when the traditional modified materials are added to the shell ash mortar,the compressive strength and elastic modulus of the mortar have been improved,but they are very limited.The 28d compressive strength of the optimized group in the three modification schemes is only 1.0 MPa,can not meet the requirements of masonry reinforcement and repair;4.Two kinds of silica-aluminum active materials were used to modify the shell ash mortar.The results show that compounding two silica-aluminum active materials in the shell ash mortar can not only significantly improve the strength and adhesion,especially the early strength,but also significantly improve the weather resistance and elastic modulus.Increased,shrinkage deformation reduced,anti-deformation ability enhanced.The modified shell ash mortar has both gas and hydraulic properties,which essentially changes the gas rigid properties of the shell ash mortar;5.Based on the consideration of the two processes of manual replacement and mechanical replacement,the hand-made,mechanical properties,weather resistance and volume stability of the modified shell ash mortar with different density.According to the requirements of different strength grades of the mortar,the artificial formulation scheme and preparation method of replacement modified shell ash mortar GM and mechanical replacement modified shell ash mortar SM;6.Use SM for small masonry structures with a size of 180mm × 240mm ×365mm.By testing the shear strength of the 28d masonry along the cross-section,completing the feasibility of replacing and strengthening the modified shell ash mortar in the masonry structure.The test shows that the adhesion of SM to the brick surface is good and meets the "reversibility" requirements of repair mortar.The 28d shear strength is increased by 649.86%compared with pure shell gray mortar,and the modification effect is significant;7.The SM mortar was applied to the reinforcement of the wall of the house which in Gulangyu Island.The compressive strength of the mortar between the brick joints was tested to complete the engineering evaluation of the modified shell ash mortar.On-site inspection shows that the use of modified shell ash mortar to replace the existing degraded mortar,the construction is convenient and fast,the gray joints are full,and there is no obvious color difference.The compressive strength of the replacement mortar is increased by nearly 11 times,and the effect of reinforcement and reinforcement is obvious.Worthy of promotion of historical building reinforcement and repair technology.