Deterioration Mechanism Of Grey Brick And Masonry Structures Under The Action Of Load And Environment

Chinese historic building is the important component of Chinese civilization, formed a unique building system in the world architectural history, full of ethical spirit, nature, wisdom of the Chinese skillful craftsman. Due to long-term changes in solar radiation, temperature and humidity, chemical action, wind and rain erosion, biological functions, war, earthquake damage, materials and structure performance inevitably of Chinese historic buildings has suffered serious damage. In order to protect the ancient architecture, the requirements for protection are becoming more and more urgent. The destruction of the historic buildings can be divided into two aspects:natural function and human action. From the perspective of building structure, it can be attributed to external factors and internal factors. External factors include the natural role of unexpected events, such as earthquake, hurricane and so on. Internal factors include building materials aging, the influence of the structure of the system, construction quality and building foundation. In order to better protect the historic buildings, the mechanism of its structure and material performance degradation mechanism research has increasingly become a hot spot of research at home and abroad.Therefore, considering the historical, artistic and scientific, the structure of these historical buildings mechanism and performance degradation mechanism for scientific research, which will provide a scientific basis for maintenance and protection.This paper studied lime bonding materials, traditional green bricks and hollow wall in Jiangsu and Anhui area. This paper trailed back systematically the development history and production technology of lime bonding materials and grey bricks by ancient literature search and the field investigation. In order to protect the precious heritage and traditional crafts left by our ancestors, accelerated aging test of materials under the action of coupling mechanics and environment was performed. After that, the life prediction model of architectural heritage materials under multiple damage factors was established, providing a new theory and new methods for the life prediction of architectural heritage. Load-displacement curves of two kinds of hollow wall under out-of-plane load and in-plane load were drawn. According to the flexural strength and shear strength, the building height limits of free masonry walls under the action of earthquake and wind load were calculated. In this paper, the innovative results obtained are as follows:(1) Quality inspection standards of grey bricks and tiles were compiled via field visit and sampling detectionInterpret the development of China’s ancient brick, tile and lime binder through literature retrieval. Record the existing traditional craft handed down by word of mouth via on-the-spot investigation and visiting traditional artist. In order to grasp the physical and chemical properties of ancient brick, tile and lime binder, representative ancient specimens are sampled and test via modern analytical instruments and analysis methods. We investigated South Kiln (Jiashan) and North Kiln (Suzhou), which are famous in producing grey brick and tile in ancient times. At the same time, we visited the famous traditional artists, Ding Weijian and Shen Buyun, recorded the traditional grey brick manufacturing, burn and post-processing technique. Text and image information were stored for protecting traditional artists. To provide improtant basic datas for compiling quality inspection standard of grey bricks. Specimens were sampled from ancient buildings at Jiangsu, Zhejiang and Anhui province. After texting via modern analysis methods, raw materials and physical properties of the specimens were studied. According to a large number of measured data through statistical analysis, the quality standards of grey bricks and tiles were established. These standards provide scientific reference for producing grey bricks and tiles mutching the ancient buildings.(2) Mechanism of good compatibility of lime and grey brick in ancient China was revealedIn this paper, experimental results for the microstructure and properties of lime binder-grey brick interface are presented and discussed. MIP results revealed that the total porosity were 0.42 (IN) and 0.25 (SF), respectively, indicating that SF had a denser microstructure than IN. While X-ray elemental mapping of the sample suggested that a large amount of calcium carbonate could accumulate in the grey brick surface. Line scans shows that the calcium carbonate are propagating from the lime binder surface through the grey brick matrix in a～1.5 mm thick layer. CT technology provides a useful tool to assess the density characteristic in the sample. An obvious increment in gray values of SF can be observed. The finding indicated that the density of SF is greater than that of IN. The micro-hardness at～1500μm (IN) away from the grey brick surface reduced a level of from 1.2GPa to 1.9GPa, whereas it was 1.8GPa to 2.5GPa for the SF. Such behavior of the difference in SF could be attributed to a higher density. XRF and XRD results indicated that the main composition of SF were calcium carbonate and quartz. It can be infered from the chemical composition studies that the calcium carbonate are propagating from the lime binder surface through the grey brick matrix in a～1.5 mm thick layer, resulting in the increase of density and micro-hardness of the SF. For SEM images, we can conclude that the stick-rice may adjust crystal growth process, restrain the crystal degree of calcite, resulting in small crystal products. Furthermore, small crystal products are conducive to the diffusion of calcium carbonate into grey brick, resulting in improving the mechanical interaction between lime binder and grey brick.(3) Damage and deterioration of grey bricks were studied and life prediction figures were drawnThree durability damage factors, freeze-thaw cycle, sodium sulfate corrosion, external compressive stress were selected for durability experiment. Under the effect of single freeze-thaw factor, the relative dynamic modulus of three pieces of samples reduced to 60% after 80 times of freeze-thaw cycle. Load effect accelerated the decline rate of relative dynamic elastic modulus of the samples under the action of freeze-thaw cycle. The relative dynamic modulus of three pieces of samples reduced to 60% under the action of 60 times of freeze-thaw cycle with 10% load. The relative dynamic modulus of three pieces of samples reduced to 60% under the action of 60 times of freeze-thaw cycle with 30% load. Load and the coupling effect of sodium sulfate have more obvious influence on their relative dynamic elastic modulus. Under the action of 10% load & 5wt% sodium sulfate solution and 30% load & 5wt% sodium sulfate solution, the relative dynamic modulus of samples reduced to 60% after 35 and 20 times of freeze-thaw cycle, respectively. The expected life was calculated by analyzing freeze-thaw fatigue damage equation model according to the obtained data. Freeze-thaw service life zoning maps were drawn via using TopMap7.(4) Mechanics performance of hollow wall were studied using loading device designed by self designA large loading device for hollow wall mechanics performance was designed and built, which can carry out the maximum size of hollow wall is 4 m×4 m. The out-of-plane and in-plane mechanical properties of two kinds of hollow wall and one kind of solid wall were analyzed; mainly study the properites of their ultimate bearing capacity and deformation at the action of masonry ways, depth-width ratios and width-to-thickness ratios. Some conclusions got from the relevant experimental study and theoretical analysises are as follows: The damage form of hollow wall is flexural failure; Out-of-plane stress controls the height limit of hollow wall; Wind bracing support structure was suggested to protect hollow wall; At last, the height limits of free masonry hollow walls were calculated.