Research On The Deterioration Characteristics And Mechanism Of Brick Buildings Facades In Lanzhou

The wuquan Mountain complex,The White Tower Mountain complex and the Three Taige buildings in Lanzhou bear witness to the development of Lanzhou,which are of great historical,social,cultural,artistic and scientific value.Under the influence of long-term natural forces and human activities,different types and degrees of diseases occurred on the facades of these three buildings.Based on the study on the deterioration of the brick building facade in the arid and semi-arid environment of Lanzhou,a set of disease investigation-degradation mechanism research and degradation evaluation system was established to provide theoretical basis and technical support for the protection and restoration of the brick building facade in Lanzhou.This paper takes the wuquan Mountain complex,the White Tower Mountain complex and the Santai Pavilion as the research objects,through field investigation,find out the brick building facade types and distribution characteristics of these diseases,and to establish its occurrence,the connection between the environment and damage distribution on this basis,through the indoor experiment study,reveals the deteriorating law of the soluble salt of blue bricks,the microstructure and mineral composition analysis and other research methods,reveals the degradation mechanism of blue bricks,soluble salt in the end,combining with the test results,based on grey correlation method of degradation of comprehensive evaluation system.There are mainly the following cognition:（1）Throughing the accurate investigation,the development of the disease t-ypes in the study area have crack,partial loss,surface weathering,disruption a-nd salt efflorescence,powering,delamination,damage by animal,damage by lo-wer plant,calciumcarbonate deposit.Disruption and salt efflorescence is the m-ost developed and most influential diseases in the study area.There were diffe-rences in the development of diseases on the facade of brick buildings in 3 d-ifferent environments.（2）Through indoor simulated accelerated degradation test,the sample appearance,quality,wave velocity,surface hardness,compressive strength of the five indicators of change research samples in different concentrations,different types of the deteriorating law of the salt solution under the action of dry-wet circulation,the experimental results showed that the concentration of 8%under the action of SO₄^2-after 30 times the largest variations in the indicators of samples after the dry-wet circulation,the most obvious degradation degree and the second is the compound chlorine salt-sulfate salt,Cl^-minimal degradation effect on sample.（3）The degradation mechanism of blue brick was studied by analyzing the changes of its chemical composition and internal microstructure.According to the analysis of mineral composition,the content of quartz and clay minerals in blue brick samples before and after the wet and dry cycle with the participation of sodium sulfate increased,while the content of feldspar decreased.The effect of sodium chloride on the mineral composition of blue brick was negligible.From microscopic structure analysis,the blue brick flies in the role of 8%SO₄^2-after 30 times of the dry-wet circulation after the porosity is 70.74%,compared with the initial state porosity increased by 25.36%,the blue brick flies in the internal pore greaten due to feldspar alteration,secondary fracture,provide channels for soluble salt migration,soluble salt crystallization in the pore is the main reason for the blue brick flies in the degradation.（4）Entropy method was used to modify the weight obtained by AHP,and grey relational theory was used to evaluate the deterioration degree of the sample.According to the value range of correlation degree,the deterioration degree is divided into five grades:excellent(0.85,1],good(0.7,0.85],general(0.6,0.7],poor(0.45,0.6]and poor[0,0.45].