Analysis On Deterioration Law Of Coated Reinforced Magnesium Oxychloride Cement Concrete In Salt Lake Environment Of Western China

The soil in the salt lakes and saline soil areas in the Western China contains a lot of chloride,sulfate,carbonate and other salts that adversely affect the durability of concrete,making ordinary reinforced concrete buildings not suitable for this area,and usually damaged far earlier than the design life.The magnesium oxychloride cement concrete(MOCC),as a kind of magnesium cementing system concrete,has good applicability in this area without modification.However,the corrosion of steel bars in MOCC limits its application.In order to solve this problem,it is proposed to use coating to protect the steel bar from corrosion.In the western region,the temperature difference between day and night is large,the wind and sand are large,and the ultraviolet rays is strong.Therefore,it is necessary to consider the influence of external environment on the working performance of coated reinforced magnesium oxychloride cement concrete(CRMOCC)while preventing steel corrosion.In this dissertation,according to the environment of western salt lakes and saline soil areas and the characteristics of MOCC,a CRMOCC collaborative performance test is designed to study the collaborative performance of coated steel bar and MOCC.A long-term solution immersion test of CRMOC and reinforced magnesium oxychloride cement concrete(RMOCC)is systematically designed to study the long-term stability of the coating during the protection of steel bar and whole durability of CRMOCC.The high and low temperature alternating test of CRMOC and RMOCC is designed to study the degradation law of CRMOC and RMOCC under high and low temperature.The CRMOCC and RMOCC constant current energization accelerated test and X-CT tests are designed to study the spatial formation of steel corrosion and corrosion-induced crack.Based on the gray-level co-occurrence matrix(GLCM)and on the basis of the traditional fracture geometric parameter analysis,the crack formationt law of CRMOC and RMOCC in the process of high and low temperature test and constant current energization test is studied.Based on the Copula function,the relative corrosion evaluation parameter?₁,relative dynamic elastic modulus evaluation parameter?₂and relative quality evaluation parameter?₃ are used as degradation indicators,and the overall durability reliability analysis of CRMOCC under the action of two factors and three factors is carried out.The main conclusions are as follows:(1)Through the salt spray test,electrochemical test,tensile test and steel bar planting pull-out test,the cooperative performance of crmocc was studied from three aspects:the protective performance of the coating on the steel bar,the integrity of the coating under the action of external load,and the bonding force of the steel bar under the action of the coating.It is concluded that for the GH(zinc rich epoxy)coating and the asphalt coating,when the thickness of the GH coating is 0.3 mm and the thickness of the YP asphalt coating is 0.4 mm,the collaborative work performance of CRMOCC is the best.(2)Long-term solution immersion tests were conducted on CRMOC and RMOCC,the corrosion current density of steel corrosion,crack formation?₂ and mass loss?₃ were used as durability evaluation parameters to study the overall durability degradation process.The results show that the corrosion degree of(coated)steel bar in four environments is chloride environment>sulfate environment>humid environment>dry environment.The damaged GH coated steel in chloride environment has reached a low corrosion state in 180 days.In dry environment,the protective effect of YP asphalt on steel bar is better than that of chloride environment,sulfate environment and humid environment.?₂ and?₃ approximately obey the linear degradation law in the degradation process,and?₂ is more sensitive in the degradation process.(3)In order to get the reliability degradation law of CRMOCC under the combined action of three factors,taking?₁,?₂,?₃ as degradation indexes,the model is established on the basis of Copula function,and the results show that the reliability of S(t₁),S(t₂),S(t₃)under the action of single factor is zero in 20000 d,16000 d,and 18000 d respectively.Under the action of two factors,the reliability of CRMOCC is zero at 13000 d by using the bivariate Gumbel copula function as the connection function.Under the action of three factors,the reliability of CRMOCC is zero at 10390 days with the ternary Clayton copula function as the connection function.(4)Through high and low temperature test and constant current energization accelerated test,the law of corrosion,crack formation and quality loss degradation of CRMOCC and RMOCC was studied.Crack formation of the specimen surface was captured by artificial recognition,edge detection,threshold segmentation and K-means clustering algorithm.It is concluded that GH coating and YP coating can protect the steel bar from corrosion.For?₂and?₃ in the same period,the larger the thickness of the protective layer is,the smaller the reduction rate is.?₂ is more sensitive to the degradation process of the specimen.Although edge detection,threshold segmentation and K-means clustering algorithm can capture surface crack,the accuracy is greatly affected by the external environment.(5)Taking the degradation of CRMOCC under constant current energization accelerated test as an example,X-CT is used to study the spatial formation of steel corrosion and corrosion-induced crack.It is concluded that the corrosion of the steel bar starts at the interface failure of the steel bar and the magnesium oxychloride cement.With the continuous corrosion of the steel,the corrosion products gradually spread across the entire surface of the steel and diffuse into the cement slurry.The crack formation starts from an outer surface of the steel bar.The crck formation is related to the interface transition zone(ITZ)between the aggregate and the cement slurry and develops in the direction of the interface transition zone.The needle-like products formed in the ITZ of MOCC interface is the key reason of weak surface.The development width of surface crack on LG(uncoated steel)and YP specimens has a linear relationship with the steel volume loss and the corrosion products formation,respectively.The volume loss of LG steel has an exponential relation with the growth of corrosion products.The volume loss of YP steel has a linear relation with the growth of corrosion products.The surface crack width has an exponential relation with the crack volume growth,and the YP specimen surface crack growth has a linear relation with the crack volume.For the LG-A and YP-A test pieces,the actual corrosion rate and theoretical corrosion rate of the steel bars in the same period are 10.72%,10.05%,13.47%,and 18.81%,respectively.(6)X-CT technology and GLCM image analysis method were used to analyze the surface and internal meso damage of rmocc under the action of rust expansion force.Four characteristic values of GLCM(contrast,correlation,energy,homogeneity)are used to reflect the change of meso damage,and the statistical analysis of the four eigenvalues shows that:with the gradual increase of concrete specimen damage,the contrast value increases,while the correlation,energy and homogeneity value decreases.Statistical analysis of contrast,correlation,energy,homogeneity of four groups of values,it is concluded that they all obey normal distribution.It is more conservative and appropriate to evaluate the degradation of concrete under the action of rust expansion force by using the characteristic value of homogeneity.By analyzing the thermal diagram of concrete specimen before and after damage,it is concluded that the bandwidth of horizontal projection of matrix peak decreases significantly before and after damage,and with the gradual increase of damage,the matrix peak extends along the main diagonal of the matrix.The smaller the ROI region is,the greater the contrast is,while the other three eigenvalues have little fluctuation.