Research On The Effect Of External And Internal Factors On Carbonation Of Existing Concrete Building Structures

Carbonation is one of the key factors that affect the durability of reinforced concrete structures.This research investigated and core sampling drilling through nearly one hundred existing concrete building structures located in Shenzhen,and the basic performance indexes of mechanics and durability of concrete are tested and statistically analyzed.The correlation between concrete compressive strength,natural carbonation depth,open porosity and chloride diffusion coefficient and its anti-carbonation performance index is discussed.The influence rule and mechanism of internal and external factors on concrete carbonation in different environmental exposure grades(e.g.XC1,XC3 and XC4)were studied.In addition,the existing model for predicting carbonization depth based on the main parameters of compression strength is calculated and evaluated,and on this basis,the prediction model is further improved.The main results are as follows:1.The results of variance analysis show that the results of basic performance indicators such as compressive strength,natural carbonation depth,open porosity,chloride diffusion coefficient,and accelerated carbonation coefficient have no significant difference between three different administrative regions(e.g.Nanshan District,Bao'an District,and Futian District).2.Through the analysis of accelerated carbonation data,it is found that the accelerated carbonation coefficient is not affected by the service life,and the fitting of the exponential function with the compressive strength is better,and the drop decreases with the increase of the compressive strength.It has a better fit with open porosity and chloride diffusion coefficient with a power function.3.After considering the relationship between natural carbonization and service life under different exposure levels,it is found that the square root model is still suitable for predicting the natural carbonization of existing concrete structures indoors and outdoors.The fitting rate of natural carbonation rate and compressive strength is the best with power function,within the range of similar compressive strength,the order of natural carbonat ion speed is XC1(indoor)> XC3(outdoor-sheltered)> XC4(outdoor-unsheltered).4.Based on the structural shelter state,the differences of indoors and outdoors,and the influence of the end cover layer,the concepts of sheltering rate RUS,carbonization rate RIO and coating ratio RCC are proposed,and it is found that the sheltering rate RUS is not related to the service life,and has a better negative correlation with the compressive strength;The carbonization rate RIO is related to CO2 concentration in the environment and shelter state;and the coating ratio RCC is independent of the end coating material and the direction of the end.5.Comparing the correlation between accelerated carbonation and natural carbonation,it is found that there is a linear relationship between of both,but the fitting is poor;In addition,the acceleration factor(Ka/Kn)is not related to the service life,which is affected by the external environment,and determines the value of the acceleration factor under the 3 classes of exposure levels,ranging in the range of 19.03-28.12.6.On the basis of the analysis and evaluation of the prediction model of existing concrete carbonation,the carbonation prediction model is further improved.This model can predict the carbonation of concrete under different exposure grades(XC1,XC3 and XC4)and different urban road grades(greening and non-greening).