Measurement And Quantitative Design Of Chloride Diffusion Properties In Concrete

Reinforced concrete has the advantages of superior performance and low cost,and is widely used in marine construction projects such as sea-crossing bridges and subsea tunnels.Chloride diffusion resistance of concrete determines the safety and durability of marine concrete structure,due to a great amount of chloride ions in marine environment.Therefore,it is necessary to develop the measuring and testing technique and quantitative design of chloride diffusion properties in concrete.The main research work of this thesis is as follows:(1)In order to accurately measure the chloride diffusion coefficient of concrete,four kinds of experimental devices were independently developed.Firstly,a cutting device with double blade was developed,which was used to make standard specimen with a thickness of 50mm.The device has the advantages of small cutting error of specimen thickness,parallel upper and lower undersides of specimen,and saving labour work.It overcomes the defet of traditional cutting device.Secondly,a cylindrical concrete specimen splitting device was developed,which was used to axial splitting the cylindrical concrete specimen.The device has the advantages of axial section of specimen is perpendicular to cut surface,flat axial section and no damage.It overcomes the defet of traditional splitting device.Thirdly,an automatic acquisition device for section image of concrete specimen was developed,which was used to obtain section image.The device has the advantages of camera lens axis is perpendicular to section of specimen and best picture quality.It overcomes the defet of traditional acquisition device for section image.Finally,three-dimensional location sampling devive for concrete was developed,which was used to get the concrete interior sample.The device has the advantages of accurate three-dimensional location sampling.It overcomes the defet of traditional sampling device.The above devices established the foundation for the the measurement and quantitative design of chloride difusion coefficient in concrete(2)74 sets of concrete specimens with different chloride diffusion coefficient were prepared based on orthogonal design,uniform design and factorial design.Constant voltage RCM test,variable voltage RCM test and compressive strength test on 74 sets of concrete specimens were performed Results show that the sample points of uniform design are representative,even if the samples are few,and the uniform design method has the same predicting effect as factorial design method(3)The effect of edge effect on chloride diffusion coefficient was studied The normal depth of chloride diffusion at each measure point was defined.The influence of edge effect on chloride diffusion depth and chloride diffusion coe:fficient was investigated based on the mean and standard deviation of the normal depth of chloride diffusion.The scope of edge effect was determined Based on regression analysis,the relationship between the chloride diffusion coefficient for the center of specimen and that for the whole specimen was studied.Results show that the scope of the edge effect is limited within about 10mm depth from the surface around the specimen,meanwhile the traditional constant voltage RCM test without obviating the influence of edge effect will overestimate the chloride diffusion coefficient.There exists a linear relationship between the chloride diffusion coefficient for the center of specimen and that for the whole specimen.(4)Based on image processing technology,the area average method was developed.The chloride diffusion area in the radial section of concrete specimen was measured,and the corresponding chloride diffusion depth and chloride diffusion coefficient were calculated respectively.The specimens were selected to compare the measurement results of manual measurement and image measurement,and the results of area average method and point average method.Results show that the location and spacing of measurement points have significant influence on the measurement results for traditional point average method,which result in unstable of test results.In contrast,the proposed method overcomes the limitation of point average method and the corresponding measurement results have higher precision and stability.The correlation between chloride diffusion coefficient obtained by point average method and area average method was investigated by statistical analysis of measurement results above,and the corresponding correlative model was developed.(5)The multi-factor models for chloride diffusion coefficient of fly ash concrete,granulated blast furnace slag concrete and fly ash and granulated blast furnace slag concrete were developed.The influential laws of various factors,including water-binder ratio,replacement of fly ash and replacement of blast furnace slag were explored.Furthermore,based on nonlinear least squares method and the constant voltage RCM test data,a multi-factor model for the initial chloride diffusion coefficient by comprehensively taking into account the influence of water-to-binder ratio,replacement of fly ash and replacement of blast furnace slag were developed.Finally,the accuracy and application of the proposed model were demonstrated by comparing with experimental data of constant voltage RCM and the predicted values of existing initial chloride diffusion coefficient models.(6)A quantitative design method for chloride diffusion properties of concrete was proposed.The relationship between standard deviation and chloride diffusion coefficient and the relationship between variable coefficient and chloride diffusion coefficient were studied,and the correlation model was developed.And then,the quality control equation of chloride diffusion coefficient was developed.The set of nonlinear equations were developed,which include the multi-factor model for chloride diffusion coefficient the multi-factor model for compressive strength,and the multi-factor model for aging factor.By solving the equation of higher degree,water-to-binder ratio,replacement of fly ash,and replacement of granulated blast furnace slag can be determined.The proposed approach was compared with concrete mix design methods in existing specifications.Results show that the proposed approach can determine quantitatively the replacement of mineral admixtures according to the requirements of durability and strength indices,and the corresponding mix proportion parameters can be determined.The proposed approach overcame the drawback of traditional mix design method that the replacement of mineral admixtures can’t be determined,and the durability can’t be quantitatively designed.