Study On Application Of Nondestructive Testing Technology For Concrete Impermeability Based On Autoclam Method

In recent years,some scholars home and abroad have continuously studied various conceptual musings and various theoretical tests on factors affecting the durability of concrete,although there is no unanimous conclusion,but it is generally agreed that the durability of concrete has some relationship with the permeability of concrete.Although the surface of concrete looks relatively strong,but due to its configuration of raw materials,concrete is actually made of many internal voids,these pores can lead to the entry of various gases and liquids.When the external conditions are conducive to the intrusion of gases and liquids into the concrete voids,different chemical composition of gases and liquids enter the concrete voids,which may lead to a decrease in the durability of concrete after its long-term effect.In particular,the concrete surface structure is in direct contact with external conditions,therefore,it is also believed by some scholars that the permeability of the concrete surface determines the durability of concrete.It is also proven that the vast majority of concrete buildings deteriorate right from the surface layer,especially concrete buildings in water environments.In this thesis,the changes in mechanical properties of concrete were analyzed by conducting 7d and 28 d compressive tests on concrete specimens at C30,C40,C50 benchmarks and with single and compound fly ash,mineral powder and CSA-II expander,respectively.The permeability testing was also carried out using the permeability height method and Autoclam method,and the changes in the permeability properties of the concrete were analyzed.On the basis of the data derived from the two testing methods,linear fitting was performed to establish mathematical conversion relationships,laying a good foundation for subsequent research on experimental and practical engineering applications related to impermeable concrete.The results show that fly ash,mineral powder and CSA-Ⅱ expander can improve the compressive strength of concrete,and the compressive strength of C50 concrete compounded with fly ash,mineral powder and CSA-Ⅱ expander is the largest.Its 7d average compressive strength was 52.88 MPa and 28 d average compressive strength was 65.64 MPa.After applying AUTOCLAM method and percolation height method to 30 groups of concrete specimens with different strengths,the results were that the C50 concrete with the strongest compressive strength compounded with fly ash,mineral powder and CSA-Ⅱ expander had the strongest percolation resistance.The C30 benchmark concrete with the weakest compressive strength has the weakest seepage resistance.It proves that the seepage resistance of concrete is proportional to the strength grade,and the better the mechanical properties of concrete,the better the seepage resistance of concreteAUTOCLAM method and percolation height method were applied to test the permeability of 30 groups of concrete specimens with different ratios prepared in the laboratory.The data results obtained by AUTOCLAM method and the data results measured by percolation height method showed the same trend,which proved that AUTOCLAM method is accurate in testing the permeability of concrete with different strength grades.Applying the two methods to test the permeability of the original beam concrete in the field,the change trend is consistent after the numerical conversion.The testing time required for the AUTOCLAM method is generally 1.5 min and 2.0 min,while the minimum testing time required for the seepage height method is 480 min.It is proved that the AUTOCLAM method is more efficient in testing the concrete impermeability compared to the seepage height method.Finally,for practical engineering application,a total of 27 concrete test points at 3different locations in 9 bridges in different environments were selected and tested for impermeability using the AUTOCLAM method.The results showed that 9 concrete test points had high permeability,8 concrete test points had high permeability,4 concrete test points had medium permeability,and 6 concrete test points had low permeability.It is proved that AUTOCLAM method can effectively perform the preliminary field evaluation of bridge concrete permeability resistance.