Experimental Research On Long-term Performance Of Marine High-performance Concrete Beams Under Freezing-thawing And Chloride Environment

Marine high-performance concrete has been applied in Hangzhou Bay Bridge,Jiaozhou Bay Bridge,Hong Kong-Zhuhai-Macao Bridge and other extra-large bridges.However generally speaking,because of its relatively short practical application time,the research on the degradation of long-term performance of marine high-performance concrete after various damage is not comprehensive enough.In addition,freezingthawing cycles and chloride attack have been the prominent problems to affect the durability of coastal concrete structures,which need to be solved.Above on,supported by the National Natural Science Foundation of China(51878319),from materials and components levels,the experimental study on the behaviors degradation of marine high-performance concrete and the flexural behaviors degradation of marine highperformance concrete beams under freezing-thawing and chloride environment was carried out,the long-term performance degradation of marine high-performance concrete after different damage was compared and analyzed,a theoretical model for ultimate moment of marine high-performance concrete beams with suitable reinforcement based on the frost-damaged constitutive relation was proposed,and the long-term service life of marine high-performance concrete based on dynamic elastic modulus damage degree(DEMDD)in East China under freezing-thawing and chloride environment was predicted,compared and analyzed in this paper.The specific contents and results are as follows:1.Experimental study on the behaviors degradation of marine high-performance concrete under freezing-thawing and chloride environment was carried out.Based on the concrete mix proportion scheme of some structural members of Hangzhou Bay Bridge,three kinds of marine high-performance concrete specimens with three kinds of concrete mix proportion were designed and fabricated.After the curing,taking the single action of freezing-thawing cycles in water and the alternate actions of freezingthawing cycles in water and chloride attack as two kinds of damage mechanisms with25,50,75 and 100 freezing-thawing cycles,the behaviors degradation test of marine high-performance concrete specimens was carried out.The behaviors degradation of three kinds of marine high-performance concrete was compared and analyzed.The results show that with the increasement of freezing-thawing cycles,the surface damage of three kinds of marine high-performance concrete gets more and more serious,and DEMDD,mass loss rate,loss ratio of compressive strength and growth ratio of chloride mobility coefficient(four freezing-thawing damage evaluation indexes)increase gradually under the actions of the two damage mechanisms respectively;When the number of freezing-thawing cycles exceeds 25 and 50,respectively,the internal damage and surface damage of marine high-performance concrete caused by freezing-thawing action are intensified;Combined with the test results,the fitting formula of each freezing-thawing damage evaluation index with freezing-thawing cycles is put forward with the good fitting results.2.Experimental study on the degradation of flexural behaviors of marine highperformance concrete under freezing-thawing and chloride environment was carried out.Ten marine high-performance concrete beams with the above three mix proportions were fabricated,and the same behavior degradation test was applied on marine highperformance concrete beams with 50 and 100 freezing-thawing cycles.After the behaviors degradation test with the same methods,the flexural behaviors test of marine high-performance concrete beams was carried out.The test results show that the height of the compression zone,the ultimate mid-span deflection and the maximum crack width of damaged marine high-performance concrete beams increase with freezingthawing cycles;The crack moment,the ultimate moment,the stiffness and the ductility rate of marine high-performance concrete beams decrease with freezing-thawing cycles.After 100 freezing-thawing cycles,the ultimate moment of concrete beams with 20%fly ash and 30% mineral powder(the mass ratios of cementitious materials)and concrete beams with 30% fly ash and 20% mineral powder decreases by 4.10% and5.61% under the single action,respectively;The ultimate moment of both of the above decreases by 5.36% and 6.58% under the alternate actions,respectively,and the decrease degree increases.3.The analysis for predicting the ultimate moment of the normal section of marine high-performance concrete beams with proper reinforcement under freezing-thawing cycles was carried out.The theoretical model for predicting the ultimate moment of the normal section of marine high-performance concrete beams with proper reinforcement based on the frost-damaged constitutive relation of concrete was proposed.When the freezing-thawing cycles is less than 300,the average value of the ratios of the experimental values to the predicted values of the ultimate moment is proved to be0.995 and the coefficient of variation is proved to be 0.103,which illustrates that the theoretical model is of good applicability.4.On the basis of DEMDD,the long-term service life of marine high-performance concrete beams in East China under freezing-thawing and chloride environment was predicted and analyzed.The results show that under the single action,the service life of the concrete beams with 20% fly ash and 30% mineral powder,those with 30% fly ash and 20% mineral powder and those with 20% fly ash,30% mineral powder and appropriate nano-silica is about 121.20 a,100.00 a and 133.60 a,respectively;Under the alternate actions,the service life of the above two is about 91.20 a and 74.40a;It can be seen that the designed marine high-performance concrete beams can meet the frost resistance safety requirements of buildings in East China.