Life Prediction Of Aqueduct Structure In Irrigation District Based On Multiple Environmental Time Similarity Theory

Under the coupling of temperature,humidity,salt ion erosion and so on,the actual useful life of concrete structure is different from that of expected service life in the process of service,which means that there is a certain difference between the actual serviceable life（no emergency condition）and the expected service life,and the service state of the structure will deviate from the expected effect in a certain time state.Therefore,it is necessary to effectively predict the actual useful life of concrete structure and correlate the service state of the whole structure with the service time so as to use it as a data basis for proper maintenance and repair of the structure.Avoid inadequate repair or excessive repair to ensure the normal allocation of human and financial resources and the full play of structural functions.In this paper,the hydraulic concrete building in the Northwest Jingtaichuan Electric Power pumping and Irrigation Project was selected as the target object,and the life expectancy of the hydraulic concrete building was forecasted by using the multi-environmental time similarity theory（METS）.The theory is based on the basic content of the similarity theory,which was adding several control buildings with the same or similar service environment as the target object and having similar construction mix ratio and different service life as the communication medium between the field test and the indoor accelerated test.In this way,the similar conditions of the service environment of the target object and the reference object were satisfied,and then by comparing the attenuation law of durability index between indoor accelerated test and field test,the time similarity relationship between indoor test and field test was obtained.Considering the similarity between the time and the environment,combined with the similarity of the attenuation laws of various indexes that characterize the durability of concrete,the hydraulic concrete structures which are mainly subjected to salt-transgression-freezing-thawing coupling can be predicted objectively and with high reliability and service life in Jingdian Irrigation area.In order to determine the actual serviceable life of aqueduct,the most widely distributed water conveyance structure in Jingdian irrigation area under the coupling of salt transgression and freezing and thawing.Based on the METS theory,the physical parameters of the indoor rapid freeze-thaw test were determined according to the temperature change in the service environment and the determination of the salt ion content.The concrete specimen with the same mix ratio as the target building and the control building was put into 3%NaCl+5%Na₂SO₄ for rapid freeze-thaw test.The apparent condition,macroscopic index and internal dense state of the specimen were measured,and the attenuation formula of the durability index of the specimen was established.At the same time,the apparent condition,macroscopic index,internal dense state and steel corrosion state of the target building and several control buildings were measured,and the numerical value and variation law of concrete durability index were obtained under different service time conditions.Then the two parts of the experiment are discussed both horizontally and vertically,and the decay constants of all kinds of indexes were compared and corrected in combination with the existing experience.Furthermore,the useful life of the target aqueduct structure in the actual service environment was evaluated and predicted on the basis of the similar conditions in this kind of environment and time relationship,and the best time and means for repairing the building itself wais determined to achieve the rational use and allocation of resources.The specific conclusions were as follows:（1）The lower part of the aqueduct body was more damaged than that of the upper part,and the lower part of the aqueduct was more damaged than the upper part of the aqueduct,and the lower part of the aqueduct was more damaged than the upper part of the aqueduct,and the lower part of the aqueduct was more damaged than the upper part of the aqueduct.The risk factor was higher in actual operation.The results of steel corrosion test showed that the corrosion probability of 47-year-old structure was more than 95%,so it is necessary to take some measures to alleviate the corrosion.（2）By testing the salt-freezing resistance of concrete specimens with different mix ratios,it was found that the water-cement ratio has a greater influence on concrete,and the smaller the water-cement ratio,the denser the concrete was,the more stable the internal structure was,the more stable the concrete was,the more stable the internal structure was.The durability of concrete specimens under salt invasion-freeze-thaw coupling was better,and the attenuation rate of each index was lower than that of concrete specimens with high water-cement ratio.Therefore,for the concrete structure in cold region,the water-cement ratio in the mixture ratio can be reduced appropriately,so as to increase the anti-freezing and invasion resistance of the structure.（3）The variation law of the compressive strength of the 24^#aqueduct（new）of the second-stage total dry was calculated based on the indoor test and the relation between the dynamic modulus,the compressive strength and the ultrasonic wave velocity was calculated based on the similar coefficient of the anti-pressure attenuation of the various buildings and the concrete test pieces.The whole service life of the aqueduct was 68.63 years,and the damage to the bent part of the trough body was small,the damage of the salt in the bent frame was serious,and the service life of the whole aqueduct was directly restricted.