Research On Chloride Ion Transport Properties And Analytical Model In Lightweight Aggregate Concrete

The problem of reinforcement corrosion caused by chloride ion intrusion is the focus of concrete structural durability research,and the mechanism and characteristics of chloride ion transport in concrete is the key to it.The mortar matrix and aggregate-matrix interface transition zone in lightweight aggregate concrete significantly affect its chloride ion transport properties,resulting in the diffusion mechanism and transport mechanism of chloride ions in lightweight aggregate concrete is not yet clear.The experimental and theoretical studies on the chloride ion transport properties of lightweight aggregate concrete under the chloride salt environment are conducted to clarify the influence of the material properties and microstructural characteristics of lightweight aggregate concrete on the chloride ion transport,and to improve the model related to the prediction of the service life of lightweight aggregate concrete,which is of great theoretical significance and practical value for the durability design of lightweight aggregate concrete structures.The main research includes:(1)Lightweight aggregate concrete chloride ion transport performance tests were carried out.Thirty-two sets of light aggregate concrete with different mix ratios and corresponding net and mortar test blocks were designed and prepared,and rapid chloride ion migration tests were completed to clarify the chloride ion transport properties in different cementitious materials and the influence laws of water-cement ratio(0.40,0.35,0.30),mineral admixtures(silica fume,fly ash)and fibers(polypropylene,polyethylene)on chloride ion diffusion coefficient.It is found that: the chloride ion diffusion coefficient of lightweight aggregate concrete is influenced by the transition zone of matrix and aggregate-matrix interface transition zone,but the correlation with concrete strength is not significant;the chloride ion diffusion coefficient of lightweight aggregate concrete gradually decreases with the decrease of water-cement ratio;the incorporation of silica fume and fly ash helps to improve the chloride ion penetration resistance of lightweight aggregate concrete,and the chloride ion diffusion coefficient gradually decreases with the increase of silica fume and fly ash incorporation;the incorporation of fiber can effectively inhibit the chloride ion diffusion in lightweight aggregate concrete.Compared with polypropylene fiber,the inhibition of chloride ion diffusion in light aggregate concrete by polyethylene fiber is more significant;the chloride ion diffusion coefficient of lightweight aggregate concrete with water-cement ratio of 0.35 is 17.2% lower than that of ordinary concrete in the same condition,and the chloride ion erosion resistance of lightweight aggregate concrete is better than that of ordinary concrete in the same condition.(2)The microstructure testing and diffusion performance analysis of lightweight aggregate concrete were completed.Ten groups of typical lightweight aggregate concrete and benchmark groups of ordinary concrete specimens were selected,and the internal structure and pore characteristics of concrete were analyzed with the help of scanning electron microscopy technique,X-ray energy spectrum analysis and mercury compression test method to reveal the chloride ion diffusion law of lightweight aggregate concrete.It is found that: the chloride ion diffusion coefficient increases with the increase of porosity and decreases with the increase of fractal dimension;compared with ordinary concrete,the water absorption and return effect of porous aggregate in lightweight aggregate concrete results in higher hydration of the aggregate-matrix interface transition zone,less calcium hydroxide enrichment,lower calcium-silica ratio than ordinary concrete with the same condition,and denser structure of the transition zone;the reduction of water-cement ratio,appropriate amount of mineral admixture and The reduction of water-cement ratio and the appropriate amount of mineral admixtures and fibers can reduce the porosity and optimize the pore structure of lightweight aggregate concrete,so that the lightweight aggregate concrete can show higher resistance to chloride ion penetration on a macroscopic level.(3)Completed the analysis of the durability service life prediction model of lightweight aggregate concrete under chlorine salt environment.Based on the theories related to the durability service life prediction of concrete structures under chlorine salt environment,the existing durability design codes at home and abroad were compared and analyzed,and the existing theoretical models were revised and the prediction of the service life of lightweight aggregate concrete was completed based on the revised models.The study shows that the Duracrete R15 and FIB 34 models are conservative,and the Yu Hongfa model has good applicability for the prediction of the durability service life of lightweight aggregate concrete;the paper optimizes the existing theoretical model based on the obtained test data,gives the suggested values of the key parameters in the light aggregate concrete life prediction model,predicts the durability service life of lightweight aggregate concrete under the chloride salt environment and gives the prediction of the protective layer of concrete.The paper also gives the design limits of the concrete protection layer.This paper investigates the chloride ion transport properties of lightweight aggregate concrete and the influence law of different factors,clarifies the connection between microstructure and macroscopic diffusion properties of lightweight aggregate concrete,analyzes the applicability of existing life prediction models to lightweight aggregate concrete,revises the existing theoretical models,and provides theoretical and experimental references for the durability design of lightweight aggregate concrete.