Transportation Of Carbonate And Sulfate Ions In Concrete Based On Compartment Model

In sessions on concrete structure design,designers and construction workers have particularly considered the safety and application property of concrete structure for a long time.However,designers and construction workers have not recognized the durability of material and structure due to complex environment actions.Many factors influence the durability of concrete,such as ions attack,drying–wetting cycle,freeze-thaw cycle,carbonation of concrete,and load.Researches in past mainly focused on the durability damage of concrete due to chloride ion but not carbonate ion.However,in the practice environment,the erosion effect to the concrete structure that suffered from carbonate and sulfate ions attack is more serious than that suffered from chloride ion attack.In this article,the influence the coupling action of ions attack and drying–wetting cycle on the durability of structure and investigate the transportation laws of carbonate and sulfate ions in concrete has been researched.Based on this issue,relying on the National Natural Science Foundation of China(41430642),National Natural Science Foundation of China(51108207),China Postdoctoral Science Foundation(2015M581403)and the State Key Laboratory of Frozen Soil Engineering Foundation(SKLFSE201514),the following researches have been done:(1)The process of degradation of concrete which was suffered from the coupling action of carbonate ion attack,sulfate ion attack and drying-wetting cycle has been described by means of indoor simulation accelerated experiments.The concrete specimen was designed to suffer a dimension attack to avoid the influence of gravity to ion transportation and the coupling action at the corner of specimen by two-dimension attack.The concrete specimen wore one-dimension coating system to achieve one-dimension carbonate ion and sulfate ion transportation in concrete.The attack depth and the concentration of ions should be detected at special drying-wetting cycle s;(2)The drying-wetting cycle provides dynamic foundation for ions ingression and elimination in the concrete.Transportation of carbonate and sulfate ions in concrete under the drying–wetting cycle environment is similar to the ingression and elimination of medicine in human body.Given this similarity,such process is described dynamically using the classic compartment model in pharmacokinetics.The compartment model was applied to predict the content of carbonate and sulfate ions in different regions in concrete;(3)In conjunction with the prediction value of the compartment model,the experiment data uniformly distributed two sides of the model curve,and the difference is within the accepted range,thus verifying the reliability of the model prediction consequence.Factors such as water–cement ratio,salt category,ions attack depth,and times of drying-wetting cycle were synthetically considered in the compartment model;(4)The article research on the micro structure of concrete: the damage mechanism of concrete has been revealed by means of chemical reaction process and the form of physical damage.The micro structure of concrete and the shape of crystal have been observed by SEM experiment.The SEM photos provide evidence to the damage mechanism of concrete.In addition,the difference damage mechanisms between carbonate ion and sulfate ion has been discussed;(5)The form of model was direct,resulting in easy application in engineering.The compartment model in this article provides references for predicting the drying-wetting cycles and ions attack depth of concrete under carbonate and sulfate ions attack.This investigation is also important to evaluation of durability and protection of concrete structure in carbonate-ion rich and sulfate-ion rich environment.