| Long-term exposure to chloride and sulfate-rich environments such as saline lake and seawater,the erosion of ions will reduce the serviceability and durability of reinforced concrete structures.The fly ash and the slag,as commonly used mineral admixture,can chemically react with cement hydration products,reduce the porosity of concrete structures and improve its internal structure,increase the impermeability and enhance the durability of the concrete.Therefore,it is of great significance to study the hydration process and the durability degradation process in chloride-sulfate environment of mineral admixture concrete,which is contribute to evaluate the full period performance of mineral admixture concrete structures in the coastal environment.In response to the problem,this paper has carried out related numerical and experimental research.The major contents and conclusions of the research are listed as follows:(1)On account of the hydration mechanism of cement and the reaction mechanism of fly ash and slag,the hydration equation of each material is given and solved numerically,which is containing different reaction rates of particle nucleation,phase boundary reaction and diffusion during the hydration process.And the euqation can be used to calculate the hydration degree of cement,fly ash and slag particles.(2)The random particle model of the mineral admixture concrete is established based on the concrete mix ratio and the particle size distribution of the cementitious material particles.By combining it with the hydration equations and considering the interaction between particles during hydration,the hydration model of mineral admixture concrete was established.The above model was compiled into a computer program using MATLAB language,which can be used to calculate the changes in porosity and related phases in mineral admixture concrete during hydration.(3)The coupled chloride-sulfate ion transmission equation for a cylindrical specimen was established based on the chloride-sulfate coupling erosion mechanism of mineral admixture concrete.By discreting variables and iterative differences,the equations were solved numerically and written as a computer program by MATLAB language.This program can be used to calculate the spatiotemporal distribution of ions in the mineral admixture concrete and the change law of phases in the coupled erosion process.(4)The immersion test of cylindrical mortar specimens with different amounts of fly ash and slag in chloride-sulfate solution was carried out,and the ion content in the specimens was periodically determined.The results show that the incorporation of fly ash and slag can effectively reduce the content of free ions in the specimen and reduce the degree of chloride-sulfate erosion.Comparing the test results with the model calculation results,the rationality of the coupled transmission model is verified.(5)The hydration model of mineral admixture concrete is used to analyze the effects of water-cement ratio and the amount of mineral admixture on the hydration degree of the gel material,the porosity of the concrete and the content of the phase during the hydration process.The coupling transmission model is used to analyze the effects of porosity and chemical reaction rate on the free chloride ion content,combined chloride ion content,free sulfate ion content,and ettringite production during the coupled transmission process. |
PDF Full Text Request