The Degradation Mechanism Of High Performance Concrete With Combined Usage Of Mineral Admixtures Under The Effect Of High Temperature And Environmental Erosion

High-performance concrete(HPC)has been increasingly applied in large-span bridges,super-tall buildings,and other special structures,due to its outstanding strength and durability.However,extreme heat and aggressive service environments place high demands on the thermal and corrosion resistance of the HPC.Mineral admixtures,as cementitious material that replaces cement,can be used to further improve the performance of concrete under environmental loads while reducing the energy and cost of concrete preparation,as well as using its physical particle characteristics and chemical properties.However,there is a lack of research on the degradation of the HPC with high-temperature loading and aggressive media.As such,this paper investigates the basic properties of mineral admixtures and their behavioral characteristics(workability and mechanical properties)in HPC,the degradation of concrete properties under high-temperature loading and aggressive media,and the degradation mechanism from the morphological effects and chemical composition of mineral admixtures.The main research contents and results of this paper are as follows.(1)The basic properties of mineral admixtures and their behavioral characteristics in HPC.The composition and particle characteristics of three commonly used mineral admixtures were investigated.The results show that the main chemical components of iron tailings fines are silicon dioxide(SiO2),aluminum oxide(Al2O3),and hematite(α-Fe2O3),which also have the potential to be used in the preparation of heat resistant concrete due to their high-temperature resistance.In addition,silica fume has a finer particle size than iron ore tailings and fly ash.Silica fume improves the workability of the mix and at the same time improves the mechanical properties of the concrete to some extent.The addition of iron tailing powder harms the slump of the concrete,while the binary/ternary composite mineral admixture can compensate to some extent for its adverse effect on the slump of the mix.(2)The degradation of the performance of HPC with compound mineral admixtures under high-temperature loadingsThe degradation of the performance of the HPC with mineral admixtures under high-temperature loading was simulated and studied in a laboratory environment.The results showed that the addition of iron tailing powder was the most effective in inhibiting concrete damage under high temperature,fly ash was the second most effective and silica fume was the least effective;binary compound fly ash and iron tailing powder were the most effective in improving the thermal conductivity and residual strength of concrete,and the residual strength of the specimens retained about 70%after being subjected to 800℃.(3)The effect of aggressive media on the transport properties of HPC.The effect of mineral admixtures on the performance of concrete in terms of water molecule transport,chloride ion transport properties,and sulfate ion transport was investigated.The results show that binary/ternary compound mineral admixtures can significantly reduce the initial water absorption,chloride ion penetration,and sulfate attack properties.Concrete specimens took longer to reach saturation and it is expected that concrete specimens with binary/ternary compounded mineral admixtures showed better durability performance when subjected to wet and dry conditions.