Study On The Properties Of High Performance Steel Slag Fine Aggregate Concrete After The Exposure To Ambient And Elevated Temperature Based On Wet Packing Density Theory

The 14th five-year plan for green industrial development clearly calls for accelerating China’s green and low-carbon development,continuously improving environmental quality,enhancing the stability of ecological bears,and increasing the utilization rate of resources.However,the materials such as cement,crushed stone and natural river sand used in the production of concrete consume a lot of energy and pollute the local environment seriously,which does not meet the requirements of high quality development of our national economy.Therefore,it is imperative to develop a new type of high performance green concrete suitable for engineering application.Steel slag is a by-product of steel making.The annual output of crude steel in our country is 1.03 billion tons,which is accompanied by more than 100 million tons of steel slag,but the comprehensive utilization rate of steel slag in our country is less than 30%,the problem of steel slag taking up a lot of land resources,and even causing environmental pollution.The production of cement emits a large amount of carbon dioxide,accounting for 8%of global carbon dioxide emissions.The reasonable use of steel slag instead of aggregate and the by-product silicon fume instead of cement in engineering application can not only save energy and reduce emission,but also release a lot of land resources and improve environmental quality.When steel slag is used instead of aggregate and silicon fume is used instead of cement to make concrete,the structure and chemical composition of concrete will change,which will affect its ambient and elevated temperature performance,at present,the research on steel slag aggregate only focuses on the experimental level,and rarely discusses the mechanism of the influence of the change of pore structure on the properties of concrete at room temperature and after fire.In order to fill up the blank of this research field and popularize the application of steel slag sand concrete in practical engineering,this research uses steel slag fine aggregate instead of natural river sand（50%,100%）based on the theory of wet packing density,using silicon fume instead of cement（5%,10%,15%）,using superplasticizer dosage of 1%-2%of the quality of cementitious material.45 design mix have been designed in this thesis.45 groups of concrete specimens with different mix ratios,such as expansion,packing density,passing rate of l-box and segregation rate,were studied,and 27groups of concrete specimens were tested for their compressive strength and chloride ion resistance at room temperature,the properties of residual strength index,mass loss and macroscopic changes after fire（600℃,800℃,1000℃）were studied,and the reasons of the properties changes of steel slag fine aggregate concrete at ambient and elevated temperature were investigated by XRD phase analysis.The results show that:（1）the workability of concrete can be obviously reduced by adding steel slag fine aggregate,and the workability of concrete can be improved by adding silicon fume and adding water reducer according to the total surface area(D_SP),steel slag fine aggregate and silica fume can be mixed into concrete at the same time to produce green and environmental friendly concrete with high workability.（2）the increase of the substitution rate of steel slag sand and silica fume can increase the wet stacking density of concrete,and the resistance to chloride ion permeability and strength of concrete are related to the wet stacking density,the higher the wet stacking density is,the higher the strength of concrete is,（3）the residual strength of concrete without silicon fume can be kept higher after 600℃high temperature.The residual strength index of concrete is related to the wet packing density,the strength predicted by the design model of post-fire strength of concrete in the European code for fire protection design of structures is too conservative,and the post-fire residual strength index of concrete is underestimated,the dosage of superplasticizer has no effect on the important hydration products of concrete.