Study On The High Temperatures Performance Of Reactive Powder Concrete With Iron Tailings

Reactive powder concrete(RPC)has been widely used in prefabricated products,seismic structures,nuclear power engineering,hydraulic construction and other fields due to its excellent mechanical properties and durability.In recent years,how to reduce the preparation cost of RPC has become a hot issue.As a by-product of iron and steel industry,the amount of iron tailings is increasing,causing environmental pollution and waste of resources.Therefore,using iron tailings to prepare RPC can not only improve its utilization rate,but also effectively reduce the preparation cost of RPC.In recent years,with the continuous development of urban construction,more and more attention has been paid to the fire safety design of buildings.According to the optimization results of design expert,the water binder ratio,binder aggregate ratio and the relative content of fly ash and silica fume are the key factors to obtain high strength of RPC at room temperature.Therefore,it is necessary to study the influence of fly ash,glue ratio and fly ash content on RPC of iron tailings at high temperature.(1)In order to find out the key factors affecting the mechanical properties of RPC mixed with iron tailings at room temperature,the orthogonal test of 7 factors was set up and the mechanical properties were tested.The test results show that the RPC prepared by replacing quartz sand with iron tailings still has good mechanical properties;Water binder ratio,binder aggregate ratio and fly ash content are the main factors affecting the mechanical properties of RPC at room temperature.(2)The results show that the water glue ratio RPC has higher anti high temperature burst ability and better mechanical performance;The critical temperature of RPC flexural strength(200 ℃)is lower than that of compressive strength(300 ℃).(3)The mechanical properties of RPC with different binder aggregate ratio were tested at high temperature,and the microstructure was observed.The effects of temperature and binder to aggregate ratio on compressive strength and flexural strength of RPC were studied.The results show that the binder to aggregate ratio has a significant effect on the high temperature mechanical properties of RPC,and the higher the binder to aggregate ratio is,the better the compressive strength of RPC at high temperature is;On the contrary,the compressive strength of RPC with smaller binder ratio is lower at high temperature;The rule of flexural strength is consistent with the compressive strength.The flexural strength is the highest when the ratio of binder to aggregate is 1:1.1,and the lowest when the ratio of binder to aggregate is 1:0.8.(4)The effect of fly ash content on the mechanical properties and microstructure of RPC at high temperature was studied.The results of mechanical properties show that the compressive strength of RPC decreases with the increase of fly ash content at each target temperature,but the change trend of flexural strength is different.When the temperature of the specimen is between 20 ℃ and 400 ℃,the flexural strength of RPC increases with the increase of fly ash content.When the sample temperature is between 400 ℃ and 1000 ℃,the matrix begins to decompose,the protective effect around the steel fiber gradually weakens,and the steel fiber is finally destroyed by high temperature oxidation,which can not effectively provide bending strength.The results show that the effect of fly ash on the microstructure of RPC matrix is different at different temperatures.At 20 ℃,the hydration rate of fly ash is slow,the particle size is large,the amount of fly ash is large,and the number of macropores in the matrix is more than 50 nm.With the increase of temperature,the hydration reaction speed of fly ash is gradually accelerated,the hydration products are gradually increased,the matrix is dense,and the total pore volume of the sample with large amount of fly ash is reduced.When the temperature is above 400 ℃,the hydration reaction of fly ash stops and the hydration products do not increase.On the contrary,due to the decomposition of products at high temperature,the change of fly ash content has little effect on the pore structure of RPC.Fly ash is an important raw material affecting the fire resistance of RPC.The change of fly ash content is related to the distribution of steel fiber in RPC and the bonding ability of matrix and steel fiber at high temperature.These factors ultimately affect the mechanical properties and microstructure of RPC.In this paper,the main factors affecting RPC at room temperature are studied by using design expert,and then the effects of these main factors(water binder ratio,binder sand ratio,fly ash content)on the high temperature mechanical properties and microstructure of RPC are studied,and the mechanism is analyzed,and some results are obtained,which is of great significance for the popularization and application of RPC in the future.