Experimental Study On The Salt Frost Resistance Of Rubber-modified Steel Fiber Reinforced Two-graded Aggregate Concrete

Compared with steel fiber reinforced concrete with single-graded aggregate,the cement content,adiabatic temperature rise,and drying shrinkage of steel fiber reinforced two-graded aggregate concrete at the same strength level are significantly reduced.As a good toughening and crack resisting material,it is used in the hydraulic concrete structure.However,due to the characteristics of frequent contact with environmental water in the process of use,the high requirements of frost resistance durability are also put forward,which directly affects its application in water conservancy projects.The incorporation of rubber particles can effectively improve the resistance of concrete to water and salt frost.Therefore,in the context of environmental protection and highquality development of the Yellow River basin,it is of great practical significance to study the anti-frost durability of rubber-modified steel fiber reinforced two-graded aggregate concrete,which can provide theoretical guidance for China’s water conservancy projects,especially the proposed and under-construction water conservancy hub projects in the Yellow River basin.Because of this,this paper investigates the effect of two rubber particle sizes(1mm～3mm and 3mm～6mm)and different volume contents(0%,5%,10%,15%,and 20%)on the performance of steel fiber reinforced two-graded aggregate concrete,especially the salt frost resistance,and the internal microstructure of concrete under the different number of salt frost cycles,to reveal the mechanism of its effect on the durability performance of steel fiber reinforced two-graded aggregate concrete against salt frost,mainly including.(1)The effect of different particle sizes and volume contents of rubber on the compressive and splitting strength of steel fiber reinforced two-graded aggregate concrete was investigated using concrete compressive and splitting strength tests.The results show that the compressive strength and splitting strength of rubber-modified steel fiber reinforced two-graded aggregate concrete decreases with the increase of rubber volume content,and the smaller the rubber particle size,the greater the decrease,in which the compressive strength of rubber-modified steel fiber reinforced two-graded aggregate concrete decreases by 20.9% relative to the matrix two-graded aggregate concrete and by 31.1% relative to the steel fiber reinforced two-graded aggregate concrete;The splitting strength of rubber-modified steel fiber reinforced two-graded aggregate concrete decreased by a maximum of 24.3% relative to steel fiber reinforced two-graded aggregate concrete e,but still increased by 17.4% compared to matrix twograded aggregate concrete.(2)The effect of different particle sizes and volume contents of rubber on the salt and frost resistance of strength of rubber-modified steel fiber reinforced two-graded aggregate concrete was investigated through concrete salt and frost resistance tests.The results show that the salt and frost resistance of rubber-modified strength of rubbermodified steel fiber reinforced two-graded aggregate concrete of 1mm to 3mm increases with the increase of rubber volume content in the range of 0% to 20% of rubber volume mix.;The salt and frost resistance of rubber-modified strength of rubber-modified steel fiber reinforced two-graded aggregate concrete of 3mm to 6mm is optimal at 10% rubber volume content.Overall,the rubber particles of 1mm～3mm were more effective in modifying the durability performance of strength of rubbermodified steel fiber reinforced two-graded aggregate concrete against salt and frost,and the best salt and frost resistance was achieved by 20% rubber-modified strength of rubber-modified steel fiber reinforced two-graded aggregate concrete of 1mm～3mm,which reduced the spalling mass by 68.1% relative to the matrix two-graded aggregate concrete and by 56.6% relative to the steel fiber reinforced two-graded aggregate concrete after 48 salt and frost cycles 56.6%.(3)Combined with the results of the concrete salt frost test and based on the Weibull probability distribution,a prediction model between the salt frost internal damage variables and the number of salt frost cycles n was established,and the correlation coefficients of all ten groups of models were greater than 0.94,which could be used to predict the changes of its salt frost internal damage.(4)The effect of different numbers of salt frost cycles and different particle sizes and volume contents of rubber on the microstructure of steel fiber reinforced twograded aggregate concrete was investigated by scanning electron microscopy(SEM)tests on concrete.The results show that the microstructure of concrete deteriorates continuously with the increase in the number of salt frost cycles,with more cracks and less compactness;Steel fibers inhibit the development of cracks so that steel fiber reinforced two-graded aggregate concrete is more resistant to salt frost than matrix twograded aggregate concrete;Due to the deformability and air-entraining effect of the rubber,the rubber-modified steel fiber reinforced two-graded aggregate concrete has a lower number of harmful pores,a higher degree of compactness and higher resistance to salt frost compared to steel fiber reinforced two-graded aggregate concrete during48 salt frost cycles.