Research On Flexural Performance Of Steam Cured GFRP Reinforced Fiber Recycled Concrete Beam

The recycling of construction waste can save natural resources and improve economic benefits.Therefore,recycled concrete has become a research hotspot in recent years.Steam curing(steam curing)can increase the early strength of concrete,thereby shortening the concrete curing cycle and effectively shortening the construction period of the building.However,recycled concrete has disadvantages such as large porosity and low strength,and the heat loss caused by steam curing to the concrete has accelerated the aging rate of the building.GFRP(Glass fiber reinforced polymer,GFRP for short)is used to partially replace ordinary steel bars to make up for the corrosion defects of ordinary steel bars.However,the increased deflection of GFRP reinforced concrete members during bending poses certain safety risks,and it is not enough to improve the durability of steam-cured recycled concrete members by replacing corrosion-resistant steel bars.The effect of concrete performance on the service life of the members is also important.Therefore,this article uses fiber type(steel fiber,polypropylene fiber,glass fiber)and volume rate(0%,0.5%,1.0%,1.5%)as variables.The compressive performance and impermeability of steam-cured fiber recycled concrete,and the flexural performance of steam-cured GFRP tendon fiber recycled concrete beams are experimentally studied.The main research contents are as follows:(1)Considering the importance of concrete performance to the durability of steamcured recycled concrete components,cube test blocks of steam-cured fiber recycled concrete were used to conduct compression tests and observe the failure characteristics of the test blocks.It is found that adding steel fiber can increase the compressive strength of steamcured recycled concrete.The volume ratio of steel fiber is 1.0%,and the compressive strength is the largest,which is 15.37% higher than that of the test block without steel fiber.Incorporating polypropylene fiber and glass fiber has little contribution to improving the compressive strength of steam-cured regeneration coagulation.Observing its failure form,it is found that the recycled concrete test block mixed with fiber will spall less when it fails,and the addition of fiber can improve the brittleness of recycled concrete.(2)Research on the impermeability of steam-cured fiber recycled concrete through a combination of micro and macro methods.The microscopic test results show that: The concrete is wrapped and covered on the fiber surface.There are only a few micro-cracks on the interface between the fiber and the concrete,which acts as a skeleton connection between the aggregate and the concrete slurry,which can break the internal crack structure of the concrete,thereby blocking the generation and development of cracks.The porosity test results show that: When the fiber volume rate is 1.0%,the porosity is the smallest.Compared with the test block without fiber,the porosity decreases by 6.89% when the steel fiber is added.The porosity decreases by 9.53% when blended with polypropylene fiber,and the porosity decreases by 14.66% when blended with glass fiber.In this experiment,glass fiber has the best effect on improving the porosity of steam-cured recycled concrete.The results of the impermeability test show that: When the fiber volume rate is 1.0%,the impermeability is the best.Compared with the test block without fiber,the water penetration height is reduced by 18.50% when the steel fiber is incorporated,and the water penetration height is reduced by 25.33% when the polypropylene fiber is incorporated.When glass fiber is added,the water seepage height is reduced by 34.41%.In this experiment,glass fiber has the best effect on improving the impermeability of steam-cured recycled concrete.Combining the results of the porosity test and the impermeability test,it is found that there is an inherent relationship between the water penetration height and the porosity,and the relationship between the porosity and the penetration height of different types of steam-cured fiber recycled concrete is initially established.(3)The test beam was used for a four-point bending test.It was found that the number of main cracks in the test beam with fiber was reduced,and the cracks were mainly small cracks.The fiber was incorporated to inhibit the development of cracks.As the fiber volume ratio increases,the cracking load and ultimate load of the test beam increase accordingly.Under the same load,the strain of the GFRP tendons of the test beam doped with fiber is reduced,and the deflection of the test beam is reduced.Compared with the test beam without fiber,the strain of the tensile GFRP bar is the smallest when the volume rate of steel fiber is0.5%,and the deflection of the test beam is the smallest when the volume rate is 1.5%;When the volume ratio of polypropylene fiber is 0.5%,the strain of tensioned GFRP bar is the smallest,and when the volume ratio of polypropylene is 1.5%,the deflection is the smallest;When the glass fiber volume rate is 0.5%,the strain of the tensioned GFRP bar is the smallest,and the deflection is the smallest when the volume rate is 1.5%.(4)All test beams conform to the assumption of flat section.Considering that the existing formula is conservative in the calculation of the deflection of steam-cured GFRP steel fiber recycled concrete beams,an equation between the maximum deflection coefficient and the steel fiber content is proposed,and the equation is basically reasonable through verification.Considering that the existing specifications on the short-term stiffness influence coefficient of the flexural members mixed with polypropylene fiber and glass fiber are not clear,the equation between the short-term stiffness influence coefficient and the fiber content is proposed,and the equation is basically reasonable after verification.