Experimental Research On Mechanical Properties Of Recycled Concrete With Polypropylene Fiber Artificial Sand

With the rapid development of society and the acceleration of urbanization construction, the concrete engineering was torn down, and the waste concrete becomes more and more, which caused serious environmental pollution. Some measures must be taken in order to solve the pollution problem. In order to protect environment, recycle of waste concrete and solve the shortage of natural sand resources, recycled concrete with ecotypic artificial sand and recycled coarse aggregate has been studied to reduce natural sand’s impact on the environment by the excessive exploitation, which also can produce certain economic benefits. That conforms to the basic state policy of conserving resources and to protecting the environment, and the ecological and social development of major strategic needs. In this paper, based on physical and mechanical properties of artificial sand which studied by the same team members, the recycled concrete with 100% recycled coarse aggregate, artificial sand and certain content of polypropylene fiber was made in order to analyse the mechanical properties.According to the two factors which are the concrete strength grade (C25、 C35、C45) and the polypropylene fiber content (0%、0.6%、0.9%、1.2%、1.5%), 45 standard cube concrete specimens and 90 standard prismoid blocks were made. The prism compressive strength test, the cube compressive strength test and modulus of elasticity test were carried out in order to study the influence of the different strength grade and different polypropylene fiber content on mechanical properties of concrete. The cube compressive strength, prism compressive strength of recycled concrete with fiber artificial sand change binary relation regularly with the change of fiber content and water-cement ratio. And the conversion equation of compressive strength and axial compressive strength was established. Based on the cube compressive strength, the experience formula of elastic modulus was established. The uniaxial compressive stress-strain of prismoid blocks of recycled concrete with fiber artificial sand was studied.The main research conclusions are as follows:1.The cube compressive strength and prism compressive strength increase first after decrease and then increase with the increase of polypropylene fiber content. The polypropylene fiber has a great influence on the low strength grade of concrete than the high strength concrete. But with the increase in fiber content, the fiber content has a limit effect to increase the prism axial compressive strength.The strength of three concrete strength grades (C25、C35、C45) of recycled concrete with fiber artificial sand can also be increased. But high polypropylene fiber content is unfavourable to the concrete strength. When the polypropylene fiber content is 0.6%, the cube compressive strength and axial compressive strength are improved.Based on least squares method, a model of binary relation between the cube compressive strength and fiber content and water-cement ratio was establised.2. The fitted value ratio of prism compressive strength and cube compressive strength of recycled concrete with fiber artificial sand is 0.75, that is fc=0.75fcu。3. The peak strain of recycled concrete with fiber artificial sand increases with the increase of concrete strength grade, as fiber increase with the increase of the polypropylene fiber content. Especially in the low strength grade of concrete, fiber has great obvious effect to increase the peak strain of concrete. Ultimate strain of recycled concrete with fiber artificial sand decreases with the increase of concrete strength grade, increased with fiber content increases. The polypropylene fiber can improve the deformation and ductility of recycled concrete with fiber artificial sand.4. The elastic modulus value of recycled concrete with fiber artificial sand is lower than that of the same strength grade of ordinary concrete. Each kind of the elastic modulus value decreases with the increase in fiber content. When the fiber content is from 0.9% to 1.5%, the loss of elastic modulus value of the high strength grade concrete is larger than that of the low strength grade of concrete. The experience formula of the elastic modulus based on the cube compressive strength was formed.5. Based on least squares method, a constitutive model of the stress-strain relationship of recycled concrete with fiber artificial sand under uniaxial compression was established.The results can provide methds and theory basis for analysis and calculation of recycled concrete with fiber artificial sand.