Experimental Study On The Microstructure And Biaxial Compressive Properties Of Concrete Made Of Manufactured Sand And Recycled Aggregate

It is an inevitable trend to seek alternative resources due to the non renewable quality of natural sand in the short term,so manufactured sand is a good choice.On the other hand,the increasing waste concrete will also become a major public hazard.The concrete made with manufactured sand and recycled coarse aggregate which consistent with the scientific concept of sustainable development can not only solve the problem of lack of natural resources,but also play a positive role in environmental protection.In this paper,190 C35 standard concrete specimens with different stone powder content(0%,5%,10%,15%)and recycled coarse aggregate replacement ratio(0%,33%,66%,100%)were made to experimental investigate on splitting tensile strength,microstructure,uniaxial and biaxial compressive of manufactured sand-recycled concrete.The main contents are as follows:Firstly,the splitting tensile test was carried out on the manufactured sand-recycled concrete with different content of stone powder and the replacement rate of recycled coarse aggregate.It is found that the optimum stone powder content is 10%,in this situation the concrete tensile strength of the manufactured sand concrete is the highest.The minimum splitting tensile strength of the low powder content(0%,5%)manufactured sand-recycled concrete is under the condition of recycled coarse aggregate replacement rate is 100%,while the high poerder content(10%,15%)and natural concrete is 66%.Secondly,the microstructure of manufactured sand-recycled concrete was studied by SEM.It is found that the stone powder can promote the hydration reaction of cement,and the content of stone powder affects the number of hydration products and crystal morphology.When the content of stone powder is 10%,the concrete reaches the best state of dense packing,the hydration product can fill the hole well,and the aggregate mortar is closely bonded.At the same time,stone powder has the role of filling in the small holes in the concrete,making the mortar more dense.The comparative analysis of the three interfacial transition zone of manufactured sand-recycled concrete shows that the strength sorting is interface transition zone between old aggregate and old mortar bigger than new mortar and old mortar bigger than new aggregate and new mortar.Thirdly,experimental study on the biaxial compressive properties of the manufactured sand-recycled concrete and observing the The failure process and failure mode.The result is that the failure mode of concrete under uniaxial compression condition is columnar failure,and the failure mode under biaxial compression is lamellar failure.However,because of the difference of strain ratio and the different aggregate,the inclination angle of fracture and the degree of thin layer failure are different.Forthly,the strength of biaxial compressive of concrete is much higher than that of uniaxial compression,but the Increase multiple is different from each other.The mutiple times is between 1.051～2.142.Under the condition of biaxial compressive stress,the maximum strength is related to the type of aggregate and strain ratio.The use of natural sand as fine aggregate concrete regardless of coarse aggregate as natural aggregate or recycled ’coarse aggregate maximum values appear in the strain ratio of 0.5,while the manufactured sand concrete and the manufactured sand-recycled concrete without stone powder appears in the strain ratio of 0.25,and the manufactured sand-recycle concrete is of 1.0.With the increase of strain rate,the spindle peak strain of the manufactured sand-recycle concrete increases first and then decreasing,while the horizontal axis only increases.Fifthly,under the condition of biaxial compressive stress,the stress-strain curves of concrete are composed of the following four parts:the compaction stage,the linear rise section,the crack development stage and the descending section.The proportion of each stage and the degree of damage are related to the content of stone powder and the type of aggregate.In the best stone powder content,the less the stone powder content is,the more the recycled coarse aggregate replacement rate is,the more serious the brittleness of the concrete is.Sixthly,the fitting curves of the stress and strain curves were fitted with the appropriate rising and falling section functions,and The fitting curve is in good agreement with the experimental data.Besides,according to the test result,the practical failure criterion of MRC-100-10 concrete is compased refer to the Guo Zhenhai failure criterion.