Compressive Performance And Hydration Mechanism Of Concrete Made With Recycled Coarse Aggregte And Manufactured Sand Incorporating Stone Power

The recycled concrete with manufactured sand is a new green building material,requiring considerable researches before it is applied in engineering.In this paper,an experimental and theoretical research is carried out to investigate the compressive strength,uniaxial compressive stress-strain relationship and cement hydration micro-mechanism of recycled concrete made with manufactured sand incorporating stone powder.Based on the formula for common concrete mix,the method of adding water was used to adjust mix ratio of the recycled concrete.The experiment be adopted the same water-cement ratio(0.4),design strength of 35Mpa,different stone powder content(0%,5%,10%,15%)and different recycled coarse aggregate replacement ratio(0%,33.3%,66.6%,100%).Main tasks fulfilled are as follows:First,120 compressive strength tests and splitting tensile strength test were conducted.The relationship between the stone powder content and recycled coarse aggregate replacement ratio on the tensile and compressive performance of recycled concrete with manufactured sand have been discussed,and the conversion relationship have been established.The experimental results show that a certain amount of stone powder can improve the concrete strength,with a recommended powder content of 10%.Compressive and tensile strength of recycled concrete firstly decreased and then increased as the incremental of recycled coarse aggregate,and reached its minimum when the recycled coarse aggregate replacement ratio was 66.6%;somewhat increased with the replacement ratio increased to 100%.The relationship between the compressive strength and splitting tensile strength is:ft=0.175fcu0.75;the splitting tensile strength is lower than that of common concrete.Then,60 axial compression tests were carried out,obtaining a series of uniaxial compressive stress-strain curves.Conversion relationship between cubic compressive strength and axial compressive strength of the recycled concrete with manufactured sand obtained from the test is:fc?0.818/cu;compared with common concrete,the axial compressive strength is higher than the same cubic compressive strength.The test results show that the uniaxial compressive stress-strain curve of recycled concrete with manufactured sand is basically the same as that for common concrete.The theory of damage mechanics can be adopted to analyze the process of uniaxial compressive damage.The uniaxial compressive stress-strain constitutive equation of recycled concrete with manufactured sand have been established.Finally,an X-ray Diffraction(XRD)phase analysis and Scanning Electron Microscope(SEM)test were performed during different hydration period to analyze the hydration product type and micro-structural features of recycled concrete with manufactured sand.The mechanism effect of stone powder on the compressive behavior was revealed.The test results indicate that the limestone powder was not only functional in fill,reaction and crystal nucleus,but also with an impact on morphological structure of the hydration products.The reaction effect mainly in hydration reaction of later period.