Study On Size Effects Of Mechanical Properities Of Recycled Concrete

In past decades,increasing concern for the environment as well as scarcity of natural resources has prompted the use of recycled concrete in many parts of the world.In recent years,many researches have been carried out on the mechanical properties of recycled concrete,such as compressive strength,tensile strength and so on.However,there is little research on the size effect of recycled concrete.In view of this,this study will focuses on the size effects on mechanical prosperities of recycled concrete.The relationship between the basic mechanical properties,such as compressive and tensile strength,and the size of recycled concrete specimens will be studied in the paper.In addition,the neutrosophic number is used to improve the size effect law to tackle the noise data.The main contents of this study are as follows:1.Using the same substitution rate of recycled aggregate,the size effect of compressive strength of recycled concrete cubes with different sizes was studied.It is found that the compressive strength of recycled concrete has obvious size effect.For the same substitution rate,the compressive strength value decreases gradually with the increasing of specimen size.2.The experimental study on splitting tensile strength of recycled concrete cubes with five sizes was carried out.It is found that the splitting tensile strength of recycled concrete also has obvious size effect.In general,the splitting tensile strength of the recycled concrete specimens increases with the increase of the specimen size.But sometimes the splitting tensile strength abnormally increases for the large size specimen.3.The dynamic modulus of the recycled concrete was measured and the damage degree was observed by the non-metallic ultrasonic test instrument.It is found that the dynamic elastic modulus of recycled concrete increases with the increasing of the size of the specimen.4.The volume strains of these recycled concrete cubes are obtained to show the corresponding size effect.It is found that there is a linear relationship between the stress and the volume strain of the recycled concrete cube in the elastic phase.In particular,anti-bending points can be observed in the stress-volume strain curves of the 70 mm and 150 mm recycled concrete cubes when the loads close to 80-90%ultimate load.5.The compressive strengths of recycled concrete cubes can be accurately predicted by Bazant's size effect law.And the size effect law using the neutrosophic number is more realistic than the original size effect law.The improved size effect law can deal with the uncertainty in the experimental data and provide an interval prediction of strength.