A Study On The Enhancement Of Recycled Aggregate And Its Effect On The Compressive Strength Of Concrete

With the renovation and reconstruction of the city,the construction industry generates about 40% of the municipal waste every year,which gives rise to some problems of environmental pollution and construction waste treatment.Besides,the building materials industry will also face the depletion of natural resources.From the perspective of environmental protection and sustainable development,the development direction of recycling waste building materials has been put on the agenda.At present,the recycled aggregate prepared by waste concrete replaces the natural aggregate mixed into concrete to achieve the recycling of resources,and the development of recycled concrete gradually attracts the attention of society.At present,there are many types of research on reclaimed coarse aggregate,but relatively few on reclaimed fine aggregate.The characteristics of recycled fine aggregate and recycled coarse aggregate are similar,with high water absorption,low strength,low apparent density,and a large amount of old mortar attached to the surface of the aggregate.In addition,the interfacial transition zone of recycled fine aggregate is weaker,which is the main factor leading to poor aggregate performance.Therefore,it is necessary to modify the recycled fine aggregate to improve its performance,and then indirectly improve the performance of recycled concrete.This experiment mainly studies the influence of recycled fine aggregate after modification on the macroscopic property and micro-Nano-view property of concrete.The experiment is divided into two parts: 1)Modification treatment of recycled fine aggregate;2)The recycled fine aggregate before and after modification was used to prepare concrete.For modification of recycled fine aggregate processing includes two processes,the water treatment in the first place,is to make the impurity in the recycled fine aggregate hydration and completely clean aggregate,then the aggregate of water treatment after carbonization,the aggregate cracks,holes,and interface transition zone of Ca(OH)2complete carbide,increase the compactness of recycled aggregates.In the concrete test,three kinds of fine aggregate will be mixed into concrete according to a certain amount.The purpose is to study the changing rules of the macroscopic and microscopic properties of concrete before and after treatment and compare them with the reference group.Macro test for compressive strength and dry shrinkage,micro Nano test respectively,scanning electron microscope(SEM)test and Nanoindentation test,through the values of compressive strength and the shrinkage of concrete value research of recycled fine aggregate on concrete macroeconomic performance before and after processing,the effect of internal microstructure observed by SEM test concrete and Nanoindentation test was used to study the changing rule of the Nanomechanical properties.The results show that with the increase of the amount of recycled fine aggregate,the strength of recycled concrete decreases gradually,and the same conclusion is obtained for the modified recycled fine aggregate concrete.Compared with the ordinary recycled concrete,the properties of the treated recycled fine aggregate concrete are significantly improved.The compressive strength of NF75+ERF25 is close to that of NF100 and much higher than that of N75+RF25.Similarly,the drying shrinkage rate of the NF75+ERF25group was significantly reduced,which was only greater than that of the NF100 group,while compared with other groups,the drying shrinkage rate of the NF75+ERF25 group was significantly reduced.SEM analysis results showed that a large number of hydration products were generated in the interface transition zone of the regenerated fine aggregate after modification,and the cracks in the interface transition zone were filled to make it more compact.The improvement effect of the NF75+ERF25 group was more obvious,and the cracks in the interface transition zone were effectively filled.The Nano-indentation test shows that the elastic modulus of Nano-indentation between the interfacial transition zone of the modified recycled concrete and the mortar is significantly increased.Besides,compared with the reference group RF100,the width of the interfacial transition zone of ERF100 is also significantly reduced.