Research On Effects Of Waste Concrete Dust On Performance Of Mortar And Pervious Concrete

In recent years,China’s urban construction is changing rapidly.Especially since the19 th National Congress of the Communist Party of China,the progress of various constructions in China,especially urbanization,has been significantly accelerated,and many real estate companies are actively participating in urban renewal and reconstruction projects.In the process of promoting urban renewal projects,it faces the problem that a large number of abandoned construction wastes are difficult to handle,among which the most difficult problem is waste concrete.At present,the treatment of waste concrete is mainly simple landfill or even stacking in the suburbs.This treatment has a serious impact on the city’s image and ecology,and it also poses a certain threat to water resources and land resources.Therefore,how to recycle waste concrete in an environmentally friendly way is urgent.At the same time,the roads in cities are mainly made by asphalt or concrete,which are impervious to water.Therefore,in the event of heavy rain,there is a high probability of urban water logging,which will have a huge adverse impact on the lives of residents.For this reason,experts and scholars have proposed the concept of building a "sponge city",and pervious concrete plays an important role in this concept.Using waste concrete to prepare recycled pervious concrete can not only improve the recycling of solid waste,but also provide new ideas for the development of the concept of "sponge city".This research is of great benefit to urban construction and development.At present,the ways of recycling waste concrete mainly include "aggregate replacement method"(ARM)and "cement replacement method"(CRM).The so-called(ARM)refers to the crushing and processing of waste concrete into recycled coarse aggregate and recycled fine aggregate to replace natural aggregate.The(CRM)means that the waste concrete is crushed,processed and ground into fine powder to substitute cement.However,these two alternatives have the possibility of reducing the mechanical properties and durability of mortar/concrete.To this end,some experts and scholars have proposed a new replacement method,called "paste replacement method"(PRM).In this method,stone powder or recycled waste powder is used to replace a portion of thecement paste(water + cement)but with water/cement(W/C)ratio unchanged.At present,the PRM has successfully applied to different recycled powder,including recycled stone powder and waste brick powder in the producing of recycled motar/concrete.The relevant test data shows that the mechanical properties,durability and dimentional stability of recycled motar/concrete could be further enhanced.Nevertheless,the study of using waste concrete dust(WCD)based on the PRM in preparing mortar and pervious concrete is still lacking.Therefore,in order to explore the feasibility of PRM effects on WCD,this thesis applied the PRM and CRM,designed 28 groups of mortar mixes and 14 groups of pervious concrete mixes with W/C ratio and WCD replacement rate as control variables,then successively carried out mini slump-flow test,cube strength test,SEM test,carbonation test,electric flux test,water absorption test,drying shrinkage test,porosity test and permeability coefficient test.Finally,the performance attributes of WCD mortar and WCD pervious concrete were analyzed and explored.The main work and conclusions are as follows:(1)Based on the CRM and PRM,the effects of WCD on the fluidity,compressive strength and microstructure of the mortar were explored.To this end,WCD mortar mixes were made for mini slump-flow test,mortar cube compressive strength test,SEM test.The test outcomes indicates that,based on PRM,the use of WCD can enhance the compressive strength,and at the same time densify the micro-structure of the hardened mortar.Although the use of WCD would reduce the fluidity of mortar,which can be compensated by increasing the dosage of super water-reducing agent.On the other hand,the addition of WCD as cement would not affect the fluidity of mortar,but reduce the cubic compressive strength and loosen the micro-structure of hardened mortar.(2)Based on the PRM,the influences of WCD on the durability and volumetric stability of the mortar were explored.For this purpose,WCD mortar mixes were prepared for launching carbonization test,electric flux test,water absorption test and180-day dry shrinkage test.The test results presents that the replacement of paste by WCD can effectively reduce the carbonation depth,electric flux value,water absorption rate and 180-day dry shrinkage of mortar specimens.Therefore,the use of WCD toreplace paste can significantly enhance the anti-carbonization resistance,chloride resistance,water resistance and volumetric stability of mortar.(3)Based on the cement replacement method and the paste replacement method,the effectiveness of WCD on the compressive strength and permeability of pervious concrete were analyzed.To this end,WCD pervious concrete mixes were made for carrying out cubic compressive test,porosity test and permeability coefficient test.The test results show that,based on the PRM,the use of WCD can enhance the compressive strength of pervious concrete,and simultaneously increase the porosity and permeability coefficient.On the contrary,based on the cement replacement method,adding WCD to replace cement would reduce the cubic compressive strength,porosity and permeability coefficient of permeable concrete.