Experimental Research On Durability Of Crushed Bricks As Aggregate In Recycled Concrete Wall Bricks

Crushed bricks as aggregate in recycled concrete wall bricks is an green wall materials,which use sintered solid clay bricks from construction waste in order to achieve sustainable development of resources.At present, physical and mechanical properties and durability of recycled concerte wall bricks made with construction waste was studied by many domestic experts and scholars.compared to concrete wall bricks, crushed bricks as aggregate in recycled concrete wall bricks exhibit great differences in performance,and durability mechanism analysis becomes more complicated,and the results of research are diverse since the accession of the recycled aggregate.In this paper, based on the study of the physical and mechanical properties,durability of crushed bricks as aggregate in recycled concrete wall bricks was majorly studied.Crushed bricks as aggregate in recycled concrete wall bricks were designed with the C20 mixing ratio,and recycled crushed brick aggregate substitution rates were 50%,60%,70%,fixed water-cement ratio was 0.66,superplasticizer content was 1.5%,and air-entraining agent content is 0.05%,which was set the control group.due to the high water absorption and low moisture content of recycled clay bricks,the additional water was provided with 15%,18% and 20% corresponding to three different substitution rate.In this paper,experimental research included 28 d and 78 d compressive strength test,bulk density,physical and mechanical test,water absorption and coefficient of saturation,drying shrinkage testing,water resistance,carbonation, freeze-thaw testing,and microstructure test was also carried on,the test results were as follows:(1)In the compressive strength test,28 d compressive strength of Y5-X group and Y6-X group reach MU15 strength grade.5-X group and 6-X group were the best all over the group,78 d compressive strength reached 22MPa;bulk density was between 1893kg/m3~2090kg/m3;After recycled wall bricks were soaked in water at room temperature 24 hours,7-X group's water absorption reached to maximum,which was 7.973%,Y5-X's water absorption was minimum,which was 4.287%,and analyzed influence factors of compressive strength from the aggregate replacement ratio,added air-entraining agent and water absorption.(2)When replacement ratio of the crushed bricks aggregate was 50%,the minimum of drying shrinkage was 0.05%,Y7-X group's drying shrinkage was maximum,which was 0.063%.There was little effect on drying shrinkage of group,which recycled crushed bricks aggregate replacement rate was 50%,but more effect on group of60% recycled crushed brick aggregate and significantly reduced drying shrinkage,and increased drying shrinkage of group with fast growth,which recycled crushed brick aggregate replacement rate was 70% when air-entraining agent was added to test.(3)In the water resistance test,5-X group's softening coefficient was greater than1,the minimum of water resistance was 0.854 in Y6-X group,six groups all had good water resistance;the compressive strength was reduced less after carbonized 3d,the minimum of carbonation coefficient is 0.713 in Y7-X group,the maximum of carbonation coefficient is 0.970 in 7-X group with the strongest anti-carbonation.(4)In the Freeze-thaw cycle test, Y5-X group's strength loss and mass loss rate respectively was 4.71% and 0.83%,and frost resistance is best;air-entraining agent is added to improve frost resistance of crushed bricks as aggregate in recycled concrete wall bricks; frost resistance decreased as bricks aggregate replacement rate increased.(5)In the porosity anylysis test of crushed bricks as aggregate in recycled concrete wall,pores were composed by the 0 ~ 4mm different chord pores,pores chord mainly in0.5mm ~ 2mm,there were harmful holes on the compressive strength and durability.In this paper,the recyled crushed bricks aggregate maxial replacement rate was70%,when substitution rate increased,quality of crushed bricks as aggregate in recycled concrete wall bricks reduced,It's convenient for construction,but also increase the amount of construction waste's disposal,however according to this study,as the rate of substitution increased to70%,compressive strength and durability reduced,so it's important to study high substitution rate of crushed bricks as aggregate in recycled concrete wall bricks in the future.In order to improve physical and mechanical properties and durability of crushed bricks as aggregate in recycled concrete wall bricks.Adding air lead agent can improve durability,so further research on the amount of it should be addedand it's not enough for durability study to analyze simply experimental data,since the complex natural environment,so it's necessary to establish contacts between the laboratory and realistic environment,and laboratory studies should not be limited to the macro,the macro should develop to the meso and micro.