Experimental Study On Performance Of Mortar And Concrete Incorporating Recycled Clay Brick Dust

With quick urbanization in China,urban village re-development and urban renewal have been carried out in large scale,especially in developed area like Pear River Delta.As most demolished buildings are brick-concrete structures,proportion of clay brick waste among construction waste is large.At present,the typical measure to deal with the construction waste is landfill or placement in open-air,which not only brings pollution to environment but also leads to an occupation of useful land.In fact,fired clay brick is manufactured by moulding and burning high-quality clay and has a pozzolanic property,which has a great potential for being reused in the production of mortar and/or concrete.Some researchers have proposed adding clay brick waste to partially replace cement(cement replacement method),while others have put forward reusing clay brick as recycled brick aggregates in concrete(aggregate replacement method).However,both of the two methods cause a decrease in performance of mortar and/or concrete(e.g.,decrease in strength and durability).In recent years,some scholars have developed a new replacement method called paste replacement method,which adds stone powder or recycled powder(from concrete waste)to partially replace the cementitious paste(water+cement)with water to cement ratio kept unchanged.This method have been successfully applied for limestone powder,recycled marble powder and recycled granit powder,which not only improves strength,durability and dimensional stability but also significantly reduces cement content and improves utilization rate of recycled powder,leading to a concrete product which is truly green and of high performence.Nowdays,whether the past replacement method is suitable for recycled clay brick dust still remains unknown,and there is a lack of related research on this issue,which necessitates the research in this area.In this MSc program,a total of 29 groups of mortar and 18 groups of concrete with warying W/C(water/cement)ratio and clay brick content were designed for the tests of mortar cube strength,scanning electron microscope analysis,XRD analysis,sulphate attack durability,water absorption,dry shrinkage and concentric compression.The main research work covered in this thesis is as follow:(1)In order to study the effect of paste replacement and cement replacement on the cube strength,microstructure and hydration reaction product of mortar incorporating recyclced clay brick dust(CBD),the mortar made by adding CBD to replace paste and the mortar produced by using clay brick dust to substitute cement were produced.Slump tests,cube strength tests,electron microscope tests and XRD analysis tests were carried out respectively.The experimental results showed that in paste replacement method,although the additions of clay brick dust increases the SP dosage for maintaining the workability of mortar,it significantly improves cube strength,densifys the microstructure of motar.However,using cement replacement,although the additions of clay brick dust does not appreciably increase the SP dosage,it evidently renduces cube strength of mortar and loosens the microstructure of mortar.(2)In order to further study the effect of paste replacement on the durability and dimensional stability of the mortar,the mortar produced by paste replacement method is used for sulphate attack tests,water absorption tests,and dry shrinkage tests respectively.The experimental results showed that in the paste replacement method,the additions of clay brick dust can signifcantly decrease strength loss after sulphate attack,water absorption rate and shrinkage strain.(3)In order to study the effect of paste replacement on mechanical property of concrete,the mortar made by the paste replacement method is used for preparing concrete cylinders in compression tests.The experimental results showed that the additions of CBD can increase the SP dosage for keeping workability of concrete,however,it significantly improves compressive strength and elastic modulus of harden concrete and has a little influence on possion's ratio.The test results also showed that the with increasing concrete strength,theOutcomes of this research are not only of great research significance,but also have important application value and environmental merit.