Quality Improvement Technique For Construction And Demolition Wastes And Its Applications

The utilization of recycled concrete aggregate(RCA)in concrete mixes opens a completely new set of potentials for using the recycled materials in the structural applications.This utilization of RCA is an efficient solution to the problem of an excess of construction and demolition(C&D)waste materials and an important breakthrough towards sustainable development.However,RCA possesses relatively higher water absorption,porosity and lower particle density due to the weak adhered mortar,which often impedes its using in the construction works.Thus,this study is undertaken to i)strengthen the attached mortar and optimize the quality of RCA by using pozzolanic materials;ii)investigate the performance of recycled aggregate concrete(RAC)with 100% strengthened RCA;iii)explore the feasibility of using the pozzolanic materials for enhancing the quality for both crushed brick aggregate(CBA)and mixed-recycled concrete aggregate(M-RCA)besides improving the performance of resultant concrete;and iv)predict the compressive strength of the treated RAC with pozzolanic materials using machine learning techniques.In order to achieve these aims,an economic and environmentally friendly surface treatment technique was proposed.Firstly,RCA was soaked in three different kinds of pozzolan slurries,namely,fly ash with silica fume(FA&SF),fly ash with cement(FA&C),and nanosilica fume(NSF),at different dosages and soaking times.Secondly,a series of laboratory tests and surface characterization of RCA were performed to identify the desirable concentration percentage and soaking time.Then,the mechanical and durability performance of concrete containing 100% strengthened RCA was investigated and the numerical model was used to simulate the migration test for the treated RAC.After that,the proposed technique was applied to enhance the performance of CBA and M-RCA as well as the resultant concrete.Finally,the compressive strength of the strengthened RAC with pozzolanic materials was predicted using machine learning techniques(ML).The innovative results of the present study are outlined as follow:(1)The proposed treatment technique effectively strengthened the attached adhered mortar and thus significantly enhanced the physical,mechanical and micro properties of RCA,CBA,and M-RCA,owing to the pozzolanic nature of the treated materials.(2)The proposed treatment technique improved the mechanical and durability properties for RAC,CBA,and M-RAC at different curing ages.Amongst the three treated pozzolan slurries,FA&SF slurry was the most efficient slurry in obtaining concrete with higher strength and more comparable to normal concrete.(3)The numerical simulation indicated a worthy agreement with the chloride ion migration laboratory test for the different concrete specimens.The chloride ion distribution profiles exhibited the lowest chloride ion diffusion depth for the treated RAC with FA&SF.Also,the treated RCA with FA&SF obtained the same predicted depth of NAC after 50 years.(4)Through SEM and X-?CT observations,the surface of untreated RCA and CBA was porous,rough,heterogeneous and irregular.Whereas the reinforced RCA and CBA surface was regular and contains fewer voids and pores in the adhered mortar.Also,the interfacial zones(ITZs)of treated RAC and BAC were enhanced and considerably become denser than that of untreated samples.(5)The small difference between the training,validating,and testing dataset revealed that the ML models could be utilized effectively for estimating the 28-days compressive strength of the treated RAC with pozzolanic materials.Finally,this research shows the feasibility of using the proposed technique for improving the adhered mortar,enhancing RCA,CBA,and M-RCA quality,managing the construction and demolition waste problem,dealing with the economic and environmental problems,and using 100% coarse RCA in concrete without varying the design and procedures of mixtures from the traditional case.