Study On The Mechanical Properties Of Recycled Aggregate Concrete Prepared With Carbonated Aggregates And The Interfacial Transition Zones

With the rapid development of urbanization,a great deal of construction and demolition waste is generated every year.In order to alleviate the environmental pressure imposed by the increasing construction and demolition waste and solve the problem of the lack of natural aggregates,using recycled concrete aggregates(RCA)derived from construction and demolition waste to replace natural aggregates has attracted the attention of scholars all over the world.However,RCA is inferior to natural aggregates because of the old mortar.Moreover,the mechanical properties and durability of recycled aggregate concrete(RAC)are worse than those of natural aggregate concrete due to the three types of interfacial transition zones(ITZ)in RAC.For the purpose of promoting the application of RCA in the engineering field,it is necessary to improve its properties.In this dissertation,the properties of RCA were effectively improved by accelerated carbonation technology.With the help of macro-test methods,micro-test techniques,and the numerical simulation methods,the correlation mechanism between the mechanical properties of RAC prepared with carbonated RCA(CRCA)and the micro-properties of ITZ was revealed.Details of the research contents are as follows:(1)The study on the quality improvement of RCA by accelerated carbonation under different pressure was carried out,with the influence law of carbonation pressure on the apparent density,water absorption and crushing value of RCA pre-soaked with saturated lime water ascertained,the linear negative relationship between the apparent density and water absorption established,as well as the linear positive relationship between the crushing value and water absorption established.By utilising micro-test techniques such as scanning electron microscope-energy dispersive spectrometer(SEM-EDS),X-ray diffraction(XRD),thermogravimetry-differential scanning calorimetry(TG-DSC)and Vickers micro-hardness,the effects of accelerated carbonation on micro-morphology,mineral crystal chemical elements,mineral phases,chemical composition contents and Vickers micro-hardness of the old mortar and ITZ in RCA were studied,and the strengthening mechanism of the properties of RCA pre-soaked with saturated lime water by accelerated carbonation was revealed.(2)The study on the mechanical properties of RAC prepared with carbonated aggregates(CRAC)and the micro-properties of ITZ was carried out,with the influence law of aggregate replacement ratios(0%,30%,70%,100%)on cubic compressive strength,splitting tensile strength and flexural strength of RAC at 7 and 28 days ascertained,the relationship between splitting tensile strength and cubic compressive strength established,as well as the relationship between flexural strength and cubic compressive strength established.By utilising micro-test techniques such as SEM-EDS,XRD and Vickers micro-hardness,the effects of CRCA on the micro-morphology,mineral crystal chemical elements,mineral phases and Vickers micro-hardness of ITZ in CRAC were studied,and the strengthening mechanism of the micro-properties of ITZ by CRCA was revealed.(3)The study on the uniaxial compressive stress-strain behaviour of CRAC was carried out,with the uniaxial compressive failure processes and modes of prismatic specimens revealed,the linear positive relationship between uniaxial compressive failure angles and aggregate replacement ratios(0%,30%,70%,100%)established,the influence law of aggregate replacement ratios on uniaxial compressive stress-strain curves discussed,the prediction models of the peak stress,elastic modulus,peak strain and limit strain proposed,as well as the constitutive model and the damage constitutive model of RAC under uniaxial compression built.(4)The study on the fracture behaviour of ITZ in modelled RAC was carried out,with the influence law of water-cement ratios(0.40,0.45,0.50)of the new mortar and CRCA on load-displacement curves,maximum loads,critical displacements and instability toughnesses ascertained,as well as the equations of load-displacement curves established.By utilising micro-test techniques such as SEM-EDS,XRD and Vickers micro-hardness,the effects of CRCA on the micro-morphology,mineral crystal chemical elements,mineral phases and Vickers micro-hardness of modelled ITZ were analysed,and the strengthening mechanism of the micro-properties of modelled ITZ by CRCA was revealed.Based on the cohesion zone model,the influence law of slit heights and interface strength on the fracture behaviour of the modelled ITZ were studied by ABAQUS.There are 108 figures,40 tables,and 191 references in this dissertation.