Stress-Strain Behavior Of FRP-Confined Waste Brick-Containing Concrete

The effective utilization of construction and demolition(C&D)waste is an important challenge faced by China's construction industry.Brick waste is the second-largest source of China's C&D waste,ranking only after concrete waste.While concrete recycling has attracted intensive research and engineering activities in recent years,brick reutilization has been paid muok less attention largely due to the associated difficulty arising from its relatively low strength,high porosity,and high water absorption.This situation necessitates the urgent need for seeking more effective methods for brick reutilization.In this context,this thesis attempts the use of brick waste in multi-scale forms(dust,aggregate and block)as a constituent for concrete production,in combination with fiber reinforced polymer(FRP)confinement as a means to enhance the properties of the resulting concrete.Such-formed FRP-confined concretes are respectively termed FRP-confined recycled brick dust concrete,FRP-confined recycled brick aggregate concrete and FRP-confined recycled brick block concrete in this thesis.Through experimental research,theoretical analysis and numerical simulation,a systematic study on the stress-strain behavior of these three types of concrete under axial compression was carried out,paving way for the applications of composite members based on such concrete.Forty-eight standard cylinder specimens made with FRP-confined recycled brick dust concrete were tested under axial compression with the paste replacement ratio of brick dust,FRP.thickness and concrete age as variables.The test results showed that FRP confinement can significantly improve the strength and deformability of recycled brick dust concrete,with the stress-strain curves featuring a bilinear shape.A high brick dust content led to an increased FRP confinement effectiveness,as compared to ordinary concrete.Jiang and Teng's analysis-oriented stress-strain model and Lam and Teng's design-oriented stress-strain model for FRP-confined ordinary concrete were modified accordingly to capture this feature.Seventy cylinder specimens made with FRP-confined recycled brick aggregate concrete were tested under axial compression with the replacement ratio of recycled brick aggregate,fiber layers of FRP tube and specimen diameter as variables.The test results showed that the stress-strain curves also feature a bilinear shape with the strength and deformability of recycled brick aggregate concrete being significantly enhanced.However,with the increase of the replacement ratio of recycled brick aggregate,the FRP confinement effectiveness decreased gradually.Again,Jiang and Teng's analysis-oriented stress-strain model and Lam and Teng's design-oriented stress-strain model were revised to reflect the effect of the replacement ratio.Forty-two cylinder specimens made with FRP-confined recycled brick block concrete were tested under axial compression with the mix ratio of recycled brick block,FRP thickness and specimen diameter as variables.The test results showed that FRP confinement is also effective for recycled brick block concrete.However,the tested specimens exhibited increased discreteness in compressive behavior owing to the large difference in strength between the recycled brick blocks and the fresh concrete,and the inhomogeneous spatial distribution of recycled brick blocks.According to the test results,a design-oriented stress-strain model for FRP-confined recycled brick block concrete was developed within the framework of Lam and Teng's design-oriented stress-strain model for FRP-confined ordinary concrete.Finite element simulation was carried out on the three types of FRP-confined concrete.For FRP-confined recycled brick dust concrete and FRP-confined recycled brick aggregate concrete,the modified analysis-oriented stress-strain model was used to calibrate the yield criterion,strengthening/softening law,flow rule and damage variable under uniform confinement of the three-dimensional concrete constitutive model.For FRP-confined recycled brick block concrete,random placement and distribution of the recycled brick blocks were realized,with the recycled brick blocks and fresh concrete being assigned with different material properties.