Properties Of The Foam Concrete Containing Recycled Powder Derived From Construction And Demolition Waste

With the rapid development of infrastructure construction in China,the increased amount of construction and demolition waste has brought about some environmental problems.Therefore,it is necessary to use construction waste as resources.At the same time,based on the implementation of building energy-saving policies,it is particularly important to develop energy-saving building materials suitable for national conditions.In order to realize the resource utilization of construction and demolition waste and meet the energy-saving requirements of the construction industry,this paper prepares construction and demolition waste as a recycled powder by means of refinement and excitation,and uses it to replace part of the cement to prepare foamed concrete.The microscopic and macroscopic tests were tested to reveal the characteristics of the cementitious material incorporating recycled powder.The effects of different recycled powder content on the dry apparent density,compressive strength and thermal conductivity of foam concrete were investigated,which aims to estimate the performance of foam concrete with recycled powder.The main investigations in work are as follows:(1)The properties of recycled brick powder(RBP),recycled concrete powder(RCP)and recycled mortar powder(RMP)were determined by microscopic tests.The increased replacement ratios of recycled powder result in the Si-O stretching vibration peak moving to a high wave number,and the polymerization degree of silica tetrahedron in C-S-H gel is also increased,which indicates that the utilized recycled powder promotes the hydration degree of cement-based materials.Therefore,the recycled powder has a pozzolanic effect and can be used as an supplementary cementitious materials.(2)The incorporated recycled brick powder has no significant effect on the dry apparent density,porosity and thermal conductivity of its prepared foame concrete.When the replacement rate of recycled brick powder is less than 15%,the compressive strength of foame concrete is similar to or even higher than that of plain foame concrete without RBP.However,the compressive strength of foame concrete decreases with the further increased replacement rate of recycled brick powder.The addition of recycled brick powder decreases the drying shrinkage of foam concrete.When the replacement rate of recycled brick powder reaches 30%,the drying shrinkage of A03 foam concrete is 22.8%lower than that of plain foamed concrete without RBP.(3)Recycled concrete powder and recycled mortar powder have little effect on the dry apparent density,porosity and thermal conductivity of prepared foamed concrete(A03 grade).However,the compressive strength of foam concrete gradually decreases with the increased replacement rate of such recycled powder.The 28-d compressive strength of foame concrete with 30%recycled concrete powder and recycled mortar powder was 30.5%and 28.8%lower than that of plain foam concrete,respectively.The shrinkage rate of foame concrete increase at first and then decrease with the increasing replacement rate of recycled concrete powder and recycled mortar powder.Incorporating proper amount of such powder can decrease the drying shrinkage of prepared foam concrete.(4)The polyvinyl alcohol fiber and metakaolin can be used to modify the properties of foam concrete with recycled powder.The compressive strength of recycled powder foam concrete increase at first and then decrease with the increased volume of polyvinyl alcohol fiber,while the shrinkage rate gradually decreases.When the volume of polyvinyl alcohol fiber is 0.2%,the foam concrete has the highest compressive strength.The incorporated metakaolin has less impact on the dry apparent density of foam concrete with recycled powder,while the compressive strength increases as metakaolin incorproated.The compressive strength of foamed concrete with both 30%recycled powder and 10%metakaolin is the highest,which is 32.9%～42.1%higher than that of foam concrete with 30%recycled powder.