Study On Mechanical Properties Of Municipal Solid Waste Incineration Fly Ash In Geopolymer Concrete

Municipal solid waste incineration fly ash（MFA）contains Si,Al,Ca,and other active ingredients,which can replace metakaolin,fly ash,and slag in the traditional geopolymer raw materials.The MFA-based geopolymer cementitious material was used to formulate green low-carbon waste incineration fly ash geopolymer concrete（MFA-GPC）,which can provide new ideas for the disposal and reuse of MFA.The current research focuses on the immobilization of MFA by geopolymer,but there is a lack of research on the mechanical properties of MFA-GPC.In view of this,this paper prepares a green and low-carbon geopolymer concrete using MFA as a partial replacement for metakaolin,and its mechanical properties and microstructure were studied systematically through experiments,and an optimal MFA replacement ratio is proposed,which can make MFA-GPC meet the requirements of engineering applications and also meet the large-scale resource utilization of MFA.The main research content and results of the thesis are as follows:（1）The physical and chemical properties and heavy metal leaching properties of MFA were systematically investigated through microscopic test analyses such as laser particle size analysis,specific surface area analysis（BET）,scanning electron microscopy（SEM）testing,X-ray diffraction（XRD）analysis,X-ray fluorescence spectroscopy（XRF）analysis and inductively coupled plasma-atomic emission spectrometry（ICP-AES）analysis.The results showed that MFA is grey powder with rough surface and loose particle arrangement,the specific surface area and average particle size are 16.84m²/g and 35.807μm respectively,the main chemical composition of Ca O and chlorine salt are 35.87%and 24.50%respectively,and the main mineral components are Na Cl、KCl、Ca Cl OH、Ca（OH）₂、Ca SO₄ and Ca CO₃,and the leaching concentrations of Pb and Cr in the MFA exceeded the standard limits.（2）The mechanical properties of MFA-GPC were measured by compressive strength test,splitting tensile strength test,axial compressive strength test and static compressive elastic modulus test,and the mechanisms of the effect of different MFA substitution ratios on the mechanical properties of MFA-GPC was analysed.The results showed that the mechanical properties of MFA-GPC decreased in different degrees with the increase of MFA substitution rate.When the MFA substitution ratio reached40%,the MFA-GPC cubic compressive strength,splitting tensile strength,axial compressive strength and static compressive modulus of elasticity decreased by 83%,81%,78%and 93%respectively compared to control group.（3）The effect of MFA on the fracture performance of MFA-GPC was investigated by three-point bending fracture tests on pre-cut beams,using the fracture parameters such as peak load,initiation fracture toughness,instability fracture toughness and fracture energy of MFA-GPC as evaluation indexes.The results showed that the peak load,fracture toughness and fracture energy of MFA-GPC showed a gradual decrease with the increase of MFA substitution ratio.（4）The effects of different MFA substitution ratios on the microstructure of MFA-GPC were investigated by microscopic test analysis methods such as XRD analysis,Fourier transforms infrared spectroscopy（FTIR）analysis and SEM test.The results showed that the microstructure of MFA-GPC was porous and more obviously carbonized compared with the specimens of the control group,but the type of its hydrated gel products did not change,and it was still a calcium silicoaluminate（C-A-S-H）based silicoaluminate gel,and the microstructure had a certain degree of denseness.（5）Toxic leaching tests of MFA and MFA-GPC were performed by inductively coupled plasma spectrometry（ICP-AES）,and combined with XRD and FTIR characterization results to reveal the effective immobilization mechanism of geopolymers for heavy metals in FMA.The results showed that the leaching concentration of each heavy metal from MFA-GPC with 40%MFA substitution was much lower than the standard limit,and the geopolymer was used to achieve the effective immobilization of heavy metals in MFA by both chemical bonding and physical sequestration mechanisms.（6）The mechanical properties of MFA-GPC with 20%MFA substitution ratio meet the standard of C25 ordinary cement concrete,and the microstructure is relatively dense,and the leaching concentration of heavy metals is far below the standard limit,which can meet the requirements of some concrete structures with low strength requirements,i.e.MFA-GPC can be used as a new green low-carbon material to replace some cement concrete in engineering applications.