| Phosphogypsum(PG)is a solid waste produced in the production of phosphoric acid by wet method,and its resource utilization is a major technical bottleneck restricting the sustainable development of the phosphorus chemical industry.Simultaneously,building energy consumption which accounts for one-third of the total energy consumption in society is a key issue that restricts the development of green and low-carbon building materials in our country.The development of lightweight building materials is one of the important means to achieve building energy conservation and reduce energy consumption.The lightweight design of phosphogypsum based cementitious materials and its products can realize the utilization of solid waste while meeting the requirements of building energy saving,which is in line with the dual strategic needs to build a resource-recycling and energy-saving society.Based on the national key research and development project(2016YFC0700904),this thesis aims at the problems of beta-hemihydrate phosphogypsum(β-HPG)including its poor mechanical strength,poor water resistance and fast setting time.The thesis proposed the mineral reorganization and chemistry modification technologies to build a high-performance hemihydrate phosphogypsum cementitious(HPCM),analyzed the effect of different lightweight aggregates(LWA)on the performance of HPCM,discovered the relationship between the composition,structure and performance of the LWA-HPCM composite,studied the service behavior of the composite at different environments,developed the green manufacturing and efficient construction technology of lightweight interior wall materials,and realized its industrial application.The main work carried out in the thesis and its innovative results are as follows:1.Proposed the mineral phase reorganization and chemical modification technologies of β-HPG,and constructed a HPCM with excellent working performance,high mechanical strength and water resistance.(1)Based on the mineral phase reorganization technology,the modified component SAC with anhydrous calcium sulfoaluminate(C4A3S_)as the main mineral phase was used to optimize the mechanical and water resistance of β-HPG.Under the effect of SAC,the hydration exothermic process of the cementitious material converts from a single peak into a bimodal synergistic hydration exothermic process.After hydration,a multiphase mixture of dihydrate gypsum(DH),ettringite(AFt),hydrated alumina gel(AH3)and hydrated calcium silicate(C-S-H)gels are formed in the hydration products,the overlap between different crystal phases and gels builds a more stable and denser microstructure.When the SAC content is 20%,compared to the specimen without SAC,the compressive strength and softening coefficient of HPCM are increased by 66.94% and 61.11%,respectively.(2)Based on the chemical modification technology,protein(SC)and citric acid(CA)retarding components were used to control the mechanical and working performance of HPCM.The incorporation of retarding components makes the hydration of sulfoaluminate and hemihydrate gypsum synergistic.The transformation of the crystal morphology of DH phase under the selective adsorption of CA makes the formed microstructures looser.However,the refinement effect of SC on DH phase can make the system form a denser microstructure,which contributes to more excellent mechanical properties while ensuring the working performance.(3)The multi-component collaborative optimization of HPCM was carried out based on the response surface method.Through the analysis of the fitting models and the response surface,the optimal mixture design of HPCM under the combined modification of mineral and chemical components can be obtained,and the optimal contents of the two modified components were 20.48% and 0.12%,respectively.Compared with the specimen without modification,the dry compressive strength of HPCM increased by 86.29%,and the initial setting time was extended from 3 min to38 min.2.Proved the relationship between the composition,structure and basic performance of the LWA-HPCM composite.(1)Based on the mechanism of particle hydrodynamics,the force mode of LWA in HPCM slurry was analyzed,and the modification method to realize its uniform dispersion was proposed.The thesis studied the uniform dispersion mechanism of LWA in the system under the effect of viscosity modifying components,and established the matching relationship between LWA and slurry viscosity in different high density differential systems.Combining the determination of the stratification degree and the numerical calculation of the stratification index,the thesis proposed that the preferred ranges of the slurry viscosity and viscosity modifying components for the ideal homogeneous structure of the pottery sand,expanded perlite and EPS particles systems.(2)Based on the analysis of microscopic pore structure and composition,the relationship between the composition,structure and performance of the LWA-HPCM composite was constructed.Analyzing the relationship between strength and bulk density,the fitting equations for the strength and bulk density of pottery sand,expanded perlite and EPS particles systems were y=-0.00003x2+0.1082x-77.02,y=0.00002x2-0.0163x+5.2929,y=0.00002x2-0.0119x+3.2515,respectively.Pottery sand can control the bulk density of the composite in a small range(900-1500 kg/m3)and have a small reduction in mechanical strength,while expanded perlite and EPS particles can achieve a large range(300-1500 kg/m3)on the bulk density of the system but have a greater effect on reducing mechanical strength,in which the reducing effect of EPS particles was more significant.The decrease in bulk density of the composite with pottery sand and EPS particles is mainly due to the increase in the number of closed pores,while the decrease in the bulk density of the composite with expanded perlite is due to the increase in the number of open pores.Pottery sand and expanded perlite can form a good interface with HPCM,but the interface between EPS particles and HPCM is poor,and the disparity in the interface causes the difference in the mechanical properties of the composite.3.Studied the service behavior of LWA-HPCM systematically,and developed key technologies of industrialized preparation and application of phosphogypsum based lightweight interior wall materials.(1)The service behaviors of the composite such as water resistance,heat preservation,and sound absorption under the effect of different LWA were analyzed.In terms of water resistance,compared to the expanded perlite system,the decrease of open pores in the composite under the effect of pottery sand and EPS particles reduces its water absorption.When the content of pottery sand is 80%,the softening coefficient of the composite reaches 0.65,increased by 12.07% compared to the specimen without LWA.In terms of thermal insulation performance,compared with the pottery sand and expanded perlite system,the introduction of a large number of closed pores under the effect of EPS particles greatly hinders the transfer of heat.When the content of EPS particles is 80%,the thermal conductivity of the composite is 0.1106 W/(m·K),decreased by 79.21% compared to the specimen without LWA.In terms of sound absorption performance,compared with the pottery sand and EPS particle system,the introduction of cavity resonance structure under the effect of expanded perlite greatly improved the ability to dissipate sound waves.When the expanded perlite content is70%,the noise reduction coefficient of the composite reaches 0.7,increased by 337.5%compared to the specimen without LWA.(2)On the basis of the research and development of materials,the thesis carried out researches on the preparation and application technology of phosphogypsum based lightweight interior wall materials.Based on the mineral and chemical modification technologies of cementitious materials and its high-efficiency compounding with lightweight aggregates,non-steaming and low-cost preparation of interior wall materials with three different bulk density grades(700 kg/m3,800 kg/m3 and 900 kg/m3)were developed.Furthermore,the thesis developed high-efficiency construction technologies such as pipeline pre-embedding and surface anti-cracking of lightweight interior wall materials,which significantly improved the construction efficiency.Compared to the traditional aerated blocks,the construction efficiency can be increased by more than 200%,and the application effect is good overall. |
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