| Industrial solid waste is one of the bottlenecks that restrict the green transformation development in China due to its large production and stockpiles volume,wide coverage,and great environmental hazards.Promoting industrial solid waste resourceful utilization is of great significance for raising resource utilization efficiency,bettering the environment,and promoting the overall green transformation development of economic and social.However,the variable physicochemical properties,limited utilization efficiency,high disposal cost and low value-added of industrial solid waste are the difficulties in the resourceful utilization of solid waste.Thus,developing innovative industrial solid waste utilization methods with wide coverage,high-performance product and high value-added is a crucial process to realizing resourceful utilization of industrial solid waste.In this research,FGD gypsum,carbide slag,red mud(RM),electroplating sludge(ES)and fly ash(FA)were used as raw material to synergistically prepare FR-SAC,which was synergistically used again with FGD gypsum to prepare non-autoclaved lightweight porous concrete(NA-LWC).Then,the pilot design and research of preparing NA-LWC from solid waste were investigated.Finally,the environmental influence of NA-LWC from solid waste was assessed using the life cycle assessment method to establish a low-carbon,energy-saving,and efficient NA-LWC preparation process.The main works are as follows.(1)The influence mechanism of thermal decomposition characteristics,chemical and mineral composition of solid wastes on the mineral composition of FR-SAC clinker were investigated,which verified the fesaibility of preparing FR-SAC clinker from industrial solid wastes.Then,FR-SAC was prepared from industrial solid wastes,and the effect of calcination process and raw mixture on the mineral composition and content of FR-SAC clinker were studied to get a high-performance FR-SAC.(2)The influence mechanism of CaO or CaSO4 on the iron-bearing mineral of FR-SAC clinker were revealed by using chemical reagents as raw material to prepare FR-SAC clinker.With decreasing CaO content involved in calcination reaction,the amounts of C4AF decrease and Fe2O3 incorporated in C4A3-xFxS increase up to 17.22(where x=0.36).With the increase of CaSO4 content in raw material,both the amount of C4AF and C4A3-xFxS decreases significantly,while the amount of Fe2O3 incorporated in C4A3-xFxS increases.In addition,the influence mechanism of CaO/CaSO4 on the mineral composition of FR-S AC clinker also was revealed from the thermodynamics.According to the thermodynamic data,the content of CaO involved in reaction affects the Gibbs free energy of the formation of C4A3S and C4AF.When the amount of CaO is excessive,C4AF is easier to be formed and the amount of Fe2O3 incorporated in C4A3-xFxS decreases.When the amount of CaO is insufficient,C4AF is difficult to form than C4A3S.More unreacted Fe2O3 are incorporated into C4A3S to form C4A3-xFxS,which improve the effective utilization of Fe2O3 and optimize the mineral composition of FR-SAC clinker.In the process of preparing NA-LWC from solid waste-based FR-SAC,to make it suitable for preparing NA-LWC,PCE,CS and HPMC were used as admixtures to change the properties of FR-SAC.The effects of PCE,CS and HPMC on the properties of FR-SAC were revealed,such as hydration performance,fluidity,water absorption and viscosity.With the increase of PCE addition,the water requirement of normal consistency of the cementitious material paste gradually decreases.When the PCE dosage is 1 wt.‰,the water requirement of normal consistency of FR-SAC paste is reduced by 27%.The FR-SAC paste with CS added shows good hydrophobicity and low early water absorption,but it has little effect on long-term water absorption.HPMC can significantly increase the viscosity but reduce the fluidity and compressive strength of the FR-SAC paste.Therefore,the added amount of HPMC and CS needs to be determined based on the production process and compressive strength requirements to present good performance in the rheological parameters and compressive strength.Modified FR-SAC and thermal decomposition FGD gypsum were synergistically used to prepare NA-LWC.The influences of cementitious materials,additives,hydrogen peroxide content and water-cement ratio on the NA-LWC properties were investigated to get a suitable raw mixture during NA-LWC production.With increasing in the amount of FGD gypsum,the apparent density and compressive strength of NA-LWC reduce and the water absorption of NA-LWC increases.With the increase of hydrogen peroxide,the pore size and porosity of the NA-LWC increase,and the apparent density and compressive strength decrease but the water absorption rate increases.When CS is added into NA-LWC,it will not only increase the hydrophobicity of NA-LWC but also increase the surface tension of the slurry and increase the closed cell ratio in NA-LWC.With the CS content increase from 0 to 1%,the compressive strength of NA-LWC increases by 18.9%,and the water absorption decreases by 40.9%.When the amount of HPMC increase,the pore diameter in NA-LWC decreases and the pore wall becomes thinner,so the compressive strength decreases and the water absorption increases accordingly.Therefore,when using FR-SAC and FGD gypsum to prepare NA-LWC,the addition ratio of FR-SAC to thermal decomposition FGD gypsum is 7:3,and the volume fraction of hydrogen peroxide is 1.6.%mL/g,and the reaction temperature is 30?,and the water-cement ratio is 0.34,and the amounts of PCE,CS,HMPC and KI are 0.1%,1%,0.05%and 0.05%g/mL H2O2,respectively.Based on the results from laboratory research,a pilot-scale line for preparation of FR-SAC and NA-LWC from industrial solid waste was established.Meanwhile,FR-SAC and NA-LWC with good performance and efficient production parameters were obtained.The pilot-scale production line for the preparation of FR-SAC from industrial solid waste is mainly composed of raw meal disposal,clinker calcination and cementitious material grinding systems.The FR-SAC obtained from this production line can meet the compressive and flexural strength properties required by grade 52.5 cement,but the setting time of FR-SAC is relatively short.The pilot system for preparing NA-LWC from FR-SAC is mainly composed of raw material preparation,mixing and pouring,mold box operation and pre-curing,cutting system.Using the formula developed in the laboratory as the raw material,when the stirring rate is 500 r/min,the stirring time and the running time are 5 min and 6 h,respectively,the production efficiency and product performance of NA-LWC reach the best state.Based on the life cycle assessment(LCA),the environmental impact and carbon reduction of solid waste-based FR-SAC and NA-LWC were evaluated,which provided a theoretical basis for green and low-carbon improvements in the NA-LWC production process.Compared with the environmental impact of AAC,the environmental impact of NA-LWC reduces by 24.38%according to LCA standardization analysis;According to the LCA analysis of NA-LWC's,the key processes during the life cycle of NA-LWC are FR-SAC clinker calcination,slurry preparation and pouring,and LWC raw material preparation;the key materials are hydrogen peroxide and electricity.It means that reducing the amount of FR-SAC clinker in NA-LWC and increasing the utilization efficiency of hydrogen peroxide are effective methods to reduce the environmental impact.In addition,the preparation of cementitious materials is the process that accounts for the largest proportion of carbon emissions in the life cycle of NA-LWC.Compared with AAC,the carbon emissions of NA-LWC reduce by 68%. |
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