| Based on the actual demand background of carbon neutralization and carbon peak,the research on the preparation of building thermal insulation materials from agricultural and forestry wastes is carried out in this study,which is of great significance for the high value utilization of agricultural and forestry wastes,the realization of negative carbon dioxide emissions,and the promotion of building energy conservation.This study puts forward and verifies the technical path for the preparation of building thermal insulation materials from agricultural and forestry wastes by experiment.It includes:exploring the preparation process of novel biomass composite insulation materials;carring out the multi-objective performance tests including density,thermal properties,mechanical properties,hydraulic properties and fire performance;analyzing the influence characteristics of key process parameters in depth,such as water cement ratio,prewetting water quantity of raw material,foaming dosage,biomass quality,biomass torrefaction degree and so on.The main contents of this paper are as follows:Firstly,geopolymer with high performance was selected as the inorganic cementitious material of biomass composite thermal insulation material,and the influence of theoretical oxide SiO2/Na2O and SiO2/Al2O3molar ratios,and water-cement ratio on the mechanical properties of geopolymer was studied by orthogonal test.Meanwhile,a new type of biomass composite insulation material was prepared by using geopolymer as inorganic cementitious material and forestry waste sawdust as raw material,and the effects of curing conditions and water-cement ratio on the physical properties of biomass composite insulation materials were studied.The experimental results show that the best experimental combination scheme of factors is:the theoretical oxide molar ratios SiO2/Na2O=3.3,SiO2/Al2O3=3.2,water-cement ratio=0.5.What's more,the two-step curing method is much better than the one-step curing method.When the water-cement ratio is 0.5?0.55,the comprehensive physical properties of biomass composite insulation material are the best,and the corresponding thermal conductivity is 0.114?0.125 W/(m·K).Secondly,the effects of mass ratios of prewetting water to biomass(mw/m B),hydrogen peroxide to geopolymer(m H/m G),and biomass to geopolymer(m B/m G)on physical properties of sawdust biomass composite insulation materials were studied.The experimental results show that:considering both the resource saving and comprehensive performance,the biomass composite insulation material with mw/m B mass ratio of 1?2 is the best choice,and its thermal conductivity is 0.125?0.118 W/(m·K).When the mH/m G mass ratio is 0.012?0.015,the thermal conductivity of the biomass composite insulation material is 0.125?0.112W/(m·K).And when the mB/m G mass ratio is 0.12,the thermal conductivity of the biomass composite insulation material is 0.125 W/(m·K).Due to the existence of biomass raw materials,the high temperature resistance of biomass composite insulation materials needs to be further improved.Next,in this study,part of volatiles contained in the biomass raw materials itself was removed to increase the ignition temperature point,and then further improve the overall fire resistance performance of biomass composite insulation materials.To study the influence of carbonization conditions on the composition and properties of biomass raw materials,the physical and chemical properties of sawdust and wheat straw raw materials and their carbonized biomass were characterized and analyzed.The experimental results show that the content of volatile matter in sawdust and wheat straw raw materials is the highest,followed by the content of fixed carbon,and the main elements were C and O.The main components of sawdust raw material are lignin and cellulose,while the lignin content of wheat straw raw material is far less than that of cellulose and hemicellulose.With the increase of pyrolysis degree,the functional group bonds related to cellulose,hemicellulose,and lignin in carbonized sawdust and wheat straw are broken gradually.Based on this,the ignition temperature point of carbonized sawdust increases from 270?to 360?,while the highest ignition temperature point of carbonized wheat straw is 258?.Finally,to improve the fire resistance performance of biomass composite insulation materials,carbonized sawdust and carbonized wheat straw were used as raw materials,and geopolymer was used as inorganic cementitious material to prepare carbonized biomass composite insulation materials,and their related physical properties were characterized and analyzed.The experimental results show that:with the increase of carbonization degree of biomass,the pore size of carbonized biomass composite insulation materials first decreases and then increases,while the thermal conductivity,compressive strength,and density first increases and then decreases.Due to the flame retardant effect of geopolymer and the improvement of the burning point of carbonized biomass,the fire resistance performance of carbonized biomass composite insulation materials is gradually improved with the increase of carbonization degree of biomass.At the same time,the carbonized biomass composite insulation material can maintain structural integrity after exposure to high temperature flame for a certain period,without slag falling and collapse.Recycling agricultural and forestry wastes to prepare biomass composite insulation materials can not only improve the economic benefits of agricultural and forestry wastes but also save resources and protect the environment.What's more,taking technical measures of selecting high-performance and environmentally friendly inorganic cementitious materials,adopting simple and low-energy preparation processes,and carbonizing the biomass can improve the comprehensive performance of biomass composite insulation materials,thus promoting the construction of green new materials and high-quality green buildings. |
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