Study On Performance Of Modified Straw Fiber Thermal Insulation Concrete At High Temperature

In order to make straw fibers play a greater role in building insulation materials,the flammability of straw fibers and the properties of straw fiber insulation concrete under high temperature are studied in this paper.First,spray modification is used to flame retardant straw fibers.The flame retardant modifiers used are three flame retardants: ammonium polyphosphate(APP),magnesium hydroxide(MH),and aluminium hydroxide(ATH).Different types of flame retardants or different dosages were used,including single flame retardant modification,two flame retardant composite modification,and three flame retardants composite modification(APP: MH: ATH = 1:1:1;1:0.8:0.2;1:0.7:0.3;1:0.6:0.4;1:0.5:0.5).The indicators,including thermogravimetric curve,oxygen index,heat release rate,effective heat of combustion,etc,can be gotten from thermogravimetric analysis,cone calorimetry,oxygen index,Fourier infrared spectroscopy,X-ray diffraction,and scanning electron microscope and other advanced testing technologies.The thermal stability,flame retardancy,and microstructure of flame retardant fibers are analyzed.And the effect of different flame retardant modification methods on the properties of straw fiber under high temperature was clarified.Then,the modified straw fiber is used to prepare thermal insulation concrete.By using a box-type resistance furnace,an electronic universal testing machine,and a thermal conductivity measuring instrument,the macro-physical and mechanical properties of the heat-insulating concrete at high temperatures are tested.Combined with microscopic performance tests such as X-ray diffraction and scanning electron microscopy,the effect of modified straw fiber on the performance of thermal insulation concrete at high temperatures and its mechanism are analyzed.The effect of the modification method on the thermal stability of straw fiber at high temperature and its effect mechanism were studied.The results showed that the compounding effect of two or more flame retardants was significantly better than that of a single flame retardant.The best compounding ratio is APP: MH: ATH = 1:0.7:0.3,followed by APP: MH: ATH = 1:0.6:0.4.The flame retardant modification method used in this paper is mainly based on physical coverage and supplemented by chemical deformation.The modifier is pyrolyzed before the straw fiber during the heating process,and the released non-flammable gas and residue cover the fiber surface,which delays the fiber pyrolysis.At the same time,a bond is formed between some ions in the flame retardant modifier and some groups exposed on the surface of the straw fiber,reducing the pyrolysis activity of the fiber surface components to improve the thermal stability.The effect of the modification method on the macroscopic properties of straw fiber reinforced concrete at high temperature and its effect mechanism are studied.The results show that: by analyzing performance indicators such as mass loss,compressive strength,flexural strength,and thermal conductivity,the modified straw fiber concrete is comprehensive The group with the best performance is APP: MH: ATH = 1:0.6:0.4,followed by APP: MH: ATH= 1:0.7:0.3.The reason for this result is that although the use of APP alone to modify straw fibers can improve fiber stability,this method has an adverse effect on the hydration and hardening of straw fiber concrete at high temperatures.With the compounding of MH,ATH and APP,the hydration and hardening of concrete under high temperature is improved.When the compounding ratio is APP: MH: ATH = 1:0.6:0.4,the effect is the best.To sum up,in the method of flame retardant modification of straw fiber,the effect of multiple flame retardants on straw fiber and concrete is better than that of single flame retardant.In the method,the best compounding ratio exists.The best compounding ratio for the composite flame retardant modification of straw fiber applied in concrete is APP: MH: ATH = 1:0.6:0.4.