| At present,70%of the urban environmental noise comes from traffic noise,and the rapid development of highways and railways,the increase of the speed and the increase of traffic volume make traffic noise pollution increasingly prominent,especially the noise caused by urban subways.There are two ways of preventing and controlling noise:controlling the sound source and the sound propagation route.For the subways tunnel traffic noise,the former has the characteristics of high cost,complicated construction,and difficult maintenance and maintenance costs,while the latter usually uses sound absorption and sound insulation.At present,laying sound-absorbing material track plates to treat subway tunnel noise has become a hot topic because of technical feasibility and economical rationality.Research on sound-absorbing materials has also become the latest research direction in the current materials science.The subway tunnel is a special environment.In addition to the sound-absorbing function,the subway sound-absorbing materials need to consider properties such as strength,fire prevention,anti-corrosion,and durability.traditional sound-absorbing materials cannot be adapt,and it is necessary to develop a new all-weather inorganic porous sound-absorbing material to meet the requirements of strength,fire prevention,anti-corrosion,durability,and sound absorption.The sintering-free fly ash ceramsite is a green and environmental porous material.In the previous study,we independently developed a special sintering-free fly ash ceramsite,and prepared a lightweight porous ceramsite concrete,and completed the development of a subway track sound-absorbing board.The noise reduction coefficient of the sound-absorbing panel reaches 0.80 or more.,and the sound-absorbing performance meets the national standard level I standard.Although sound-absorbing board work well for sound absorption of mid-and high-frequency noise,their effect on low-frequency noise still needs improvement.For this reason,this paper combines the theory of porous materials'microstructure and sound absorption properties of materials,starting from the research and development of raw materials,in the independent research and development of sintering-free fly ash ceramsite preparation process,increase the foaming process and heat treatment process,by controlling the amount of foaming agent,heating rate,curing time,three control factors,the microscopic structure of ceramic materials was adjusted to increase the porosity and apparent porosity of the ceramic particles,improve their low-frequency sound absorption performance,and optimize the sound absorption effect of the entire frequency band of railway traffic noise.The subject has studied the microstructure of porous ceramics under the influence of the amount of foaming agent added,heat treatment rate,and curing time by searching data,using theoretical analysis,macroscopic testing,and microscopic characterization.A mature method for synthesizing porous sound-absorbing ceramsites by a foaming method is proposed.(1)The thermal analysis(Thermo Gravimetric analysis(TG),Differential Scanning Calorimetry(DSC))was used to study the mechanism of decomposition of ammonium bicarbonate as a foaming agent.Observe the influence of temperature increase on the shape of the ceramic particles and the temperature value of the particles during the heat treatment of the ceramic particles.The range of temperature regulation in the heat treatment mechanism of the ceramsite synthesis process was determined as 30°C~300°C.(2)Using a single factor variable control method,design of ammonium bicarbonate foaming agent were added in an amount 0.0wt%,0.5wt%,0.7wt%,1.0wt%,2.0wt%,The followed by heating rate 3?/min,5?/min,10?/min,15?/min,20?/min,25?/min,according to the direct heat treatment(curing time 0h)and 72h after curing,the heat treatment method controls the porous ceramic process.A total of 61 samples were designed and synthesized,including a set of ceramic comparison samples(referred to as the original sample)prepared under the same conditions and prepared by the original process.Through macroscopic tests such as apparent porosity,water absorption,numerical tube pressure,and bulk density,it was measured that the apparent porosity of the porous ceramic cerams synthesized under different control conditions was between 20.23%and32.67%,and the water absorption distribution between 18%~23%,the bulk density was between 860 kg/m~3 and 916 kg/m~3,and the numerical tube pressure was between 2.82MPa and 6.04 MPa,The effect of three control factors on the physical properties of porous ceramics is shown.(3)Using microscopic analysis methods such as scanning electron microscopy(SEM)and X-ray diffraction(XRD),combined with macroscopic test data,16 representative representative samples were designed:(1)The heating rate was 20°C/min,Consider 10 sets of samples corresponding to changes in the amount of foaming agent added and the curing time;(2)The optimum amount of foaming agent was 2.0wt%.The observation and contrast analysis of 6 groups of samples corresponding to the change of heating rate was considered.The pore structure of porous ceramsites under different control factors was explored,The influence of the three control mechanisms of foaming agent dosage,heating rate,and curing time on the microstructure of ceramsites was clearly defined.The results show:With the increase of the amount of foaming agent,the curing time is shortened,and the heating rate is increased,the apparent porosity of the ceramsite can be improved,and the pore size can be uniformly and orderly distributed.The size and distribution range of apparent pore size of the ceramsite were measured and calculated using Photoshop software's ruler function to further define the effect of the control mechanism on the pore size of the porous ceramsite.The average pore size of the porous ceramsite synthesized by the three control mechanisms is basically maintained between 0.2?m and 1?m,which is an important conclusion of the micron-sized pores,and reaches the size range of the low-frequency sound-absorbing pore size,which indicates that the foaming and heat treatment mechanisms can improve the ceramics low frequency sound absorption effect.(4)Using the standing wave tube method to analyze and study the sound absorption performance of 12 groups of porous ceramsites(including common ceramsite contrast samples)synthesized under the three control mechanisms.the results show:The porous ceramsite synthesized by controlling the amount of the foaming agent ammonium bicarbonate with an addition amount of 2.0 wt%,a heating rate of 20°C/min,and a curing time of 0 h(direct heat treatment)is a lightweight aggregate.The sound-absorbing coefficient of the ceramsite concrete sound-absorbing material in the full range of subway noise is greater than 0.3,and the numerical distribution of each point tends to be uniform,meet the requirements of the sound absorption material standard>0.2,the average sound absorption coefficient is 0.54,achieve the requirements of the ideal sound-absorbing material standard 0.5,effectively improve the low-frequency sound absorption performance of the material and achieve a good broadband sound absorption effect.(5)Based on the completion of experimental research,microscopic characterization,and theoretical analysis,the broad application features and research prospects of this application material are proposed,It also has clear ideas for the later research work. |
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