Study On The Performance Of Corn Straw Fibre Asphalt Mastic Based On Surface Modification

Corn straw is a by-product of maize cultivation,but only a small part of it has been reasonably developed and utilised,causing loss of resources and environmental pollution,which is not in line with the national policy of energy conservation and environmental protection.Corn straw fibre has the characteristics of environmental protection,low processing difficulty and low cost,so its application in asphalt road engineering is of great significance to its performance in improving asphalt roads.In this paper,the physical structure and chemical properties of corn straw fibres were analysed,and on this basis,two chemical reagents,hydrochloric acid and sodium hydroxide,were used to modify the surface of straw fibres in single and binary combinations,and three optimal modification methods were selected by constructing an evaluation index system through oil absorption and heat resistance.Modern material analysis techniques were used to compare the changes in microscopic morphology,infrared spectra,crystallinity and thermal stability of straw fibres before and after surface modification to reveal the surface modification mechanism of corn straw fibres.The lignin fibre asphalt mastic was compared with the lignin fibre asphalt mastic.The shear strength and high temperature rheological properties of the surface modified fibre asphalt mastic were evaluated by cone penetration test and dynamic shear rheology test,and the low temperature rheological properties of the surface modified fibre asphalt mastic were evaluated by bending beam rheology test,and the optimum type and dosing of the modified fibre were derived.The results show that the surface of corn straw fibre has an uneven groove structure,which can increase the surface area of the fibre and is conducive to the adsorption and binding with asphalt mastic.The main components of corn straw fibre are cellulose,hemicellulose and lignin,with a crystallinity of 54.8%,close to 58.5%of lignin fibre.The thermal decomposition stage is 180 ℃ ～ 350 ℃,with good thermal stability,can be applied to asphalt road projects.All three modification methods can improve the oil absorption rate and heat resistance of straw fibres.The binary composite modified straw fibre has the best overall performance,with an oil absorption multiple of 9.13 times and a heat loss rate of 3.34%.Before and after the surface modification,the straw fibre performance was improved because the lipids and impurities on the fibre surface were removed to varying degrees by the chemical reagent modification,which could largely improve the fibre looseness on the outer surface of the corn straw fibre,thus better absorbing most of the oil and grease,while at the same time,the thermal decomposition temperature onset of the fibre was increased,which greatly enhanced the thermal stability of the straw fibre.The taper penetration test showed that the depth of penetration of the taper needle of the straw fibre incorporated into the surface modified asphalt mastic decreased and the shear resistance increased compared to the blank asphalt mastic control group.The shear strength of the lignin fibre was the best at 198.5 k Pa and the binary composite modified fibre was similar at 173.8 k Pa.The dynamic shear rheology test showed that with the incorporation of the modified fibre,the asphalt mastic could be more stable and toughened,with the amount of binary composite modified fibre having a greater strengthening effect on the asphalt mastic than the lignin fibre.Through the bending beam rheological test results show that the addition of binary composite modified fibres have a low impact on the low temperature rheology of asphalt slurry,the effect is comparable to that of lignin fibres,the modified fibre content of 3% is appropriate.At this dosage,the straw fibre can significantly exert its strengthening effect and improve the high temperature deformation resistance of the asphalt slurry,but when its dosage is greater than 3%,the effect of the straw fibre on improving the high temperature rheological properties of the asphalt slurry will be weakened,while the low temperature rheological properties will have a negative impact.Therefore,the fibre type recommended in this paper is a binary composite modified fibre with an optimum admixture of around 3%,providing a new idea for the re-use of corn straw fibre,while increasing the feasibility of the application of fibre asphalt road projects.