Study On Anti-wear Characteristics Of Bauxite Clinkers And Anti-skid Performance's Of Asphalt Mixture

The anti-skid performance of asphalt pavements directly determines the service life and levels of driving safety.Aggregation is an important part of the asphalt mixture that impacts the attenuation of skid-performance.At present,under the action of traffic load,the wear resistance of conventional road aggregate decays rapidly,which leads to the accelerated decay of pavement skid resistance.The selection of highly resistant and anti-sliding aggregates can be used to improve the skid resistance of pavements.Bauxite clinker is calcined from bauxite ore at high temperatures and is an important raw material in high alumina products and amorphous refractories.The excellent anti-skid performance and durability of bauxite clinker have resulted in its widespread use in skid-resistant pavements in Europe and across America.China has very rich bauxite resources yet domestic research efforts into the application of bauxite clinker in highway engineering remain relatively low.To improve the skid resistance of pavements and to fully exploit local resources,there is a need for further research into the anti-wear characteristics and anti-skid performance of bauxite clinker in asphalt mixtures used in pavements.In this paper,the physicochemical properties and structural composition of bauxite clinker were investigated using various analytical methods including X-ray fluorescence spectrometer(XRF),scanning electron microscope(SEM),energy dispersive spectrometer(EDS)and mercury intrusion detectors.The three-dimensional micromorphology and friction characteristics of the aggregates were measured by laser confocal scanning microscopy and a RTEC friction wear test.These data were used to develop a model of wear resistance in bauxite clinker.The anti-slide performance of bauxite clinker wassystematically studied based on CATIA and ABAQUS/CAE tools,the Ames pavement texture laser scanner and an indoor accelerated test.The adhesion properties of bauxite clinker and asphalt were characterized using a‘peeling off'test,the agitated water static adsorption method and surface energy theory.The influence of different types and differentiation of mineral aggregates,asphalt film thickness,and ultraviolet and thermal aging on the wear and skid resistance of bauxite clinker mixture were investigated.Finally,the high and low-temperature performances,water stability and the anti-cracking properties of the bauxite clinker asphalt mixture were also characterized.Based on the texture characteristics of asphalt mixture under the accelerated test,the effects of mineral type and differentiation,asphalt film thickness and ultraviolet and thermal aging on the anti-slide performance were investigated.The main results from the study were:(1)Based on the structure,composition and texture characteristics of different types of bauxite clinker,a reproducible method was established to evaluate the wear resistance of bauxite clinker.This method was used to determine the influence of wear resistance,mineral composition,equivalent Young's modulus,nano-hardness and hardness dispersion on performance.The relationship between wear resistance,nano-hardness and hardness dispersion was established,and the anti-wear properties of different types of bauxite clinker were evaluated.The physical and chemical properties of bauxite clinker were combined with the results from long-term wear resistance tests to establish technical indices of bauxite clinker.The method and model used to evaluate the wear resistance presented in this paper can be used to evaluate the wear resistance of aggregates.The established technical indices and standards for bauxite clinker provide a basis for optimizing the properties of anti-slide surfaces.(2)Based on the analysis of the anti-slide gradation design and the other influencing factors,it wasconcluded that the size and the proportion of the maximum nominal particle size and the 4.75 mm?9.5mm particle size had the greatest influence on the anti-slide performance.Analysis of the long-term anti-slide performance of asphalt mixture showed that when mineral aggregates with different particle sizes are replaced,the maximum nominal particle size and the 4.75mm?9.5mmpart of the mixture should improve the anti-slide high-quality of the aggregate.The MPD value of the mineral aggregate gradation increased with the increasing coarseness of the aggregate content.The MPD value can be used as an index to evaluate the density of the skeletal structure of the mineral aggregate.In the process of mineral aggregate gradation compaction,the minimum MPD value of the mineral aggregate gradation corresponds to the densest state of the mineral aggregate gradation.The finite element simulation showed that the larger the contact area between the tire and the aggregate,the greater the friction.The effectiveness of the model was verified using the indoor asphalt mixture test results.The results from the accelerated loading tests showed that the smaller particle sizes of different aggregates had smaller differences in the friction coefficient.According to the decay law of long-term anti-slide performance of bauxite clinker,the main reason for the difference in the long-term anti-slide performance of the asphalt mixture is due to differences in the sizes of aggregate particles and aggregate wear resistance.(3)The low temperature,anti-cracking performances and the water stability of bauxite clinker asphalt mixture are weaker than the same type of mixtures containing limestone and basalt.The addition of limestone and increasing the amount of asphalt in the mixture can improve the water temperature and anti-cracking performance of the bauxite clinker asphalt mixture.The high-temperature performance of bauxite clinker asphalt mixture is higher than mixtures containing limestone and basalt.The research results of abrasion resistance of aggregate and skid resistance of asphalt mixture show that the abrasion resistance of bauxite clinker and skid resistance of its mixture are better than basalt and limestone.(4)The internal structure of the asphalt mixture and the abrasion of aggregates are the main reasons for the accelerated decay of the anti-slide performance.The aging,spalling and rheology of asphalt play secondary roles in the accelerated and slow decay stages of anti-slide performance.A decay model of the anti-slide performance of asphalt mixture was established and used to determine the impact of different factors on performance.Data showed that the anti-slide performance grade of asphalt mixture is based on the long stationary period of the anti-slide performance as a standard to classify anti-slide performance.R_skwas used as the evaluation index of pavement wear.This model provides a novel anti-slide performance classification standard and pavement wear evaluation index.Also,the mechanisms of performance attenuation at different stages of the process were determined.These data provide a reference point for implementing effective measures to maintain and improve the anti-slide performance of asphalt mixture during the design and construction of pavements.