Experimental Research On Composition And Performance Of Fiber Reinforced Asphalt Mixture

Through a series of tests on the packing characteristics of mineral aggregates, high temperature stability, low-temperature crack resistance, water stability and self-healing capability of different type of fiber reinforced asphalt mixture, A systematically theoretical analysis on the packing component laws and gradation properties of mineral aggregates, mix design method, road performances and self-healing capacity of fiber reinforced asphalt mixtures was carried out, conclusions obtained are as follows:(1)The closely packing status and the optimal skeleton status of a binary system correspond to different composition of the two aggregates respectively, the volume ratio of6:4corresponds to closely packing status of the two aggregates, nevertheless, the volume ratio of7:3corresponds to the optimal skeleton status of the two aggregates. The component laws on closely packing status and optimal skeleton status derived from binary system can also be applied for design and evaluation on aggregate gradation.(2) A direct method to measure the inner frictional resistance of aggregate skeleton using plastic mould sample compression test was developed, and the measured compressive strength can be taken as a indicator of inner frictional resistance of the aggregate skeleton, the friction resistance has a positive correlation with coarse aggregate content.4.75mm can be regarded as the dividing point between coarse aggregates and fines for aggregate gradation with the nominal maximum size of13.2mm.(3) A prediction method on the optimal asphalt content of fiber reinforced asphalt concrete is proposed, the sum of effective asphalt caculated by asphalt film thickness and excess asphalt inhaled by opening pores of aggregates could be as the minimum asphalt content, and the amount of asphalt obtained by compacting grading aggregates with Marshall test mould as the maximum asphalt content.(4) It is not enough to make a reasonable assessment on the optimal gradation of SMA using traditional method based on the volume indexes of Marshall specimens, however, friction resistance test with plastic mould samples is a more suitable method. The optimal asphalt content of SMA could be determined accurately by effective synthetic density of aggregates.(5) A mix design method for skeleton fiber reinforced asphalt mixture, named as "Skeleton Clearance Volume Optimization Packing Method", was put forward based on predecessors’researches, which turns the mix design process of skeleton asphalt mixture into an optimization process of aggregate gradation, optimal asphalt content and fiber content. This design method has obvious advantages over traditional design method when designing SMA and OGFC asphalt mixtures.(6) Aggregate gradation has important influence on road performances of asphalt mixture, dense-graded asphalt concrete has better low temperature performance and water stability, while skeleton asphalt mixtures such as SMA and OGFC have better high temperature stability.(7) Fibers have different improving effects on high temperature stability, low temperature crack resistance and water stability of asphalt mixtures, however, the improving effect is restricted by the correspondingly increased asphalt content. Comprehensive consideration, asphalt adsorption coefficient K for steel fiber and polyester fiber playing their best improving effects on dense-graded asphalt concrete are0.07and0.95respectively, K for cellulose fiber added to SMA and OGFC should be1.7and1.7to2, and it should be1.1for basalt fiber added to SMA and OGFC.(8) Fiber can significantly change the failure mode of dense-graded asphalt concrete at low temperature, from brittle failure mode to failure with somewhat yield characteristics, the higher the fiber content, the greater the improving ranges of the failure stress and strain of dense-graded asphalt concrete. Though the stiffness modulus has limitation to evaluate low temperature performance of fiber reinforced asphalt concrete, which can reflect the relative improving effects of fibers on strength and deformation of asphalt concrete, on the country, it is more reasonable to evaluate the failure characteristics of fiber reinforced asphalt concrete using critical bending strain energy density.(9) Under the same conditions, the improving effects of combined fibers on road performances of asphalt concrete are much better than that of a single kind of fiber, which shows the superimposed effect of the combined fibers, but not a linear superposition rule.(10) The optimal asphalt content determined by Marshall method of dense-graded asphalt concrete with larger fiber content is higher than it needs. The road performances of SMA asphalt mixtures designed by the Skeleton Clearance Volume Optimization Packing Method are better than that designed by traditional method.(11) Prediction models such as bending strength, critical bending strain energy density, dymamic stability, residual Marshall stability(or freeze-thaw splitting strength ratio) considering the interaction influence of fiber and asphalt were established according to the test results, which could be a reference for practical engineering application.(12) Fiber has an important impact on the form of temperature cracks and has significant improving effects on cracking self-healing capacity of asphalt concrete, in fact, the improving mechanism of fiber on self-healing capacity of asphalt concrete derives from the improvement on anti-cracking ability of asphalt concrete. It is more reasonable to characterize the self-healing capacity by the energy recovery rate. The interaction of introduced rest period and fiber affects the self-healing capacity of asphalt concrete evidently. The prediction model of crack self-healing capacity was established considering the influences of temperature and fiber.