| Excellent road surface function layer can ensure driving safety and reduce traffic accidents.However,the conventional asphalt materials have poor cohesion,and the asphalt film on the aggregate surface is easy to fall off,which leads to the rapid deterioration of the performance of the functional layer,which requires regular maintenance.Epoxy asphalt has excellent adhesion and long-lasting anti-skid properties and is an ideal high-performance asphalt material for new road surface layers or preventive maintenance functional restoration overlays.The ultra-thin cover can save resources and reduce the cost of epoxy asphalt and has good social and economic benefits and application prospects.However,the ultra-thin cover has the inaccurate design of the strong skeleton dense asphalt mixture,which is prone to cracking and interlayer shear damage,and the thin paving thickness makes the temperature of the mixture dissipate quickly,and there is a mismatch between the indoor molding method and the construction environment question.Based on the previous research results of the research group on post-mixed warm-mix epoxy asphalt materials,this study aimed at the defects of the current ultra-thin cover,combined with the grading requirements of the ultra-thin overlay,carried out the mix proportion design and optimization of sand epoxy asphalt mixture,the research on indoor thin-layer specimen forming method and road performance evaluation.It also focuses on the crack resistance and interlayer shear resistance of sand-type epoxy asphalt mixture,aiming to solve the durability problem of ultra-thin asphalt pavement,to realize the long life of the pavement.The main work and conclusions are as follows:(1)Using the coarse aggregate skeleton clearance ratio(VCA)as an index to evaluate the compactness of the skeleton,by adjusting the mixing ratio of different coarse aggregates,the dry tamping and vibration compaction molding tests are used to jointly measure the VCA of different proportions of coarse aggregates;according to the principle of smaller VCA,select the proportion of coarse aggregate with high skeleton density,combine with the gradation design of Bailey method,conduct orthogonal tests to optimize the gradation with different proportions of coarse aggregate and the design density of coarse aggregate.At the same time,the Course Aggregate Void Filling method(CAVF)was introduced to examine the gradation composition,and the multi-index control of the three-parameter test of VCA and Bailey’s method is established.Finally,a strong skeleton compact gradation design method based on Bailey + CAVF method is proposed.(2)The ultra-thin cover construction process is difficult to compact due to the rapid cooling down.To simulate the construction environment of the ultra-thin layer on-site,change the indoor molding thickness,and study the effect of temperature and compaction work on the volume characteristics and performance of the epoxy thin layer.Combined with the volume characteristics and retention time requirements of epoxy thin layer,and the verification of mechanical properties and road performance,the technical requirements for the design of indoor sand-grained or fine-grained epoxy asphalt mixture thin layers are proposed.Among them,the best compaction times of epoxy thin-layer Marshall specimens are 25 times on both sides,the best compaction temperature is 110℃,and the compaction thickness is 30 mm±0.6 mm.(3)The impact toughness test was used to evaluate the impact load resistance of epoxyasphalt mixtures by impact toughness and maximum load.The results show that increasing the amount of asphalt and adding fiber can significantly increase its maximum load,and the impact toughness value of the mixture with polyester fiber and basalt fiber is increased by 40% and 93.9%,respectively.Therefore,the amount of fiber and oil can be increased simultaneously to improve the cracking resistance of epoxy asphalt mixtures.Using the indirect tensile cracking(IDEAL-CT)test,the maximum load and displacement,the absolute value of the slope at 75% of the maximum load of the load-displacement curve(|m75|),and the crack resistance index(CT)were used as evaluation indicators to study multiple factors influence on the crack resistance of sand-type epoxy asphalt mixture.The results show that adding quantitative fibers and increasing the amount of asphalt to the epoxy asphalt mixture can delay the development of cracks and improve its crack resistance,and the basalt fiber has the best crack resistance performance.The crack resistance of epoxy asphalt mixture is negatively correlated with the nominal maximum particle size of aggregate,and the crack resistance of skeleton dense type is better than that of suspension dense type.The density of the mixture increases the overall strength,reduces the deformation resistance,and accelerates the crack growth rate,resulting in a decrease in crack resistance.On the evaluation index,the maximum displacement has poor sensitivity to the evaluation of crack resistance of epoxy asphalt mixture,and cannot be used to evaluate the crack resistance of thermosetting materials.(4)The adhesive properties between epoxy ultra-thin asphalt layers of different adhesive layers(non-adhesive layer,matrix asphalt adhesive layer,SBS asphalt adhesive layer,and epoxy asphalt adhesive layer)were studied by oblique shear test at 25 ℃,60 ℃,immersion conditions,interface thermal aging and freeze-thaw.The results show that the amount of epoxy asphalt adhesive layer oil spray has a great influence on the interlaminar shear strength,and the shear strength first increases and then decreases with the increase of the amount of spraying.Under all conditions,epoxy asphalt bonding performance is the best;temperature is the most significant factor affecting the interlaminar shear strength.The shear strength of the epoxy adhesive layer is as high as 7.2Mpa at room temperature and reduced to 2.34 Mpa at high temperature.The interlaminar shear strength decreases sharply with the increase in temperature,and the failure mechanism of the epoxy adhesive layer is related to temperature.It is suggested that in high-temperature areas,the bonding material should be reasonably selected and the amount of bonding oil should be appropriately reduced,and special attention should be paid to the shear resistance of the whole structure.Epoxy asphalt bonding material with high adhesion should be used for the pavement with high interlayer shear resistance,paving ultra-thin layer on a high-grade asphalt pavement or sections with special requirements. |
