Influencing Factors And Meso Mechanism Of Asphalt Pavement Damages Caused By Condensate Ice

In Yunnan, Guizhou, Sichuan, and other high altitude humid mountain areas,freezing disaster appears very commonly in winter or early spring due to localclimatic and geographical conditions. Condensate ice would appear on pavementbecause of freezing disaster, which not only affect the traffic safety and transportefficiency adversely, but also damage the asphalt pavement performance seriouslydirectly or indirectly. The damage forms and characteristics of pavement caused bycondenstare ice are significantly different from the cold regions of northern China,where continuous low temperature and humidity in winter. At present, theresearches about pavement damage caused by condensate ice is also less. Therefore,the researches were carried out focusing on the asphalt pavement damages causedby condensate ice in high altitude humid mountain areas, which included thedamage characteristics, influencing factors, microscopic mechanism and evaluationmethod. The conclusions could provide a basis for pavement curing after freezingdisaster, and pavement materials design resisting condensate ice damage in theseareas.Firstly, field invertigation, detection and core samples tests of typical pavementwere carried out to analyze the effect of condensate ice on pavement performanceand mixture composition structure. The results showed that the main effect ofcondensate ice are on the pavement surface conditions, which lead to aggregatestripping off, forming surface pockmark, loosening diseases, and increasing thesurface textuer depth.The materials features of different ability pavemets in resistingcondensate ice damage were analysed, which had gone through the same freezingdisaster, but showed differernt externt of damage. The results indicate that the voidratio, voids in mineral aggregate, asphalt saturation degree and the firm thicknessaround aggregate would influence the ability of mixture resisting condensate icedamage. And the aggregate strength, adhesion with asphalt at low temperatureinfluence mixture damage aslo.Secondly, the main factors of mixture damage caused by condensate ice wereresearched in this paper, and the void was considered to be the most importantfactor. Single-side freeze-thaw test and ravelling test at low temperature of mixtures indicate that the initial void ratio will impact seriously on pavement condensate icedamage. The critical void ratio6%of AC-16mixture resisting condensate icedamage is proposed. Since void could impact mixture performance seriously, themechanism of void ratio and void distribution impacting on mixture damage causedby condensate ice, or condensate ice and vehicle load together were revealed basiedon CT tests, image processing technology finite element method. Addition, otherfators of mixture subjecting from condensate ice and vehicle load were researchedalso. SMA-13mixture is superior to the AC-13and AC-16mixtures, and the twoAC mixtures are similar. Compared with common asphalt, modified asphalt couldimprove significantly aggregate anti-stripping capacity after freeze-thaw, and morenumbers of freeze-thaw, the advantages more obvious. Basalt is better thanlimestone in mixture resisting frost swelling, vehicle striking and polishing in thecase of mixtues with the same void ratio.As the vehicle load could seriously aggravate the asphalt pavement condensateice damage, the mechanism was simulated using finite element method. The stressof different location mortar and asphalt film may be exacerbated or diminished bydynamic water pressure, but would exacerbate mixture damage overall. And waterfrost swelling in void would cause or aggravate the mixture destruction obviously.Thirdly, since the surface pockmark and loosening diseases of pavement areclosely associated with the bonding properties between asphalt and aggregate.“pull-off test about asphalt paste-untreated aggregate bonding properties” wasdeveloped to reveal the meso mechanism of asphalt pavement damage caused bycondensate ice according actual pavement condition. Some results can be obtained.①The destruction stype of asphalt paste-aggregate bonding structure becomesadhesion failure from cohesion failure because of water immersion, and the failureload reduces greatly. And the pavement damage most seriously at-4℃.②Thepaste-aggregate bonding structure would be impacted slightly by freeze-thaw ifthere is no water in the interface; while the bonding interface would debond quicklyin early freeze-thaw if water had immersed to interface.The effects of raw material on mixture condensate ice damage were verified inthe meso view of asphalt paste-aggregate bonding structure. SBS modified asphaltis better than common asphalt, and the advantage is more obvious if water esists ininterface. Filler-asphalt ratio should be controlled between0.7and1.3. Basaltaggregate is better than limestone in bonding with asphalt paste at above about-4℃ if suffered from water frost swelling in interface, but the bonding properties of thetwo kinds of aggregates are similar under about-4℃.At last, as the damage of asphalt pavemen caused by condensate ice only isundercover, the “fast testing equipment of asphalt pavement freeze-thaw damage”was developed to detect the degree of aggregate stripping off according to thedamage form and characteristics. And verify the mass per unit area of stripped offaggregate is sensitive in evaluating the condensate ice damage degree of asphaltpavement. Combined with the field results,0.4g/cm~2is proposed as the criticalmass loss per unit area detected by “fast testing equipment” focusing on AC-16mixture of Guizhou region asphalt pavement top layer, which could procid basis forrapair work of local pavement damage after condensate ice.