Research On Thermal Diffusion Process Of Asphlat Paving And Mix Improvement At Low Temperature

If paving at low temperature envirnoment, asphalt mixture would cool rapidly,andcould’t be compacted to certain density or would cause significant temperature－densitysegregation, then the mixture performance in service. But in northern china and Tibetplateau, asphalt pavement construction would in trouble of large temperature differenceor low temperature environment inevitably, paving at low temperature envirnoment is aproblem that road engineers must faced. When paving at disadvantage environoment,engineers have an urgent need of efficient compaction time which mixture cooling fromthe highest temperature to the lowest allow compaction temperature, or in a lowtemperature environment and must construction, need know what measures should betaken to ensure the quality of the engineering. For above problems, the paper has set upa paving temperature field simulation model based on the theory of heat transfer, andconducted sensitivity analysis of thermal diffusion influencing factors at lowtemperature by simulation test. Then, the paper has proposed effective and feasibletechnology mix improve techniques on the basis analysis of influencing factors.Thermal diffusion influencing factors of asphalt paving are complex and variable,comprehensive and reliable law can’t be obtained only based on field observations andstatistics. The research had first determined heat transfer modes and energyconservation at the inner and interface of paving layer, then, proposed aone-dimensional paving temperature field simulation model based on theCAE(Computer Aided Engineering) software by study of material properties andboundary conditions in the process of paving. The characteristics of the model arematerial thermal properties would be changed with compacted times and temperature;and three boundary conditions, such as convection, effective radiation and sprayingwater heat exchanger would be changed with compacted times and temperature also; thethickness of paving layer would be changed with compacted times. By the initialconditions iterations, different non-continuity conditions are applied in continuous fieldsimulation simultaneously. Simulation examination based on in situ observations dataproved: the simulation model is accurate and the simulation results are consistent withthe observed results.By simulation test, the article has carried out univariate and multivariate sensitivityanalysis to environmental conditions, paving layer conditions, bottom layer conditionsand paving operation conditions. Analysis at0~10℃environment shows that if theinitial compaction temperature is increased10℃, the effective compaction time of4~6cm paving layer would extend about5min; while if the thickness is decreased1cm, the effective compaction time of same initial temperature would reduced10min. Ifpaving layer thickness is less than or equal to5cm, compaction time would be very poor,and some improve improvement techniques must be used to ensure compaction quality.Amplifying asphalt mixture‘s operable temperature range is very effective toextend the effective compaction time and has universality and applicability to pavingwork. Compare to warm mix, when paving at low-temperature environment,maintaining hot mix is the basic needs to ensure the compaction quality, the mixturequality and the pavement long-term performance. The research has proposed that themixture improvement direction at low temperature paving is maintaining hot mix andreducing allow compaction temperature at the same time. And the asphalt stageviscosity reducing technique based on dilution mechanism was determined to realize theimprovement goal by balancing viscosity reducing impact to mixture atmix-paving-service stages.For evaluating full impact from construction to service of diluted mechanismadditives to mixture, the author had designed test evaluation system that include asphalthigh temperature mixing aging impact, mixture’s best compaction temperatures reduceeffect and mixture’s performance impact in service. though comprehensive technicalevaluation, get the results as follow: the additives which kerosene as the main ingredientdoes not have significant adverse impact on aging of asphalt hot mix; the bestcompaction temperature relative reduces20℃，so that a thin paving layer’s compactiontime can be added about20min. At the same density, the service road performance ofhot mix-warm compacted additives mixture do not less than hot mix-hot compactedcommon mixture in general. By the actual use at test road,the research has examinedthe application effect of hot mix dilution viscosity reduction mixture. With the use ofthe improved mixture,4cm and5cm paving layer have achieved high compactionstandard at extreme environments temperature lower than0℃and did not adjust thecompaction process. By follow-up observations, the mixture used in road test canwithstand the loads and environmental impact.The innovative research in asphlat paving temperature field simulation model,asphalt mixture improved technology mechanism suitable for low-temperatureenvironment paving, and compaction temperature evaluation of asphlat mixture withstage viscosity reducing techniques help to solve the technical problems of asphaltpavement construction at low temperature environment.