Research On The Water Stability Evaluation Method Of Hot In-place Recycling Asphalt Mixture

In recent years,hot in-place recycling of asphalt pavement has many excellent performance,such as energy-saving,environmental protection,old materials recycling,and its good performance in repairing pavement.So,hot in-place recycling of asphalt pavement is widely used in highway engineering especially in preventive maintenance of highway practices.In the using capabilities of hot in-place recycling of asphalt pavement,water stability is of great significance in terms of design,construction and the using of assessment of hot in-place recycling technology of asphalt pavement.Current evaluation method of asphalt mixture's water stability are Immersion Marshall test and Freeze-thaw splitting test.These two methods can be used to reflect damage that free water flows into open spaces of asphalt mixture to pavement,but you can't simulate that water infiltrate and break pavement structure of inner micro-pore which comes from tire-pavement pressure pavement.This paper,through summarizing the influence factors of hot-in place asphalt mixture water stability,analysis the advantages and disadvantages of existing evaluation of the hot mix asphalt mixture water stability,the temperature-pressure coupling water stability test instrument with the simulation of temperature and dynamic water pressure has been developed,and the temperature-pressure coupling water stability evaluation method which is more suitable for hot-in place asphalt mixture has been put forward.Firstly,main influence factors of hot-in place asphalt mixture water stability has been summaried by the analysis of theory and construction site:In internal factors,the adhesion of asphalt with aggregate and the aggregate gradation of hot-in place asphalt mixture are worse than hot mix mixture,regeneration agent can promote water stability.In external factors,the main reason of water damage is hydrodynamic pressure produced by Action of water and wheels.In construction factors,secondary aging,gradation segregation,temperature segregation and paving segregation which can seriously affect the ability to resist water damage.Secondly,the effect of asphalt mixture water stability evaluation methods in the present standard has been compared according to the hot-in place project entity of(Nan)Chang-Jiu(Jiang)expressway.The result shows:immersion Marshall test and vacuum water saturated Marshall test have the general evaluation results,but the latter has the better idea and is worth using for reference with pressurized water entering into the mixture;Freeze-thaw splitting test and immersion splitting test have the good evaluation effect,the immersion split test is worthy of reference because it can make the mixture thoroughly destroying by providing a long time and high temperature environment.Thirdly,this paper has developed the temperature-pressure coupling water stability test instrument which can regulate water temperature and pressure control and the water stability test method:Standard Marshall test and split test use the current specification,immersion Marshall test and the splitting tensile test use the void control method in the current standard to product Marshall samples,then testes the residual stability and splitting strength ratio after soaking 8h in a temperature of 60 DEG C and pressure 0.4MPa.By using this method,water mixture rate has increased by 80%,residual stability and splitting strength has decreased by 20%?30%,and the minor differences in mechanical properties between different materials are amplified.These results indicate that temperature-pressure coupling water stability test can be used to simulate the attenuation of anti-water damage ability after long-term use,and be better to distinguish different engineering.Fourthly,the research and indoor water stability analysis are carried out for the long track of the highway in the Chang-Jiu hot-in place project.The results show that the pavement quality is good after two years with no obvious water damage;existing test methods cannot distinguish the water stability of asphalt mixture with different using time,but the temperature-pressure coupling test results show that the water stability decreases with the increase of operation time,the temperature-pressure coupling splitt test can amplificate the difference in splitting tensile strength of asphalt mixture with different time,and it can reflect the changes of pavement long term water stability better.