Effect Of Setting Time On Accuracy Of Experimental Evaluation Of Hot Mix Asphalt In Laboratory

In recent years,asphalt pavements contributes to the rapid development of transportation undertakings in China.And asphalt pavement has become the main form of road pavement structure in the world due to its advantages,such as driving comfort,fast building,easy maintenance,low noise and less glare,etc.Therefore,the demand for asphalt mixtures has been increasing too.Before production of the hot mix asphalt(HMA),it must be tested in laboratory about the mechanics and road performance.The test results are closely linked to design,construction and service of asphalt pavement.So,each country or area has reported the test methods standard to make the test results more reasonable and accurate.However in current reported test methods standard in laboratory,there is no detail description for the setting time of asphalt mixture from molding to testing.And the preliminary study in author's research group had shown that setting time has some effect on the road performance of HMA.To keep asphalt mixture specimens test results more comparative.This paper would investigate the influence of setting time on the laboratory performance of asphalt mixture.The researcher chose different setting time on the mechanics and road performance test.These tests were based on dense mixture type AC-13 with air void content equal to 4%.After molding,all samples were placed in laboratory until testing at room temperature.Based on the test results under different setting time,the findings drawn from the test results are summarized as follows: With the setting time increased,the compressive strength and resilient modulus by uniaxial compression test would increase,the dynamic modulus by uniaxial compression dynamic modulus test would increase and the flexural-tensile strength by SCB test would increase.The evaluation about mechanics of a same sample would be better.With the setting time prolonging,Marshall stability and Marshall modulus would be improved while the flow values decrease.Moreover,the rutting depth in Hamburger wheel tracking test(HWTT)and Rutting test would be decreased but dynamic stability(DS)would be increased.So the high temperature stability evaluated by Marshall stability test,HWTT and dynamic stability test would be better in a same HMA sample.And a longer setting time would lead to a greater value of flexural-tensile strength and stiffness modulus but a smaller value of flexural-tensile strain in three-point bending test under a low temperature.So the evaluation of anti-crack behavior about a same specimen would be worse.The TSR tested by freezing and thawing spilt test would decrease with a longer setting time.When tested after a longer setting time,the test results would suggest the HMA specimens were more sensitive to moisture damage.With a longer setting time,the peak load of first cycle would increase.But the number of cycles by OT and fatigue life by four-point bending test would decrease.These results would lead to worse evaluation of fatigue behavior about a same HMA specimen.To be sure,setting time has a significant influence on the evaluation of mechanics and road performance test in laboratory.Therefore,to keep asphalt mixture specimens test results more comparative,it is of highly necessary to rule the setting time in laboratory testing standard,and ruling the setting time in laboratory testing could also make the evaluation of performance of HMA specimens more reasonable.