Study On Setting Time Recommendation For Laboratory Evaluation Of Hot Mix Asphalt

To regulate and unified test method of asphalt and asphalt mixture,Guarantee the quality of highway engineering construction,Various countries and regions have formulated the corresponding test procedures,For example,Test procedures for asphalt and asphalt mixtures(JTG E20-2011)is formulated by China,ASTM standard is developed by the American Society for Testing and Materials,and the CEN standards is set by the European Committee for Standardization and so on.Although the operation of the experiment process in these procedure are described in detail,most of them have no clear provisions of specimens storage environment before the test except the single axial compression dynamic modulus test and four-beam fatigue test,What is more,no rules has been raised to regulate the which means the completed specimens go through the time from molding to testing.The existing research from our team points out that the length of the Setting Time has obvious effect on the results of the asphalt pavement performance test.However,the influence of different storage environment on Setting time,and the Setting time recommended value of different test has not been confirmed.In order to further clarify the above problems,this article has studied the influence of the setting time on hot mix asphalt mixture under winter(January and February)and summer(July and August)these two indoor environments.And the Setting time is set to 1 day,3 days,5 days,7 days,14 days.This research chooses AC-13 and AC-20 two types of grading.First of all,mold the specimens at 7% void fraction,then put the molded specimens under the two kinds of indoor environment,and to complete the test within the given time.Through a large number of experiments,with growth of the setting time under two kinds of conditions,the main conclusions are as follows.(1)SCB experiment: the bending tensile strength differ from 1 day to 14 days under AC-13,and 1 day to 7 days have bigger difference under AC-20.The flexural tensile strength of specimen under the same grades type change slightly at 14 days.So,the Setting time recommended value of SBS trials under AC-13 and AC-20 is 14 days.(2)Uniaxial static creep: the results have bigger difference from 1 day to 7 days under AC-13 and AC-20.The stiffness modulus of specimen under the same grades type change slightly at 14 days.So,the Setting time recommended value of uniaxial static creep test under AC-13 and AC-20 is 14 days.(3)Hamburg wheel tracking test: the results differ from 1 day to 14 days under AC-13,and 1 day to 7 days have bigger difference under AC-20.The results under the same grades type change slightly at 14 days.(4)Dynamic modulus of uniaxial compression test: the specification require to storage specimens at 5~27?,setting time should not be more than two weeks.with growth of the setting time,the dynamic modulus is present growth trend at 0.1 Hz,0.5 Hz,1 Hz,5 Hz,10 Hz,25 Hz loading frequency under AC-13 and AC-20.From 1 day to 7 days is growing rapidly,7 days to 14 days are stable.So,the Setting time recommended value of dynamic modulus test under AC-13 and AC-20 is 7 days.Whether in winter or summer environment,the influence of Setting Time on hot asphalt mixture mechanics character and asphalt pavement performance is obvious.And the test results are different between two kinds of different environment.So,it is necessary to make specific provision of specimen storage environment and Setting Time values.