By Sandy Brown, P. Eng.
This January I was part of a delegation of North American engineers in Shandong Province to discuss the Binzhou Perpetual Pavement Test Road with representatives of the Shandong Highway Bureau and the Shandong Transportation Research Institute.
China is in the process of building modern highways. Some of their newest expressways look just like any major highway in North America—four-lane toll roads with divided medians and roadside amenities every 75 kilometers.
This was the delegation’s fourth trip to China. On previous visits, the team designed the pavement test sections and installed the monitoring equipment. Since construction is now complete, the team reviewed the field work, inspected the monitoring installation, verified the calibration of the monitoring stations and set up the data analysis software.
Yongshun Yang, Shandong Highway Bureau
Xuechi Gao, Shandong Highway Bureau
Lin Wang, Shandong Research Institute
North American Partners:
The Shandong Highway Bureau is particularly interested in the Perpetual Pavement concept. The typical transport truck in China has a single steering axle and tandem axles on the tractor with triple axles on the trailer—typical except that the design load of the vehicle is 120 tonnes (264,000 pounds). With this kind of load, the life of a Chinese road can be short, and the provincial authorities would like some options to increase pavement life.
The Perpetual Pavement Option
One of the options for increased pavement life is a Perpetual Pavement. A Perpetual Pavement is designed from the bottom up to resist structural failure and to minimize cracking and rutting. If the hot mix asphalt (HMA) is thick enough so that the tensile strain at the bottom of the HMA layer is less than 75 microstrain and the compressive strain at the top of the subgrade is less than 200 microstrain, the pavement structure can last indefinitely. The only maintenance needed is to replace the surface course because of wear from traffic and the environment. While the limiting strains are well documented, the design concepts still have to be validated in the field by monitoring test sections.
The team built five test sections on a new motorway near Binzhou in the eastern part of Shandong Province. The typical cross section is an HMA pavement with a stone matrix asphalt (SMA) surface course over pozzolanic stabilized granular layers. Four alternate designs were built, including three full depth HMA sections and a thicker layer of HMA and pozzolanic stabilized materials. In the full depth test sections, the overall thickness of the HMA was 500 mm for the section designed for 75 microstrain and 370 mm for the two sections designed for 120 microstrain. All three Perpetual Pavement trials use 75 mm of rich bottom mix (RBM). PG 76–22 was used in the upper 100 mm with PG 64–22 for the lower lifts with the exception of one of the 120 microstrain sections where PG 76 22 was used in the RBM for increased fatigue tolerance.
|Sandy Brown holds the dual position of Technical Director of the Ontario Hot Mix Producers Association and Candian Field Engineer for the Asphalt Institute. He has over 30 years experience with pavement materials, asphalt mixtures, design, construction and evaluation. Brown has been active on industry technical committees and regularly teaches seminars within the asphalt industry. He assumed his current duties in October 2005.|