1. Research and Development Center of Transport Industry of Technologies, Materials and Equipment of Highway Construction and Maintenance, Gansu Road & Bridge Construction , Gansu , China ;
2. School of Highway, Chang an University , Xi an , China ;
3. Key Laboratory of Special Area Highway Engineering, Ministry of Education , Xi an , China ;
4. US Department of Labor , Washington DC , 20210 , US ;
5. Department of Civil, Construction and Environmental Engineering, Iowa State University , Ames , IA , USA