The authors gratefully acknowledge financial support for this research from Major State Basic Research Development Program of China (973Program) (2009CB623203), the National Natural Science Foundation of China (50808042) for youth, and Six Projects Sponsoring Talent Summits of Jiangsu Province (1112000053), the Project-sponsored by SRF for ROCS, SEM. and Key laboratory
for concrete and prestressed concrete of Ministry of Education, Southeast University