[1] Univ Ghent, Dept Struct Engn, Magnel Lab Concrete Res, B-9052 Ghent, Belgium
[2] Univ Stuttgart, Mat Testing Inst, Dept Nondestruct Testing & Monitoring Tech, D-70550 Stuttgart, Germany
[3] Tech Univ Munich, Ctr Bldg Mat, Nondestruct Testing Lab, D-81245 Munich, Germany