1. Laboratory of Civil Engineering and Mechanics, National Advanced School of Engineering of Yaoundé, University of Yaoundé 1, P.O. Box 8390, Yaoundé, Cameroon
2. Local Materials Promotion Authority, P.O. Box 2396, Yaoundé, Cameroon
3. Department of Physics, Faculty of Science/School of Chemical Engineering and Mineral Industries, Group of Mechanics, Materials and Acoustics, University of Ngaoundere, P.B: 454, Ngaoundere, Cameroon
4. Laboratory of Mechanics, University of Douala, P.O. Box 2701, Douala, Cameroon