Evaluation of Grouting Condition of Post-Tensioned Concrete using R-wave Method Kah Kian Cheong, Foo Wei Lee, Kah Hon Leong, Ming Kun Yew and Yee Ling Lee E3S Web Conf., 65 (2018) 02004 Published online: 26 November 2018 DOI: 10.1051/e3sconf/20186502004