Use of Stress Wave to Evaluate The Repair Quality of Concrete Crack Keng-Tsang Hsu, Chia-Chi Cheng, Chih-Hung Chiang and Hung-Hua Wang MATEC Web Conf., 138 (2017) 02019 Published online: 30 December 2017 DOI: 10.1051/matecconf/201713802019