Optical pH imaging of concrete exposed to chemically corrosive environments Cyrill Grengg, Bernhard Mueller, Florian Mittermayr, Torsten Mayr, Sergey Borisov and Martin Dietzel MATEC Web Conf., 199 (2018) 02007 Published online: 31 October 2018 DOI: 10.1051/matecconf/201819902007