Interfacial properties determine the performance of embedded IrOx pH sensor in cement mortar

IrO x electrode has been reported to show promising application in pH determination in many environments. Once embedded in cement mortar, the performance of IrO x electrode is poor. The failed pH determination is due to inaccurate potential measurement of embedded IrO x electrodes, including potential difference across aqueous solution/mortar interface ( E 1 ), potential difference generated due to transport of charge carriers in pore structure of cement mortar ( E 2 ), and potential difference across interfacial transition zone (ITZ)/IrO x electrode interface ( E 3 ). E 1 is measured to be 19.6 mV, leading to a lower calculated pH by 0.39. E 2 is 20.9 mV, indicating E 2 associated error in pH determination is also minor (0.42 pH). E 3 (of −317.3 mV) is confirmed to introduce serious errors in potential measurement, due to excessive resistance across the ITZ area. The microstructure of ITZ is studied by X-ray computed tomography (μXCT). In the case of OPC, abnormal porosity is observed. Although the continuous pores can't be detected by μXCT, it is proposed the presence of abundant continuous pores is essential for a meaningful measurement of the IrO x electrode potential and the subsequent calculation of pH in pore water.