Spatial and temporal heterogeneity of surface pH in corroding concrete sewers

A method for measuring the surface pH of corroding concrete was developed in the lab and tested in the field. The method is based on direct application of pH indicator solution on the corroding surfaces. Comparison against point measurements using a flat surface pH electrode confirmed the accuracy of the method. Blind testing of concrete specimens exposed to different acid concentrations demonstrated that it was possible to determine the surface pH within ±0.5 pH units in the pH range of one to five. The developed method provides a simple and reliable estimate on the extent of concrete corrosion. Relatively large surface areas, e.g. an entire sewer manhole, can be sprayed and assessed within a matter of minutes. Field-testing of the method has revealed that the surface pH of corroding concrete sewers is subject to a significant spatial and temporal variability.