The pH measurement of cement-based materials: Effect of leaching time, leaching technique and water-to-solid ratio

Corrosion of steel is an electrochemical process that is affected by pH and potential difference. The pH of concrete may change due to physical, chemical, and biological influence over time. Therefore, it is important to measure and monitor the pH of reinforced concrete as a structural health monitoring parameter related to durability. Ex-situ leaching (ESL) method is commonly applied to produce the equilibrated aqueous solutions for the pH measurement of cement-based materials. However, there are limited studies about the effect of leaching time, leaching technique and water-to-solid (w/s) ratio when applying this method. This may lead to underestimation of pH and unnecessary prolonged leaching time. The solution temperature compensated pH value was used during analysis of the data. By testing on the OPC mortar with cement-to-sand ratio of 1:3 and water-to-cement ratio of 0.55, the optimum w/s ratio and minimum leaching time are 2 and 5 min, respectively. The minimum quantity for solid per sample shall not be less than 5.0 g. The findings of this research will contribute to a more accurate pH measurement and may play a part in regulating a standard for cement-based materials.