scope:

Introduction

A review of published literature indicates that there is plenty of information regarding the pH of concrete as it relates to carbonation, embedded steel corrosion, alkali-silica reaction, and effects of mineral admixtures such as fly ash and silica fume. There are, however, only a few research papers published that are related to test methods to measure the pH of a concrete surface.

Portland cement and many other hydraulic-cement-based concretes are highly alkaline materials. Depending on the actual chemistry of the portland cement and amount of alkalis present, the pH of freshly placed concrete can vary from approximately 12 to over 13. The carbonation of concrete is known to lower the surface pH to a value in the vicinity of 9.

The pH of a concrete surface plays an important role in the selection of flooring adhesive and placement of flooring materials, especially with resilient flooring such as sheet vinyl. A concrete pH below 7.0 and above 10.0 is known to negatively affect resilient flooring, its adhesive, or both. The flooring installer is typically required to clean and prepare concrete slab surfaces prior to flooring installation. Pressure washing is not used to clean the concrete surface, as the process will saturate the concrete surface with water and cause flooring failure due to excess slab moisture. Flooring installers often clean and scarify the concrete surface with sandpaper, or shotblast the surface. The process of sanding or shot blasting can remove the carbonated surface layer of concrete and expose a concrete surface that has higher pH.

When using the ASTM F710 test procedure (Appendix A), testing laboratories have reported concrete surface pH values as low as 6 or 7 because the test method is incorrect. In fact, it essentially measures the pH of water and readily-soluble materials on the concrete surface versus the true pH of the concrete. Incorrect pH test results could lead to the selection and use of an incompatible adhesive for the flooring, resulting in the risks of flooring failure. The concrete and flooring industries require a test method that measures the pH of concrete surface more accurately.