Examination of Asbestos Cement Pipe Deterioration with Scanning Electron Microscopy

Abstract

Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) microanalysis technique has distinct advantages in providing high resolution images for identification of microscopic structure changes in hydrated cement matrix and the chemical compositions. Therefore, this technique can be a very useful tool for characterization of asbestos cement (AC) pipe deterioration. Microscopic structural changes in AC pipes can be related to leaching, chemical and biological processes, which include the free lime leaching, secondary gypsum and ettringite formation, acid attack, and the microorganism induced deterioration. These processes have resulted in losses of free lime, cracks in cement matrix, dissolution of Ca-bearing minerals and increased porosity in the cement paste. Carbonation, as calcite precipitation, on the other hand, is more often observed on the outer surface of the pipe in an alkaline soil environment, and may help to protect AC pipes. This paper is focused on the SEM evidence of these deterioration processes. With the elemental composition data from EDX technique, SEM can be used to quantitatively evaluate AC pipe deterioration. A four stage of deterioration of AC pipes in drinking water distribution system is proposed based on the morphology and elemental compositions of the pipe samples. The understanding of degradation mechanisms provides a scientific basis for the development of operational practices and management strategies that can be used to extend the service life of AC pipes.