Leaching corrosion of asbestos cement pipes

Abstract

This paper describes the leaching corrosion of asbestos cement pipes and its influence on their durability and failure in service. The chemical stability, and ultimately the durability, of cementitious products is related to the free lime content Ca(OH) 2 present in the hydrated products and the aggressiveness of the surrounding media. Free lime content of asbestos cement samples from new and used pipes, conducting fresh and brackish water has been measured and analysed. Special apparatus was fabricated to measure the permeability of the asbestos cement matrix to demonstrate the leaching phenomena. The average free lime content of unused asbestos cement pipes was found to vary between 13.1% and 23.3% with an average value of 16.8%, while the free lime content of samples from burst pipes conducting fresh water varied between 3.5% and 13% with an average value of 8.7%. On the other hand, samples from burst pipes carrying brackish water had a free lime content in the range of 11.5% and 20.7%. It is concluded that leaching of free lime is taking place in fresh water pipes for the very soft water, affecting the porosity and permeability of the asbestos cement pipes; once leaching has progressed, it will lead to deterioration and eventual bursting under pressure.