Durability of reinforced concrete sewer pipeline over 23 years

Abstract

A reinforced concrete sewer pipeline in Johannesburg, South Africa, is exposed to the weather where it crosses three dry valleys over a series of pipe bridges. In 1975, a year after commissioning the sewer in May 1974, it was discovered that the pipes were cracking, that the cracking was spreading on each affected pipe, and that more and more pipes were being affected. A programme of field measurements soon established that the cracking resulted from restrained thermal bending. Pipes were insulated experimentally and it was shown that the thermal bending could be very much reduced by this means. It was therefore decided to permanently insulate the pipes on all three pipe bridges. Twenty-three years later in 1998, poor people living in shack settlements near the pipe bridges began to steal the aluminium sheeting protecting the insulation and also removed the insulation, thus exposing the pipes to the elements once more. This provided an opportunity to inspect the condition of the pipes and to assess the long-term efficacy of the insulation. It was found that the pipes had been almost perfectly protected by the insulation and it was decided to reinsulate them immediately, using an equivalent insulation system that it is hoped will not be so susceptible to theft.