CMA PUBLISHES SEWER DESIGN MANUAL:
Article Date: 29 April 2009
The Concrete Pipe, Infrastructural Products and Engineering Solutions (P.I.P.E.S.) Division of the Concrete Manufacturers Association (CMA), has published the first edition of a design manual for concrete pipe outfall sewers.
Aimed at specifiers, consulting engineers and contractors, the purpose of the manual is to provide the designer with the basic guidelines and tools needed for the cost-effective design of concrete sewers including the selection of the most appropriate pipe materials.
CMA director, John Cairns, says although the containment of sewer corrosion and corrosion assessment is its main focus, the manual also covers hydraulic design, material strengths and pipe loading, and field testing. There is also a chapter on existing sewers and how best to assess them.
“All the salient features required for selecting, specifying and testing concrete pipes are included. Related topics such as sewer size and jointing are also addressed and the chapter sequence follows the typical design procedure used on a sewer project,” notes Cairns.
Much of the material included in the manual is scientifically researched, including a predictive theory, known as the Life Factor Model (LFM), which was developed in the United States. It is used to anticipate the corrosion rate of piping material under a given set of conditions and the appropriate design procedures to be followed under those conditions are outlined.
The manual draws on extensive South African and overseas research on sewer corrosion, from the Virginia Sewer Experiment in the Free State, which began in 1989 under the control of the CSIR, and before that from earlier NBRI/CSIR research begun in 1950. Part of this early research included a finding by JHP van Aardt of the NBRI/CSIR which proved that the resistance to pipe corrosion was improved when siliceous aggregate was replaced by calcareous aggregate, a finding which was subsequently implemented in sewer pipe production world-wide.
The CSIR’s involvement in sewer corrosion terminated on completion of Phase 1 of the Virginia Experiment in 1994 and the published results of this phase meant that various pipe materials could be rated on a scale of 1-10, one yielding the best resistance and 10 the worst. Thereafter, the research continued, initially under the auspices of the University of Cape Town (Phase 2) and after that through an independent consultant (Phase 3), which is still ongoing.
Although the manual focuses on the design of outfall sewers, the principles included can also be applied to reticulation and collector pipelines which transport effluent to the outfalls. However, designers of these smaller components should familiarise themselves with local requirements before embarking on any design work, as several of South Africa’s larger municipalities have compiled guidelines and procedures based on local experience.
Pipes and manholes manufactured in concrete are the most frequently used products for the construction of outfall sewers and South Africa’s concrete pipe industry has grown enormously over the past 80 to meet the country’s sewer and other piping requirements. Modern technology and SABS standards, to which all CMA manufacturers adhere, ensure that concrete pipes and manholes are manufactured to consistently high standards.
DATE : April, 2009
ISSUED BY: David Beer Communication Consultants
FOR: Concrete Manufacturers Association
ENQUIRIES: John Cairns (011) 805 6742
David Beer (011) 478 0239 or 082 880 6726. Email: bigsky@ibi.co.za
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