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Maths and software pave the way

Dr James Maina and his team at the Pavement Design and Construction Group within the Built Environment Unit of the Council for Scientific and Industrial Research (CSIR) are integral to its progress.

Pavements are created to protect the natural ground and to allow for smooth driving. Taking into account expected traffic volumes and environmental conditions (rainfall and temperature), specific materials are needed to create a long-lasting pavement.

Maina, chief engineer and research group leader, specialises in the characterisation of mechanical properties of pavement materials, the contact stresses between tyres and road surfaces, non-destructive field testing and the use of high-performance computing for numerical analysis. All this contributes to the development of better pavements that benefit the transport industry and road users.

Maina has formulated mathematical models and a consequent suite of software packages that translate the data, including the contact stress distribution and pavement material properties, to show how a pavement will respond under the action of traffic loading.

Mathematical models
"It was necessary to formulate mathematical models that relate loading (traffic volume), temperature and moisture regimes with pavement materials behaviour in terms of stress, strain and displacement relationships to illustrate how the overall pavement structure will behave over a period of time," says Maina.

The software packages cater for different road materials properties, loading characteristics and pavement configuration.

The CSIR team has also developed a world-first system, called Stress-in-Motion, which captures the actual three-dimensional contact stress distribution. The software packages are capable of using the measured contact stresses for analysis. The resulting information enables road owners to plan proper road construction, rehabilitation and maintenance.

A version of one of the software packages is already in use as a standard pavement evaluation tool in Japan. (Between 1994 and 2005, Maina worked and did research in Japan.)

The packages will form the engine of a new South African pavement design method. "Current methods were developed in the 1970s and 1980s but are limited to predefined materials," says Maina. "Knowledge and materials have progressed and we needed a method that allows for any type of material as long as you can predict its mechanical behaviour."

The South African Roads Agency Limited and the CSIR are currently funding the new design method, with technical input from other stakeholders, and the new method will be used nationally and in the SADC region as the standard for design of new construction and rehabilitation of roads. The intention is to introduce the new method in 2013.

Maina says he chose to work within the pavement environment because of the challenges it brings and the multidisciplinary knowledge it requires, but this comes with a downside. "We really need new young graduates in the field, especially when it comes to developing mathematical models and software," says Maina.

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