The new Australian standard for fibre reinforced concrete pipes will go a long way to simplify the design and specification of concrete pipelines. Designers will now be able to specify one pipe class e.g. class 2 RCP, and an installer can now use either class 2 FRCP (fibre reinforced concrete pipe), or class 2 SRCP (steel reinforced concrete pipe).

The previous standard for FRCP significantly over-designed the pipe and essentially underestimated its true performance capabilities. This was partially corrected by the ability to design for construction loads, separately to working loads, when using FRCP. However, this lead to some confusion, as in many cases a lesser class of FRCP could provide a suitable alternative to a higher class of SRCP. The changes incorporated into the new standard have established a market where the pipe classes of steel and fibre reinforced concrete pipes now generally equate.

AS4139 is the Australian Standard that specifies the minimum requirements for pipes and fittings manufactured from fibre reinforced concrete, for the transportation of gravity water supply, stormwater, wastewater and sewage drainage (although FRCP today only carries stormwater). The 1993 standard incorporated some very conservative design parameters, which subsequently lead to the over-design of the pipe. Since this time however, the knowledge about FRCP behaviour has increased, specifically the way pipes perform in buried conditions.

A committee of industry experts managed the development and subsequent adoption of the new pipe standard; to ensure that performance parameters were adequate for Australian design conditions, in particular, those specified in AS3725 ‘Loads on Buried Concrete Pipes’. The committee included representatives from the Institute of Engineers Australia, CSIRO, Austroads, Brisbane City Council, and a number of other leading asset managers, who have specialist knowledge in pipe design. The committee again took a conservative approach to this standards revision and they addressed minimum performance criteria for the pipe including durability and serviceability. The committee reviewed and accepted in-depth testing and performance analysis, including soil box testing and Finite Element Analysis (FEA). The standard was officially published in August.

The significant acknowledgment included in the new standard is FRCP’s ability to gain extra load capacity by engaging support from the surrounding soil in which it is buried. This extra strength has been demonstrated experimentally by soil box testing. It can range from three times the design load in very weak loam soils, up to six times the design load in coarse-grained sandy soils. As the extra load capacity that is gained from the soil is not utilised in the actual design of the pipe, it therefore serves as an additional factor of safety over the service life of the pipe.

Additionally, AS4139 recognises that the performance environment for most pipes is saturated, not dry. Other concrete pipe standards do not allow for this condition even though all concrete pipes carry less load when saturated. AS4139 tests fibre reinforced concrete pipes in a saturated condition, which provides for an additional in-built factor of safety over traditional steel reinforced concrete pipes (as SRC is tested in dry conditions).

The Australian stormwater industry continues to embrace world’s best practice, through the exploration of new information, technologies, and design requirements. This new pipe standard introduces new performance concepts to Australian pipe design, and broadens our understanding of concrete pipe performance.

Richard Carr, General Manager of James Hardie FRC Pipes said ‘James Hardie’s commitment to continuous improvement promises to provide real benefits to our end-users through increased design efficiencies, and improved performance abilities. We look forward to further improvements in the standard that will realise the true benefits of FRC pipes as a superior pipeline solution.’