Why concrete pipe?
Steel reinforced concrete pipe is a material unlike most other concrete products. It has a unique history, is made using specialised processes, and results in a material that provides strength, durability, and sustainability.
Concrete pipes are rigid wall structures combining the properties of steel and concrete, provided in a range of diameters and strength classes that enable designers to confidently design load bearing structures for a diverse range of installation conditions and applied loads.
Concrete pipe has been the cornerstone of the Australian pipe industry for over 100 years. The concrete pipe of today in Australia is founded on innovation, sustainable practices, proven performance, longevity, reliability.
Strength
Steel reinforced concrete pipe is the strongest pipe available.
Ongoing In process strength testing underpins the reliability of concrete pipe. Both Proof and Ultimate load testing is performed by manufacturers to prove the structural strength of concrete pipe to give purchasers the confidence that the product they are buying is the right strength.
It doesn’t matter what manufacturer the pipe is purchased from, the minimum performance strength of the pipe is identical. The pipe class number, e.g., Class 4, ensures the same tested strength no matter the manufacturer, whereas for flexible wall pipes, the marketing number SN might be the same, but the long term strength under test varies by manufacturer.
Concrete pipe is manufactured in a range of strength classes. The most common strength classes utilised are Class 2, Class 3, and Class 4, however Australian and New Zealand manufacturers design and manufacture pipe to Class 12 which has 6 times the load carrying capability of a Class 2.
Unlike flexible wall pipe, it has minimal reliance on installation to support loads; it relies primarily on its inherent brute strength manufactured into the pipe. That adds up to a tremendous difference in the design, the installation, and the long-term success of a project.
The strength of a concrete pipe improves with age. The required 28-day strength, guaranteed at the point of manufacture is readily surpassed as the pipe ages. Concrete pipe has no time dependent negative change in properties as does flexible wall pipes manufactured from plastics.
Dependability
Steel reinforced concrete pipe’s long-term performance is proven, not theoretical. Innovation has made concrete pipe more reliable and dependable than ever. Innovation includes improvements to concrete mixes, manufacturing processes, improved quality control and more.
Dependability is not just a matter of how a product performs on its own. It also has a lot to do with how well it is understood by the people who plan, design, construct and install a project. How well does the engineer know its properties? How adept is the project team at spotting and correcting potential problems before they happen? How experienced are the crews when it comes to flawless installation and execution?
In this vital area, no material is better understood and more commonly used in the field than concrete pipe. That adds up to fewer mistakes and a greater level of comfort and confidence.
Sustainable
Historically, concrete is the most durable and sustainable material for infrastructure and major construction. It continues to function long after a projects life is reached, by maintaining structural integrity, thus reducing the costs associated with repair and replacement.
Precast concrete pipe’s staying power has another benefit; it’s not a passing fad. When concrete pipe is specified, the projects you build today are more likely to be compatible with any future expansions or alterations.
Australian and New Zealand steel reinforced concrete pipe is the lowest mass per diameter in the world, underpinning a sound sustainable position.
Combinations of a range of standard pipe strengths and installation support types, provide designers and contractors with the advantage of always choosing the sustainable option based on available material options, low transport distances and reuse of existing materials negating the need for imported trench materials.
Concrete pipes can be laid using trenchless technology known as pipe jacking or micro tunnelling. This method avoids disruption caused by excavation and reinstatement of trenches. Additionally, the excavated material going to landfill is minimised, there is no imported backfill required and movement of heavy vehicles is significantly reduced.
Steel reinforcement is generally recycled and more often than not the cementitious content includes recycled and waste products meaning, by mass per diameter, concrete pipe utilises more recycled material than any other drainage pipe product in Australia and New Zealand.
Concrete pipe is recyclable either as crushed material used in other construction activities or as repurposed whole pipes. Recycling of concrete pipe is a simple activity with no capital-intensive equipment required.
Installed and whole life cost savings.
The costs of managing an asset throughout its life must be acknowledged from the outset. The choice of pipe material will have a major impact on these life cycle costs.
The following key elements are the basis of economic and technical assessment of life cycle costing for stormwater drainage assets:
Initial creation cost
Steel reinforced concrete pipe installed cost can be minimised with appropriate choice of class of pipe and installation support types. A higher class of pipe and lower installation support type minimises the cost implications related to expensive imported bedding and support materials.
Effective life (to future replacement)
With a proven history of 100 year life without the need for replacement, steel reinforced concrete pipe provides asset owners a high confidence level of achieving a 100 year effective life. Its ability to survive unanticipated events including bushfires and flooding are important life cycle considerations.
Ability to renovate and Maintenance costs
Steel reinforced concrete pipe has been proven to not require renovation or maintenance in the application of stormwater. Crack widths under normal loading are limited to widths that are not detrimental to durability. The phenomenon of autogenous healing results is an important consideration ensuring steel reinforced concrete pipe asset life.
Others- Consequence of failure
Steel reinforced concrete pipe ultimate load strength is at least 1.5 times the required working load design strength. The inherent strength of concrete pipe limits the consequence of failure compared to flexible wall pipe systems that fail under deflection, buckling or wall strain.
CPAA commissioned an independent review of pipe costs by OPUS. The results are interesting and counter to the myth that plastic is cheaper than concrete. If you ‘do things right’ then concrete is the most cost effective solution. The document makes interesting reading and highlights some important considerations when making decisions about the choice of material. The report concludes that ‘The requirements for more imported material and ovality testing mean that rigid pipes should be cheaper to install than flexible pipes and have a corresponding lower whole of life cost.’ The exercise was completed for both the Australian cost base and the New Zealand cost base using an identical methodology.
Structure and Conduit
Concrete pipe is a rigid wall pipe that provides both structure and conduit when it arrives on site. Unlike flexible wall pipe alternatives, concrete pipe can have little dependence on the surrounding soil for its structural performance.
The inherent strength of concrete pipe compensates for construction shortcomings and higher fill heights and trench depths. Flexible pipe is at least 95% dependent on soil support and the installation expertise of the contractor. Backfill must be properly engineered and applied to provide structure. Imported fill is usually required for flexible pipe systems. Concrete pipe is less susceptible to damage during construction, and maintains its shape, by not deflecting as does flexible wall pipe.
As a rigid wall pipe, concrete pipe has high beam strength and can be pushed to proper grade. Only concrete pipe can bridge over uneven bedding without affecting the pipe hydraulics. Flexible wall pipe has little beam stiffness and deflects with uneven bedding, thereby inducing strain along the pipe axis.
Deflection testing of flexible wall pipe is critical to measure the strain and any circumferential deflection. Allowable deflection of flexible pipe is 3% initial and 5% long term. Deflection testing should not end or be taken when backfilling has been completed. Installation problems that may be associated with flexible wall pipe are deflection, deformation or buckling, wall strain or crush, and buckling. When installation or manufacturing failures occur with flexible wall pipe, there is often reduced hydraulic capacity of the drainage system and leaking joints. Mandrel testing of flexible wall pipe is mandatory activity to confirm the structure’s installed integrityDeflection testing of flexible wall pipe is critical to measure the strain and any circumferential deflection. Allowable deflection of flexible pipe is 3% initial and 5% long term. Deflection testing should not end or be taken when backfilling has been completed. Installation problems that may be associated with flexible wall pipe are deflection, deformation or buckling, wall strain or crush, and buckling. When installation or manufacturing failures occur with flexible wall pipe, there is often reduced hydraulic capacity of the drainage system and leaking joints. Mandrel testing of flexible wall pipe is mandatory activity to confirm the structure’s installed integrity
Lower Risk Installation
Concrete pipe’s strength facilitates successful installation. This lessens the liability on the owner, engineer, and contractor. When proper installation is specified and inspected, concrete pipe has the lowest installed cost and risk, compared to alternative products.
Concrete pipe’s strength facilitates successful installation. This lessens the liability on the owner, engineer, and contractor. When proper installation is specified and inspected, concrete pipe has the lowest installed cost and risk, compared to alternative products.
Concrete pipe far outperforms plastic or metal. Concrete pipes rigidity and mass allow for easy and secure placement in the trench, without disrupting line or grade. Plus, precast concrete pipe joints are easily assembled, which helps minimize the time needed for installation. When installation time matters, or when the soil poses challenges to installation, precast concrete pipe is quite simply the most logical and responsible option. Since concrete pipe is a rigid wall pipe system that is primarily dependent on the pipe strength and only marginally dependent on the strength derived from the soil envelope, installation is made easy. In many situations, the installation of plastic or metal flexible wall pipes can take longer than precast concrete pipe. That’s because the structural and hydraulic integrity of flexible wall pipes rely heavily on how well you prep the surrounding soil at installation, rather than on their own inherent brute strength. Making sure all conditions are right and installing per national specifications can be a costly and time-consuming proposition when installing flexible wall pipe.
Concrete pipe has a wide range of standard pipe strengths from which to choose, and special classes can be manufactured when required. Importantly strength is demonstrated prior to installation. By specifying concrete pipe:
- The designer has more control over pipe strength than any other facet of the project.
- There is less reliance on quality installation by the installer.
- There is lower embedment material cost.
- There is less compaction required.
- It is easier to maintain grade and alignment.
- There are no excess deflection concerns
- There is a lower life cycle cost of the project.
- There is a lower maintenance cost over the design life of the project.
- There is a reduced likelihood of failure.
- A lower risk for the specifier, designer and owner of the project, and reduced overall liability to the public after the project has been commissioned.
AS/NZS 3725 Design for installation of buried concrete pipes provides a range of standard support types that permit a large choice of backfill materials and levels of compaction. These standard support types combined with selecting from the range of standard pipe strength classes provide several benefits when using concrete pipe:
- Provides flexibility to meet design requirements and site conditions.
- Provides flexibility to deliver the best sustainability outcomes.
- Allows for narrower excavation limits.
- Less expensive backfill materials may be used.
- Can reduce the level of compaction.
- Increases contractor productivity in installing reinforced concrete pipe.
The short lengths of concrete pipe make it easier to work with around existing services. Concrete pipe installations using trench boxes do not require special attention to sliding the trench box and disturbing the bedding and backfill in the process, an activity that proposes high risk to the integrity of flexible pipe installations. Using standard lengths of concrete pipe, line and grade can be checked frequently for accuracy.
Design and Construction Flexibility
Steel reinforced concrete pipe provides strength and flexibility to ensure the success of the most demanding projects. Pipes are manufactured in a variety of sizes, classes, joints, and seal options. Plus, an array of linings and coatings can handle the most aggressive environments.
Some projects have design elements that are a little more complex or intricate than others. Precast concrete pipe provides solutions for these projects, whether they are embankment, deep trench, tunnels, trenchless, shallow burials, or with vertical structures or complex alignment changes. Concrete pipe design is simple to do; the math is sound and easily definable. All of concrete pipe’s material and pipe characteristics are readily available and easily understood. Reliance is not on hard to obtain information from one manufacturer, as in the case of flexible pipes.
Concrete pipe produced in the early twenty-first century is a consequence of:
- Computer aided design and analysis
- Advanced concrete mix designs
- Automated and computer-controlled batching
- Precision fabricated wire reinforcement
- Quality driven manufacturing techniques
- Improved watertight joints
- Materials minimisation to ensure sustainability
Quality Control
Concrete pipe has the most rigorous quality control testing in the drainage industry. From raw materials and mould setups to batching equipment and tests during concrete placement, every step of the manufacturing process is meticulously monitored to ensure design strengths and durability are met.
Characteristics of pipe manufacturing operations normally include:
- Input materials monitoring and QA checks
- Computer controlled weighing and proportioning systems.
- Computer controlled mixing systems.
- Automated recording systems
- Precision machine manufactured steel reinforcement.
- Proof load testing
- Ultimate load testing
- Water Absorption testing
- Dimensional checks
Disaster resilient
Concrete pipe will not burn, importantly the structure remains functional if installed in a location affected by bush fires or fires caused by accidents.
In heavy rainfall or catastrophic flooding situations, concrete’s density keeps pipes in place against upward, buoyant forces.
When concrete pipe is under roadways, evacuation routes remain safe as their failure is not by deflection and buckling.
Concrete pipe will not corrode prematurely.
Concrete pipe will not collapse under loads designed into the pipe structure
Hydraulic Performance
Precast concrete pipe’s rigidity and mass allow it to greatly outperform flexible wall pipe systems in the critical area of hydraulic performance, which in turn helps to improved hydraulic efficiency by minimising the resistance to water flow that often occurs when the shape or integrity of a flexible pipe is compromised.
In a low laying or marshy environment, the buoyancy of buried pipelines depends on the mass of the pipe material, the weight of the volume of water displaced by the pipe, the weight of the liquid load carried by the pipe, and the weight of the backfill material. Whenever the water table level is above the invert of the pipeline, the potential for flotation or buoyancy exists. Although the trench for a pipe installation in a marshy area is dewatered, the trench area downstream (after initial backfill) may become saturated. This would lead to a buoyant effect on the pipe. The mass of the concrete pipe typically counteracts this buoyant force. Alternate materials such as flexible wall thermoplastic pipe and corrugated metal pipe may heave vertically or snake horizontally in wetland conditions. During the backfill operation, the fill may accumulate more on one side of the pipe than the other. The mass of the concrete pipe resists lateral forces, and the structure remains true to line and grade.
Manufactured locally
Steel reinforced concrete pipe is locally manufactured in numerous location is Australia and New Zealand.
Manufacturing occurs in every state in Australia and both islands of New Zealand providing for low sustainability transport options, minimisation of costs associated with transport and the convenience of local supply.
Local manufacturing means the materials are designed to meet local state authority requirements and supports the local economy.
Material compatibility
When constructing a pipeline, concrete construction is the standard structural solution for end treatments and pit structures. Concrete pipe can be easily and confidently integrated into the other pipeline structures without the need for specialist materials.
Repair when necessary is easily accommodated with known procedures and off the shelf materials, minor installation damage never requires complete replacement of a pipe length as is the case with many flexible pipe products.
