Frequently asked Questions and Information on Precast Headwalls
What is a headwall for?
Precast headwalls can be used as inlets and outlets for pipework discharging into attenuation ponds, rivers, ditches and swales
What is the difference between an inlet (outfall) and outlet headwall?
Althon call headwalls discharging into attenuation ponds inlets or outfalls. Althon can provide headwalls with a fall on the spillway to use as inlets or outfalls. Typically the invert level of the pipe will be up 100, 150 or 225mm from the apron of the headwall
Althon call headwalls taking water away from the pond outlet headwalls. These can be made with a flat spillway and often the pipe opening on the headwall will be set flush with the spillway
Why use a precast headwall?
Precast headwalls mean the amount of concrete poured by the watercourse is significantly reduced compared to constructing an in-situ structure
Using precast headwalls means Althon can factory fit accessories such as handrails, flap valves and trash screens
Do you do low carbon headwalls?
Althon headwalls are manufactured with Eco1® which replaces a significant portion of cement with supplementary cementitious materials (SCMs) like GGBS
ECO 1 Low-Carbon Precast ECO 1: Matches or exceeds traditional performance.
ECO 1 retains CEM I standards while reducing cement content by 46% achieving over 75 N/mm² at 28 days.
It’s fully compliant with BS 8500-2:2023, including Design Chemical Class 4 and Design Sulphate Class 4 making it suitable for even the most aggressive environment
Do you do headwalls with CARES accredited reinforcement?
When required Althon can provide precast headwalls with CARES accredited reinforcement
CARES accredited steelwork ensures :
- Compliance with BS standards for reinforcement
- Full traceability from Mill to Site
- Responsible Sourcing & Sustainability
This is often a requirement on infrastructure projects such as HS2
What is the design life of your headwalls?
Althon offer headwalls with either a 120 year design life or 50 year design life. This is based on the concrete cover to steel reinforcement
What mix and exposure class is the concrete in your precast headwalls?
Concrete
- Mix ref: Self-compacting DC4/DS4 Mix
- Lifting strength based on 2 cubes = 20N/mm²
- Characteristic 28 day cube strength = 50N/mm²
- Concrete provides Design Chemical Class 4 (DC4) to special Digest 1, Table F2.
What standards do you manufacture your precast headwalls to?
Manufacture of our headwalls is to BS EN 15258:2008 precast concrete products - Retaining wall
elements, Factory Production Control certificate number: 0086-CPR-650448 & BS EN 13369
- Tolerances to BS EN 13369 clause 4.3.1.1
C Marking: Units shall be indelibly marked to show:
- Mould reference code
- De-mould date
- Job reference number & unique product number
- Unit weight (kg)
Will Water Authorities use your precast headwalls?
Althon have headwalls and metalwork available to comply with Sewerage Sector Guidance (formerly headwalls compliant with sewers for adoption)
Althon have a range of headwalls specific to Anglian Water requirements and Severn Trent Water headwalls
Althon can also work with enquiries for United Utilities headwalls and metalwork
If you let us know the headwall requirements of any water authority we can work with you to design a suitable precast headwall option
Do you factory fit metalwork and water management devices
Althon offer the option to have trash screens, gratings, handrails, flap valves and other flow control devices to our headwalls
Unlike others Althon cast in the fixing points for these items into our headwalls. This means that the headwalls do not have to be drilled. This is important because when you drill the headwall you risk exposing the reinforcement which can compromise the design life of the product
What openings do you put in your headwalls?
Althon cast the opening into the headwall slightly larger than the OD of the connecting pipework. The pipe is then brought through the back of the headwall and typically will finish flush with the front face of the back wall
The small gap is then filled in with a suitable grout or mortar
Where can the pipe go on the headwall?
Althon can set the invert level of the pipe anywhere you like on the headwall, this can be flush with the apron of the headwall or high up the back wall. As long as there’s 150mm concrete cover above the opening we can put it wherever you need it
As long as there is room we can even put openings into the side walls (wingwalls) of the headwalls
Can I have more than one pipe coming into the headwall?
Yes! Althon can put multiple pipe openings into any of our headwalls. As long as there is room on the back wall of the headwall you can have as many openings as you like. Typically all we require is a minimum of 150mm of concrete between the openings
How do Althon SFA headwalls compare to cast-in-situ concrete installations?
Althon SFA precast headwalls eliminate the need for on-site shuttering, steel reinforcement tying, and concrete curing time. A standard precast installation can be completed in a single afternoon, offering up to a 70% reduction in on-site labour time and eliminating weather-dependent installation delays common with poured-in-place concrete.
Can Althon SFA headwalls be customized before delivery to the site?
Yes. Althon precision-engineers and factory-fits accessories to the headwall unit prior to shipment. This includes the factory installation of Althon flap valves, penstocks, handrails, and bespoke safety grilles, ensuring the entire outfall assembly arrives on-site ready for immediate pipe connection.
If you require any assistance or more information please contact us by phone on 01603 488700 or by email sales@althon.co.uk