Pavement
Cars and vans cross it every day, a P4 slip rating underfoot. Pour it deeper, and it carries heavy axles.
Permeable pavement design
Permeable pavement, designed from the subgrade up
The slab is what you see. Beneath it, a base holds the rain until the ground or an outlet takes it.
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Outlet, subgrade, base, surface
The four parts stack in order, from the outlet up. The outlet, usually an under-drain, releases whatever the ground won't take, at a rate your drainage engineer sets. Above it, the subgrade takes water away wherever the soil allows. The base stores it, and on top, the surface carries the traffic while letting the rain in.
Put a strong slab over a thin base and a long storm fills the screenings; from then on, rain lies on a surface that could pass 8,000 to 10,000 mm per hour.
That surface is Permcon, poured as one continuous slab with no joints, with 7 mm stone in Victoria and 10 mm in every other state. The real design questions sit underneath, and the surface figures a specifier needs are kept on their own page.
Permeable pavement design: three typical profiles
Car parks and rights of way usually start at 150 mm of slab or more, on a 150 mm base course with a sub base beneath, and store 42 litres to 56 litres per square metre, the heaviest of the three profiles here, though slab depth shifts with the heaviest vehicle on site.
Driveways step down to a slab of 125 mm to 150 mm over a similar depth of base and hold 37 litres to 42 litres. At 100 mm on 100 mm, footpaths hold 28 litres a square metre. Shared paths take a 125 mm slab.
All three sit on clean screenings, and each storage figure is detention held in the base at 85% design capacity. Geotextile goes in where the subgrade calls for it.
Loading: thickness does the work
A pram on a footpath and the cars in a car park get the same 25+ MPa concrete from us. Only the slab depth changes. Permcon is a rigid pavement, so each step in thickness buys a lot: the estimated maximum axle load goes from 3.7 t at 100 mm to 8.3 t at 150 mm.
Deeper again, at 175 mm it takes an estimated 11.3 t axle. The full chart and its Benkelman beam back-analysis help with early sizing. Your engineer designs the final pavement for the actual subgrade and traffic, and we pour to it.
There is more on car park pavements on their own page.
What the base does with a storm
Sand lets water pass straight through. Once water is in the base, the design decides where it goes next, and on free-draining ground, infiltration lets the base empty into the subgrade with no pipe leaving the pavement.
Detention is about the peak. The base holds the storm and lets it out slowly, so less reaches council's system at once; count the surface as pervious in a passive design and the tank a sealed site would need can shrink or go.
Clay, or a site where soakage isn't allowed, gets controlled discharge: an under-drain in the base meters water to the legal point of discharge at a rate your engineer sets. We will work with anyone that wants the Permcon product. We just need to make a design that suits their needs.
Permcon is MUSIC certified. Ask for the node parameters with your profile.
One surface, three functions
Stormwater quantity
Drainage designers count the storage in the base, and it does the work of a pit and the pipe that would drain it.
Stormwater quality
What drains out is cleaner, because up to 70 per cent of heavy metals, hydrocarbons, detritus and suspended solids stays behind.
Maintenance belongs on the asset register
Once a month, someone walks it. A permeable pavement is an asset like any pit, and that short routine is what a design life of more than 30 years assumes:
- Each month, leaves and debris come off, and there should be no sediment building up on top.
- Check it has drained after rain.
- Garden soil stays off it. A landscaping change that sends new overland flow across it gets corrected.
- Once a year it's swept, if the monthly walks haven't already called for that, and the voids are checked for moss and organic matter.
Structural failure is a different matter: inside 10 years, we assess the area and remove and replace the slab under our structural warranty, with terms and conditions attached.
Permeable pavement design questions
What do you need from us before you design the profile?+
Mostly the traffic, right down to the heaviest vehicle, and a geotechnical report (the soil type will do if there's no report yet). If your drainage engineer or council has set a storage or discharge target, send that too. It can all go through the enquiry form. What comes back, in writing, is a slab thickness and base depth with the storage they give.
Can a car park have more than one slab thickness?+
It usually should. The zones come from the estimated axle load chart and your engineer's traffic.
Will this count toward our stormwater targets?+
Yes, where the authority accepts it. Council makes that call against its own controls; what we supply is the storage in litres per square metre and the treatment figures for your profile. See the water section above.
First, the loading and the soil
We have a team in each state, so someone local walks the site before slab and base depths come back on paper, storage included.
Start with the ground
Check if permeable concrete suits your site
A few quick questions about your site. You get a straight answer about whether permeable concrete is the right call, including when it isn't, before anyone asks for your details.
Site check · 1 of 5
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Tell us about your project
Tell us where the site is and what you're planning. An estimator from your state team will call you back, look at the site with you and give you a real figure, from a single driveway to a council car park.
📞Call us1300 010 499✉️Email us[email protected]
📍Head officeFactory 7, 25-39 Cook Road, Mitcham VIC 3132
Pavements we've poured
