Every source-control device puts a material directly in the path of runoff bound for a creek. That makes materials a water-quality decision, not a procurement line item – and it is a decision the TNS™ makes deliberately. The flow path is precast pervious concrete: mineral aggregate bound in cement, nothing else as standard. This page is the whole materials story – what it is, why, and where the unit goes at end of life.
Both kerb-line inlets are precast products of PPC Australia, made to a patented permeable concrete formula. Structurally the material is conventional concrete with the fine fraction removed – coarse mineral aggregate held in a cement paste, with the void network that sand would normally fill left open. Those interconnected voids are the working part: they are what admits water at up to 500 mm per minute, tested to ASTM 1701, while carrying a Class D trafficable load rating at the tray.
It is a deliberately short ingredient list. Mineral aggregate. Cement. Water. As standard, nothing else is in the flow path – and the age of the recipe is a feature, not a limitation. Concrete's behaviour in water, under load, and over decades is among the most thoroughly characterised of any construction material on earth. When a council asset engineer asks what this inlet is made of, the answer is a material their own standards, their own testing regimes and their own demolition contractors have understood for a century.
All three are mineral aggregate and cement as standard. The full flow path, step by step, is on How it works.
The kerb line is where a catchment's runoff converges, and the inlet is the final surface that flow contacts before entering the system built to protect the receiving water. BGI's design position is that this convergence point should contribute nothing of its own to the water passing through it.
Mineral aggregate and cured cement paste deliver that. The constituents are geologically stable minerals and a hydrated cement matrix – no organic binders to age, no polymer to weather, no additive package to mobilise. Water moves through the void structure by gravity, contacts stone and cured paste, and continues to the manifold. BGI has not commissioned leachate testing on the flow-path elements, on the straightforward basis that the material contains no constituent of concern to test for; where an authority requires characterisation for a specific approval, that is a reasonable request and BGI would work with PPC Australia to obtain it.
The one caveat, stated fully: freshly crushed concrete in bulk produces strongly alkaline leachate, with reported pH values above 12, falling toward neutral as the material carbonates (Engelsen et al., 2012). That is a property of crushed recycled aggregate stockpiles, not of a cured precast unit in service – but it is why we describe the flow path as contributing no constituent of concern, rather than claiming concrete is inert in the abstract. Precision over slogan.
The question rarely asked at tender is where a unit goes when it is lifted out at the end of its service life, decades from now. It is the harder half of the circularity question – and the one the TNS™ can answer with a national statistic rather than a promise.
Concrete is the most successfully recovered material stream in the country. Building and demolition materials achieved an 84% resource recovery rate in 2022–23, up from 76% in 2016–17, with established, liquid markets for recycled concrete aggregate as road base, aggregate and hardstand (DCCEEW, 2024). A TNS™ unit lifted from a kerb line by a demolition contractor in 2065 enters that mature, high-volume, domestic stream the same day. No bespoke take-back scheme, no specialist processor, no dependency on a supplier still existing – the recovery pathway is the ordinary operation of the Australian construction industry.
"Recyclable" is not "recycled". The figures above describe a national material stream, not a guarantee about any individual unit; what a specific unit meets at end of life depends on the demolition contractor and receiving facility, decades from now. And a spent unit is renewed by replacement, not reuse – it is not lifted, cleaned and reinstalled.
The strong claim is the true one: the unit is made of the single most recovered construction material in Australia, and its end-of-life pathway already exists at national scale.
This page describes BGI's own system – its materials, its design decisions, its end-of-life pathway. It compares the TNS™ to nothing.
Cement production has a significant footprint and BGI does not pretend otherwise. This page concerns what enters the water and where the unit goes; no comparative life-cycle assessment has been run and none is presented.
Mineral composition of the porous elements is the standard specification, not a manufacturing limit.
BGI is a participant in it rather than a spectator – see Research below.
We would rather publish a narrower claim we can hold than a broader one we would have to defend.
Not in the sense of being lifted, cleaned and put back – a unit at end of service life is renewed by replacement. What it is is recyclable: it is concrete, and it enters the same recovery stream as any other demolition concrete. That is a material-class claim, and a strong one; a claim that individual units are reused would not be.
Cement production does, and we would not claim otherwise. The materials case here concerns the water and the end of life. We have not run a comparative life-cycle assessment and do not present one.
Not from BGI. The material is conventional mineral aggregate and cement, and we have not commissioned leachate testing on the basis that it contains no constituent of concern. If an authority requires characterisation for a specific approval, that is a reasonable request and we would work with PPC Australia to obtain it.
Because of where it sits. The kerb line is where a catchment's runoff converges, and the inlet is the last surface the flow touches before the receiving system. Our design position is that the convergence point should contribute nothing of its own to the water passing through it – and the material is how that position is delivered.
What urban surfaces contribute to the water that leaves them – thermally, chemically, and as particles – is an active research field, and one where BGI holds a stake rather than a spectator's seat. Our existing research stream on reflected heat and pollutant mobilisation from hot urban surfaces sits inside this question, and our materials work extends it: how surfacing materials across a catchment behave over decades of Australian ultraviolet, heat, wetting and wear, and what reaches the kerb line as a result.
We are pursuing these as research questions, as an industry partner of the ARC Training Centre for Climate-Resilient Water – a national centre led by The University of Queensland with Griffith University and the University of Technology Sydney.
The practical consequence for an asset owner is the same as it is for maintenance: we would rather hand you a measured answer in five years than a confident one now.
Where our own observations inform a question, we say so and we treat them as observations. They are not presented as findings until they have been measured.
Two sources carry the literature claims on this page – each verified against the publisher's own record. Everything else is product specification or a design position, stated as such.
Department of Climate Change, Energy, the Environment and Water. (2024). Resource recovery and waste material analysis 2024. Australian Government. https://www.dcceew.gov.au/environment/protection/waste/publications/national-waste-resource-recovery-reporting/resource-recovery-waste-material-analysis-2024
Engelsen, C. J., Wibetoe, G., van der Sloot, H. A., Lund, W., & Petkovic, G. (2012). Field site leaching from recycled concrete aggregates applied as sub-base material in road construction. Science of the Total Environment, 427–428, 86–97. https://doi.org/10.1016/j.scitotenv.2012.04.021
If your project or procurement policy asks something this page does not answer, ask us. Materials questions go to the people who made the design decisions described here.
