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    Technology: Possibilities flow with permeable paving

    David Wheeldon

    With much of Australia’s urban environment paved in an impermeable skin of concrete, stone and other materials, related problems like flash flooding and urban heating are driving ever more stringent planning and construction regulations.

    Stormwater management in particular comes under closer scrutiny, with councils requiring that greater percentages of sites under development be ‘soft landscaped area’.

    In many cases, pervious, or ‘permeable paving’ will meet or exceed the requirements, be it pavers with porous material between, special pavers or gravel stabilised with epoxy resin or other bonding agents.

    The built outcome should be something more akin to a natural landscape, the water passing through to underlying structures before infiltration into the water table, or to be redirected through drainage systems.

    As well as reducing runoff, water quality can be improved as pollutants are filtered in the substrata layers.

    Importantly, such systems can function without compromising the amenity of above-lying floor areas, with products now available to suit everything from lightweight requirements for covering areas around tree roots and roof gardens, to heavy duty durability for car parks and driveways.

    The benefits of these permeable paving solutions can go beyond meeting regulations, for instance, creating low-maintenance floor areas, cost-effective erosion control and eliminating the problem of tree roots lifting and cracking concrete pathways.

    Australian firms like Place Design Group in Queensland are making excellent use of these products. Design manager Shaun Egan says they  utilise materials that allow surface water to penetrate back into the ground wherever possible.

    “In larger civic spaces and especially around existing trees, using a porous pavement is a big advantage as it will allow additional water to infiltrate down to the plants root system rather than the impervious concretes of tiles,” he says. “These materials are usually smaller pebbles bonded together with resins, producing pockets between, which allow water through.”

    Place Design Group is installing the resin and stone product in the Brunswick Street Mall, Brisbane around existing trees (3D image).  Brisbane City Council uses the product on all new street tree planting.

    Such applications have the added benefit of still providing a hard wearing, trafficable surface. Loose laid granite setts are one of the  preferred options for Egan.

    “In company with this, we still provide ‘air vents’ (pipes filled with gravel) from the surface down into the tree roots, to allow oxygen and additional water of fertilisers to reach the root zone,” he adds. 

    “The porous pavement is also helpful as it provides a stable and secure surface for pedestrians, and allows all of the space to be utilised.  As a result we are helping to reduce the latent heat loads by creating healthier trees and increasing shade to the footpaths and plazas."

    An example of a porous stone and resin solution comes from StoneSet, which uses a wide range of stones from river gravel to crushed rock. The crushed rock range is tested to meet and exceed the Class V rating for Slip Resistance required for public access areas of paving.

    This kind of product can be installed directly over existing surfaces such as concrete, asphalt or blocks. The flexible structure can also handle cracked concrete and pavers, making it a quick option for renovating old driveways, pathways and commercial paving.

    6mm Cream Stoneset being floated to a smooth finish

    Another option is Waterpave’s Sudscape, a patented resin-bonded continuous porous paving system. Voids in the rubber base retain the water until it can naturally drain back into the water table.

    Aesthetics-wise, stone and resin products can be specified in range of colours and provide continuous and flexible cover with no expansion joints.

    Another design practice at the forefront in applying the technology is HBO+EMTB, which recently used Hydroston 80 porous pavers in a large car park in Sydney’s east and Melbourne’s west. At both locations, the bulk of stormwater collected is directed to tree pits to irrigate street trees, with the excess draining through porous paving to the sand below.

    HydroCon’s permeable concrete products have been developed using German technology blended with Australian-specific research and manufacturing.

    HBO+EMTB principal landscape architect Darren Mansfield says, “In the eastern suburbs of Sydney a lot of development occurs over the extensive Botany Bay aquifer. As landscape architects it is important to consider simple ways to replenish this and to prevent its contamination. Solutions like porous pavers are part of the tool kit we use to achieve this.”

    Permeable interlocking concrete paving systems (PICP) are an option gaining prevalence worldwide. The interlocking Ecotrihex paver is produced by Adbri Masonry in Australia, and consists of permeable surface overlaying permeable base and sub-base materials. 

    One of Australia’s most famed applications of porous paving, Sydney Olympic Park. Adbri Masonry supplied 163,000 sqm of paving including Trihex and Ecotrihex pavers in Terracotta, Charcoal and Sunstone.

    The Concrete Masonry Association of Australia (CMAA) has sponsored local studies on the systems and provides a number of technical papers and guidelines that may assist designers.

    While current research points to Australia lagging behind other parts in the world in the uptake of permeable paving products, there is a steadily growing demand, which manufacturers are meeting by investing in new, locally suited technology.

    There are the widely used porous asphalts, and an increasing number of plastic-based products like the Flo-Grid permeable paver from Atlantis, which is supported by a suite of products to makeup a total stormwater management system, is yet another option with burgeoning application possibilities. 

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