New Zealand’s urban environment is rapidly growing, increasing the amount of land areas becoming paved with roads, footpaths and carparks.
At the same time, sustained heavy rainfall has increased by 50%, causing problems for our country’s infrastructure.
To combat this, councils and planners have begun utilising permeable solutions, which prevent contaminated stormwater from flooding our natural waterways and from damaging infrastructure.
Also known as pervious or porous concrete
Permeable concrete, is a robust, easy to install, sustainable building material.
It is a highly porous concrete, which allows water to pass directly through the base layer of the concrete into the ground beneath, eliminating the need for stormwater drains, and preventing ponding.
Rainwater is therefore returned to the natural environment in the sub-grade (natural ground beneath), allowing soils to recharge.
Furthermore, permeable concrete provides opportunities for a larger building footprint, as this material doesn’t count as a ‘hard surface area’ (an area without natural ground i.e. grass, plants, rocks and soil).
Therefore, permeable concrete is a good option for property developers looking to maximise their available space.
How Permeable Concrete is Constructed
First, the surface level is made up of permeable concrete - which drains water through to the base course.
Second, the base course, is made up of stone aggregates (materials loosely compacted together), and comprises the structural foundation. Water then drains though to the sub-grade.
Third, the filter cloth (geotextile layer), is sometimes required depending on the soil type. It allows water to filter through, while preventing the sub-grade from clogging the base course.
Fourth, the sub-grade, is the undisturbed soil at the bottom. The strength of this influences how thick the base course needs to be.
Optional, is a sub-surface drain which directs excess water to the stormwater system.
Permeable paving has the same benefits as permeable concrete, and goes through a similar installation process.
The main difference between the two, is in aesthetic appeal. Whereas permeable concrete is one flat, connected slab, permeable pavers can provide an interesting design feature to your home or commercial build.
Grasslok (Bowers Brothers) permeable pavers installed for residential customer.
Lower carbon footprint
Up to 40% lower than conventional concrete.
Compared to asphalt, has a 56-70% lower carbon footprint at time of installation - as it requires less energy to be produced.
Reduces surface run-off (excess rain or stormwater that pools on the ground) by approximately 20 – 25%.
Thus, it mitigates first flush pollution: at the start of heavy rain, high concentrations of pollution in stormwater drains get rapidly flushed out to our waterways.
It also prevents hydrocarbons, heavy metals and other contaminants from entering stormwater systems and polluting our natural waterways.
Returns the moisture to the ground, benefiting the immediate environment.
Reduces the impact of urban infrastructure near trees, as it allows water and air to reach the root system.
Trees planted in permeable concrete plots have shown a 68% higher growth rate than trees in traditional concrete plots.
Can be made using industry by-products like fly ash, slag, micro silica and recycled aggregate, thus increasing its recycled content and lowering its life cycle cost.
Doesn’t require plastic sheet filming like traditional concrete.
Since it is made directly on-site and as needed, there is very little overproduction.
Heat island effect
Reduces surface temperatures, since permeable concrete reflects heat instead of absorbing it like traditional concrete.
Heat islands can cause higher: energy usage (air-conditioning), air pollution, greenhouse gas emissions, and water pollution.
The EPA (Environmental Protection Agency) has identified permeable concrete as a Best Management Practice (BMP) for stormwater management.
Can qualify for green credits with LEED, Living Building Challenge, CAL Green and Green Point Rated systems. For LEED, permeable concrete can earn project credits for Sustainable Sites, Recycled and Local Materials, Innovation in Design and Water Efficiency.
Increases land utilisation
Reduces the need for additional land housing retention ponds, or other water-retention and filtering systems; allowing a larger building footprint.
Because the concrete is reflective and typically a lighter-shade, the need for lighting at night is reduced.
Permeable concrete channels more water to tree roots and landscaping, so there is less need for additional irrigation.
Lower installation costs
Permeable concrete reduces the need for stormwater systems, which can be double or triple the installation cost of permeable concrete.
Lower lifetime costs
Whilst the cost per square metre can be slightly higher, the overall lifetime costs can be substantially lower than alternatives such as asphalt, as it requires fewer repairs, and has a longer overall lifespan.
WHY CHOOSE SITEWORKS
In 2007, we were the first approved contractor to install permeable concrete in New Zealand. For over 10 years, we have been at the forefront of permeable concrete’s development here and in Australia, working alongside the Auckland Council, concrete suppliers, and engineers to improve the mix design and installation process.
Partnering with the Readymix Concrete Industry, we have placed over 10,000 square meters of permeable concrete for our clients, and are one of the few companies recommended by Readymix suppliers and engineers throughout New Zealand.
Dave Stewart, our permeable concrete enthusiast, has been involved in the concrete industry for nearly 30 years, and has completed the Permeable Concrete Installation Certification in the USA, as well as working with a number of leading installers in the US and Australia.
In 2015, we were presented with the “MOST INNOVATIVE” award for the Stillwater Pervious Concrete Parking Bay project by New Zealand Master Concrete Placers Association (MCPA).