The most commonly used construction material in the world today is concrete and every year in Australia there is 25 million cubic metres of concrete produced. The manufacturing of cement in Australia leads to about 700kg of carbon dioxide being emitted per tonne of cement produced.
As with any industry, sustainability and being environmentally friendly are necessities in today’s day and age. But when the manufacturing of cement has a by-product of CO₂, more needs to be done for it to be sustainable.
According to Cement Concrete and Aggregates Australia CEO Ken Slattery, quite a lot is being done to lower the carbon footprint in cement and concrete.
Slattery says developments in the concrete industry are currently addressing sustainability through a number of strategies which are aimed at reducing greenhouse gases, preserving natural and virgin materials by developing and refining the use of alternate materials, and reducing the amount of waste through intelligent re-use and application of its products.
Manufacturing cement is an energy-intensive process which produces CO₂. The industry is addressing this by using alternative fuels, reducing waste from other industries and lowering the amount of fossil fuels required, he says.
It has also upgraded the efficiency of manufacturing equipment, reducing the electrical requirement for production.
Substitution of materials in cement instead of clinker is also a major change to increase sustainability and reduce CO₂. It is being replaced with materials such as limestone, fly ash and blast furnace slag.
As concrete is produced from a mixture of coarse and fine aggregate, with water and cement to bind the materials, it is possible to substitute natural coarse and fine aggregates with other materials, Slattery says.
An aggregate supply industry has been developed, which refines the material streams to increase the amount of useable aggregate and reduce the amount of waste materials.
“Reclaimed and recycled aggregates may be used in concrete to preserve the natural materials and reduce waste streams. Examples such as the use of slag aggregates, a co-product of iron manufacture, will help to make a more sustainable concrete industry,” Slattery says.
Research into the use of water in the production of concrete has seen the increased use of recycled and reclaimed water in production, reducing the amount of potable water used.
Lastly, at the end of the life of the structure, it can be repurposed or recycled back into other structures, demonstrating the versatility and sustainability of concrete.
An example of this is Ballast Point Park in Birchgrove, NSW, the overall winner of the CCAA National Domain Awards 2011. Remnant concrete from past industrial buildings on the site is reused in basket cage retaining walls and as aggregate in drainage channels. It is said to represent one of the most innovative uses of concrete in Sydney, while also showcasing old concrete structures, which have been retained on site.
Precast concrete is one particular area that makes sustainability achievable with modern construction as it actually absorbs CO₂.
National Precast Concrete Association Australia CEO Sarah Bachmann says over the last 10 years the financial investment in the precast manufacturing industry has dramatically increased.
Additionally, there has been a change in the structure of the industry, with more multinationals, such as Brickworks, establishing factories throughout Australia, Bachmann says.
Precast concrete supports sustainability through a variety of ways including minimising waste produced with most waste recycled, high thermal mass properties resulting in reduced heating and cooling costs, and minimal maintenance.
Exact elements can be delivered to a construction site meaning fast construction, less trades on site, and less waste on site. Precast concrete is locally manufactured using local products in reusable moulds. Less concrete and steel are required for precast concrete because of its higher quality.
Of particular note are the advances in technology with precast concrete, including insulated sandwich panels being specified a lot more, as well as the use of hollowcore floor slabs.
Insulated Sandwich Panels are comprised of three layers - an outer skin of non-structural reinforced precast concrete, an insulation layer and an internal layer of structural reinforced precast concrete. This setup gives it a high thermal mass and, when combined with other energy saving elements could eliminate the need for air-conditioning or heating altogether in some climates.
Hollowcore floor slabs behave as passive heat exchange elements that release or absorb heat through the air in the slabs, allowing them to heat, cool and ventilate a room. As a result, a building’s requirements for heating and cooling is reduced along with costs.
An example of environmentally sustainable precast concrete in use is the University of New South Wales Village project. It comprises 19 buildings, ranging from one to nine storeys with various accommodation styles to house more than 1000 students of the university.
The project used 1200 sandwich panels and 17,500 square metres of precast hollowcore flooring planks to help achieve the thermal efficiency.
