Construction and demolition waste in Australia weighs 15.1 million tonnes, with 7.6 million tonnes being recycled materials such as recycled concrete. Buildings and their users are responsible for almost a quarter of Australia's greenhouse emissions, the contribution of the re-use and recycling of construction materials can lower the embodied impact of greenhouse emissions.
What is recycled concrete?
Old and unwanted concrete from demolition sites can inhibit or delay the process of a construction project. Concrete recycling is the use of rubble and crushed concrete from preexisting concrete forms consisting of demolished structures, concrete pavements, concrete slabs and other construction waste. Recycled concrete aggregate consists of a large volume of natural resources, which reduce landfill space by being reused in the construction of other buildings, the base layer of foundations, structures and much more.
Concrete recycling options
After the demolition of old roads and buildings, the leftover concrete is often considered worthless and disposed of at landfills; however, by collecting and breaking up the used materials, recycled concrete aggregate can be created. The raw material conserves natural resources by reprocessing the cement into new reusable material.
Determining exactly how to recycle concrete will depend on the type and size of the used concrete. Recycled aggregates can be formed into a range of sizes determined by the kind of project it is being used for once it becomes a new concrete.
Benefits of concrete recycling
Recycling concrete is cheaper and more environmentally friendly than trucking crushed concrete from a construction site to a landfill. The most significant benefits of recycled aggregate are the economical and environmental factors.
The economic benefits of recycling concrete consist of:
- Expenses would be minimised as the cost to secure, process and transport all-new material are eliminated, reducing construction costs in general.
- Using recycled concrete to rebuild or repair at the same location it was demolished minimises cost
- Recycled concrete waste is more lightweight than virgin materials, resulting in less money spent on building costs and materials.
The environmental benefits of recycled concrete consist of:
- Reducing the number of raw materials being sent to landfills.
- Since concrete is not biodegradable, old concrete and demolition waste will not break down over time.
- Recycled concrete aggregates reduce overfilling landfills and wasting limited resources.
- Energy waste and harmful gas emissions from vehicles are minimised by eliminating the need of transporting material and processing new materials.
Investing in recycled products will not affect the quality of the material. Repurposed materials allow for great environmental benefits by preserving precious and limited resources, while also being as effective as brand new materials.
How concrete is recycled?
The concrete recycling process is relatively straightforward, consisting of a four-step process.
The first step is harvesting the concrete rubble from demolished structures, buildings, parking lots, roads, sidewalks, highways, building foundations, and more. Once concrete rubble has been harvested, the rest of the processes are done on-site, off-site, or at a concrete recycling facility.
Once the concrete is harvested, the second step is crushing concrete using industrial crushing equipment, including the use of a portable crusher, mobile or stationary jaw crushers, cone crushers or impact crushers. Depending on the concrete pieces' size, the construction and demolition waste is put through jaw and impact crushers for the initial crushing. Once initial crushing is completed a secondary crushing process can be done if recycled materials are required to be of a specific size.
There are many different types of equipment that can be used during the crushing process: portable crushers, mobile or stationary cone crushers, impact crushers or cone crushers.
Raw materials are fed through the first crushing machines (the jaw crusher), where the breakdown of materials begins. The concrete is fed through a second crusher to break it further down into usable formats.
The third step is screening the concrete aggregate as often other materials such as clay, plastic, dirt, metal, wood chips and asphalt pavement can be found mixed in. The crushed concrete needs to be screened using scalping, separators, water flotation, and magnets to separate the different materials. The recycled aggregates often go through several screening processes depending on the source of the concrete and what the end product will be used for.
There are multiple different types of equipment that can be used for the removal of contaminants through selective demolition, screening, water flotation, magnets, and/or air separation. Scalping screens are the ideal machine used for the removal of contaminated waste proper to the recycled material being cleaned and sorted.
Lastly, the concrete is ready to be cleaned before it can be recycled into new concrete, any remaining residue must be removed through a cleaning process. This can be done through hand-picking, magnetic separation, or air and water separators.
Uses for recycled concrete
Recycled concrete can be used for various residential and commercial projects, including landscaping, construction, roadways, and development.
The large and small aggregate material of recycled concrete can be used in the building process of road constructions, they can be used as a layer of gravel in road construction instead of new materials.
Recycled concrete can be used to prevent and control erosion of structures found at river banks and shorelines which are at the edge of a water source. Many companies use this cement to build these foundations because it is an environmentally friendly and cost-effective solution for minimising the use of virgin materials.
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The benefits and uses of recycled concrete have been shown to have positive effects in terms of economic and environmental factors. The process of recycling concrete has also shown to be a relatively simple process with endless benefits.