Lake Macquarie City Council is increasing its use of recycled glass sand with a new footpath trial underway.
With numerous councils now starting to look at increasing recycled glass sand in their civil works, Lake Macquarie City Council (LMCC) is taking the lead in this space.
Located within NSW’s Hunter region, its estimated population of 204,914 has required a shift in the way it manages its local economy. Non-centre-based economic activity, including home-based industries and businesses, remains important to the prosperity of the local government area.
However, as part of its quadruple bottom line approach, sustainability and reducing waste to increase productivity remains key to the council’s future financial prosperity.
LMCC is on track towards achieving its target of diverting 75 per cent of municipal waste from landfill by 2023. The city is also seeking to minimise resource consumption impacts from its own activities. One of the ways the council achieves this is by recovering around 90,000 tonnes of spoil, concrete, asphalt and aggregates from the civil works it undertakes each year for reuse and recycling at other appropriate job sites and facilities.
Having spent more than $100 million on capital works projects in 2018-19, LMCC has endeavoured to incorporate sustainable practises into its agenda.
A report to council in September 2017 found it needed to actively look for uses of recycled materials supported by councillors. This provided impetus for a number of projects that followed.
Earlier this year, LMCC announced a trial of crushed glass sand and recycled plastic strips in a Hunter footpath construction project.
Dubbed “greencrete” by its developer and supplier Redicrete, the fine aggregate blend comprised 50 per cent crushed glass sand and polypropylene strips made from 100 per cent recycled plastic to help reinforce the concrete and replace steel mesh traditionally used in concrete.
The footpath construction project is part of council’s asset management program, which identified more than 700 metres of new footpath to be installed in the coastal suburb of Redhead in the 2018-19 financial year.
The decision followed a trial of glass sand in its civil works in mid 2018 based on existing design and regulatory standards and a review of works by Lismore Council incorporating recycled glass sand. Glass sand was sourced from a local purpose-built glass sand manufacturing facility on the Central Coast and used in reinforced concrete stormwater pipe trenches in three road crossings. These are being monitored for stability as part of the trial.
According to Nadine Tilley, Strategic Projects Coordinator, a variety of construction methods were applied to test the material.
“In one of the trenches we used a more traditional method of installing the pipes and that hasn’t performed as well, but the other two with a slightly wider trench are both doing very well,” she says.
Towards the end of 2018, LMCC granted approval for an $8 million asphalt plant overhaul in the suburb of Teralba, paving the way for soft plastics and other recycled materials to be used in further local road construction. Owned by infrastructure company Downer, the plant will recycle and repurpose waste materials such as soft plastics and packaging, glass and toner from used printer cartridges.
Nadine says that greencrete was developed by supplier Redicrete, a local ready-mixed concrete organisation. She says that Port Stephens Council recently used the material in a roundabout pedestrian island, though this was the first time the material had been used in a footpath and included recycled plastic fibres.
She says that Redicrete had conducted its own trials and determined an optimal mixed blend of 50 per cent crushed glass sand.
“To put it into perspective, glass is slightly water repellent and natural sand absorbs water so it changes the ratios required for water and cement in a concrete mix,” Nadine says.
One of the challenges of using the recycled material is ensuring that it is not only durable, but does not become a legacy waste issue and instead follows the circular economy.
Nadine says that council is waiting on confirmation as to whether concrete recyclers would be able to take the material with glass in it as lifecycle analyses are being performed. LMCC is also awaiting reports on the compaction and flexural strength, which needs to be 4.5 megapascals to meet the council’s requirements.
“One thing council is aware of is that when we do introduce new products, we want to ensure we’re not going to be causing a legacy issue,” she says.
“We have confirmation from the EPA that in future, recycled glass sand could still be treated as recycled glass products, so if we had to dig up pipes with glass sand in their trenches, we’re not going to be left with something that we can’t use.”
Nadine says that LMCC will be monitoring the footpath for cracks, spalling or unusual wear patterns.
“This includes the driveways to a commercial carpark in the trial and will give us a good indication of performance as there will be a lot of traffic movements and we can see how the product works under commercial wheel loads.”
She says that should this trial prove successful, council will look at using the material on more of its footpaths and potentially look at trialling it on bigger projects such as cycleways.
Pictured: Lake Macquarie City Council Mayor Kay Fraser.