The engineer and his two pals were boiling pot after pot of plastic on the stove. Plastic bottles, diapers, carrier bags -- it was all going in the melting pot.
But McCartney wasn't going mad, he was concocting the perfect recipe for plastic roads.
"We went through about five-to-six hundred different designs of different polymers that we were mixing in before we found one that actually worked," he tells CNN.
This final recipe of blended waste plastics is mixed in with ordinary asphalt to create a stronger, longer-lasting road, explains McCartney.
"We are wanting to solve two world problems. On one side we call it the waste plastic epidemic, and on the other side the poor quality of roads that we have to drive on today."
Plastic waste is "pelletized" into small granules and replaces 20% of the sticky, oil-based bitumen that seals traditional roads.
Every ton of asphalt contains approximately 20,000 single-use plastic bottles or around 70,000
single-use plastic bags.
According to McCartney, his plastic additive is more cost effective and makes for a stronger "glue."
McCartney claims his plastic roads are 60% stronger than traditional roads, and lab tests project these roads may last up to three times longer. However, time will be the true test to see if they withstand wear and tear.
To date, McCartney's business, MacRebur Plastic Roads Company, has provided plastic pellets for roads in the United Kingdom and the Gulf, as well as Canada, Australia and New Zealand.
Related: Our children's plastic lives seen through lunches
Inspired by India's plastic potholes
McCartney first encountered plastic in roads while traveling in Southern India. There he saw how waste plastics were put into potholes and set alight until they melted into the craters, sealing the potholes.
In fact, India has been using plastic in the construction of roads since the turn of the century, following a process developed by Rajagopalan Vasudevan, a chemistry professor at Thiagarajar College of Engineering in the city of Madurai in the South Indian state of Tamil Nadu.
Vasudevan's process involves scattering shredded plastic over hot stones to form a thin, primer coat. This is then added to bitumen, resulting in a strong bond.
To date, this method has been used on an estimated 100,000 kilometers of roads across India.
In November 2015, the Indian road transport ministry made it mandatory to construct roads using waste plastic in most urban areas.
However, a number of states have yet to begin using plastic in road construction, saying the guideline doesn't concern them, explains Indian environmentalist Almitra Patel.
"Potentially plastic roads will make it possible for a city or state or the whole country for that matter to become zero waste to landfill if one follows the rules, but is a long way from happening," she tells CNN.
Related: McDonald's and Starbucks hit by plastics ban in India
Environmental cost?
Both Patel and McCartney are adamant that plastics in roads will not wash back into our rivers and oceans when it rains.
"If the plastic is permanently sandwiched between the stone and bitumen, there's no way it will ever see the environment," says Patel. "It will be ages before enough tar rubs off that you ever reach the plastic layer."
"All our plastics are heated to around 180 degrees," adds McCartney. "They then fully homogenize in, so they mix in with the remaining bitumen in the road... So there is no micro-plastic present in any of our roads."
Furthermore, Patel says PET and PVC plastics are excluded and the process of softening plastic is strictly controlled at a temperature that does not produce harmful fumes. "The point is you're not melting the plastic at any point... so there's no question of anything escaping."
While plastic waste is a mounting issue, McCartney believes the material's properties are perfectly suited for roads.
"At the end of the day plastic is a great product," he says. "It lasts for long, which is a problem if it's a waste product, but not a problem if we want it to last."
