Costa Rican company turning plastic waste into building blocks

It sounds too good to be true. At a time when barely a day goes by without plastic waste being mentioned somewhere in the mainstream media, with politicians currently falling over themselves to be seen taking the issue seriously, a Costa Rica-based firm may have found a cunning solution to the problem of what to do with contaminated and unwanted plastic.

The Costa-Rica-based Centre for Regenerative Design and Collaboration (CRDC) has developed a new process that takes the waste material and turns it into an aggregate that can be used as a constituent material in concrete building blocks for housing and civil infrastructure projects.

It’s taken the company roughly two and a half years to take the idea from drawing board to a launch at the Sustainable Brands Oceans conference in Porto, Portugal, last November. “We wanted to make sure that we had everything in order, from the recovery of the plastic in the processing until we went onto the higher volumes,” explains the Centre’s CEO Donald Thomson, a Canadian national who moved to Latin America over thirty years ago to work in the affordable housing sector.

Thomson claims that the system CRDC has put in place uses ‘all’ types of plastic, no matter  which polymer. “We use all types of post-consumer and post-industrial plastic, including foil laminates,” he insists. “We recover the plastic from various waste streams, environmental cleanup programmes, municipalities, institutional and post-industrial.” To increase collection efficiency CRDC has also designed a collection truck called MOBI, which includes an on-board facility to shred plastic waste at the point of collection.

Once it is shredded, the plastic is cleaned, mixed with mineral components and heat extruded. After that it is crushed into the desired aggregate size and shape to perfectly simulate standard construction fine aggregate or sand. Essentially the product, pre-conditioned resin aggregate (PRA), is a plastic/mineral hybrid.

“It’s typically 80 per cent plastic resins and 20 per cent mineral additives,” explains Thomson. “It’s around 25 per cent the weight of natural sand. The heating and batching processes ensure that the plastic changes to a grey colour tone similar to lava stone and therefore is also visually benign, so it cannot be detected by colour or shape within the concrete mix.”

Stronger than it looks

The process of developing the aggregate has not been without its problems. CRDC wanted to clean the plastic using an environmentally-friendly sustainable process, avoiding huge amounts of water. To fulfill this objective they had to develop a ‘dry cleaning’ method that uses alkaline lime to spread over the shredded co-mingled plastics, killing all odours, bacteria, and pathogens.

However, unlike other processes involving plastic reuse, one thing that isn’t a worry is contamination, as any organic material is made inert and broken down by the heating process. It’s this that has led CRDC to claim that PRA is, essentially, a ‘zero waste’ solution in that no plastic that the firm collects goes to landfill.
The process of creating the concrete blocks is “identical” to the cement industry, according to Thomson: “We mix the sand, the water and cement and simply add the right proportion of our PRA into that mix. What comes out the other side is a mix that goes into the block mould, which is a 90 per cent cement product block and 10 per cent plastic aggregate.”

The whole process, Thomson argues, has a similar carbon footprint to recycling. “Ours is a very similar grinding and extrusion process. Other than that we co-mingle the plastic resins, so from that perspective the processing carbon footprint isn’t that different to all mechanical recycling systems.”

Crucial to the development of the product was a rigorous testing process – costing some $850,000 (£654,000) and carried out in the main by a Costa Rican construction firm, Grupo PEDREGAL. The testing covered four main areas: compression strength, fire, abrasion and water absorption. Certainly, the PRA blocks tested well on strength. With a five per cent addition of PRA there was a 10 per cent increase in strength after 28 days – it scored 18.2 MPa (megapascals), well above the minimum requirement of 13 MPa: crucial for use in an earthquake zone such as Costa Rica. The blocks have now achieved compliance with the appropriate international standards, ASTM and C90.

The product is fully fire tested too. “We did the fire testing with a giant petrochemical company called Branscombe,” explains Thomson. “They wanted to try our product and actually build a wall around a dangerous chemical unit that they had at one of their centres.

We passed that test – the PRA wall actually fared much better than a standard concrete block.” Thomson suggests that the PRA building blocks have a number of advantages over their standard equivalent.

“They are lower weight, have greater compression strength, thermal and acoustic values.” However, they do retail at around 5-10 per cent higher than standard building blocks. And if the company is capturing “all” polymers, surely this includes the higher-quality polyethylene terephthalate (PET) that would be better off being recycled than being turned into aggregate? Not so, claims Thomson: “All the clean market value PET and PE that we find is sent for recycling. We don’t use either for our aggregate until it eventually degrades into non-
marketable material. We do eventually capture a lot of dirty or low-quality PET and PE (polyethylene).”

Going global

In addition to its Costa Rican headquarters, the company has opened pilot plants in South Africa, the US and Cambodia. Thomson suggests that 2020 will be a year of further expansion: “We have had multiple requests from around the world. We have some very ambitious growth plans.” He claims that both the developed and developing world are potential markets for PRA, indeed anywhere where there is a need for low-cost housing: “We have a plastic waste problem all over the world. We have a housing problem all over the world. This product adapts to any market.”

This article was taken from Issue 99

There have been some criticism of CRDC’s plans, that the blocks are in effect ‘hiding’ plastic. “I think the government of New Zealand has called it ‘horizontal landfill’,” says Thomson. “I just think we have found a very practical way to use huge volumes of plastic in an industry that can absorb a lot of it. If you took every gramme of plastic that was landfilled or unmanaged in the world in 2019 – all 250 million tonnes of it – and turned it into our aggregate it would still only equate to 2.1 per cent of the aggregates used every year in the
global construction industry.”

Thomson asserts that the construction industry has been accepting, at least in Costa Rica. “The engineers really love the product because you can’t tell the difference – it looks and feels almost exactly the same as standard concrete. And they are thrilled because they feel that they are making a contribution in terms of reducing the environmental impact – they know they are using a green building material.”

He also claims that PRA could be used in other applications: “Our product can be used to replace sand in any concrete mix. For example, in South Africa we’re building three metres by 80 centimetres drainage tubes using PRA.” The key will be if the PRA aggregate can make inroads into the North American and European markets. But with concern over waste plastic rising to panic level, this technological breakthrough may have a vital role to play in the next decade and beyond.

“It’s exactly what the plastic industry and waste management industry have been looking for as a way to practically deal with stuff that doesn’t have a market,” argues Thomson. He could be right.