How to Mix PET Plastic With Concrete

Polyethylene terephthalate, or PET, plastic -- the type of plastic marked on the bottom with “1” inside the recycling symbol, is suitable for use as pea-sized aggregate -- gravel particles -- in concrete. The result is a lighter weight concrete suitable for concrete blocks and many other uses. Because cement doesn’t bond with plastic as completely as it does rock, the resulting concrete blend of portland cement, virgin sand, ground PET and water develops an open honeycomblike texture that expands and contracts with weather extremes -- preventing cracks and splits. You can substitute PET for up to half the total aggregate for most concrete uses.

Things You'll Need

• Safety glasses
• Waterproof gloves
• Dust mask
• Clean construction sand
• Portland cement
• Ground PET particles (flakes or granules)
• Large tub
• Water
• Large bucket
• Wheelbarrow
• Mixing hoe
• Scrub brush

Instructions

1. Measure out the dry ingredients for your PET concrete. Basic concrete may contain 7 to 15 percent cement, 14 to 21 percent water and 60 to 80 percent gravel and “fines,” or total aggregates. Assuming a blend of 10 percent cement and 20 percent water, the remaining 70 percent would be aggregate -- let’s say equal volumes of sand and pea gravel. Substitute PET for all of the gravel, or half the total aggregate, for 35 percent plastic by volume. Mix all dry ingredients together in the tub.

2. Place the water in the wheelbarrow. Start with a small amount of water, about 10 percent or 15 percent instead of 20 percent, to avoid a soupy, weak mix. You can always add more later. Slowly and gradually add dry ingredients to the water, dragging the hoe through all ingredients to mix them.

3. Add more water if the mix is too dry or if the concrete is crumbly and won’t hold together when disturbed. The ideal texture has some “flow,” such as a gritty cake batter, and holds together well. Pour the PET plastic concrete into forms or molds, depending on your intended use, and let it set and cure.

4. Wash out and clean up the wheelbarrow and hoe immediately -- while the concrete is still wet -- using running water and the scrub brush to clean all surfaces.

Tips & Warnings

• Hold back several cups of dry concrete mix before starting to add water to your concrete. If you end up mixing a batch of concrete that’s too wet, this way you’ll be able to add more dry ingredients to correct the balance.

• Conigliaro Industries in Massachusetts uses 50 percent PET in its Plasti-Crete concrete blocks, according to American Recycler magazine.

• PET bottles also serve in Plastisoil, a permeable plastic paving material similar to permeable concrete that allows water to pass through the paved surface.

• Cement is the glue that holds together the concrete mix -- cement, aggregates and water -- though people often use the words “cement” and “concrete” interchangeably, causing confusion.

References

• American Recycler: Used Plastic Takes Place of Stone in Concrete Blocks
• National Technical University of Athens, School of Civil Engineering: A Study of Concretes Containing Thermoplastic Wastes as Aggregates
• Giz Mag: "Plastisoil" Could Mean Cleaner Rivers and Less Plastic Waste
• Sim Science: What is Concrete?
• The Family Handyman: How to Properly Mix Concrete