It’s only waste if it goes into the landfill.
Otherwise the excess concrete that is returned to your concrete plant is a material resource you can harvest for your benefit.
If you run a lean operation, you’re probably doing many of these practices already. But you may be missing out on some of the newer technologies and surprising waste materials you hadn’t realized you could use to reduce your plant’s overall waste footprint and become more sustainable.
One of the most impactful technologies uses excess CO2 captured from industrial processes or directly from the air to strengthen your concrete mixes and enable a reduction in cement while maintaining performance. At CarbonCure, we have two such carbon mineralization technologies: CarbonCure Reclaimed Water and CarbonCure Ready Mix. Both permanently remove CO2, reducing production costs and embodied carbon at the same time.
2. Concrete washout
Many producers are reluctant to reuse reclaimed wash water, or they use it sparingly, because of the unpredictable results the cement fines can have on their concrete. Our latest technology, CarbonCure Reclaimed Water, not only consumes waste CO2 but also enables producers to reuse all their reclaimed wastewater in new batches without negatively impacting fresh or final properties. The CO2 injected into the reclaimed water reacts with the cement fines, converting them to a mineral that strengthens the concrete. The mineral stays suspended in the reclaimed water, and when accounted for, enables an effective stabilized replacement of virgin cement in new batches. Concrete producers save on the cost of municipal treatment and safe disposal, reduce virgin water use up to 20%, recapture the value of the cement in their washout and earn revenue from the sale of high-quality carbon credits.
3. Fine and coarse aggregate
If you have a reclaimer, you’re able to harvest the sand and stone from excess concrete and/or wash water for reuse in new batches, reducing the amount of virgin material required. Reclaimers are much more widely used in Europe and in areas in North America with stricter environmental controls. Unfortunately, for producers with lower volumes, the capital cost can be prohibitive. However, if you’ve been thinking about installing a reclaimer and are on the fence, maybe this will help. If your plant produces at least 100,000 cubic yards (about 76,500 cubic meters) of concrete a year, and you combine use of a reclaimer and both CarbonCure carbon mineralization technologies, the total savings could pay for a reclaimer in as little as one year.*
4. Blocks, bolos or sound wall forms
Many producers use excess concrete to make blocks and other non-structural concrete products which they sell. Others find the time it takes to pour the concrete into forms isn’t cost-effective if it reduces the number of loads their trucks can deliver in a day. The key to making it work is to have a good site setup. Trucks need to be able to pour the excess concrete and wash out their drums in a seamless flow that avoids bottlenecks, allowing them to maximize their daily deliveries. Space to store the blocks before resale may also be a factor. However, being able to advertise that you minimize waste may be yet another way you demonstrate your commitment to environmental sustainability.
5. Crush & run
Many producers – especially those short on time or space for pouring forms and blocks and who don’t have a reclaimer – pour into a pit any excess concrete that is returned to their plant. Once the concrete has hardened, they break it into smaller pieces with a chipper and sell it as an aggregate base for the construction industry. Landscaping businesses also tout this mixture of gravel and limestone as a particularly good top layer for gravel driveways, helping them last longer. Unfortunately, because of the limited applications of the hardened crushed material, the economic returns on crushed concrete don’t maximize the amount of profit possible from other methods of recycling the returned materials.
6. Slag, fly ash, ground glass pozzolans and silica fume
Slag, fly ash, ground glass pozzolans and silica fume are all industrial waste products that can be used by the concrete industry as supplementary cementitious materials to reduce the amount of Portland cement required. As well as being less expensive than cement, you’re putting a waste product to good use and further reducing the carbon footprint of the concrete you produce. What you may not realize is that these industrial waste products can be used in conjunction with carbon mineralization technologies to layer the benefits. If you’re already doing some or all of these, it can help differentiate yourself as a lower-carbon, sustainable concrete supplier and potentially gain new business with the sustainable design and building community.
*Based on a reclaimer cost of USD $250,000, and the plant producing 100,000 cubic yards (76,456 cubic meters) of 4,000 psi (27.6 MPa) mix concrete a year using CarbonCure Reclaimed Water and CarbonCure Ready Mix; this calculation assumes a conservative 4.4% reduction in cementitious material, resulting in a net savings of about USD $2.50/yard, including the elimination of disposal fees and the addition of new revenue from the sale of carbon removal credits.