Caltrans (California Department of Transportation (DOT)), Cal.gov’s Division of Measurement Standards (DMS), and the ready mixed concrete industry have accomplished a specification for a product that will:
- Reduce greenhouse gases
- Reduce waste
- Save embodied energy
- Conserve natural aggregates
- Save water
- Decrease transportation
- Decrease infrastructure costs
- Supply quality concrete for construction projects
The team recently found a solution by developing a specification that will allow the use of returned plastic concrete—leftover concrete in a mixer drum—in certain applications. The concrete is still fresh and liquid, termed “plastic”, and still usable. Plastic concrete occurs when a project does not require as much concrete as originally expected—2% to 8% of all concrete goes unused. Until recently, it had to be dumped out, dried, and sorted … or sent to a landfill. This unused concrete has been a major concern of regulators. CalEPA estimates it results in 997.9 metric tons (2.2 million pounds) of excess carbon emissions per year.
According to California Construction and Industrial Materials Association (CalCIMA), Caltrans is the first Department of Transportation in the United States to allow returned plastic concrete. This specification came about through 2 state agencies and industry working together. By November of 2012, a work group was formed including industry members from Central Concrete Supply, Sully-Miller, CalPortland, CEMEX, BASF, and more. The team met monthly for 18 months until a final version was formed in June 2014. The final product of the Caltrans specifications contained the following:
- Returned plastic concrete can be used in curbs, gutters, sidewalks, and slurry applications
- Concrete may contain a maximum of 15% returned plastic concrete
- It may not exceed 100° F
- Must be proportioned within 4 hours after original batching if hydration stabilizing ad-mixture (HSA) is not used
- If HSA is used, must be added within 4 hours of original batching
- Procedures were worked out with the DMS to address weighing and measuring of the returned concrete
According to the carbon study completed for the project, specification is available that can help reduce the carbon footprint by 15% and the embodied energy per yard of concrete by 16.2%.
Dan Speer, Chief of Caltrans Office of Structural Materials, said, “The development of the new Returned Plastic Concrete specification is a great example of engineering innovation, sound sustainable practice, and positive teamwork between Caltrans, Industry Partners, and DMS. The collaboration among the various stakeholders was extraordinary, and certainly embodied Caltrans’ goal of making long-lasting, smart mobility decisions that improve the environment and support California’s economy.”
Because specification was developed by Caltrans, it is now available to all entities in California—including local governments. Ready mixed concrete producers now have an important tool available to demonstrate environmental benefits.
The article titled “State Gives Returned Concrete a Green Light” was written by Charlie Ray, Director of Communications-CalCIMA for ‘The Conveyor’ Fall 2015 Online Magazine. To read the entire article on PAGE 14 of Fall 2015 ‘The Conveyor’ online magazine, please go to: http://issuu.com/calcontractor/docs/the_conveyor_fall_issue_2015.