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Blast furnace slag, a byproduct of iron-making, qualifies as a supplementary cementitious material in the Cool Climate Concrete program.

For many years, concrete producers heard that promoting sustainability was good business. Now, there's proof that being green adds to the bottom line.

Up to $800,000 is available for participating in the Cool Climate Concrete (C3) program, a greenhouse gas program that rewards concrete producers for reducing their use of portland cement.

Precast and ready-mixed producers earn incentives by reducing their average portland cement use per cubic yard of concrete beyond company-specific baselines by substituting supplementary cementitious materials (SCM). These producers are reducing emissions while earning $4 per metric ton of avoided carbon dioxide (CO2) emissions. In the first phase, payments ranged from $600 to $68,000 per participant.

C3 is one of several off set programs funded by The Climate Trust, an Oregon nonprofit founded in 1997 to provide off-sets to Oregon fossil-fueled power plants required to meet emission standards. The Climate Trust's offset portfolio contains a variety of offset projects, including renewable energy, forest sequestration, and material substitution.

Reducing cement emissions

The C3 program is based on the concept that CO2 emissions are avoided and offsets are generated when concrete producers reduce portland cement use beyond established baselines by replacing it with SCMs. This strategy for reducing emissions emerged because most concrete-related emissions are from cement production. For every metric ton of portland cement produced, almost one metric ton of CO2 is produced.

After verifying 250,000 metric tons of avoided CO2 emissions, or offsets, the first phase of C3 was completed in September 2008. Since then, West Main Consultants, a sustainable materials consulting firm, secured additional funding from The Climate Trust to manage a second phase. With another $1.25 million committed to the second phase, C3 is on track to verify 200,000 offsets by September 2012, and additional funding may be available upon demand.

Precast and ready-mixed producers that buy portland cement and SCMs from suppliers and blend their own cement and SCMs into mix designs are eligible. At least one of the following five SCMs must be used as a portland cement replacement:

  • ASTM C 618 fly ash
  • ASTM C 989 grade 100 or 120 ground granulated blast furnace slag
  • ASTM C 1240 silica fume
  • Rice hull ash
  • Cement kiln dust

Approved SCMs were selected because they do not represent a net increase in emissions (except in the case of blast furnace slag, where associated emissions are accounted for in program calculations).

Producers enrolled in C3 provide initial documentation showing cement usage, SCM usage, and concrete manufactured from the immediately preceding three years, and provide similar documentation on an ongoing quarterly basis during participation. With the initial documentation, company-specific quarterly cement-to-concrete ratios (averages of cement content per cubic yard) are established based on the three-year historical data, which function as the baselines under the program.

The quarterly documentation provides the amount a producer has reduced its average cement content per cubic yard beyond the baseline. West Main Consultants calculates avoided emissions and offsets generated based on this reduction. All offsets are reported to participating producers and The Climate Trust quarterly, and incentives are paid to producers for verified offsets when The Climate Trust accepts delivered offsets.

C3 calculates avoided emissions based on reductions in portland cement use rather than increases in SCM use, because the cement has the associated CO2 emissions. Avoided emissions and offsets are calculated by first using the baseline cement-to-concrete ratios to establish baseline emissions, or the emissions that would have occurred had the company been operating under business-as-usual conditions.

Next, actual emissions are calculated using quarterly cement-to-concrete ratios based only on current consumption and production data. When actual emissions are less than baseline emissions for a quarter, emissions are avoided and are equal to the difference between baseline and actual emissions.