GUIDELINES FOR APPROVING PRODUCERS FOR UP TO 3 PERCENT

PORTLAND CEMENT REDUCTION WHEN USING CARBONCURE OR OTHER CARBON DIOXIDE SEQUESTRATION SYSTEMS

Description

A. CarbonCure and other carbon dioxide sequestration systems is a technology that introduces a precise dosage of recycled CO₂ into fresh concrete during mixing.  Once injected, the CO₂ undergoes a mineralization process and becomes permanently embedded in the concrete.  Theory and practice indicate that the mineralization enhances strength allowing for reductions in Portland cement content.

B. Prior to allowing for up to a 3 percent Portland cement reduction, producers must verify that a DOT mix with carbon dioxide addition and Portland cement reduction has comparable properties to the same DOT mix without carbon dioxide and Portland cement reduction.  The carbon dioxide addition rate and Portland cement reduction rate used for the comparison will be the approved rates for a producer.

Materials

Meet the requirements of Division 41 for the appropriate materials.

Mix Design

The control mix shall be an Iowa DOT C or CWR mix typically produced at the plant with a typical target air content and w/c ratio.

The mix with carbon dioxide addition shall be the control mix with the addition of a precise dosage of carbon dioxide and up to a 3 percent reduction in Portland cement.  The air content and w/c ratio used for the carbon dioxide addition mix shall be as close as practicable to the air content and w/c ratio of the control mix.

Control and carbon dioxide addition mix proportions shall be determined according to IM 529.  The producer shall submit all material sources, proportions, Carbon dioxide addition rate, and Portland cement reduction rate to the District Material Engineer for review at least 7 calendar days prior to conducting trial batching.

Trial Batch Validation

1. Provide the District Materials Engineer at least 3 calendar days advance notification of the trial batches and afford them the opportunity to witness the trial batching and any associated placement and finishing of the trial batch concrete.

2. Mix the control and carbon dioxide addition trial batches each with a minimum of 3 cubic yards at least 30 calendar days prior to any planned placement.

3. Limit the time between completing the control and carbon dioxide addition trial batches to try and minimize potential differences in weather, materials, and placement conditions.

4. For each trial batch, obtain representative samples and conduct the following:

· Test slump - IM 317

· Test air content - IM 318

· Cast and cure a minimum of 6 4 X 8 inch cylinders - IM 315

5. Cylinders from the control and carbon dioxide addition trial batches shall be cured under similar conditions.

6. Cylinders shall be tested according to AASHTO T 22. Three cylinders will be tested for strength at each age of 7 and 28 days.

7. Prior to testing the cylinders for strength, at each age, conduct surface resistivity testing on 2 of the 3 cylinders according to AASHTO T358.

8. Afford the District Materials Engineer the opportunity to witness compressive and resistivity testing.

9. Submit a summary report to the District Materials Engineer that details the mix proportions, w/c ratio, slump, air content, compressive strengths, surface resistivity, carbon dioxide addition rate, and Portland cement reduction rate for each trial batch.

Review and Approval

The District Materials Engineer will coordinate with the Construction and Materials Bureau in review and comparison of the trial batches.  If results of the carbon dioxide addition mix are found to be similar to the control mix, the plant will be approved for utilizing carbon dioxide at the reported Portland cement reduction rate and carbon dioxide addition rate. 

This approval will be for all state mixes on state projects.  The plant name and rates will be added to IM 211 Appendix D Table 2.

Plants of the same company using the same materials, will be approved at the reported carbon dioxide addition rate and Portland cement reduction rate without additional testing.