Methods and compositions for concrete production
The invention provides compositions and methods directed to carbonation of a cement mix during mixing. The carbonation may be controlled by one or more feedback mechanisms to adjust carbon dioxide delivery based on one or more characteristics of the mix or other aspects of the mixing operation.
1. A method of carbonating a wet cement mix comprising delivering a dose of carbon dioxide to the wet cement mix during mixing in a mixer, wherein
the dose is 1.5% or less by weight cement (bwc) in the mix,
the dose of carbon dioxide is a dose that produces a carbonated cement mix with a flowability at one or more time points after mixing that is within 50% of the flowability of a cement mix of the same mix design that is uncarbonated, and
the carbon dioxide is delivered by a process that comprises converting liquid carbon dioxide to a mixture of gaseous and solid carbon dioxide and contacting the wet cement mix with the mixture of solid and gaseous carbon dioxide,
thereby carbonating the wet cement mix.
2. The method of claim 1 wherein the cement mix comprises Portland cement comprising gypsum.
3. The method of claim 1 wherein the mixer is an open mixer.
4. The method of claim 1 wherein the dose of carbon dioxide is 1.0% or less bwc.
5. The method of claim 1 wherein the dose of carbon dioxide is 0.5% or less bwc.
6. The method of claim 1 wherein the carbon dioxide is delivered to the surface of the wet cement mix.
7. The method of claim 6 wherein the carbon dioxide is delivered to the surface of the wet cement mix at a distance from the surface of the wet cement mix of at least 5 cm, on average.
8. The method of claim 1 wherein the contacting of the wet cement mix with the carbon dioxide lasts no more than 5 minutes.
9. The method of claim 1 wherein the dose of carbon dioxide is a dose based at least in part on a type of cement used in the mix.
10. The method of claim 9 wherein the dose of carbon dioxide is a dose based at least in part on testing one or more doses of carbon dioxide on test wet cement mix comprising the type of cement to be used in the wet cement mix in the mixer.
11. The method of claim 10 wherein the testing comprises determining, for each carbon dioxide dose tested, a carbonation level of the test cement mix, a compressive strength of the test cement mix after hardening, a flowability of the test cement mix, or a calorimetry curve for the test cement mix, or a combination thereof.
12. The method of claim 1 wherein the mixer is a mixer that is fixed or relatively fixed in location.
13. The method of claim 1 wherein the mixer is a transportable mixer.
14. The method of claim 13 wherein the mixer is a drum of a ready-mix truck.
15. The method of claim 1 further comprising assessing at least one characteristic of the mix operation during the delivery of the carbon dioxide and modulating the dose of carbon dioxide based on the characteristic.
16. A method of carbonating a wet concrete mix having a mix design comprising delivering a dose of carbon dioxide to the wet concrete mix during mixing in a mixer, thereby carbonating the wet concrete mix, wherein
the concrete mix comprises Portland cement comprising gypsum;
the dose of carbon dioxide is 1.5% or less by weight cement (bwc) in the mix;
the dose of carbon dioxide is a dose that produces a carbonated concrete mix with a flowability at one or more time points after mixing that is within 50% of the flowability of a concrete mix of the same mix design that is uncarbonated; and
the carbon dioxide is delivered to the concrete mix via a conduit with an opening, wherein the opening is at least 5 cm, on average, from the surface of the mixing concrete mix.
17. The method of claim 16 wherein the dose of carbon dioxide is 1.0% or less bwc.
18. The method of claim 16 wherein the mixer is a transportable mixer.
19. The method of claim 18 wherein the transportable mixer is a drum of a ready-mix truck.
20. The method of claim 16 wherein the carbon dioxide dose is based at least in part on a cement type in the mix design.
21. The method of claim 20 wherein the carbon dioxide dose is a dose based at least in part on testing one or more doses of carbon dioxide on test wet cement mix comprising the type of cement to be used in the concrete mix in the mixer.
22. The method of claim 21 wherein the testing comprises determining, for each carbon dioxide dose tested, a carbonation level of the test cement mix, a compressive strength of the test cement mix after hardening, a flowability of the test cement mix, or a calorimetry curve for the test cement mix, or a combination thereof.
23. The method of claim 16 wherein the dose of carbon dioxide is a dose that produces a carbonated concrete mix with a compressive strength at one or more time points after mixing that is at least 5% greater than a compressive strength of a concrete mix of the same mix design that is uncarbonated.
24. The method of claim 9 wherein the dose of carbon dioxide is based at least in part on testing two or more doses of carbon dioxide on test wet cement mix comprising the type of cement to be used in the wet cement mix in the mixer.
25. The method of claim 9 wherein the dose of carbon dioxide is based at least in part on testing three or more doses of carbon dioxide on test wet cement mix comprising the type of cement to be used in the wet cement mix in the mixer.
26. The method of claim 1 wherein the dose of carbon dioxide is a dose that produces a carbonated concrete mix with a compressive strength at one or more time points after mixing that is at least 5% greater than a compressive strength of a concrete mix of the same mix design that is uncarbonated.
27. The method of claim 2 wherein the wet cement mix further comprises aggregates.
28. The method of claim 27 wherein the wet cement mix further comprises a supplementary cementitious material (SCM).
29. The method of claim 6 wherein the carbon dioxide is delivered to the surface of the wet cement mix at a distance from the surface of the wet cement mix of 0.5 to 2 meters, on average.
30. The method of claim 21 wherein the dose of carbon dioxide is based at least in part on testing two or more doses of carbon dioxide on test wet cement mix comprising the type of cement to be used in the wet cement mix in the mixer.
31. The method of claim 21 wherein the dose of carbon dioxide is based at least in part on testing three or more doses of carbon dioxide on test wet cement mix comprising the type of cement to be used in the wet cement mix in the mixer.