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 in a stationary mixer or a transportable mixer, such as a drum of a ready-mix truck.
1. A method for treating wash water from a concrete production process comprising:
exposing the wash water to carbon dioxide at a concentration greater than that of carbon dioxide in the atmosphere to produce carbonated wash water; and
adding at least a portion of the carbonated wash water to a concrete mixer that is open to the atmosphere so that the carbonated wash water mixes with a cement mix in the mixer to produce a carbonated cement mix, wherein the carbonated wash water comprises at least 6 g of carbon dioxide/L of water, and efficiency of carbonation of the cement mix is at least 60%.
2. The method of claim 1 wherein the carbonated wash water has a pH between 7 and 8.
3. The method of claim 1 further comprising adding a portion of carbonated non-wash water to the mixer to mix with the cement mix.
4. The method of claim 3 wherein the carbonated wash water and carbonated non-wash water together make up total carbonated mix water, and wherein the carbonated wash water comprises 5-100% of the total carbonated mix water.
5. The method of claim 1 further comprising adding carbon dioxide to the mixer that is not carbon dioxide in the mix water.
6. The method of claim 4 wherein the non-mix water carbon dioxide is added as a mix of solid and gaseous carbon dioxide.
7. The method of claim 1 wherein solids are not removed from the carbonated wash water.
8. The method of claim 1 wherein the carbonated wash water is not filtered.
9. The method of claim 1 wherein the carbon dioxide to which the wash water is exposed is gaseous carbon dioxide at a concentration of 20-100%.
10. The method of claim 1 wherein the carbonated cement mix, when allowed to set and harden, has a compressive strength at least 95% of the compressive strength of the same cement mix that is uncarbonated.
11. The method of claim 1 , wherein the carbonated wash water comprises at least 10 g of carbon dioxide/L of water.
12. The method of claim 1 , wherein the carbonated wash water comprises at least 16 g of carbon dioxide/L of water.