Methods for carbonation of a cement mix in a mixer
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 for producing a carbonated cement mix in a mix operation in a cement mix apparatus comprising
(i) contacting a cement mix comprising cement binder and aggregate in a mixer with carbon dioxide while the cement mix is mixing,
(ii) monitoring at least a first characteristic of the cement binder, the cement mix, a gas mixture in contact with the cement mix or the mixer, or a component of the cement mix apparatus, wherein the first characteristic comprises carbon dioxide content of a gas mixture exiting from the mixer; and
(iii) modulating the exposure of the cement mix to the carbon dioxide or another characteristic of the cement mix operation, or a combination thereof according to the characteristic monitored in step (ii).
2. The method of claim 1 wherein the exposure of the cement mix to carbon dioxide is modulated when the carbon dioxide content of the gas mixture reaches a threshold value.
3. The method of claim 1 wherein the exposure of the cement mix to carbon dioxide is modulated when rate of change of the carbon dioxide content of the gas mixture reaches a threshold value.
4. The method of claim 1 wherein the exposure of the cement mix to carbon dioxide is modulated when the temperature of the cement mix or a component of the mix apparatus in contact with the cement mix reaches a threshold value.
5. The method of claim 1 wherein a second characteristic that is different from the first characteristic is monitored in step (ii), the second characteristic comprising
(a) mass of cement binder added to the cement mix,
(b) location of the cement binder in the mix apparatus,
(c) carbon dioxide content of a gas mixture within the mixer in contact with the cement mix,
(d) carbon dioxide content of gas mixture in the vicinity of the mix apparatus,
(e) temperature of the cement mix or a component of the mix apparatus in contact with the cement mix,
(f) rheology of the cement mix,
(g) moisture content of the cement mix, or
(h) pH of the cement mix.
6. The method of claim 5 wherein a third characteristic that is different from the first and second characteristics is monitored in step (ii), the third characteristic comprising
(a) mass of cement binder added to the cement mix,
(b) location of the cement binder in the mix apparatus,
(c) carbon dioxide content of a gas mixture within the mixer in contact with the cement mix,
(d) carbon dioxide content of gas mixture in the vicinity of the mix apparatus,
(e) temperature of the cement mix or a component of the mix apparatus in contact with the cement mix,
(f) rheology of the cement mix,
(g) moisture content of the cement mix, or
(h) pH of the cement mix.
7. The method of claim 1 wherein the other characteristic of the mix operation comprises
(a) whether or not an admixture is added to the cement mix,
(b) type of admixture added to the cement mix,
(c) timing of addition of admixture to the cement mix,
(d) amount of admixture added to the cement mix,
(e) amount of water added to the cement mix,
(f) timing of addition of water to the cement mix,
(g) cooling of the cement mix during or after carbon dioxide addition, or a combination thereof.
8. The method of claim 1 wherein the first characteristic is monitored by one or more sensors which transmit information regarding the first characteristic to a controller which processes the information and determines if a modulation of carbon dioxide exposure or another characteristic of the mix operation is required and, if so, transmits a signal to one or more actuators to carry out the modulation of carbon dioxide exposure or other characteristic of the mix operation.
9. The method of claim 8 wherein the controller stores and processes the information obtained regarding the characteristic monitored in step (ii) for a first batch of cement mix and adjusts conditions for a subsequent second cement mix batch based on the processing.
10. The method of claim 8 wherein the controller, one or more sensors, one or more actuators, or combination thereof, transmits information regarding the characteristics monitored and conditions modulated to a central controller that receives information from at least one other controller, sensor, actuator, or combination thereof, from at least one other separate mix operation.
11. The method of claim 1 wherein the exposure of the cement mix to the carbon dioxide is modulated in such a way as to achieve an efficiency of carbonation of at least 60%, wherein efficiency of carbonation is the amount of carbon dioxide retained in the cement mix per the total amount of carbon dioxide to which the cement mix is exposed during mixing.
12. The method of claim 1 wherein the carbon dioxide is contacted with the surface of the cement mix.
13. The method of claim 12 wherein the carbon dioxide is directed to the surface of the cement mix from an opening or plurality of openings that is/are at least 5 cm from the surface of the cement mix during carbon dioxide flow, on average.
14. The method of claim 13 wherein the opening or plurality of openings is/are opening or openings of a flexible tube.
15. The method of claim 12 wherein the surface of the cement mix is contacted with the carbon dioxide for a period of time that is less than or equal to 5 minutes.