TWO STEP CARBONATION HARDENING OF HYDRAULIC CEMENT BASED CONCRETE

Abstract

A method for manufacturing concrete parts has the steps of: providing a hydraulic cement and aggregate; mixing the cement and aggregate with water to provide a fresh concrete; introducing CO.sub.2 into the fresh concrete in an amount resulting in a carbonation degree of more than 0.5 wt.-% and less than 5 wt.-% of the total carbonatable Ca and Mg phases for a first carbonation step; curing the fresh concrete until at least 15 wt.-% of the calcium aluminates are hydrated to provide a green concrete part; subjecting the green concrete part to CO.sub.2 in an amount resulting in a carbonation degree of more than 10 wt.-% of the total carbonatable Ca and Mg phases for a final carbonation step; and storing the part for 0.5 hours to 28 days for further hydration of not-yet carbonated, not-yet hydrated cement to provide the concrete part. and concrete parts obtainable with the method.

Claims

1-15. (canceled)

16. A method for manufacturing concrete parts comprising the following steps: providing aggregate and a hydraulic cement containing calcium aluminates, mixing the cement and aggregate with water to provide a fresh concrete, introducing CO.sub.2 into the fresh concrete in an amount resulting in a carbonation degree of more than 0.5 wt.-% and less than 5 wt.-% of the total carbonatable Ca and Mg phases which are calculated as 0.785×(CaO−0.56 CaCO.sub.3−0.7 SO.sub.3)+1.091×(MgO−0.479 MgCO.sub.3) for a first carbonation step by (i) mixing of cement, aggregate and water in the presence of CO.sub.2 and/or by (ii) adding solid CO.sub.2 during mixing, curing the fresh concrete until at least 15 wt.-% of the calcium aluminates are hydrated to provide a green concrete part, subjecting the green concrete part to CO.sub.2 in an amount resulting in a carbonation degree of more than 10 wt.-% of the total carbonatable Ca and Mg phases which are calculated as 0.785×(CaO−0.56 CaCO.sub.3−0.7 SO.sub.3)+1.091×(MgO−0.479 MgCO.sub.3) for a final carbonation step, and storing the part for 0.5 hours to 28 days for further hydration of not-yet carbonated, not-yet hydrated cement to provide the concrete part.

17. The method according to claim 16, wherein additional CO.sub.2 is provided in the fresh concrete by (iii) dissolving CO.sub.2 in an aqueous component added to form the fresh concrete, (iv) pre-carbonating the dry cement before mixing, and/or (v) soaking a part or all aggregate with a CO.sub.2 containing solution before addition to the fresh concrete.

18. The method according to claim 16, wherein the hydraulic cement is selected from the group consisting of Portland cements, Portland composite cements, calcium aluminate cements, calcium sulfoaluminate cements and dicalcium silicate cements.

19. The method according to claim 16, wherein the water:cement weight ratio in the fresh concrete is set to range from 0.1 to 1.

20. The method according to claim 16, wherein the fresh concrete additionally contains one or more admixture(s) and/or one or more additive(s).

21. The method according to claim 16, wherein the CO.sub.2 is introduced into the fresh concrete by dissolving the carbon dioxide in the mixing water or a part of it, in an admixture solution/suspension, in an additive solution/suspension or in more than one aqueous component.

22. The method according to claim 17, wherein the CO.sub.2 is introduced into the fresh concrete by a combination of two or more of the variants (i) to (v).

23. The method according to claim 16, wherein the CO.sub.2 introduced in the first carbonation step has a concentration from 5 to 99 Vol.-% and/or is provided in the form of gas, solution or as solid material.

24. The method according to claim 16, wherein the amount of CO.sub.2 introduced in the first carbonation step results in a carbonation degree of less than 4 wt.-%.

25. The method according to claim 16, wherein the fresh concrete is cured for 60 to 300 minutes and/or until a strength of 0.5 MPa is reached and/or until at least 5 wt.-% of the calcium aluminates are hydrated.

26. The method according to claim 16, wherein the CO.sub.2 used for subjecting the green concrete part to CO.sub.2 is provided in the form of gas with a concentration from 5 to 99 Vol.-%.

27. The method according to claim 16, wherein the CO.sub.2 is a gas from modified clinker production lines or from carbon capture technologies.

28. The method according to claim 16, wherein the fresh concrete is filled into a mold after mixing or after the first carbonation step and demolded after curing.

29. The method according to claim 18, wherein the hydraulic cement is selected from the group consisting of Portland cements, Portland composite cements and dicalcium silicate cements.

30. The method according to claim 19, wherein the water:cement weight ratio in the fresh concrete is set to range from 0.2 to 0.5.

31. The method according to claim 22, wherein the CO.sub.2 is introduced by using a carbon dioxide solution depleted in CO.sub.2 by soaking the aggregate according to variant (v) as mixing water according to variant (iii) or by using gaseous carbon dioxide with a CO.sub.2 concentration decreased by having been bubbled through the fresh concrete during mixing in variant (i) for pre-carbonating the dry cement according to variant (iv).

32. The method according to claim 16, wherein the first carbonation step results in a carbonation degree of less than 3 wt.-% and more than 1 wt.-%.

33. The method according to claim 16, wherein the fresh concrete is cured for 30 to 240 minutes and/or until a strength of 1 MPa is reached and/or until at least 15 wt.-% of the calcium aluminates are hydrated.

34. The method according to claim 16, wherein the fresh concrete is cured for 10 to 120 minutes, and/or until a strength of 2 MPa is reached and/or until at least 15 wt.-% of the calcium aluminates are hydrated.

35. A method for manufacturing concrete parts comprising the following steps: providing aggregate and a hydraulic cement containing calcium aluminates, mixing the cement and aggregate with water to provide a fresh concrete, providing CO.sub.2 in the fresh concrete in an amount resulting in a carbonation degree of more than 0.5 wt.-% and less than 5 wt.-% of the total carbonatable Ca and Mg phases which are calculated as 0.785×(CaO−0.56 CaCO.sub.3−0.7 SO.sub.3)+1.091×(MgO−0.479 MgCO.sub.3) for a first carbonation step by (iii) dissolving CO.sub.2 in an aqueous component added to form the fresh concrete, (iv) pre-carbonating the dry cement before mixing, and/or (v) soaking a part or all aggregate with a CO.sub.2 containing solution before addition to the fresh concrete, curing the fresh concrete until at least 15 wt.-% of the calcium aluminates are hydrated to provide a green concrete part, subjecting the green concrete part to CO.sub.2 in an amount resulting in a carbonation degree of more than 10 wt.-% of the total carbonatable Ca and Mg phases which are calculated as 0.785×(CaO−0.56 CaCO.sub.3−0.7 SO.sub.3)+1.091×(MgO−0.479 MgCO.sub.3) for a final carbonation step, and storing the part for 0.5 hours to 28 days for further hydration of not-yet carbonated, not-yet hydrated cement to provide the concrete part.

36. The method according to claim 35, wherein additional CO.sub.2 is introduced into the fresh concrete by (i) mixing of cement, aggregate and water in the presence of CO.sub.2 and/or (ii) adding solid CO.sub.2 during mixing.

37. The method according to claim 35, wherein the hydraulic cement is selected from the group consisting of Portland cements, Portland composite cements, calcium aluminate cements, calcium sulfoaluminate cements and dicalcium silicate cements.

38. The method according to claim 35, wherein the water:cement weight ratio in the fresh concrete is set to range from 0.1 to 1.

39. The method according to claim 35, wherein the fresh concrete additionally contains one or more admixture(s) and/or one or more additive(s).

40. The method according to claim 36, wherein the CO.sub.2 is introduced into the fresh concrete by dissolving the carbon dioxide in the mixing water or a part of it, in an admixture solution/suspension, in an additive solution/suspension or in more than one aqueous component.

41. The method according to claim 36, wherein the CO.sub.2 is introduced into the fresh concrete by a combination of two or more of the variants (i) to (v).

42. The method according to claim 35, wherein the CO.sub.2 introduced in the first carbonation step has a concentration from 5 to 99 Vol.-% and/or is provided in the form of gas, solution or as solid material.

43. The method according to claim 35, wherein the amount of CO.sub.2 introduced in the first carbonation step results in a carbonation degree of less than 4 wt.-%.

44. The method according to claim 35, wherein the fresh concrete is cured for 60 to 300 minutes and/or until a strength of 0.5 MPa is reached and/or until at least 5 wt.-% of the calcium aluminates are hydrated.

45. The method according to claim 35, wherein the CO.sub.2 used for subjecting the green concrete part to CO.sub.2 is provided in the form of gas with a concentration from 5 to 99 Vol.-%.

46. The method according to claim 35, wherein the CO.sub.2 is a gas from modified clinker production lines or from carbon capture technologies.

47. The method according to claim 35, wherein the fresh concrete is filled into a mold after mixing or after the first carbonation step and demolded after curing.

48. The method according to claim 37, wherein the hydraulic cement is selected from the group consisting of Portland cements, Portland composite cements and dicalcium silicate cements.

49. The method according to claim 38, wherein the water:cement weight ratio in the fresh concrete is set to range from 0.2 to 0.5.

50. The method according to claim 41, wherein the CO.sub.2 is introduced by using a carbon dioxide solution depleted in CO.sub.2 by soaking the aggregate according to variant (v) as mixing water according to variant (iii) or by using gaseous carbon dioxide with a CO.sub.2 concentration decreased by having been bubbled through the fresh concrete during mixing in variant (i) for pre-carbonating the dry cement according to variant (iv).

51. The method according to claim 35, wherein the first carbonation step results in a carbonation degree of less than 3 wt.-% and more than 1 wt.-%.

52. The method according to claim 35, wherein the fresh concrete is cured for 30 to 240 minutes and/or until a strength of 1 MPa is reached and/or until at least 15 wt.-% of the calcium aluminates are hydrated.

53. The method according to claim 35, wherein the fresh concrete is cured for 10 to 120 minutes, and/or until a strength of 2 MPa is reached and/or until at least 15 wt.-% of the calcium aluminates are hydrated.

54. A concrete part obtained by the method according to claim 16.

55. The concrete part according to claim 54, wherein the amount of carbonate in the concrete part ranges from 5 to 100 wt.-% of the clinker content of the dry hydraulic cement.

56. A concrete part obtained by the method according to claim 35.

57. The concrete part according to claim 56, wherein the amount of carbonate in the concrete part ranges from 5 to 100 wt.-% of the clinker content of the dry hydraulic cement.

Description

[0071] FIG. 1 shows a flow chart of a first preferred embodiment of the method according to the invention,

[0072] FIG. 2 shows another preferred embodiment, and

[0073] FIG. 3 yet another preferred embodiment.

[0074] In the embodiment of FIG. 1 the cement and the further constituents like aggregate and admixtures are mixed with water while carbon dioxide is injected into the fresh concrete mixture. Exhaust gas from a cement kiln operating in the oxyfuel mode is used, which has a CO.sub.2 concentration of about 75 Vol.-%. Approximately 500 to 750 I/minute are injected via a nozzle per m.sup.3 of mixture. Thus, mixing and introducing CO.sub.2 occur concurrently. Further, after about 5 minutes of mixing, the fresh concrete is poured into a mold made from formwork and left to cure via hydration for 20 minutes. During this time, some additional carbonation occurs with remaining CO.sub.2. Then a containment is placed over the formwork and further exhaust gas introduced into the containment at a rate of about 1000 I/minute and m.sup.3 of concrete part. Final carbonation is continued for 2 hours. Afterwards, the containment and formwork are removed. The concrete part continues to hydrate for 1 day and then shows a carbonate content of about 50 wt.-% of the original clinker in the cement.

[0075] FIG. 2 illustrates a method useful for manufacturing precast concrete parts, e.g. pavers. The plant is located adjacent a cement kiln and exhaust gas from the kiln is passed through water basins to dissolve it in water. The cement is mixed with sand and pigments and made into a fresh concrete by adding water from the water basins. After 10 minutes mixing, the fresh concrete is poured into the molds and left to hydrate for 30 to 60 minutes. Then, the green parts are removed from the molds, placed onto racks and subjected to the exhaust gas emerging from the water basins for 5 days. During this time, final carbonation and hydration occur simultaneously.

[0076] The embodiment in FIG. 3 shows the manufacturing of big precast concrete parts like wall and floor elements. Here, the cement as well as aggregate and admixtures and possibly additives are mixed with introduction of gaseous carbon dioxide during mixing. Carbon dioxide from an amine based CO.sub.2 scrubber is used to provide the carbon dioxide. For the first carbonation step, the gas recovered from the final step is utilized. This still has a CO.sub.2 concentration of about 50 Vol.-%. The paste is filled into the molds and left to hydrate for 15 minutes. Then, the parts are demolded and subjected to the highly concentrated (about 90 Vol.-%) carbon dioxide for 1 day. Again, hydration occurs as post-curing simultaneously. As mentioned the gas left from the final carbonation step is used in the first carbonation step. Through using highly concentrated CO.sub.2 in the method according to the invention the production rate can be increased significantly. This optimizes efficacy of the process.