Hazing control for carbonatable calcium silicate-based cements and concretes
The invention provides novel methods and compositions that mitigate the occurrence of hazing of products made from carbonatable calcium silicate-based cements. The methods and compositions of the invention may be applied in a variety of cement and concrete components in the infrastructure, construction, pavement and landscaping industries.
1. A method for mitigating or reducing hazing on a concrete product, comprising:
prior to curing cement to form a concrete product, adding to the concrete mixture an admixture comprising one or more components capable of reacting with one or more of soluble alkali, alkaline earth, sulfate or chloride ions to form a low solubility material; and
wherein the admixture comprises at least one highly soluble calcium salt.
2. The method of claim 1 , further comprising:
curing the cement to form a concrete product.
3. The method of claim 1 , wherein adding to cement an admixture comprises adding a solid admixture.
4. The method of claim 1 , wherein adding to cement an admixture comprises adding a liquid admixture.
5. The method of claim 1 , wherein adding to cement an admixture comprises adding a solid admixture and a liquid admixture.
6. The method of claim 1 , wherein the cement is a carbonatable calcium silicate-based cement.
7. The method of claim 6 , wherein the carbonatable calcium silicate-based cement comprises calcium silicate and one or more discrete calcium silicate phases selected from CS (wollastonite or pseudowollastonite), C3 S2 (rankinite), C2S (belite, larnite, bredigite), and an amorphous calcium silicate phase at about 30% or more by mass of the total phases.
8. The method of claim 6 , wherein in the carbonatable calcium silicate-based cement elemental Ca and elemental Si are present in the composition at a molar ratio from about 0.8 to about 1.2 and metal oxides of Al, Fe and Mg are present in the composition at about 30% or less by mass.
9. The method of claim 6 , wherein the admixture is a solid admixture comprising one or more selected from calcium aluminate, calcium hydroxide and calcium sulfoaluminate.
10. The method of claim 6 , wherein the admixture is a solid admixture comprising ground granulated blast furnace slag (GGBFS) and/or fly ash.
11. The method of claim 10 , wherein the solid admixture further comprises gypsum.
12. The method of claim 11 , wherein the amount of GGBFS and/or Fly Ash together account for from about 1% to about 25% by weight of cement mixture, and the amount of gypsum accounts for from about 0.5% to about 10% by weight of cement mixture.
13. The method of claim 9 , wherein the solid admixture comprises calcium aluminate and is added to the cement in an amount such that calcium aluminate accounts for about 0.1% to about 10% by weight of the cement mixture.
14. The method of claim 9 , wherein the solid admixture comprises calcium sulfoaluminate.
15. The method of claim 9 , wherein the solid admixture comprises calcium hydroxide.
16. The method of claim 15 , wherein the solid admixture is added to the cement in an amount such that calcium hydroxide accounts for about 0.1% to 10% by weight of the cement mixture.
17. The method of claim 1 , wherein the admixture comprises an aqueous solution.
18. The method of claim 1 , wherein the highly soluble calcium is selected from calcium nitrate, calcium nitrite, and calcium chloride.
19. The method of claim 1 , wherein the admixture comprises calcium nitrate and is added to the cement at 0.5 g to 30 g calcium nitrate per kg of cement.
20. The method of claim 1 , wherein the alkali, alkaline earth, sulfate or chloride ions are selected from Ca 2+ , Na + , K + , Mg 2+ , Cl − , and SO 3 2− ions.
21. The method of claim 2 , wherein curing is by CO 2 at a temperature of about 50° C. to about 70° C.
22. The method of claim 21 , comprising a temperature ramping period, wherein the temperature of concrete is changed at a controlled heating rate of not more than 15° C. per hour with concurrent relative humidity of greater than about 70%.