Set retardant for hydraulic cement compositions
A zinc-oxide based set retardant additive and admixture for use in Portland cement or other hydraulic cement mixtures. The admixture may comprise silica fume, vitreous calcium aluminosilicate, magnesium aluminum silicate hydrate, a cellulose ether derivative, or their equivalents. The zinc-oxide based set retardant may be interground or pre-blended, pre-packaged, or added on the jobsite, as an admixture, additive, or addition. The zinc-based set retardant may be subsequently added or mixed into a ready mix or wet mixture of portland cement or other hydraulic cement, sand and/or aggregate, with or without fillers, and water, with or without other pozzolans or polymers.
1. A set retarder for hydraulic cement achieving a set time of between 2 to 5 hours, the set retarder comprising about 0.01 wt % to about 2.0 wt % zinc oxide;
about 5 wt % to about 45 wt % of one or more pozzolans; and about 0.01 wt % to about 2 wt % cellulosic polymer.
2. The set retarder of claim 1 , wherein the zinc oxide comprises about 0.01 wt % to about 0.25 wt %.
3. The set retardant additive retarder of claim 1 , wherein the first amount of zinc oxide comprises acicular zinc oxide powder.
4. The additive retarder of claim 1 , wherein the first amount of zinc oxide comprises spherical or globular zinc oxide powder.
5. The set retarder of claim 1 , wherein the set retarder is added to cement at a temperature of between about 70° F. and about 120° F.
6. The set retarder of claim 1 , wherein for an hydraulic cement mixture comprising about 40 wt % of white cement and about 60 wt % of marble sand prior to addition of the set retarder, the zinc oxide comprising at least 95% of zinc oxide powder smaller than about 325 mesh (45 micron).
7. The set retarder of claim 1 , wherein the at least 95% of the zinc oxide is ground at least to a fineness of at least 200 mesh (75 micron).
8. The set retarder of claim 1 , wherein the zinc oxide comprises an acicular zinc oxide powder containing at least about 95% of zinc oxide ground sufficiently so that about the powder passes 325 mesh (45 micron).
9. The set retarder of claim 1 , wherein the pozzolan comprises at least one of silica fume, fly ash, calcined kaolin and vitreous calcium aluminosilicate.
10. The set retarder of claim 1 , wherein the pozzolan comprises about 0 wt % to about 30 wt % silica fume, about 0 wt % to about 45 wt % fly ash and about 0 wt % to about 40 wt % vitreous calcium aluminosilicate.
11. The set retarder of claim 10 , wherein the fly ash comprises about 3 wt % to about 27 wt %.
12. The set retarder of claim 11 , wherein the silica fume comprises about 1 wt % to about 15 wt %.
13. The set retarder of claim 12 , wherein the calcined kaolin or vitreous calcium aluminosilicate comprises about 5 wt % to about 27 wt %.
14. The set retarder of claim 1 , wherein the retarder is used in concrete, gunnite, and plaster.
15. The set retarder of claim 1 , wherein the retarder is used for cement for the construction of structures exposed to water, heat, and pressure.
16. The set retarder of claim 1 , wherein the retarder is used in cement for the construction of bridges, piers, damns, freeways, and airport runways.
17. The set retarder of claim 1 , wherein the set time is between about three to about four hours.