Cement compositions containing nano sized boehmite crystallites
A composition comprising cement and nano-sized crystalline particles of boehmite alumina or nano-sized crystalline particles of boehmite alumina which have been modified by the inclusion of silicon oxide, calcium oxide, or magnesium oxide. The boehmite alumina has an average crystallite size from about 2 nm to about 80 nm and a content of non-crystalline alumina of less than about 25 mol percent based on total aluminum.
1. A composition of matter comprising:
cement; and
an effective amount of a boehmite alumina having an average crystallite size on the plane of from about 2 nm to about 80 nm.
2. The composition of claim 1 , wherein the boehmite alumina has a content of non-crystalline alumina of less than about 25 mol % based on total aluminum.
3. The composition of claim 1 , further comprising:
a metal oxide selected from the group consisting of silicon oxide, calcium oxide, magnesium oxide, or mixtures thereof.
4. The composition of claim 1 , wherein the boehmite alumina has an agglomerated particle size of less than 350 nm as measured in water.
5. The composition of claim 1 , wherein said boehmite alumina has a calcined surface area of from about 2 m 2 /g to about 300 m 2 /g and a purity of greater than about 99% by weight.
6. The composition of claim 5 , wherein said boehmite alumina has a calcined surface area of from about 35 m2 /g to about 275 m 2 /g.
7. The composition of claim 1 , wherein said boehmite alumina has an average crystallite size on the plane of from about 3 nm to about 60 nm.
8. The composition of claim 1 , wherein said boehmite alumina is obtained from alkoxide precursors.
9. The composition of claim 1 , wherein said boehmite alumina is subjected to hydrothermal aging.
10. The composition of claim 1 , wherein said boehmite alumina is dispersible in water.
11. The composition of claim 2 , wherein said metal oxides comprise up to 10% by weight of the total boehmite alumina/metal oxide mixture.
12. The composition of claim 1 , wherein the boehmite alumina is present in an amount of from about 0.001% to about 1% by weight based on the total weight of the cement.
13. The composition of claim 1 , wherein the boehmite alumina is present in an amount of from about 0.05% to about 0.75% by weight based on the total weight of the cement
14. A concrete comprising the composition of claim 1 in an admixture with an aggregate.
15. The concrete of claim 14 , wherein the concrete has a water-to-cement ratio of from about 0.28 to about 0.56.