Low pH compositions for hardening concrete and associated methods
A composition for hardening concrete that has a pH of less than 10, and may have a pH of 8 or less. Thus, the hardening composition may be free of or substantially free of alkaline materials. The hardening composition is water-based and includes silica particles and an aluminum-based (e.g., alumina, etc.) stabilizer, which may be present on portions of the surfaces of the silica particles. In use, the hardening composition is applied to the surface of concrete, either alone, with curing compounds, or as part of a polishing process. Any residue that remains on the treated surface may simply be swept, blown, or sprayed away.
1. A method for hardening concrete, comprising:
applying a hardening composition having a pH of less than 10 and comprising colloidal silica and a stabilizer comprising aluminum or aluminum oxide to a finished surface of the concrete, the colloidal silica penetrating into the finished surface of the concrete and reacting with calcium hydroxide beneath the finished surface of the concrete,
without leaving a residue of the hardening composition on the finished surface of the concrete.
2. The method of claim 1 , wherein applying comprises applying a hardening composition having a pH of 8 or less to the finished surface of the concrete.
3. The method of claim 1 , further comprising:
polishing the surface while the hardening composition is present on the surface.
4. The method of claim 1 , wherein applying comprises applying the hardening composition to a finished surface of concrete that has not completely cured.
5. The method of claim 1 , further comprising:
removing the residue of the hardening composition from the surface, the act of removing consisting essentially of sweeping, blowing, or spraying the residue from the surface.
6. A method for hardening or densifying a hardened cementitious substrate, comprising:
applying a colloidal silica to a hardened surface of the hardened cementitious substrate;
enabling the colloidal silica to penetrate the hardened surface; and
enabling the colloidal silica to react with calcium hydroxide beneath the hardened surface to increase a hardness of the hardened surface,
with no residue of the colloidal silica on the hardened surface.
7. The method of claim 6 , wherein applying the colloidal silica comprises applying a colloidal silica, including:
water;
silica particles in a concentration tailored to harden concrete while minimizing silica residue remaining on a treated surface; and
a stabilizer comprising aluminum or alumina on the colloidal silica for keeping the silica particles in solution, the low pH composition having a pH of less than 10,
to the hardened surface of the hardened cementitious substrate.
8. The method of claim 7 , wherein applying the colloidal silica comprises applying a colloidal silica having a pH of 8 or less to the hardened surface of the hardened cementitious substrate.
9. The method of claim 7 , wherein applying the colloidal silica comprises applying a colloidal silica having a neutral pH to the hardened surface of the hardened cementitious substrate.
10. The method of claim 7 , wherein applying the colloidal silica comprises applying colloidal silica having a pH of about 4 to about 7 to the hardened surface of the hardened cementitious substrate.
11. The method of claim 7 , wherein applying the colloidal silica comprises applying to the hardened surface of the hardened cementitious substrate colloidal silica in which the stabilizer is present on the silica particles.
12. The method of claim 7 , wherein applying the colloidal silica comprises applying to the hardened surface of the hardened cementitious substrate colloidal silica in which the silica particles have diameters of about 3 nm to about 50 nm.
13. The method of claim 7 , wherein applying the colloidal silica comprises applying to the hardened surface the hardened cementitious substrate colloidal silica in which the silica particles have diameters of about 12 nm.
14. The method of claim 7 , wherein applying the colloidal silica comprises applying to the hardened surface the hardened cementitious substrate colloidal silica in which the silica particles comprise about 1.5% to about 6% of the weight of the colloidal silica.
15. The method of claim 7 , wherein applying the colloidal silica comprises applying to the hardened surface the hardened cementitious substrate colloidal silica in which the silica particles comprise about 4.5% of the weight of the colloidal silica.
16. The method of claim 7 , wherein applying the colloidal silica comprises applying to the hardened surface of the hardened cementitious substrate colloidal silica further including at least one surfactant.
17. The method of claim 7 , further comprising:
planing, honing or polishing the hardened surface of the hardened cementitious substrate before applying the colloidal silica to the hardened surface of the hardened cementitious substrate.
18. The method of claim 7 , further comprising:
polishing the hardened surface of the hardened cementitious substrate while the hardening composition is present on the hardened surface.
19. The method of claim 7 , further comprising:
removing the residue of the colloidal silica from the hardened surface, the act of removing consisting essentially of sweeping, blowing, or spraying the residue from the surface.
20. The method of claim 4 , further comprising:
polishing or further finishing the finished surface with the hardening composition thereon and before the finished surface is fully cured.
21. The method of claim 1 , wherein applying the hardening composition comprises applying a hardening composition in which the colloidal silica will remain in suspension at a pH of about 3.5 or less.
22. The method of claim 1 , wherein applying the hardening composition comprises applying a hardening composition including a stabilizer comprising aluminum or alumina on the colloidal silica.
23. The method of claim 1 , wherein applying the hardening composition comprises applying an aqueous hardening composition having a solids content based on the weight percent the colloidal silica.
24. The method of claim 23 , wherein applying the aqueous hardening composition comprises applying an aqueous hardening composition in which the solids content of the colloidal silica is about 1.5% of the weight of the aqueous hardening composition to about 6.5% of the weight of the aqueous hardening composition.
25. The method of claim 23 , wherein applying the aqueous hardening composition comprises applying an aqueous hardening composition in which the solids content of the colloidal silica is about 4.5% of the weight of the aqueous hardening composition.
26. A method for finishing concrete, comprising:
applying a hardening composition to a surface of uncured, fresh concrete, the hardening composition including colloidal silica;
the colloidal silica of the hardening composition reacting with calcium hydroxide at the surface; and
polishing the surface, with no residue of the hardening composition on the surface.
27. The method of claim 26 , wherein applying the hardening composition to the surface comprises applying the hardening composition to a surface of uncured concrete.
28. The method of claim 26 , wherein applying the hardening composition to the surface occurs within about thirty minutes of finishing the surface.
29. The method of claim 26 , wherein finishing the surface of the fresh concrete occurs with the hardening composition in place on the surface.
30. The method of claim 29 , wherein finishing the surface occurs while the surface is wet.
31. The method of claim 30 , wherein finishing the surface continues until the surface is dry.
32. The method of claim 29 , wherein finishing the surface comprises polishing the surface.
33. The method of claim 26 , wherein applying the hardening compound occurs before finishing the surface.
34. The method of claim 26 , wherein applying the hardening composition comprises applying a hardening composition having a solids content of colloidal silica comprising about 4.5% to about 6%, by weight, of the hardening composition.
35. The method of claim 26 , wherein applying the hardening composition comprises applying a hardening composition including a stabilizer on particles of the colloidal silica, the stabilizer comprising aluminum or alumina.
36. The method of claim 35 , wherein applying the hardening composition comprises applying a hardening composition including an anionic surfactant.
37. The method of claim 26 , wherein applying the hardening composition comprises applying a hardening composition in which the colloidal silica will remain in suspension at a pH of about 3.5 or less.
38. The method of claim 26 , wherein applying the hardening composition comprises applying a hardening composition having a pH of less than 10 and including a stabilizer comprising aluminum or aluminum oxide.
39. The method of claim 6 , wherein applying comprises applying the colloidal silica to a hardened surface comprising cured cement.
40. A method for treating a surface of concrete, comprising:
applying a hardening composition to a surface of concrete, the hardening composition consisting of:
colloidal silica;
a stabilizer selected from the group consisting of aluminum and alumina;
surfactant; and
water.
41. The method of claim 40 , wherein applying comprises applying the hardening composition to a surface of fresh concrete.
42. The method of claim 40 , wherein applying comprises applying the hardening composition to a surface of hardened concrete.
43. The method of claim 42 , wherein applying comprises applying the hardening composition to a cured concrete surface.
44. The method of claim 40 , further comprising:
imparting the surface of the substrate with a polished appearance.
45. The method of claim 40 , wherein no residue of the hardening compound remains on the surface.
46. The method of claim 12 , further comprising:
removing residual hardening compound from the surface.