A mine seal constructed from blocks adhered with a polyurea adhesive, the adhesive being formed by reacting a first prepolymer comprising an aromatic isocyanate with a second prepolymer comprising an aliphatic isocyanate, thereby forming an A-side mixture, and then reacting this mixture with a B-side mixture comprising an amine functional resin that includes a secondary amine.
1. A mine seal comprising a wall of rigid blocks and an adhesive composition, wherein the rigid blocks are adhered to each other using the adhesive composition, the wall comprising an upper surface adjacent a roof of a mine shaft and two sides, each side of the wall being adjacent to a vertical wall portion of the mine shaft, wherein the adhesive composition is formed by:
providing an aromatic isocyanate with an NCO content of between 15% and 35% by weight;
preparing a first prepolymer by mixing the aromatic isocyanate and a polyol;
providing an aliphatic isocyanate with an NCO content of between 8% and 24% by weight;
preparing a second prepolymer by mixing the first prepolymer with the aliphatic isocyanate;
providing an amine functional resin comprising a secondary amine;
mixing the second prepolymer and the amine-functional resin to form a castable adhesive composition.
2. The mine seal of claim 1 , wherein the blocks are porous.
3. The mine seal of claim 2 wherein the blocks are concrete masonry unit blocks.
4. The mine seal of claim 1 , wherein a polymer foam is applied between the roof of the mine shaft and the upper surface of the wall of the mine seal, and between the sides of the wall and the respective vertical wall portions of the mine shaft.
5. The mine seal of claim 4 , wherein the adhesive composition is applied to the roof of the mine shaft, the upper surface of the wall of the mine seal, the vertical sides of the wall, and the respective vertical wall portions of the mine shaft before the polymer foam is applied.
6. The mine seal of claim 4 , wherein the polymer foam is a polyurethane foam having a flexural strength ranging from 465 to 815 pounds per square inch.
7. The mine seal of claim 1 , wherein the isocyanate of the first prepolymer has an NCO content of between 16% and 18% by weight.
8. The mine seal of claim 1 , wherein the isocyanate of the first prepolymer is selected from the group consisting of diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), and hexamethylene diisocyanate (HDI).
9. The mine seal of claim 1 , wherein the isocyanate of the first prepolymer is MDI and comprises between 50% and 60% by weight of the first prepolymer.
10. The mine seal of claim 1 , wherein the polyol comprises between 40% and 50% by weight of the first prepolymer.
11. The mine seal of claim 1 , wherein the first prepolymer and the aliphatic isocyanate form a 50:50 mixture by weight.
12. The mine seal of claim 1 , wherein the aliphatic isocyanate of the second prepolymer has an NCO content of between 12% and 15% by weight.
13. The mine seal of claim 1 , wherein the aliphatic isocyanate of the second prepolymer is HDI.
14. The mine seal of claim 1 , further comprising the step of adding a water scavenger to the amine functional resin.
15. The mine seal of claim 14 , wherein the water scavenger is a molecular sieve.
16. The mine seal of claim 15 , wherein the molecular sieve comprises between 0.1% and 5% by weight of the amine functional resin.
17. The mine seal of claim 1 , further comprising a colorant, wherein the colorant is added to either the secondary prepolymer or to the amine functional resin.
18. The mine seal of claim 17 , wherein the colorant is an organic dye.
19. The mine seal of claim 1 , wherein a first colorant is added to the second prepolymer and a second colorant added to the amine functional resin, wherein the resulting colors of the second prepolymer and the amine functional resin have wavelengths which differ by at least 20 nanometers.
20. The mine seal of claim 1 , wherein the amine functional resin is mixed with a further component selected from the group consisting of a plasticizer and an air release agent prior to mixing the amine functional resin with the second prepolymer.