Freeze-thaw durability of dry cast cementitious mixtures
An improved freeze-thaw durability dry cast cementitious composition is provided that uses very small (0.1 μm to 100 μm average diameter) polymeric microspheres that are blended directly into the mixture and optionally gas-generating additives. The polymeric microspheres provide void spaces in the material matrix that act to increase freeze-thaw durability of the material. In this dry cast cementitious composition, polymeric microspheres act as pre-formed voids.
1. A cementitious freeze-thaw damage resistant dry cast composition comprising hydraulic cement, polymeric microspheres, and optionally gas generating additives.
2. The cementitious dry cast composition of claim 1 wherein the water to cement ratio is from about 0.2 to about 0.8.
3. The cementitious dry cast composition of claim 1 wherein the polymeric microspheres comprise a polymer that is at least one of polyethylene, polypropylene, polymethyl methacrylate, poly-o-chlorostyrene, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polymethacrylonitrile, polystyrene, or copolymers or mixtures thereof.
4. The cementitious dry cast composition of claim 1 wherein the polymeric microspheres comprise at least one copolymer of vinylidene chloride-acrylonitrile, polyvinylidene chloride-copolyacrylonitrile, vinyl chloride-vinylidene chloride or mixtures thereof.
5. The cementitious dry cast composition of claim 1 wherein the polymeric microspheres are present in a range from about 1% to about 4% by weight of dry cement.
6. The cementitious dry cast composition of claim 1 wherein the polymeric microspheres are present in a range from about 0.05% to about 4% by volume percent of the cementitious mixture.
7. The cementitious dry cast composition of claim 1 wherein the polymeric microspheres are at least one of gas filled or liquid filled.
8. The cementitious dry cast composition of claim 1 wherein the polymeric microspheres have an average diameter of about 0.1 μm about 100 μm.
9. The cementitious dry cast composition of claim 1 wherein the polymeric microspheres have an average diameter of about 10 μm or less.
10. The cementitious dry cast composition of claim 1 wherein the cementitious composition contains gas generating additives.
11. The cementitious dry cast composition of claim 1 wherein the gas generating additive is at least one of hydrazide, hydrazine, azide, or azo compound.
12. The cementitious dry cast composition of claim 1 wherein the gas generating additive is at least one of azodicarbonamide, sodium bicarbonate, organic peroxide, inorganic peroxide, toluenesulfonylhydrazide, benzenesulfonyl hydrazide, toluenesulfonyl acetone hydrazone, toluenesulfonylsemicarbazide, phenyltetrazole, sodium borohydride, activated carbon or dinitroso-pentamethylenetetramine.
13. The cementitious dry cast composition of claim 1 wherein the gas generating additive is present in a range from about 0.05 to 2 weight percent by dry weight of cement.
14. The cementitious dry cast composition of claim 1 further comprising at least one of air entrainers, aggregates, pozzolans, dispersants, set and strength accelerators/enhancers, set retarders, water reducers, wetting agents, water soluble polymers, rheology modifying agents, water repellents, dampproofing admixtures, permeability reducers, pumping aids, fungicidal admixtures, germicidal admixtures, insecticide admixtures, finely divided mineral admixtures, alkali-reactivity reducer, bonding admixtures, shrinkage reducing admixtures or mixtures thereof.
15. The cementitious dry cast composition of claim 14 wherein the dispersant is at least one of calcium lignosulfonates, sulfonated melamine formaldehyde condensates, polyaspartates, sodium naphthalene sulfate formaldehyde condensate resins, oligomers, or polycarboxylates.
16. A dry cast cementitious article comprising the composition of claim 1 .
17. A method for preparing a freeze-thaw damage resistant dry cast cementitious article comprising:
a. mixing hydraulic cement, polymeric microspheres and optionally a gas generating additive to produce a cementitious composition mixture; and
b. forming the mixture into an article.
18. The method of claim 17 , wherein the polymeric microspheres or gas generating additives are added in at least one of the following forms:
a. compact mass;
b. powder; or
c. liquid admixture.
19. The method of claim 17 wherein the mixture contains a gas generating additive.
20. The method of claim 17 wherein the polymeric microspheres are at least one of gas filled or liquid filled.