High Early Strength Engineered Cementitious Composites

Abstract

Rapid repair and retrofit of existing infrastructures demand durable high early strength materials that not only deliver sufficient strength within a few hours of placement but also significantly prolong the maintenance interval. The invention comprises a class of newly developed polyvinyl alcohol (PVA) fiber-reinforced high early strength engineered cementitious composites (ECC) materials featuring extraordinary ductility. The tailoring of preexisting flaw size distribution through non-matrix interactive crack initiators in the composite matrix results in high tensile ductility. The resulting high early strength ECC materials are capable of delivering a compressive strength of 21 MPa (3.0 ksi) within 4 hours after placement and retaining long-term tensile strain capacity above 2%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1—Compressive strength development of rapid hardening (SC01 and SC19) and Type III (HP08 and HP09) cement based mixtures in contrast to that of an ECC mix based on Type I ordinary portland cement (OP08).

FIG. 2—Tensile behavior of ECC with Type III cement-based mixture composition without (HP08) and with (HP09) artificial crack initiators. This figure demonstrates the effectiveness of the artificial crack initiators to regain tensile ductility, which is lost due to the use of Type III cement.

FIG. 3—Typical bending behaviors of ECC HP09 with Type III cement-based mixture composition containing artificial crack initiators at 4 hrs, 24 hrs and 28 days. This figure illustrates HP09 maintains high early age flexural strength and ductility significantly exceeding those typically specified for high early strength concrete, (3.1) MPa (450 psi), which are brittle. The horizontal line represents 3.1 MPa.

Claims

1. A high early strength engineered cementitious composition comprising: (a) a hydraulically settable cement, comprising hydraulic calcium silicates;(b) a chemical accelerator admixture;(c) matrix interactive fibers;(d) non-matrix interactive crack initiators having a mean particle size and concentration sufficient to produce a desired high tensile ductility;(e) one or more fine grained aggregates;(f) a chemical dispersant admixture;such that when mixed in a water to cement ratio of about 0.25 to 0.5, and allowed to set, a compressive strength of 21 M Pa is attained within about 4 hours and a tensile strain of greater than about 2% is maintained after curing.

2. The composition of claim 1, wherein the ingredients are present in about the following amount (% by weight): (a) hydraulically settable cement—38.2% to 48.5%;(b) chemical accelerator admixture—1.3% to 2.0%;(c) matrix interactive fibers—1.1% to 1.9%;(d) non-matrix interactive crack initiators—1.7% to 2.9%;(e) fine grained aggregates—28.6% to 47.7%;(f) chemical dispersant admixture—0.2% to 1.0%; andwater in a ratio of water to cement of 0.25 to 0.5.

3. The composition of claim 1, wherein the ingredients are present in about the following amount (% by weight): (a) hydraulically settable cement—40.6% to 43.0%;(b) chemical accelerator admixture—1.5% to 1.85;(c) matrix interactive fibers—1.4% to 1.7%;(d) non-matrix interactive crack initiators—1.9% to 2.6%;(e) fine grained aggregates—33.4% to 42.7%;(f) chemical dispersant admixture—0.3% to 0.9%; andwater in a ratio of water to cement of 0.3 to 0.4.

4. The composition of claim 1 wherein the chemical accelerator admixture is mixed into the final composition prior to casting.

5. The composition of claim 1 wherein the chemical accelerator admixture is selected from the group consisting of soluble inorganic salts, soluble organic compounds, solid accelerator admixtures, and mixtures thereof.

6. The composition of claim 5 wherein the soluble inorganic salt is selected from the group consisting of chlorides, bromides, fluorides, carbonates, nitrites, nitrates, thiosulfates, silicates, aluminates, alkali hydroxides, and mixtures thereof.

7. The composition of claim 5 wherein the soluble organic compound is selected from the group consisting of thiocyanates, carboxylic acid salts, alkanolamine, calcium formate, and mixtures thereof.

8. The composition of claim 1 wherein the chemical accelerator admixture includes calcium nitrate.

9. The composition of claim 1 wherein the chemical dispersant admixture includes a superplasticizer.

10. The composition of claim 10 wherein the superplasticizer is selected from the group consisting of melamine formaldehyde sulfonate, carboxylated polyether, polycarboxylates, and mixtures thereof.

11. The composition of claim 1 wherein the chemical dispersant admixture and the chemical accelerator admixture are combined.

12. The composition of claim 1 wherein the matrix interactive fiber comprises a polyvinyl alcohol (PVA) fiber.

13. The composition of claim 1 wherein the matrix interactive fiber is approximately 8 to 40 mm in length and 20 to 60 μm in diameter with a concentration of about 1 to 6 volume %.

14. The composition of claim 1 wherein the matrix interactive fiber is approximately 12 to 25 mm in length and 40 to 50 μm in diameter with a concentration of about 3 to 5 volume %.

15. The composition of claim 1 wherein non-matrix interactive polymeric beads are selected from the group consisting of polypropylene, polystyrene, polyethylene, and mixtures thereof.

16. The composition of claim 1 comprising disc shaped non-matrix interactive crack initiators.

17. The composition of claim 1 comprising cylindrical non-matrix interactive crack initiators.

18. The composition of claim 1 wherein the non-matrix interactive crack initiators create cracks with an average crack width of less than 100 μm.

19. The composition of claim 1 wherein at least one fine grained aggregate is selected from the group consisting of sand, clay, bauxite, shale, iron ore, and mixtures thereof.

20. The composition of claim 1 wherein at least one fine grained aggregate has a mean particle size of about 50 μm to 400 μm.

21. A method for preparing the composition of claim 1, comprising the steps of: (a) mixing cement, fine grained aggregates, and non-matrix interactive crack initiators;(b) mixing the ingredients of step (a) with water;(c) preparing a chemical dispersant solution for combination with the mixture of step (b);(d) mixing the chemical dispersant with the mixture of step (b);(e) adding matrix interactive fibers; and(f) mixing the chemical accelerator with the mixture of step (e) prior to casting.

22. A method for using the composition of claim 1, comprising replacing damaged cementitious structures such that the curable composition contracts and adheres to remaining parts of the damaged structure.

23. A method for using the composition of claim 1, comprising preparing one or more structures from the composition.

24. A high early strength engineered cementitious composition comprising: (a) a hydraulically settable cement, comprising a rapid hardening cement;(b) fly ash;(c) matrix interactive fibers;(d) non-matrix interactive crack initiators having a mean particle size and concentration sufficient to produce a desired high tensile ductility;(e) one or more fine grained aggregates with a mean particle size of 50 μm to 400 μm; and(f) a chemical dispersant admixture;such that when mixed in a water to cement ratio of 0.25 to 0.50 and allowed to set, a compressive strength of 21 M Pa is attained within about 4 hours, and a tensile strain capacity of greater than about 2% is maintained after curing.

25. The composition of claim 24, wherein the ingredients are present in about the following amounts (% by weight): (a) hydraulically settable rapid hardening cement—38.2% to 48.5%;(b) fly ash—3.8% to 4.8%;(c) matrix interactive fibers—1.1% to 1.9%;(d) non-matrix interactive crack initiators—1.7% to 2.9%;(e) fine grained aggregates—28.6% to 47.7%;(f) chemical dispersant admixture—0.2% to 1.0%; andwater in a ratio of water to cement of 0.25 to 0.5.

26. The composition of claim 24, wherein the ingredients are present in about the following amount (% by weight): (a) hydraulically settable rapid hardening cement—40.6% to 43.6%;(b) fly ash—4.1% to 4.3%;(c) matrix interactive fibers—1.2 to 1.7%;(d) non-matrix interactive crack initiators—1.95% to 2.6%;(e) fine grained aggregates—33.4% to 42.7%;(f) chemical dispersant admixture—0.3% to 0.9%; andwater in a ratio of water to cement of 0.3 to 0.4.

27. The composition of claim 24 wherein the chemical dispersant admixture includes a superplasticizer.

28. The composition of claim 27 wherein the superplasticizer is selected from the group consisting of melamine formaldehyde sulfonate, carboxylated polyether, polycarboxylates, and mixtures thereof.

29. The composition of claim 24 wherein the chemical dispersant admixture and the chemical accelerator admixture are combined.

30. The composition of claim 24 wherein the matrix interactive fiber comprises a polyvinyl alcohol (PVA) fiber.

31. The composition of claim 24 wherein the matrix interactive fiber is approximately 8 to 40 mm in length and 20 to 60 μm in diameter with a concentration of about 1 to 6 volume %.

32. The composition of claim 24 wherein the matrix interactive fiber is approximately 12 to 25 mm in length and 40 to 50 μm in diameter with a concentration of about 3 to 5 volume %.

33. The composition of claim 24 wherein non-matrix interactive polymeric beads are selected from the group consisting of polypropylene, polystyrene, polyethylene, and mixtures thereof.

34. The composition of claim 24 comprising disc shaped non-matrix interactive crack initiators.

35. The composition of claim 24 comprising cylindrical non-matrix interactive crack initiators.

36. The composition of claim 24 wherein the non-matrix interactive crack initiators create cracks with an average crack width of less than 100 μm.

37. The composition of claim 24 wherein at least one fine grained aggregate is selected from the group consisting of sand, clay, bauxite, shale, iron ore, and mixtures thereof.

38. The composition of claim 24 wherein at least one fine grained aggregate has a mean particle size of about 50 μm to 400 μm.

39. A method for preparing the composition of claim 24, comprising the steps of: (a) mixing cement, fly ash, fine grained aggregates, and non-matrix interactive crack initiators;(b) mixing the ingredients of step (a) with water;(c) preparing a chemical dispersant solution for combination with the mixture of step (b);(d) mixing the chemical dispersant with the mixture of step (b);(e) adding matrix interactive fibers.(f) mixing prior to casting.

40. A method for using the composition of claim 24, comprising replacing damaged cementitious structures such that the curable composition contracts and adheres to remaining parts of the damaged structure.

41. A method for using the composition of claim 24, comprising preparing one or more structures from the composition.