FLOWABLE CONCRETE WITH SECONDARY ACCELERATOR

Abstract

A concrete, mortar or grout formulation comprises two separate components: a concrete admixture comprising: (a) a concrete mixture; (b) alkali carbonate; (c) aretarder; and (d) water, an accelerator mixture comprising: (a) anaccelerator component; and (b) water.

Claims

1. A concrete, mortar or grout formulation comprising two separate components: a concrete mixture comprising: (a) a concrete mixture; (b) alkali carbonate; (c) a retarder; and (d) water. an accelerator mixture comprising: (a) an accelerator component; and (b) water.

2. The concrete composition of claim 1, wherein the alkali carbonate is selected from the group consisting of: potassium carbonate; sodium carbonate, lithium carbonate; ammonium carbonate and mixtures thereof.

3. The concrete composition of claim 1, wherein the amount of alkali carbonate is from 0.1 to 2% by dry weight of the concrete mixture.

4. (canceled)

5. Canceled.

6. The concrete composition of claim 3, wherein the amount of alkali carbonate is from 0.35 to 0.4%.

7. The concrete formulation of claim 1, wherein the retarder is selected from the group consisting of hydroxycarboxylic acids and salts thereof and phosphonic acids and salts thereof.

8. The concrete composition of claim 7, wherein the hydroxycarboxylic acid is selected from the group consisting of citric acid, gluconic acid, tartaric acid and salts thereof.

9. The concrete composition claim 1, wherein the retarder comprises a sugar composition.

10. The concrete composition of claim 9, wherein the retarder comprises a sugar composition selected from the group consisting of: glucose, molasses; corn syrup and mixtures thereof.

11. (canceled)

12. The concrete composition of claim 7, wherein the retarder is a phosphonic acid selected from aminotris(methylphosphonic acid), phosphonobutane tricarboxylic acid and aminotris(dimethylphosphonic acid).

13. (canceled)

14. The concrete composition of claim 1, wherein the ratio of carbonate to retarder is in the range of 5:1 to 3:1 by dry weight.

15. (canceled)

16. A method of applying a concrete composition comprising the steps of: providing a concrete admixture; adding a retarder to the admixture and mixing; adding an aqueous alkali metal carbonate and mixing to provide a cementitious composition comprising: (a) a concrete mixture; (b) alkali carbonate; (c) a retarder; and (d) water; providing an accelerator composition comprising: (a) an accelerator; and (b) water; combining the cementitious composition and accelerator to form a concrete composition: immediately applying the concrete composition to a substrate; and allowing the concrete composition to cure.

17. The method of applying a concrete composition as claimed in claim 16, wherein the wherein the alkali carbonate is selected from the group consisting of: potassium carbonate; sodium carbonate, lithium carbonate; ammonium carbonate and mixtures thereof and wherein the amount of alkali carbonate is from 0.1 to 2% by dry weight of the concrete mixture.

18. (canceled)

19. (canceled)

20. (canceled)

21. The method of applying a concrete composition as claimed in claim 17, wherein the amount of alkali carbonate is from 0.35 to 0.4%.

22. The method of applying a concrete composition of claim 21, wherein the retarder is selected from the group consisting of hydroxycarboxylic acids and salts thereof.

23. The method of applying a concrete composition of claim 22, wherein the hydroxycarboxylic acid is selected from the group consisting of citric acid, gluconic acid, tartaric acid and salts thereof.

24. The method of applying a concrete composition of claim 21, wherein the retarder comprises a sugar composition.

25. The method of applying a concrete composition of claim 24, wherein the retarder comprises a sugar composition selected from the group consisting of: glucose, molasses; corn syrup and mixtures thereof.

26. The method of applying a concrete composition of claim 21, wherein the retarder is selected from the group consisting of phosphonic acids and salts thereof.

27. The method of applying a concrete composition of claim 26, wherein the retarder is selected from aminotris(methylphosphonic acid), phosphonobutane tricarboxylic acid and aminotris(dimethylphosphonic acid).

28. (canceled)

29. The method of applying a concrete composition of claim 27, wherein the ratio of carbonate to retarder is in the range of 5:1 to 3:1 by dry weight.

30. (canceled)

Description

DETAILED DESCRIPTION

[0044] The composition and method of the present invention facilitate use of blended cements which may contain supplementary materials selected from: fly ash; ground granulated blast furnace slag (GGBS) or silica fume or mixtures thereof. For example, up to 20% fly ash may be employed. In such an application the early strength provided by the cement needs to be increased due to the less reactive supplementary material.

[0045] A further advantage is that the secondary accelerator does not need to be supplied to the spray head using a separate feed, so that modification of existing spray equipment is not necessary.

[0046] The invention is further described by means of examples, but not in any imitative sense, with reference to the accompanying tables, of which:

[0047] Table 1 shows compressive strength values versus time for two sprayed concrete compositions; and

[0048] Table 2 shows compressive strength values after 2 hours for two TBM backfill grouts.

[0049] Table 1: Shows the effect of a secondary accelerator on early age compressive strength of a sprayed concrete measured according to standard test methods used in-situ.

[0050] The concrete used was, Norwegian sprayed concrete mix design with 480 kg CEM II per m.sup.3 concrete.

[0051] The retarder referred to was a standard Consistence control admixture meeting EN 934-5, and is a blend of citric acid and PBTC. The retarder including a secondary accelerator was the same retarder made slightly alkaline using sodium hydroxide and with an additional portion of potassium carbonate.

TABLE-US-00001 A (without B (with secondary secondary accelerator) accelerator) Concrete mixture incl. superplasticiser Same composition for A and B Retarder in the concrete mixture (% by 0.21 weight of cement) Retarder incl. secondary accelerator in the 0.78 concrete mixture (% by weight of cement) Main accelerator added at the nozzle of 8.5 8.5 the sprayer (% by weight of cement) Compressive strength (MPa) at different times after spraying: 5 min 0.25 0.71 10 min 0.43 0.91 20 min 0.61 >1.0 60 min 0.85 >1.0 90 min 1.0 2.2

[0052] Table 2: shows the effect of a secondary accelerator on the compressive strength of a two-component TBM backfill grout two hours after mixing component 1 (cementitious mixture) and component 2 (sodium silicate accelerator).

[0053] The measurements were performed according to standard test methods used in-situ.

[0054] The weights referred to are kg per m.sup.3 of hardened material. The water content is not shown. The retarder referred to is a standard sugar/gluconate retarder used for backfill grouts, while the retarder incl. a secondary accelerator is the same retarder with an additional portion of potassium carbonate.

[0055] The difference in cement and sodium silicate content (the two most costly ingredients in TBM backfill grouts) illustrates the economic gain obtained by the secondary accelerator.

TABLE-US-00002 A (without secondary B (with secondary accelerator) accelerator) Ordinary Portland cement (kg) 300 280 Bentonite clay (kg) 30 30 Retarder in the concrete mixture (kg) 4.3 Retarder incl. secondary accelerator in 4.4 the concrete mixture (kg) Sodium silicate; main accelerator (kg) 110 83 Compressive strength (MPa) 2 hours 0.38 0.51 after mixing component 1 and 2