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 sprayable concrete, mortar or grout formed from two separate components that when combined by spray application form the concrete, mortar or grout wherein the two separate components are: (1) a non-acidic concrete admixture that remains flowable through a spray nozzle comprising a combination of a concrete component; a water-soluble, secondary accelerator chosen from the group consisting of: potassium carbonate, sodium carbonate, lithium carbonate, ammonium carbonate and mixtures thereof; a retarder; and (2) a main accelerator mixture comprising: an accelerator component and water.

2. The sprayable concrete, mortar or grout of claim 1, wherein the water-soluble, secondary accelerator is present in an amount of from 0.1 to 2% by dry weight of the non-acidic concrete mixture and wherein the non-acidic concrete admixture further comprises a superplasticizer.

3. The sprayable concrete, mortar or grout of claim 2, wherein the amount of the water-soluble, secondary accelerator is from 0.35% to 0.4% by dry weight of the concrete mixture.

4. The sprayable concrete, mortar or grout of claim 1, wherein the amount of the water-soluble, secondary accelerator is from 0.35 to 0.4% by dry weight of the concrete mixture and wherein the concrete, mortar or grout initially has an alkaline pH.

5. The sprayable concrete, mortar or grout of claim 1, wherein the concrete, mortar or grout initially has an alkaline pH.

6. The sprayable concrete, mortar or grout of claim 5, wherein the retarder comprises a hydroxycarboxylic acid selected from the group consisting of citric acid, gluconic acid, tartaric acid and salts thereof.

7. The sprayable concrete, mortar or grout of claim 1, wherein the retarder comprises a sugar composition and wherein the concrete, mortar or grout initially has an alkaline pH.

8. The sprayable concrete, mortar or grout of claim 7, wherein the sprayable concrete, mortar or grout is a tunnel boring machine backfill grout have a compressive strength of at least 0.51 MPa after two hours.

9. The sprayable concrete, mortar or grout of claim 5, wherein the retarder is a phosphonic acid selected from aminotris(methylphosphonic acid), phosphonobutane tricarboxylic acid and aminotris (dimethylphosphonic acid).

10. The sprayable concrete, mortar or grout of claim 1, wherein the ratio of carbonate to retarder is in a range of 5:1 to 3:1 by dry weight and the sprayable concrete, mortar, or grout is sprayable concrete and the sprayable concrete has a compressive strength of 1 MPa or higher after one hour.

11. A method of applying a concrete composition to a rock surface in a tunnel or a surface of a void created by a tunnel boring machine comprising the steps of: adding a liquid retarder to the concrete mixture and mixing; adding a water soluble, secondary accelerator selected from the group consisting of: potassium carbonate; sodium carbonate; lithium carbonate; ammonium carbonate; and mixtures thereof and mixing to provide cementitious composition comprising: (a) a concrete admixture; (b) the water soluble, secondary accelerator; (c) a retarder; and (d) water; providing a liquid accelerator composition comprising: (a) a main accelerator; and (b) water; combining the cementitious composition and the liquid accelerator composition via two separate feeds to a spray head to apply to the rock surface a concrete composition formed from the combination of the cementitious composition and the liquid accelerator composition; and allowing the concrete composition to cure on the rock surface or the surface of the void created by the tunnel boring machine and form a cured concrete.

12. The method of applying a concrete composition of claim 11, wherein the amount of the water soluble, secondary accelerator is from 0.1 to 2% by dry weight of the concrete mixture and wherein the cured concrete has an alkaline pH.

13. The method of applying a concrete composition of claim 12, wherein the amount of the water soluble, secondary accelerator is from 0.35 to 0.4% by weight of the concrete mixture.

14. The method of applying a concrete composition of claim 13, wherein the retarder is selected from the group consisting of hydroxycarboxylic acids and salts thereof and the main accelerator is a sodium silicate.

15. The method of applying a concrete composition of claim 14, wherein the hydroxycarboxylic acid is selected from the group consisting of citric acid, gluconic acid, tartaric acid and salts thereof.

16. The method of applying a concrete composition of claim 13, wherein the retarder comprises a sugar composition and the main accelerator comprises a sodium silicate.

17. The method of applying a concrete composition of claim 16, wherein the retarder comprises a sugar composition selected from the group consisting of: glucose; molasses; corn syrup; and mixtures thereof; and wherein the concrete composition has a strength of 1 MPa or higher after curing for one hour.

18. The method of applying a concrete composition of claim 13, wherein the retarder is selected from the group consisting of phosphonic acids and salts thereof and the water soluble, secondary accelerator is an accelerator containing aluminum sulfate.

19. The method of applying a concrete composition of claim 18, wherein the retarder is selected from aminotris(methylphosphonic acid), phosphonobutane tricarboxylic acid and aminotris (dimethylphosphonic acid).

20. The method of applying a concrete composition of claim 19, wherein the ratio of water soluble, secondary accelerator to retarder is in the range of 5:1 to 3:1 by dry weight; and wherein the concrete composition has a strength of 1 MPa or higher after curing for one hour.

Description

DETAILED DESCRIPTION

(1) 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.

(2) 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.

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

(4) Table 1 shows compressive strength values versus time for two sprayed concrete compositions; and

(5) Table 2 shows compressive strength values after 2 hours for two TBM backfill grouts.

(6) 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.

(7) The concrete used was, Norwegian sprayed concrete mix design with 480 kg CEM II per m.sup.3 concrete.

(8) 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.

(9) 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

(10) 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).

(11) The measurements were performed according to standard test methods used in-situ. 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.

(12) 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.

(13) 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