ACCELERATOR FOR MINERAL BINDER COMPOSITIONS

Abstract

An accelerator for mineral binder compositions, especially for mortars or concrete, including: aluminium sulfate, at least one pozzolane, optionally at least one defoamer, and water. The accelerator is particularly useful for shotcrete, in the field of free-forming construction, or for additive manufacturing.

Claims

1. An accelerator composition for mineral binder compositions comprising a) 5-16 wt. % of aluminium sulfate, b) 16-65 wt. % of at least one pozzolane, c) optionally at least one defoamer, and d) at least 30 wt. % of water.

2. The accelerator composition according to claim 1, further comprising aluminium hydroxide.

3. The accelerator composition according to claim 1, wherein the molar ratio of aluminium to sulfate is from 0.5-2.

4. The accelerator composition according to claim 1, wherein the at least one pozzolane is selected from the group consisting of silica fume, fly ash, volcanic tuff, trass, diatomaceous earth, rice husk ash, calcined clays, and metakaolin.

5. The accelerator composition according to claim 1, wherein the particle size of the at least one pozzolane is from 0.1-100 μm, and the D50 value is from 0.5-20 μm.

6. The accelerator composition according to claim 1, wherein the at least one defoamer is selected from the group consisting of ethoxylated 2,4,7,9-tetramethyl-5-decyn-4,7-diol, a combination of fatty alcohol alkoxylate and polysiloxane, and a combination of a mineral oil and a silicone oil comprising hydrophobic silica.

7. The accelerator composition according to claim 1, wherein the accelerator composition is essentially free of alkali metals and/or chloride.

8. The accelerator composition according to claim 1, wherein the accelerator composition is in the form of a liquid suspension.

9. The accelerator composition according to claim 8, it wherein the accelerator composition has a viscosity of higher than 500 m Pa.Math.s at a shear rate of 1 s and at 23° C.

10. The accelerator composition according to claim 1, wherein the accelerator composition comprises: a) 7-16 wt. % of the aluminium sulfate, b) optionally 0.01-5 wt. % of aluminium hydroxide, c) 16-65 wt. % of the at least one pozzolane, wherein the at least one pozzolane is metakaolin, d) 30-80 wt. % of the water, and e) 0.5-5 wt. % of the at least one defoamer.

11. A process for the acceleration of a mineral binder composition, comprising the steps of mixing at least one mineral binder with a) the accelerator composition as claimed in claim 1, and b) water in any given order.

12. The process as claimed in claim 11, wherein the process is a continuous process.

13. The process as claimed in claim 11, wherein the accelerator composition is mixed with the at least one mineral binder composition in an amount of from 0.5-25 wt. % based on the total weight of the mineral binder.

14. A method comprising: coating a substrate with the accelerator composition according to claim 1, wherein the accelerator composition is applied to a one or more surfaces of the substrate, the surfaces of the substrate being surfaces of tunnels, mines, excavations, bays, wells, and drains.

15. A method comprising: performing a free forming application with sprayed concrete or sprayed mortar, wherein the accelerator composition according to claim 1 is applied and/or mixed with the sprayed concrete or the sprayed mortar during the free forming application.

16. A method comprising: performing an additive manufacturing process with concrete or mortar, wherein the accelerator composition according to claim 1 is applied and/or mixed with the concrete or the mortar during the additive manufacturing process in an amount effective to accelerate the setting and/or hardening of the concrete or the mortar.

17. A method comprising: applying and/or mixing the accelerator composition according to claim 1 with mortar or concrete in an amount effective to accelerate the setting and/or hardening of the mortar or the concrete, wherein neither the mortar nor the concrete contain a pozzolanic material.

Description

EXAMPLES

[0162] Preparation of Accelerator Mixtures A1-A3

[0163] An accelerator A1 according to the present invention was prepared by mixing 14.5 parts by mass of Al.sub.2(SO.sub.4).sub.3, 3.9 parts by mass of Al(OH).sub.3, 1.3 parts by mass of Mg(OH).sub.2, 4 parts by mass of formic acid, and 41.1 parts by mass of water. This mixture was stirred at 70° C. for 2 h and then cooled to 23° C. 31.4 parts by mass of metakaolin and 3.8 parts by mass of a defoamer (ethoxylated 2,4,7,9-tetramethyl-5-decyn-4,7-diol) were then added and the resulting suspension was vigorously mixed until homogeneous.

[0164] An accelerator A2 which is not according to the present invention was prepared by mixing 45 parts by mass of Al.sub.2(SO.sub.4).sub.3, 12 parts by mass of Al(OH).sub.3, 4 parts by mass of Mg(OH).sub.2, and 12.5 parts by mass of formic acid in 26.5 parts by mass of water. This mixture was stirred at 70° C. for 2 h and then cooled to 23° C.

[0165] An accelerator A3 which is not according to the present invention was prepared by mixing 14.5 parts by mass of Al.sub.2(SO.sub.4).sub.3, 3.9 parts by mass of Al(OH).sub.3, 1.3 parts by mass of Mg(OH).sub.2, 4 parts by mass of formic acid, and 62.5 parts by mass of water. This mixture was stirred at 70° C. for 2 h and then cooled to 23° C. 10 parts by mass of metakaolin and 3.8 parts by mass of a defoamer (ethoxylated 2,4,7,9-tetramethyl-5-decyn-4,7-diol) were then added and the resulting suspension was vigorously mixed until homogeneous.

[0166] Dry Mortar Preparation

[0167] A dry mortar composition was prepared by intermixing 20 parts by mass of Portland cement (CEM I 52.5), 8.4 parts by mass of fine calcium carbonate filler, 47.8 parts by mass of silica sand (0.1-0.3 mm), 4 parts by mass of metakaolin, 1.4 parts by mass of calcium sulphoaluminate cement, 18.3 parts by mass of GGBFS, and 0.1 parts by mass of synthetic polymer powder for 1 minute at 23° C. and 50% relative humidity in a Hobart mixer.

[0168] Preparation of Cementitious Compositions

[0169] A cementitious composition C1 according to the present invention was prepared by mixing 100 g of the above dry mortar composition with 1 g of a polycarboxylate ester (PCE), 0.5 g of a defoamer, 3 g of the accelerator A1 and 12 g of water. Mixing was done for 2 minutes at 23° C. and 50% relative humidity in a Hobart mixer.

[0170] A reference composition R1, which is not according to the invention, was prepared in the same way as C1 without the addition of any accelerator A1. R1 is thus free of accelerator.

[0171] A reference composition R2, which is not according to the invention, was prepared in the same way as C1. However, instead of adding 3 g of the accelerator A1, 1 g of non-inventive accelerator A2 were added.

[0172] Another reference composition R3, which is not according to the invention, was prepared in the same way as R2. However, an additional 0.94 wt.-%, relative to the total dry weight of the mortar, of metakaolin were added to the dry mortar. The total content of metakaolin of reference composition R3 was thus the same as the total content of metakaolin of inventive example C1. The difference being that in R3, the whole metakaolin is contained in the mortar dry mix.

[0173] Still another reference composition R4, which is not according to the invention, was prepared in the same way as C1. However, instead of adding 3 g of the accelerator A1, 3 g of non-inventive accelerator A3 were added.

[0174] The following table 1 shows an overview of the compositions of inventive example C1 and reference examples R1-R4.

TABLE-US-00001 TABLE 1 Example compositions C1 R1 R2 R3 R4 CEM I 52.5 20 g 20 g 20 g 20 g 20 g CSA*.sup.1 1.4 g 1.4 g 1.4 g 1.4 g 1.4 g GGBFS*.sup.2 18.3 g 18.3 g 18.3 g 18.3 g 18.3 g Fine CaCO.sub.3*.sup.3 8.4 g 8.4 g 8.4 g 8.4 g 8.4 g Silica sand*.sup.4 47.8 g 47.8 g 47.8 g 47.7 g 47.8 g Metakaolin*.sup.5 4 g 4 g 4 g 4.94 g 4 g RDP*.sup.6 0.1 g 0.1 g 0.1 g 0.1 g 0.1 g PCE*.sup.7 1 g 1 g 1 g 1 g 1 g Water 12 g 12 g 12 g 12 g 12 g Defoamer*.sup.8 0.5 g 0.5 g 0.5 g 0.5 g 0.5 g Accelerator 3 g A1 none 1 g A2 1 g A2 3 g A3 *.sup.1calcium sulfoaluminate cement (Denka CSA 20) *.sup.2ground granulated blast furnace slag (Blaine specific surface: 2'452 m.sup.2/kg, activity index acc. EN 15167-1: 41%, methylene blue value: <1.67 g/kg) *.sup.3ground calcium carbonate (purity: 99.3%, BET surface: 10 m.sup.2/g, particle size distribution: D98: 5 μm, D50: 0.8 μm) *.sup.4silica sand with particle size 0.1-0.3 mm *.sup.5<0.02 wt.-% residue on 325 mesh; Chapelle index 1'000 mgCa(OH).sub.2/g (according to NF P18-513: 2012) *.sup.6Starvis S5514F (available from BASF) *.sup.7polycarboxylate ester with and a carboxylate I ester ratio of appr. 3, made from esterification of a polymethacrylate backbone(Mn = 7'000 g/mol) with a mix (weight ratio 1:3.5) of two methyl-terminated PEG with Mn = 1'000 g/mol and 3'000 g/mol respectively *.sup.8ethoxylated 2,4,7,9-tetramethyl-5-decyn-4,7-diol

[0175] Performance Testing

[0176] Compressive strength and flexural strength were measured according to DIN EN 196-1 on prisms of 40×40×160 mm after the time indicated in below table 2.

[0177] Linear shrinkage was measured according to EN 12617-4 on prisms of 40×40×160 mm within 5 h and 16 h of mixing with water.

[0178] The following table 2 shows the results.

TABLE-US-00002 TABLE 2 Measurement results Example C1 R1 R2 R3 R4 Linear shrinkage after −496 −82 −687 −564 −4020 5 h [μm/m] Linear shrinkage after −742 −722 −856 −824 −4320 16 h [μm/m] Compressive strength 33 6 33 34 n.m. after 24 h [MPa] Compressive strength 53 60 46 45 53 after 7 d [MPa] Flexural strength 5.4 1.1 5.5 4.9 n.m. after 24 h [MPa] Flexural strength 6.2 8.2 5.3 5.9 n.m. after 7 d [MPa] n.m.: not measured

[0179] From the above table 2 it becomes clear that composition C1, which is in accordance with the present invention, shows a faster strength development than compared to the reference R1 which was made without accelerator. The increase in strength development is similar or better as compared to the references R2-R4. Additionally, the inventive composition C1 does show significantly lower shrinkage as compared to reference R2 (where no pozzolane was present in the accelerator), reference R3 (where the respective additional amount of pozzolane was added to the dry mortar), and reference R4 (where a lower amount of pozzolane was present in the accelerator).