Method for producing a calcium silicate hydrate-comprising hardening accelerator in powder form

Abstract

The invention relates to a method for producing a calcium silicate hydrate-comprising hardening accelerator in powder form, which comprises the steps of (a) providing an aqueous suspension comprising calcium silicate hydrate; (b) mixing at least one calcium compound, selected from calcium acetate, calcium formate, calcium hydroxide, calcium oxide, and mixtures of two or more of said compounds, with the aqueous suspension comprising calcium silicate hydrate; and (c) drying the resulting mixture. The invention also relates to the hardening accelerator obtainable by this method, to the use thereof, and to building material mixtures which comprise the hardening accelerator.

Claims

1. A method for producing a calcium silicate hydrate-comprising hardening accelerator in powder form, which comprises the steps of (a) providing an aqueous suspension comprising calcium silicate hydrate; (b) mixing at least one calcium compound, selected from calcium acetate, calcium formate, calcium hydroxide, calcium oxide, and mixtures of two or more of said compounds, with the aqueous suspension comprising calcium silicate hydrate; and (c) drying the resulting mixture.

2. The method according to claim 1, wherein the suspension comprising calcium silicate hydrate is obtained by reacting an aqueous solution or suspension of a calcium source with an aqueous solution or suspension of a silicate source in the presence of at least one polymeric dispersant which comprises structural units having anionic or anionogenic groups and structural units having polyether side chains.

3. The method according to claim 1, wherein the calcium compound is selected from calcium hydroxide, calcium oxide, and mixtures thereof.

4. The method according to claim 1, wherein the calcium compound in an amount of 0.5 to 150 wt % based on the solids content of the calcium silicate hydrate-comprising suspension from step (a), is mixed with the calcium silicate hydrate-comprising suspension from step (a).

5. The method according to claim 1, wherein the drying is accomplished by spray drying or roll drying.

6. The method according to claim 1, wherein the calcium compound in an amount of 1 to 30 wt %, based on the solids content of the calcium silicate hydrate-comprising suspension from step (a), is mixed with the calcium silicate hydrate-comprising suspension from step (a).

7. The method of claim 1 comprising utilizing the calcium compound as a drying aid in the drying of the aqueous suspension comprising calcium silicate hydrate.

8. The method of claim 1 comprising utilizing the calcium compound for improving the redispersibility of the calcium silicate hydrate-comprising hardening accelerators in powder form.

9. A calcium silicate hydrate-comprising hardening accelerator in powder form, obtained by the method according to claim 1.

10. A building material mixture which comprises the calcium silicate hydrate-comprising hardening accelerator in powder form according to claim 9, and a hydraulic and/or latent hydraulic binder.

11. A process comprising mixing the calcium silicate hydrate-comprising hardening accelerator in powder form according to claim 9 in a building material mixture which comprises a hydraulic and/or latent hydraulic binder.

12. A process comprising mixing the calcium silicate hydrate-comprising hardening accelerator in powder form according to claim 9 as an admixture for hydraulic and/or latent hydraulic binders.

13. A method for accelerating the hardening of a building material mixture which comprises adding the calcium silicate hydrate-comprising hardening accelerator of claim 9 in powder form to the building material mixture comprising a hydraulic and/or latent hydraulic binder and allowing the obtained mixture to harden.

Description

EXAMPLES

(1) To produce the inventive powders, the original suspension was admixed, prior to drying, with different calcium compounds and different masses of calcium compounds. The suspension was thereafter stirred for 10 minutes and then dried by means of spray drying, at 230 C. entry temperature and 98 C. exit temperature, under inert conditions (N.sub.2 atmosphere) on a Mobile Minor type MM-I laboratory spray dryer from GEA Niro. For comparison, for each powder obtained from the original suspension mixed with Ca compound, a physical mixture of the Ca compound and the dried C-S-H was produced. All of the powders have their acceleration performance verified by means of heat flow calorimetry. For the determination of the hydration kinetics by means of heat flow calorimetry, therefore, 1 g of each C-S-H powder (corresponding to the solid of the original suspension from step (a)) plus, where appropriate, calcium compound was mixed with 100 g of cement (Mergelstetten CEM I 42.5 N) at a w/c ratio of 0.45 for 30 seconds by means of an overhead stirrer (IKA Labortechnik, RW20.n) at 500 rpm in a 200 ml beaker. For the blank value, no C-S-H was added. For the C-S-H suspension comparison, the hardening accelerator was used as C-S-H suspension. For the C-S-H powder comparison, a C-S-H powder obtained without adding a calcium compound during drying was used. For the inventive examples, the percentage amount of calcium compound indicated in table 1 was added prior to drying. For the physical mixtures, the same percentage amount of calcium compound was mixed with 1 g of C-S-H powder dried without calcium compound.

(2) In order to characterize the acceleration performance, the cumulative heat (HoH, Heat of Hydration) was determined after 6 hours (at 20 C.), and the acceleration factor was ascertained from the slope of the heat flow curves. The acceleration factor (AF) was determined as follows: 1. determination of the maximum slope (m.sub.max) between 1 h and 6 h over the 1st derivation of the heat flow curve after the hydration time in this time interval 2. ratio of the maximum slope between reference and sample
AF=m.sub.max(sample)/m.sub.max(reference)

(3) The results are compiled in table 1 below. Surprisingly it emerges that adding a Ca salt prior to spray drying causes substantially no loss of performance on the part of the C-S-H powders of the invention, in contrast to the comparative powders.

(4) A further aspect of the invention is the influencing of the rate of redispersion. For this purpose, a powder with 15% addition of calcium hydroxide prior to drying was prepared (example 4), and the performance of the powder was compared with that of a powder without addition of salt added (C-S-H powder without addition of salt) after different batching times. For the determination of the hydration kinetics by means of heat flow calorimetry, the C-S-H powder was mixed with 100 g of cement (Mergelstetten CEM I 42.5 N) at a w/c ratio of 0.45 by means of an overhead stirrer (IKA Labortechnik, RW20.n) at 500 rpm in a 200 ml beaker for different mixing times (30, 60, 90 and 120 seconds). The results are compiled in table 2 below.

(5) TABLE-US-00002 TABLE 1 Co-dried CSH powder Physical mixture (invention) (comparative) Calcium compound HoH after 6 h Acceleration HoH after 6 Acceleration Calcium compound (mass %).sup.1) (J/g cement) factor (J/g cement) factor Blank mixture None (cement only) 8.08 1.00 Comparative None 22.55 2.61 CSH suspension Comparative None 17.23 1.42 CSH powder Example 1 Ca(OH).sub.2 1 19.68 2.03 17.15 1.46 Example 2 Ca(OH).sub.2 5 23.47 2.74 17.19 1.42 Example 3 Ca(OH).sub.2 10 23.02 2.62 18.28 1.83 Example 4 Ca(OH).sub.2 15 22.84 2.58 17.54 1.48 Example 5 Ca amidosulfonate 1 17.75 1.57 17.66 1.57 Example 6 Ca amidosulfonate 5 19.80 1.96 17.57 1.53 Example 7 Ca amidosulfonate 10 20.80 2.14 17.33 1.60 Example 8 Ca amidosulfonate 15 21.88 2.33 18.08 1.60 Example 9 CaCl.sub.2 5 22.15 2.50 18.18 1.46 Example 10 Ca methanesulfonate 5 19.97 2.02 18.134 1.62 Example 11 Ca acetate 5 21.72 2.24 19.19 1.68 Example 12 Ca formate 5 20.85 2.11 17.68 1.46 .sup.1)based on the solids content of the original suspension .sup.2)based on 100 g cement

(6) TABLE-US-00003 TABLE 2 Incorporation time (stirring with Acceleration HoH after 6 h Sample lka mixer) factor (J/g cement) Cement only 30 s 1.00 8.08 Accelerator suspension 30 s 2.46 22.55 Example 4 30 s 2.74 23.47 Example 4 60 s 2.69 23.36 Example 4 90 s 2.73 23.23 Comparative CSH 30 s 1.59 17.23 powder (without calcium compound) Comparative CSH 60 s 1.64 18.45 powder (without calcium compound) Comparative CSH 90 s 1.75 18.94 powder (without calcium compound) Comparative CSH 120 s 1.89 19.08 powder (without calcium compound)

(7) It is apparent that the addition of a calcium compound prior to spray drying means that the resulting powders no longer suffer substantially any loss of performance, in contrast to a mere physical mixture; see table 1.

(8) Table 2 shows that the powder of the invention co-spray-dried with a calcium compound has a redispersibility which is a significant improvement over the prior art. Even short incorporation times of 30 seconds are already enough to obtain the full performance of the powder. In contrast, even after a relatively long batching time, specimens produced in accordance with the prior art exhibit an activity which is a sharp reduction on that of the original suspension.

Example 13

(9) Raw Materials for Synthesis:

(10) TABLE-US-00004 Abbreviation Name Formula Purity ASA amidosulfonic acid H.sub.3NSO.sub.3 100% CH calcium hydroxide Ca(OH).sub.2 98% NaSi sodium metasilicate Na.sub.2SiO.sub.35H.sub.2O 99% pentahydrate

(11) The polymer used as a dispersant is a comb polymer and is based on the monomers maleic acid, acrylic acid, and vinyloxybutylpolyethylene glycol 5800. The molar ratio of acrylic acid to maleic acid is 7. Mw=40 000 g/mol as determined via GPC. The solids content is 45 wt %. The synthesis is described for example in EP 894 811. The charge density is 930 eq/g.

(12) Synthesis of Hardening Accelerator Suspensions

(13) 4 different C-S-H containing hardening accelerator suspensions were produced. The weight of the different materials for the synthesis is given in table 3. The synthesis was performed according to the steps described below and the weight of starting materials used for each suspension is given in table 3. Step 1: Preparation of calcium source CVL for the synthesis by (i) dissolution of amidosulfonic acid (ASA) in water and (ii) addition of calcium hydroxide (CH). Step 2: Preparation of silicate source SVL for the synthesis by dissolution of sodium metasilicate pentahydrate (NaSi) in water. Step 3: A dispersant solution PL was prepared by mixing a solution of polymer 4 (45 wt % strength polymer solution) and water. Step 4: The dispersant solution (PL) was introduced initially and pumped in circulation through a high-energy mixer with a mixing volume of 20 ml and equipped with a rotor/stator system. In the high-energy mixer, the calcium source CVL and the silicate source SVL are metered completely into the initially introduced dispersant solution over 80 minutes, with the rotor/stator system operating at a rotational speed of 8000 rpm. During this procedure, the initially introduced solution is maintained at 20 C.

(14) The solid content of the suspensions CSH 2.1 to 2.4 was determined by drying the suspensions at 60 C. for 12 hours in a laboratory oven. The solid content was determined from the weight loss before and after drying.

(15) TABLE-US-00005 TABLE 3 CVL SVL PL molar Solid weight weight amido- weight weight weight weight solution weight ratio content sample Ca(OH).sub.2 (g) sulfonic acid (g) water (g) Na.sub.2SiO.sub.35H.sub.2O (g) water (g) of polymer A (g) water (g) Ca/Si (%) CSH 43.76 112.38 280.70 104.95 93.09 101.93 263.19 1.17 24.8 2.1 CSH 47.52 122.06 304.86 98.78 87.62 95.94 243.22 1.35 25.1 2.2 CSH 50.34 129.29 322.92 94.17 83.53 91.46 228.29 1.5 25.6 2.3 CSH 55.25 141.90 354.42 86.13 76.40 83.65 202.24 1.8 26.3 2.4
Production of Powdered Samples:

(16) For the production of the hardening accelerators of the invention the suspensions CSH 2.1 to 2.4 were mixed with calcium hydroxide before drying. The dosage of calcium hydroxide was 5% by weight of solids in the suspension CSH 2.1 to 2.4. The mixture of the accelerator suspensions and calcium hydroxide was stirred for 10 min. The resulting suspensions were used as feedstock for the drying process.

(17) Each feedstock was dried in a lab spray dryer type Mobile Minor Type MM I manufactured by company GEA Niro. The drying conditions were: Inlet temperature: 230 C. Outlet temperature: 98 C. Drying gas: Nitrogen Nozzle: 2-fluid nozzle

(18) The resulting powders according to the invention are labelled CSH-CH-P 2.1 to CSH-CH-P 2.4.

(19) For comparative purposes each suspension was also dried without addition of calcium hydroxide (labelled CSH-P 2.1 to CSH-P 2.4) at the same drying conditions as described above.

(20) An overview over the powdered samples and the composition of the feedstock is given in table 4 below.

(21) TABLE-US-00006 TABLE 4 Weight CSH CSH suspension Weight calcium Powder Type suspension (g) hydroxide (g) CSH-CH-P 2.1 Invention CSH 2.1 400 4.96 CSH-CH-P 2.2 Invention CSH 2.2 400 5.02 CSH-CH-P 2.3 Invention CSH 2.3 400 5.12 CSH-CH-P 2.4 Invention CSH 2.4 400 5.26 CSH-P 2.1 Comparative CSH 2.1 400 0.00 CSH-P 2.2 Comparative CSH 2.2 400 0.00 CSH-P 2.3 Comparative CSH 2.3 400 0.00 CSH-P 2.4 Comparative CSH 2.4 400 0.00

(22) The effect of the hardening accelerators CSH-CH-P 2.1 to CSH-CH-P 2.4 and CSH-P 2.1 to CSH-P 2.4 in powder form was tested for mortar by measuring the release of heat using heat flow calorimetry.

(23) Mortar Composition: 500 g OPC (CEM I 52.5 R Milke premium, HeidelbergCement) 500 g Sand (BCS221, Strobel Quarzsand) M g powder containing hardening accelerator for CSH-CH-P 2.1 to CSH-CH-P 2.4: M=10.53 g for CSH-P 2.1 to CSH-P 2.4: M=10.00 g 225 g water

(24) The hardening accelerator was mixed with the batching water, and the resulting suspension was mixed with Portland cement and quartz sand in a mortar mixer (Eirich lab mixer EL 01) at a shear rate of 2 m/s for 60 seconds. The water-to-cement ratio (w/c) was set at 0.45. 6 g of the resulting mortar were put into the measurement cell of a heat flow calorimeter (TAM Air, TA instruments) and the heat release was measured over time for 24 hours. The addition of the accelerator of the invention accelerates the hardening of the mortar. The heat released between 0.5 hours and 6 hours after addition of water to the cement was calculated and is reflecting the degree of hydration in this time. The degree of hydration is a measure of the hardening of the mortar (L. Frlich Engsig: Compressive strength prediction at 1 day using isothermal calorimetry heat of hydration. Oral presentation, Meeting on Applications of Isothermal calorimetry in the Cement Industry. TU Berlin, 10.-15. Apr. 2014).

(25) For a further comparison with the mortar compositions of the invention the mortars containing the powders CSH-P 2.1 to CSH-P 2.4 were also mixed with calcium hydroxide (physical mixture) to determine the effect of calcium hydroxide on the hydration kinetics (see mortars labelled M4, M8, M12, and M16) The compositions of the mortars tested are shown in table 5.

(26) TABLE-US-00007 TABLE 5 Weight of accelerator Ca(OH).sub.2 OPC Sand Water Mortar Type Accelerator (g) (g) (g) (g) (g) M1 Comparative 500 500 225 M2 Comparative CSH 2.1 40.32 500 500 194.7 M3 Comparative CSH-P 2.1 10.00 500 500 225 M4 Comparative CSH-P 2.1 10.00 0.53 500 500 225 M5 Inventive CSH-CH-P 2.1 10.53 500 500 225 M6 Comparative CSH 2.2 39.84 500 500 195.2 M7 Comparative CSH-P 2.2 10.00 500 500 225 M8 Comparative CSH-P 2.2 10.00 0.53 500 500 225 M9 Inventive CSH-CH-P 2.2 10.53 500 500 225 M10 Comparative CSH 2.3 39.06 500 500 195.9 M11 Comparative CSH-P 2.3 10.00 500 500 225 M12 Comparative CSH-P 2.3 10.00 0.53 500 500 225 M13 Inventive CSH-CH-P 2.3 10.53 500 500 225 M14 Comparative CSH 2.4 38.02 500 500 197.0 M15 Comparative CSH-P 2.4 10.00 500 500 225 M16 Comparative CSH-P 2.4 10.00 0.53 500 500 225 M17 Inventive CSH-CH-P 2.4 10.53 500 500 225

(27) The measured cumulated heat between 0.5 and 6 hours of all mortars tested is shown in table 6.

(28) TABLE-US-00008 TABLE 6 Molar Ca/Si Specific heat Difference to ratio in of hydration in corresponding Mortar Type Accelerator accelerator J/g mortar suspension (%) M1 Comparative 13.07 M2 Comparative CSH 2.1 1.17 40.97 0.0 M3 Comparative CSH-P 2.1 1.17 26.87 34.4 M4 Comparative CSH-P 2.1 1.17 27.03 34.0 M5 Inventive CSH-CH-P 2.1 1.17 38.61 5.8 M6 Comparative CSH 2.2 1.35 38.70 0.0 M7 Comparative CSH-P 2.2 1.35 30.81 20.4 M8 Comparative CSH-P 2.2 1.35 31.18 19.4 M9 Inventive CSH-CH-P 2.2 1.35 37.99 1.8 M10 Comparative CSH 2.3 1.50 37.81 0.0 M11 Comparative CSH-P 2.3 1.50 32.48 14.1 M12 Comparative CSH-P 2.3 1.50 33.22 12.1 M13 Inventive CSH-CH-P 2.3 1.50 37.17 1.7 M14 Comparative CSH 2.4 1.80 35.62 0.0 M15 Comparative CSH-P 2.4 1.80 32.34 9.2 M16 Comparative CSH-P 2.4 1.80 32.97 7.4 M17 Inventive CSH-CH-P 2.4 1.80 34.86 2.1

(29) The cumulated heat of hydration is calculated between 0.5 hours and 6 hours. To start the calculation beginning after 0.5 hours was made to eliminate errors in the measurement resulting from placing the sample into the calorimeter. The determination of the heat of hydration until 6 hours was made to describe the maximum acceleration which should be between 4 to 8 hours.

(30) As shown in table 6, the accelerators according to the invention show a performance which is only slightly lower as compared to the accelerators CSH 2.1 to CSH 2.4 (CSH suspension). M3 to M5 are representing the performance of powdered accelerators based on a suspension with a molar Ca/Si ratio of 1.17. M3 and M4 are comparative examples representing the accelerators of the prior art where the starting suspension (used in M2) is dried without further addition of calcium hydroxide. The performance of these powders is much lower compared to the corresponding powder M5 of the invention where the calcium hydroxide was added to the suspension before the drying step. Even an addition of the same amount of calcium hydroxide to a comparative powder (dried without addition of calcium hydroxide) in the mortar test (M4) cannot improve the performance of the non-inventive powder (CSH-P-2.1).

(31) A corresponding result is obtained with compositions M6 to M17.

(32) The mortar tests clearly show that independent from the initial molar Ca/Si-ratio of the corresponding suspension which is used for the production of the powdered accelerator of the invention, the addition of a Ca-salt before the drying step improves surprisingly the performance of the resulting accelerator powder.