CORE-SHELL EXPANDING AGENTS AND THEIR USE IN CEMENTITIOUS SYSTEMS

Abstract

Coated inorganic expanding agent particles comprise a core of an inorganic expanding agent and a sol/gel-formed coating comprising a mixed oxide of two or more metals and/or metalloids, in particular a mixed oxide of silicon and at least one metal and/or metalloid selected from aluminum, boron, titanium, zirconium and zinc. The coated inorganic expanding agent particles are added to cementitious systems to avoid shrinkage during hardening. The coating is effective to delay the expanding effect.

Claims

1. Coated inorganic expanding agent particles comprising a core or a plurality of cores of an inorganic expanding agent and a sol/gel-formed coating comprising a mixed oxide of two or more metals and/or metalloids.

2. The coated inorganic expanding agent particles of claim 1, wherein the inorganic expanding agent accounts for not less than 90% by weight of the core(s).

3. The coated inorganic expanding agent particles of claim 1, wherein the inorganic expanding agent is selected from calcium oxide, magnesium oxide, strontium oxide, barium oxide, and mixed oxides thereof, calcium sulfate hemihydrate, anhydrite, sodium sulfate, magnesium sulfate, phyllosilicates, and mixtures of two or more thereof.

4. The coated inorganic expanding agent particles of claim 3, wherein the inorganic expanding agent comprises not less than 90% by weight of at least one of calcium oxide and magnesium oxide.

5. The coated inorganic expanding agent particles of claim 1, wherein the sol/gel-formed coating comprises a mixed oxide of silicon and at least one other metal and/or metalloid selected from aluminum, boron, titanium, zirconium and zinc.

6. The coated inorganic expanding agent particles of claim 5, wherein the mixed oxide comprises 0.1 to 15.0% by weight, of the other metal and/or metalloid, relative to the sum of silicon and metal and/or metalloid calculated on an elemental basis.

7. The coated inorganic expanding agent particles of claim 1, having a particle size d(50) in the range from about 50 m to about 1000 m.

8. The coated inorganic expanding agent particles of claim 1, wherein the sol/gel-formed coating has a thickness in the range from about 0.5 m to about 50 m.

9. The coated inorganic expanding agent particles of claim 1, wherein the weight ratio between inorganic expanding agent and the sol/gel-formed coating is in the range from 15:1 to 1:2.

10. A method for preparing coated inorganic expanding agent particles according to claim 1, comprising (a) providing particles of an inorganic expanding agent, (b) depositing a sol from sol/gel-forming precursors on the particles of the inorganic expanding agent to form a film, (c) gelling the sol.

11. The method of claim 10, further comprising (d) subjecting the coated particles to a heat treatment.

12. The method of claim 10, wherein the sol/gel-forming precursors comprise at least a first sol/gel-forming component of a first metal(loid) and a second sol/gel-forming component of a second metal(loid).

13. The method of claim 10, wherein the first sol/gel-forming component is a silica precursor and the second sol/gel-forming component is selected from a sol/gel-forming compound of aluminum, boron, titanium, zirconium and/or zinc.

14. The method of claim 10, comprising preparing a first solution containing an acid-catalyzed sol/gel-forming component at a pH at which the acid-catalyzed sol/gel-forming component is stable, preparing a second solution containing a base-catalyzed sol/gel-forming component at a pH at which the base-catalyzed sol/gel-forming component is stable, combining the first solution and the second solution and depositing the mixed solution on the inorganic expanding agent particles.

15. The method of claim 14, wherein the first solution comprises a water-soluble alkali metal silicate at a pH of from 10 to 12, and the second solution comprises a sol/gel-forming compound of aluminum, boron, titanium, zirconium and/or zinc at a pH of from 1 to 5.

16. The use of the coated inorganic expanding agent particles of claim 1 as a constituent of building material formulations and/or for producing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0090] FIG. 1 is a schematic illustration of the production process for coated inorganic expanding agent particles.

[0091] FIG. 2 shows representative SEM images of the coated inorganic expanding agent particles after calcination. a. with silica shell (Ref.), b. with Si/Al-oxide (sample 6), c. with Si/B-oxide (sample 5) and d. with Si/B/Al-oxide (sample 7).

[0092] FIG. 3a shows cement expansion profiles of the inventive coated inorganic expanding agent particles in comparison with silica-coated expanding agents (Reference) for the full test period (>48 h); FIG. 3b shows expansion profiles of the initial 8 h.

[0093] The particle size d(50) Is determined by static light scattering (SLS) using a Malvern Mastersizer 2000 (Malvern Instruments GmbH, Germany). The software utilized for measurement and evaluation is the Malvern software package belonging to the instrument. The measurement principle is based on laser diffraction by measuring the intensity of light scattered as a laser beam passes through a particulate sample. This data is then analyzed to calculate the size of the particles that created the scattering pattern.

[0094] Quick Test for Determining the Expansion of the Expanding Agent Particles:

[0095] 3 g of the particles to be tested are placed in glass containers having a diameter of 2 cm and a height of about 8 cm. The particles are then dispersed in 10 ml of a 1 M NaOH by shaking and allowed to settle. The height of the sediment is determined. Thereafter, the particles are allowed to expand at 60 C. The height of the expanded particles is measured after a 5 days.

[0096] In the examples the following sodium water glasses were used:

[0097] NaSi 37/40: 8% Na.sub.2O, 26.8% SiO.sub.2 and 65.2% H.sub.2O; modulus 3.4; solids content 34.8%.

[0098] NaSi 40/42: 8.8% Na.sub.2O, 29.5% SiO.sub.2 and 61.7% H.sub.2O; modulus 3.4; solids content 38.3%.

EXAMPLE 1. SOL/GEL COATING WITH MIXED PRECURSOR SOLUTION

[0099] A basic precursor solution was prepared by diluting 75 parts of NaSi 40/42 with 25 parts of water with stirring. An acidic solution was prepared with boric acid or sodium aluminate in the concentrations and amounts given in tables 1 below. The acidic solution was added slowly with vigorous stirring to the basic precursor solution. The data are given in tables 1 below.

[0100] CaO/MgO particles (mixture in a molar ratio of 1:1) having a particle size d(50) of 40 m and a particle size distribution of (d(90) 200 m/d(10) 2 m) were placed into a pilot fluidized bed apparatus in which the particles were heated to 65 C. The basic precursor solution was sprayed onto the particles via bottom spray (air inlet temperature: 120-130 C.; outlet temperature: 65 C.; gas volume: 47 m.sup.3/h; drying gas velocity: 0.9-1.0 m/s; nozzle gas volume: 4-7.5 m.sup.3/h; nozzle pressure: 3.3 bar). The dried particles had a water content of <1% by weight.

[0101] All the coated particles described in the examples were calcined as following method. The coated particles were placed into ceramic crucibles and heated in a muffle furnace. The particles were heated within 2 h to the selected temperature (325 C.-350 C.). The selected temperature was maintained for 3 h and thereafter the particles were allowed to cool to room temperature within 3 h to 9 h.

TABLE-US-00001 TABLE 1 CaO/ Sam- MgO Water glass NaSi coating ple in kg solution in g in g relative Acidic Solution Ref. 2 NaSi 40/42 1810 500 20% 0.5M HCl 1448 g 75% 1 2 NaSi 40/42 1810 500 20% 4% boric acid 75% 1448 g 2 2 NaSi 40/42 1810 500 20% 4% boric acid 724 75% g + 1.3% NaAlO.sub.2 724 g .sup.2) The boric acid and sodium aluminate were mixed before spraying

EXAMPLE 2. SOL/GEL COATING BY ALTERNATING SPRAY OF PRECURSOR SOLUTIONS

[0102] A basic precursor solution was prepared by diluting 90 parts of NaSi 37/40 with 10 parts of water with stirring (sample 3) or using neat NaSi 37/40 (sample 4). The acidic solution was prepared with boric acid in the concentrations given in table 2 below. The basic precursor solution (BS) and the acidic solution (AS) were sprayed alternately in the following order: 40% of BS, 50% of AS, 40% of BS, 50% of AS, and 20% of BS.

TABLE-US-00002 TABLE 2 CaO/ Sam- MgO water glass NaSi coating ple in kg solution in g in g relative Acidic Solution 3 2 NaSi 37/40 1590 499 20% 4% boric acid 90% 1400 g 4 2 NaSi 37/40 1410 492 20% 4% boric acid 100% 1400 g

EXAMPLE 3. SOL/GEL COATING BY SIMULTANEOUS SPRAY OF PRECURSOR SOLUTIONS

[0103] A basic precursor solution was prepared by diluting 90 parts of NaSi 37/40 with 10 parts of water with stirring (sample 5) or diluting 75 parts of NaSi 37/40 with 25 parts of water with stirring (samples 6 and 7). The acidic solution was prepared with boric acid or sodium aluminate in the concentrations and amounts given in table 3 below.

[0104] The basic precursor solution and the acidic solution were sprayed simultaneously via the bottom nozzle (spraying upwards) and via the top nozzle (spraying downwards) respectively.

TABLE-US-00003 TABLE 3 CaO/ Sam- MgO water glass NaSi coating ple in kg solution in g in g relative Acidic Solution 5 2 NaSi 37/40 1590 499 20% 3.5% boric acid 90% 1590 g 6 2 NaSi 37/40 1890 495 20% 10% aluminum 75% sulfate 1890 g 7 2 NaSi 37/40 1890 495 20% 3% boric acid 75% 945 g 10% al. sulfate 945 g (total 1890 g) .sup.7) The boric acid and aluminum sulfate solutions were mixed before spraying

EXAMPLE 4. EXPANSION TEST OF THE CORE-SHELL EXPANDING AGENTS

[0105] The expansion test for concrete was carried out in accordance with DIN EN ISO 10426-5 by making a well cement slurry including 10% by weight of cement (bwoc) of the particles of the invention, 0.5% (bwoc) Liquiment K3F (dispersant, suffonated acetone resin), 0.6% bwoc Polytrol FL34 (fluid loss additive, modified polyacrylamide) and a small amount <0.1% by volume defoamer (triisobutylphosphate).

[0106] The percentage expansion over the time is shown in FIG. 3. As seen in FIG. 3, all core-shell expanding agents with a sot/gel-formed coating comprising a mixed oxide of B and Si, Al and Si or B/Al and Si showed retarded on-set time of expansion as compared to the reference sample with silica shell.