COMPOSITION FOR AERATED OR LIGHTWEIGHT CONCRETE

Abstract

Aqueous compositions may be used preparing special concretes like aerated concrete or lightweight concrete. Such an aqueous composition for preparing such concretes, may combine water, a hydraulic binder, and an aggregate that is ground in the presence of a particular anionic polymer. The ground aggregate is selected from slag, fly ash, sand, and combinations thereof.

Claims

1. An aqueous composition (C) suitable for preparing aerated concrete or for preparing lightweight concrete, the composition (C) comprising: water; an aggregate (A) comprising a silicon dioxide comprising material ground in the presence of an aid comprising a polymer (P) having a molecular weight M.sub.w, measured by SEC, of less than 20,000 g/mol and a polymolecularity index (PI) of less than 3.5, the polymer being prepared by a radical polymerization reaction in water or in a solvent, at a temperature of at least 20° C., of a polymerization mixture comprising (i) an anionic monomer (M) comprising a polymerizable olefinic unsaturation and a carboxylic acid group, (ii) a radical-generator comprising hydrogen peroxide, ammonium persulfate, tertiobutyl hydroperoxide, an alkaline metal persulfate, (iii) optionally, an ion comprising Fe.sup.II, Fe.sup.III, Cu.sup.I, and/or Cu.sup.II and (iv) optionally, sodium bisulfite, potassium bisulfite, ammonium bisulfite, sodium hypophosphite, potassium hypophosphite, ammonium hypophosphite, and/or disodium 2,2′-(thiocarbonylbisthio)dipropanoate (DPTTC); and a hydraulic binder (B).

2. The composition of claim 1, wherein the aggregate (A) comprises at least 10 wt. % of silicon dioxide.

3. The composition of claim 1, wherein the polymer (P): has a weight-average molecular weight M.sub.w of less than 15,000 g/mol; or has a weight-average molecular weight M.sub.w greater than 1,000 g/mol; or has a polymolecularity index (PI) of less than 3.2.

4. The composition of claim 1, wherein the anionic monomer (M) comprises acrylic acid, methacrylic acid, an acrylic acid salt, and/or a methacrylic acid salt.

5. The composition of claim 1, wherein the polymerization reaction is carried out with: 100 wt. % of the anionic monomer (M); or the anionic monomer (M) in a range of from 70 to 99.5 wt. % and at least one further monomer in a range of from 0.5 to 30 wt. %.

6. The composition of claim 1, wherein the hydraulic binder (B) comprises cement, Portland cement, aluminous cement, calcium sulfoaluminate cement, and/or cement as defined in EN 197-1 standard.

7. The composition of claim 1, comprising: the water in a range of from 20 to 45 wt. %; the aggregate (A), in ground form, in a range of from 35 to 70 wt. %; and hydraulic binder (B) in a range of from 10 to 20 wt. %.

8. The composition of claim 1, further comprising: a further aggregate.

9. The composition of claim 1, that is: an aqueous composition (C1) suitable for preparing an autoclaved aerated concrete and further comprising (v) an expansion agent and (vi-a) lime and/or (vi-b) a lime comprising material; or an aqueous composition (C2) suitable for preparing a foam concrete and further comprising (vii-a) a foaming agent or (vii-b) an air-entraining agent.

10. The composition of claim 9, wherein the composition (C1) is present and comprises: the water in a range of from 20 to 45 wt. %, the aggregate (A), in ground form, in a range of from 35 to 65 wt. %, the hydraulic binder (B) in a range of from 10 to 20 wt. %, the lime comprising material (vi-b) in a range of from 3 to 9.98 wt. %, and the expansion agent (v) in a range of from 0.02 to 2 wt. %.

11. The composition of claim 9, wherein the composition (C2) is present and comprises: the water in a range of from 20 to 45 wt. %, the aggregate (A), in ground form, in a range of from 35 to 65 wt. %, the hydraulic binder (B) in a range of from 10 to 20 wt. %, the foaming agent (vii-a) or air-entraining agent (vii-b) in a range of from 5 to 10 wt. %.

12. An aerated or lightweight concrete item that is: an autoclaved aerated concrete item prepared by a method comprising: (A) casting the composition of claim 9 comprising the composition (C1), to obtain a casted composition, and (B) heating and pressurizing the casted composition, or a foamed concrete item prepared by a method comprising: (A) casting the composition of claim 9 comprising the composition (C2), to obtain a casted composition; and (B) drying the casted composition.

13. An aggregate (A) suitable for preparing an aerated concrete composition or a lightweight concrete composition, comprising composition of claim 1.

14. A method for preparing the aggregate (A) of claim 13, the method comprising: grinding a silicon dioxide comprising material in the presence of the polymer (P), wherein the polymolecularity index (PI) is less than 3.

15. A method for preparing an aqueous formulation of the composition (C) of claim 1, the method comprising: reducing an amount of the binder (B) compared to a similar composition wherein the aggregate (A) has not been ground in the presence of the polymer (P).

16. The composition of claim 2, wherein the aggregate (A) is slag, fly ash, sand, or a combination thereof.

17. The composition of claim 1, wherein the aggregate (A) is ground in the presence of at least one polymer (P), prior to its addition to the composition.

18. The composition of claim 1, wherein the aggregate (A) has an average particle size below 149 μm.

19. The composition of claim 1, wherein the aggregate (A) has less than 15 wt. % of particles having an average particle size above 74 μm.

Description

PREPARATION OF POLYMER (P1) USED ACCORDING TO THE INVENTION

[0104] Polymer (P1) according to the invention is prepared into a one liter glass reactor, equipped with mechanical stirring and an oil bath heating, by introducing 212 g of water and 0.08 g of a sodium salt of heptahydrated sulfate iron.

[0105] In a 500 mL beaker fitted with a metering pump, 303 g of 100% by weight acrylic acid and 15 g of water, are introduced.

[0106] 25.6 g of sodium hypophosphite monohydrate dissolved in 30 g of water are introduced into a 100 mL test tube fitted with a dosing pump.

[0107] 21 g of 130 V hydrogen peroxide and 35 g of water are introduced into a 100 mL test tube fitted with a dosing pump.

[0108] The reactor is heated to 95° C. and acrylic acid, hypophosphite solution and hydrogen peroxide solution are added in parallel over 120 min while maintaining the temperature of the reaction medium at 95° C. Finally, the pumps are rinsed with water and the medium is heated for 60 min to 95° C.

[0109] The polymer solution is then treated up to pH 8, using sodium hydroxide 50% by weight in water, and then diluted to a dry extract of 42% by weight. Resulting polymer (P1) has a molecular weight (Mw measured by SEC) of 4,800 g/mol and an IP of 2.2.

Preparation of Ground Aggregate (A) according to the Invention Starting from Fly Ash

[0110] An aqueous suspension (S1) of aggregate (A) is prepared starting from fly ash originating from fine solid particles in flue gas ash produced by fuel combustion (200 g), that is mixed with water (80 g) and polymer (P1) (2 g as dry matter) into a 0.5 L jar containing ceramic beads (type aluminum oxide, diameter 2 cm) (200 g) as grinding media. Grinding time is 5 min. Suspension (Si) has a solid content of 54%.

[0111] A comparative suspension (CS1) is prepared in the same manner without any polymer (P1). Comparative suspension (CS1) has a solid content of 54%.

[0112] A second aqueous suspension (S2) according to the invention is prepared from aggregate (A) similarly than suspension (S1) while using a reduced amount of water (35 g).

[0113] Suspension (S2) according to the invention has a solid content of 64%.

[0114] According to the invention, properties of the prepared suspensions are evaluated by measuring fluidity, density and granulometry.

[0115] Fluidity is measured by flow test mold of which the diameter is 3 cm and the height is 5 cm.

[0116] Density is measured by density cup which the volume is 100 mL.

[0117] Granulometry is measured by 200 mesh sieve. The amount of aggregate particles having a size greater than 200 mesh (74 μm) is weighted.

[0118] Results are displayed in table 1.

TABLE-US-00001 TABLE 1 Suspension Fluidity (mm) Density (g/ml) Granulometry (wt. %) CS1 180 1.43 7.4 S1 230 1.43 6.6 S2 190 1.59 5.5

[0119] Using polymer (P1) during the preparation of suspensions (S1) and (S2) according to the invention allows maintaining or improving fluidity, density and granulometry in comparison to comparative suspension (CS1).

Preparation of Ground Aggregate (A) according to the Invention Starting from Slag

[0120] An aggregate (A) aqueous suspension (S3) is prepared starting from slag originating from the by-products in the process of blast furnace iron making (200 g) that is mixed with water (160 g) and polymer (P1) (2 g as dry matter) into a 0.5 L jar containing ceramic beads (type aluminum oxide, diameter 2 cm) (300 g) as grinding media. Grinding time is 10 min. Suspension (S3) has a solid content of 54 wt. %.

[0121] A comparative suspension (CS2) is prepared in the same manner without any polymer (P1). A further comparative suspension (CS3) is prepared similarly than comparative suspension (CS2) with an increased amount of water (220 g). Suspension (CS3) has a solid content of 47 wt. %.

[0122] Properties of the prepared suspensions are evaluated by measuring fluidity, density and granulometry. Results are displayed in table 2.

TABLE-US-00002 TABLE 2 Suspension Fluidity (mm) Density (g/ml) Granulometry (wt. %) CS2 80 1.47 13 S3 170 1.47 11 CS3 150 1.38 17

Preparation of Ground Aggregate (A) According to the Invention Starting from Sand

[0123] An aggregate (A) aqueous suspension (S4) is prepared starting from river sand (200 g) that is mixed with water (100 g) and polymer (P1) (2 g as dry matter) into a 0.5 L jar containing ceramic beads (type aluminum oxide, diameter 2 cm) (300 g) as grinding media. Grinding time is 10 min. Suspension (S4) has a solid content of 64 wt. %.

[0124] A comparative suspension (CS4) is prepared in the same manner without any polymer (P1). A further comparative suspension (CS5) is prepared similarly than comparative suspension (C S4) with an increased amount of water (160 g). Suspension (CS5) has a solid content of 54 wt. %.

[0125] Properties of the prepared suspensions are evaluated by measuring fluidity, density and granulometry. Results are displayed in table 3.

TABLE-US-00003 TABLE 3 Suspension Fluidity (mm) Density (g/ml) Granulometry (wt. %) CS4 95 1.66 11 S4 210 1.66 10 CS5 210 1.49 15

[0126] Aerated or lightweight concrete compositions according to the invention can then be prepared by incorporating different aggregates (A) ground according to the invention, in combination with a cement binder (B) and water. Improved granulometry of aggregate suspensions prepared according to the invention allows improving properties of the concrete compositions so prepared. In particular, the reduced amount of ground aggregate particles having a size greater than 200 mesh (74 μm) in the suspension prepared while using polymer (P1) allows preparing aerated or lightweight concrete compositions having improved mechanical properties thus allowing obtaining improved concrete items.

[0127] Improving granulometry of the ground aggregate also allows reducing the amount of binder that is required for obtaining an aerated or lightweight concrete composition having acceptable specifications in the manufacture of aerated or lightweight concrete items. Higher solid content of the aggregate suspension prepared according to the invention also results in aerated or lightweight concrete compositions having a reduced content in water, hence allowing a reduction in binder consumption.

[0128] In addition, improved granulometry allows reducing or eliminating poor dispersion, segregation risk or bleeding risk due to the presence of large amounts of aggregate particles having an excessive particle size.