Belite-calcium aluminate as an additive

Abstract

The present invention relates to the use of a belite calcium aluminate obtainable in a method comprising the following steps: a) providing a starting material that has a molar Ca/(Si+Al+Fe) ratio from 1.0 to 3.5 and a molar Al/Si ratio from 100 to 0.1, b) mixing the raw materials, c) hydrothermal treating of the starting material mixture produced in step b) in an autoclave at a temperature from 100 to 300 C. and a residence time from 0.1 to 24 h, wherein the water/solids ratio is 0.1 to 100, d) tempering the intermediate product obtained in step c) at 350 to 600 C., wherein the heating rate is 10-6000 C./min and the residence time is 0.01-600 min
as an accelerator for Portland cement.

Claims

1. A method for accelerating the early stiffening/setting and/or the hardening of Portland cement comprising adding to the Portland cement a belite calcium aluminate accelerator produced according to the following steps: (a) providing one or more raw materials selected from the group consisting of Ca-, Al-, Fe-, and Si-containing solid materials, (b) mixing the raw materials to form a starting material mixture, wherein the starting material has a molar Ca/(Si+Al+Fe) ratio from 1 to 3.5 and a molar Al/Si ratio from 100 to 0.1, (c) hydrothermally treating the starting material mixture produced in step (b) in an autoclave at a temperature from 100 to 300 C. and a residence time from 0.1 to 24 hours, wherein a water/solids ratio is 0.1 to 100, to form an intermediate product, and (d) tempering the intermediate product obtained in step (c) at 350 to 600 C., wherein a heating rate is between 10-6000 C./min and a residence time is between 0.01-600 min to form the belite calcium aluminate accelerator.

2. The method according to claim 1, further comprising adding calcium sulfate to the Portland cement.

3. The method according to claim 2, wherein calcium sulfate is added in an amount from 10 to 40% by weight based on the accelerator.

4. The method according to claim 1, wherein the belite calcium aluminate accelerator comprises at least one compound selected from the group consisting of calcium silicate, calcium aluminate, calcium aluminium silicate, calcium (aluminium, iron) silicate, and at least one X-ray amorphous phase, wherein the sum of calcium silicates, calcium aluminates, calcium aluminium silicates and calcium (aluminium, iron) silicates is at least 30% by weight.

5. The method according to claim 1, wherein the belite calcium aluminate accelerator comprises the following components: 1-95% by weight reactive calcium aluminates, in the form of crystalline C.sub.12A.sub.7, or semi-crystalline or amorphous aluminate phases, 1-80% by weight calcium (aluminium, iron) silicates, in the form of crystalline, semi-crystalline or amorphous phases, 1-80% by weight C.sub.2S polymorphs, in the form of crystalline, semi-crystalline or amorphous phases, 1-80% by weight calcium aluminate silicates, in the form of crystalline, semi-crystalline or amorphous phases, up to 30% by weight traces and minor components, and 0-30% by weight hydrates from the step (c) hydrothermal treatment.

6. The method according to claim 5, wherein the traces and minor components are one or more compounds selected from the group consisting of C.sub.5A.sub.3, CA, calcium oxide, aluminas, quartz, limestone, CaO, calcium sulfate, FeO, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, iron silicates, Fe.sub.2SiO.sub.4, and amorphous iron-containing phases.

7. A binder containing Portland cement and an accelerator consisting of a belite calcium aluminate produced according to the following steps: (a) providing one or more raw materials selected from the group consisting of Ca-, Al-, Fe-, and Si-containing solid materials, (b) mixing the raw materials to form a starting material mixture, wherein the starting material has a molar Ca/(Si+Al+Fe) ratio from 1 to 3.5 and a molar Al/Si ratio from 100 to 0.1, (c) hydrothermally treating the starting material mixture produced in step (b) in an autoclave at a temperature from 100 to 300 C. and a residence time from 0.1 to 24 hours, wherein a water/solids ratio is 0.1 to 100, to form an intermediate product, and (d) tempering the intermediate product obtained in step (c) at 350 to 600 C., wherein a heating rate is between 10-6000 C./min and a residence time is between 0.01-600 min to form the accelerator.

8. The binder according to claim 7, wherein a measured Brunauer-Emmett-Teller surface area of the binder ranges from 1 to 30 m.sup.2/g.

9. The binder according to claim 7, wherein the binder further contains latent hydraulic materials and/or pozzolans.

10. The binder according to claim 7, wherein the binder further contains metakaolin and/or limestone.

11. The binder according to claim 7, wherein the belite calcium aluminate comprises at least one calcium silicate, calcium aluminate, calcium aluminium silicate, calcium (aluminium, iron) silicate, and at least one X-ray amorphous phase, wherein the sum of calcium silicates, calcium aluminates, calcium aluminium silicates and calcium (aluminium, iron) silicates is at least 30% by weight.

12. The binder according to claim 7, wherein the belite calcium aluminate comprises the following components: 1-95% by weight reactive calcium aluminates, in the form of crystalline C.sub.12A.sub.7, or semi-crystalline, or amorphous aluminate phases, 1-80% by weight calcium (aluminium, iron) silicates, in the form of crystalline, semi-crystalline, or amorphous phases, which may contain foreign ions such as Ca, Fe and Al 1-80% by weight C.sub.2S polymorphs, in the form of crystalline, semi-crystalline, or amorphous phases, 1-80% by weight calcium aluminate silicates, in the form of crystalline, semi-crystalline or amorphous phases, up to 30% by weight traces and minor components, and 0-30% by weight hydrates from the step (c) hydrothermal treatment.

13. The binder according to claim 12, wherein the traces and minor components are one or more compounds selected from the group consisting of C.sub.5A.sub.3, CA, calcium oxide, aluminas, quartz, limestone, CaO, calcium sulfate, FeO, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, iron silicates, Fe.sub.2SiO.sub.4, and amorphous iron-containing phases.

Description

EXAMPLE 1

(1) A starting material mixture containing 35.44% CaO and 64.56% Geloxal was produced from the raw materials listed in Table 1.

(2) TABLE-US-00001 TABLE 1 Raw material CaO Geloxal Loss on ignition at 0% 45.65% 1050 C. SiO.sub.2 Al.sub.2O.sub.3 .sup.50% TiO.sub.2 MnO Fe.sub.2O.sub.3 CaO 100% 0.14% MgO 0.10% K.sub.2O Na.sub.2O 1.14% SO.sub.3 0.38% P.sub.2O.sub.5

(3) The starting material mixture was mixed with water at a water/solids ratio of 10, and was treated for 16 hours at 185 C. and 1.1 MPa in a high-grade steel autoclave. The intermediate products were tempered for 1 hour at 500 C. Mixtures of 10% of the obtained accelerator with Portland cement and of 10% of the accelerator and 3% gypsum with Portland cement were reacted in a calorimeter to check the hydraulic reactivity with a water/solids ratio of 0.5. For comparison, pure Portland cement with the same water/solids ratio was used. The obtained heat flows and cumulative heat flows are shown in FIG. 1. In the figure, OPC denotes pure Portland cement, OPC+accelerator denotes the mixture of OPC and the accelerator according to the invention, and OPC+accelerator+gypsum denotes the mixture of OPC, accelerator and gypsum.

(4) It can be seen that the binder accelerated in accordance with the invention is very reactive and that even small amounts of the accelerator accelerate the hydration of Portland cement. The main peak of the heat development is clearly shifted to the left, that is to say the heat development initiates more quickly. The cumulative heat flow determined after 8 hours for the binder with accelerator and gypsum is twice as high as that for pure Portland cement. After 16 hours it is still 40% more.

EXAMPLE 2

(5) A starting material mixture containing 62.5% Portlandite, 20.27% quartz and 17.23% Geloxal was produced from the raw materials listed in Table 2 and reacted in accordance with Example 1 to form an accelerator.

(6) TABLE-US-00002 TABLE 2 Raw material Portlandite Quartz Geloxal Loss on ignition at 24.33% 45.65% 1050 C. SiO.sub.2 100% Al.sub.2O.sub.3 .sup.50% TiO.sub.2 MnO Fe.sub.2O.sub.3 CaO 75.67% 0.14% MgO 0.10% K.sub.2O Na.sub.2O 1.14% SO.sub.3 0.38% P.sub.2O.sub.5

(7) The hydraulic reactivity was checked as in Example 1. The measured heat flows and cumulative heat flows are illustrated in FIG. 2.

(8) It can be seen that again the main peak of the heat flow is earlier, that is to say the heat development initiates more quickly. The cumulative heat flow for the binder with accelerator and gypsum, after 8 hours, is 113% of that measured for pure Portland cement. It is still 38% higher after 16 hours.

EXAMPLE 3

(9) A starting material mixture containing 66.55% Portlandite, 24.28% quartz and 9.17% Geloxal was produced from the raw materials listed in Table 2 and reacted in accordance with Example 1 to form an accelerator. The hydraulic reactivity was checked as in Example 1. The measured heat flows and cumulative heat flows are shown in FIG. 3.

(10) It can be seen that the main peak of the heat flow is also earlier here, that is to say the heat development initiates more quickly. The cumulative heat flow for the binder with accelerator and gypsum, after 8 hours, is 72% of that measured for pure Portland cement. It is still 25% higher after 16 hours.

(11) It is clear from the examples that the accelerator according to the invention leads to binders based on Portland cement that have high early strength, that is to say the hardening can be significantly accelerated. Energy use and CO.sub.2 emissions can be lowered compared with accelerators based on yeelimite, for example.