METHOD FOR PRODUCING HIGHLY REACTIVE CEMENTS

Abstract

The invention relates to a method for producing cements by hydrothermally treating a starting material containing sources of CaO and SiO.sub.2 in an autoclave at a temperature of 100 to 300 C., and tempering the obtained intermediate product at 350 to 700 C., wherein water formed during tempering is dissipated by grinding the intermediate product and/or tempering taking place under a continuous gas stream. The invention also relates to cements obtained in this manner, hydraulic binders therefrom, and building materials which contain said binders.

Claims

1. Method for producing cement by means of hydrothermal treatment of a starting material, which includes sources for CaO and SiO.sub.2, in an autoclave at a temperature of 100 to 300 C., and tempering the obtained intermediate product at 350 to 700 C., wherein water formed during tempering is removed by the tempering taking place under a continuous gas flow to remove the water and/or the intermediate product being ground, in order to remove water formed during tempering.

2. The method according to claim 1, wherein the tempering takes place under a continuous gas flow to remove the water.

3. The method according to claim 1 wherein the tempering takes place at 400 to 495 C.

4. The method according to claim 1, wherein the intermediate product is ground for 0.1 to 30 minutes.

5. The method according to claim 4, wherein the grinding duration is 0.5 to 10 minutes, and in particular 1 to 5 minutes.

6. The method according to claim 1, wherein the grinding energy is limited in such a way that no or substantially no chemical and mineralogical conversions take place.

7. The method according to claim 1, wherein seed crystals containing calcium silicate hydrate, Portland clinker, ground granulated blast furnace slag, magnesium silicates, calcium sulphate aluminate (belite) cement, water glass, and/or glass powder are added for the hydrothermal treatment, preferably in an amount from 0.01 to 30% by weight.

8. The method according to claim 1, wherein, during tempering, during heating, a temperature ranging from 400 to 440 C. is maintained for 1 to 120 min.

9. The method according to claim 1, wherein, during tempering, a heating rate of 1 to 6000 C./rain and a residence time of 0.01 to 600 min are set.

10. Cement obtainable according to claim 1.

11. The cement according to claim 10, characterised in that wherein 20-100% of the following compounds are contained: x-Ca.sub.2SiO.sub.4, X-ray amorphous compounds of variable composition and -Ca.sub.2SiO.sub.4.

12. The cement according to claim 11, wherein >30% by weight of x-Ca.sub.2SiO.sub.4 and >5% by weight of X-ray amorphous compounds, and <20% by weight of -Ca.sub.2SiO.sub.4 are contained.

13. The cement according to claim 10, wherein is has a fineness (according to Blaine) of 2000 to 20000 cm.sup.2/g, preferably from 3000 to 6000 cm.sup.2/g and particularly preferred from 4000 to 5000 cm.sup.2/g.

14. A hydraulic binder containing the cement according to claim 10 and at least one of supplementary cementitious materials, admixtures and additives.

15. The hydraulic binder according to claim 14, wherein 5 to 95% by weight of supplementary cementitious material and 5 to 95% by weight of cement, preferably 30 to 85% by weight of supplementary cementitious material and 15 to 70% by weight of cement, particularly preferred 40 to 80% by weight of supplementary cementitious material and 20 to 60% by weight of cement are included, wherein the values are based on the total amount of binder and the proportions with all further binder components add up to 100%.

16. The hydraulic binder according to claim 15, wherein the supplementary cementitious material is selected from pozzolans and latent hydraulic materials, in particular tempered clays (e.g. metakaolin) and shale, V and W fly ashes with high glass proportion and/or amount of reactive phases, ground granulated blast furnace slags and artificial (pozzolanic and latent hydraulic) glasses, and mixtures of two or more thereof.

17. The hydraulic binder according to claim 14, wherein additives in an amount ranging from 1 to 25% by weight, preferably from 3 to 20% by weight and yet more preferably 6 to 15% by weight are contained, preferably selected from ground limestone/dolomite, precipitated CaCO.sub.3, Mg(OH).sub.2, Ca(OH).sub.2, CaO, silica fume, glass flour and mixtures thereof.

18. The hydraulic binder according to claim 14, wherein mixtures, preferably one or more setting and/or hardening accelerators and/or concrete water reducing agents and/or plasticizers and/or retarders are contained.

19. Construction material, in particular concrete, mortar, plaster, screed or joint sealant, containing the hydraulic binder according to claim 14, and aggregates.

Description

EXAMPLE 1

[0045] A starting material mixture was made of Ca(OH).sub.2 and highly dispersed SiO.sub.2 was produced in a molar ratio of 2:1. After the addition of 5% by weight of -2 CaO.SiO.sub.2.H.sub.2O as seed crystals, the mixture was homogenised with water. The ratio of water/solid was 10. An autoclave treatment at 200 C. for 16 h followed. Subsequently, a drying at 60 C. took place. The intermediate product contained 92% by weight of -2CaO.SiO.sub.2.H.sub.2O, 2% by weight of calcite, and 6% by weight of amorphous components.

[0046] The dry intermediate product was ground in a disc vibration mill for 1 min. for improved removal of water during tempering. No change of the phase composition of the intermediate product was determined by X-ray, as a result of the grinding. The hydraulic activity of the ground intermediate product was checked by means of heat flow calorimetry. The result is depicted in FIG. 3. After initial low heat release, this product did not display any kind of hydraulic activity. Thus, an activation by means of the grinding is excluded; it is not a reactive grinding.

[0047] The ground intermediate product was then converted into an end product according to the invention by tempering at 420 C. The end product consisted of 30% by weight of x-Ca.sub.2SiO.sub.4, 3% by weight of -Ca.sub.2SiO.sub.4, 3% by weight of calcite and 64% by weight of X-ray amorphous material. The corresponding X-ray diffractogram is depicted in FIG. 4. The end product was examined in terms of the hydraulic reactivity by means of heat flow calorimetry. The results are also depicted in FIG. 3. A high hydraulic reactivity was proven. As a result of the light grinding, an increase of the heat amount by approx. 40% after 3 days was achieved (in comparison to comparative example 2). The binder according to the invention could be mixed and processed with a water/binder ratio of 0.4.

COMPARATIVE EXAMPLE 2

[0048] The intermediate product from Example 1 was converted, without measures for removing water such as grinding or a gas flow, into an end product not according to the invention by tempering at 420 C. The end product consisted of 47% by weight of X-ray amorphous material, 30% by weight of x-Ca.sub.2SiO.sub.4, 20% by weight of -Ca.sub.2SiO.sub.4 and 3% by weight of calcite. The corresponding X-ray diffractogram is depicted in FIG. 3. The end product was examined in terms of the hydraulic reactivity by means of heat flow calorimetry. The results are also depicted in FIG. 4. The product not according to the invention shows a clearly lower heat release than the product according to the invention from Example 1. In order to mix the product to form a paste, a water/binder ratio of 1.5 was necessary.

EXAMPLE 3

[0049] A starting material mixture was made of Ca(OH).sub.2 and nano-SiO.sub.2 in the molar ratio of 2:1. After adding 5% by weight -2CaO.SiO.sub.2.H.sub.2O as seed crystals, the mixture was homogenised with water. The ratio of water/solid was 2. An autoclave treatment at 200 C. for 16 h followed. Subsequently, drying at 60 C. took place. The intermediate product contained 93% by weight of -2CaO.SiO.sub.2.H.sub.2O, 1% by weight of calcite, and 6% by weight of amorphous components.

[0050] The dry intermediate product was spread on a steel sheet for improved removal of water during tempering with a layer thickness of approx. 1 mm, i.e. with high surface/volume ratio, and tempered in the muffle furnace at 420 C. for 1 hour. Subsequently, an increase of the temperature to 495 C. takes place. This temperature was maintained for 1 h. The water vapour expelled could thus quickly escape and a low water vapour partial pressure was ensured. The end product according to the invention consisted of 17% by weight of X-ray amorphous material, 63% by weight of x-Ca.sub.2SiO.sub.4, 8% by weight of -Ca.sub.2SiO.sub.4, 11% by weight of -C.sub.2S and 1% by weight of calcite. The end product was examined in terms of the hydraulic reactivity by means of heat flow calorimetry. The results are depicted in FIG. 5.

COMPARATIVE EXAMPLE 4

[0051] The intermediate product from Example 3 was converted into a binder not according to the invention under increased water vapour partial pressure. For this, the intermediate product was wrapped by aluminium foil when tempering. This foil prevents a quick escape of the water vapour during tempering. Otherwise, the tempering took place as in Example 3. The product not according to the invention consisted of 17% by weight of X-ray amorphous material, 22% by weight of x-Ca.sub.2SiO.sub.4, 60% by weight of -Ca.sub.2SiO.sub.4 and 1% by weight of calcite. The end product was examined in terms of the hydraulic reactivity by means of heat flow calorimetry. The results are depicted in FIG. 5.

EXAMPLE 5

[0052] A starting material mixture was made of Ca(OH).sub.2 and highly dispersed SiO.sub.2 in the molar ratio of 2:1. After the addition as seed crystals of 5% by weight of -2CaO.SiO.sub.2.H.sub.2O, the mixture was homogenised with water. The ratio of water/ solid was 10. An autoclave treatment with constant stirring at 200 C. for 16 h followed. Subsequently, a drying at 60 C. took place. The intermediate product contained of 87% by weight of -2CaO.SiO.sub.2.H.sub.2O, 2% by weight of calcite, 2% by weight of scawtite and 9% by weight of amorphous components.

[0053] The dried intermediate product was mixed with 40% by weight of limestone flour (KSM) and ground in a planetary mill for 3 min. to improve the removal of water during tempering. Subsequently, a tempering at 420 C. took place. The result of measuring of the heat development by means of heat flow calorimetry is depicted in FIG. 6. Since limestone flour in this system can be considered to be inert, the reactivity of the end product is considerably increased as a result of the grinding together with limestone flour in comparison to the unground product (comparative example 6). The end product was able to be mixed with a water/binder ratio of 0.4 to form a paste.

[0054] The end product was examined in terms of the tensile strength development. The water/binder value (w/b) was set to 0.3 by using plasticizer. The strength was checked on cubes with an edge length of 4 cm. Strengths of 46 N/mm.sup.2 emerged after 2 days, 46 N/mm.sup.2 after 7% and 49 N/mm.sup.2 after 28 days.

COMPARATIVE EXAMPLE 6

[0055] The intermediate product from Example 5 was converted into an end product not according to the invention without grinding by tempering at 420 C. This consisted of 64% by weight of X-ray amorphous material, 7% by weight of x-Ca.sub.2SiO.sub.4, 23% by weight of -Ca.sub.2SiO.sub.4 and 5% by weight of calcite. The end product was examined in terms of the hydraulic reactivity by means of heat flow calorimetry. The results are depicted in FIG. 5. The end product not according to the invention requires a water/binder ratio of 1.4 in order to achieve a paste-like consistency.