CZ2015882A3 - A method of preparation of a non-clinker hydraulic binder - Google Patents

Abstract

A process for the preparation of a non-sintered hydraulic binder by mixing the coal fly ash with ground limestone, which in addition to the aluminosilicate substance also contains at least 2 wt. % of free CaO and at least 2 wt. CaSO4, or mixtures thereof with substances selected from the group consisting of silica fly ash and Ca (OH) 2, with water containing a plasticizer to improve the rheological properties at a concentration of 0.2 to 3 % by weight, based on the weight of the fly ash, according to the invention, in that the fluidized ash from the combustion of coal with ground limestone is artificial to a specific surface area of 350 to 650 m.sup.2 / kg. The mixing water is mixed with the ground fluid ash or its mixture in a weight ratio of 0.2 to 0.65. Fluid fly ash is artificial prior to mixing with Ca (OH) 2 and / or silica fly ash or is mixed with Ca (OH) 2 and / or silica fly ash. The mixing water contains a plasticizer which is selected from the group consisting of sulfonated melamine polymers with formaldehyde, polycarboxylate polymers, or phosphonate polymers.

Description

Method of preparation of clinker-free hydraulic binder

Field of technology

The invention relates to a process for the preparation of a clinker-free hydraulic binder.

Prior art

In the production of electricity by burning coal and subsequent desulphurisation of flue gases, fly ash and gypsum are formed as the main secondary products. Fly ash is formed during the combustion of coal at temperatures above 950 ° C (often above 1100 ° C).

In the case of fluidized bed combustion of coal, desulphurisation can be carried out by mixing the ground coal with ground limestone to produce fluidized ash. These products are produced worldwide in huge quantities.

Fly ash (in the sense of ČSN EN 450, ČSN 72 2071 ... called silica fly ash) is formed during the combustion of coal in thermal power plants. They are non-combustible coal residues and their chemical, mineralogical composition and morphology depend on the composition of the coal and the combustion conditions. The chemical composition is different and ranges in a relatively wide range (calculated on oxides) S1O210 to 5%, Al2O3 19 to 30%, Fe ₂ O ₃ 5 to 1%, CaO 2 to 20%, MgO 0.3 to 2%. ₀ , SO ₃ 0.1 to 0.9%. They may contain a number of other elements, depending on the location of the coal. The fly ash contains a glassy or strongly sintered phase based on silicates, which contains a number of elements, especially Al, Ca, Mg, Fe and others. They also contain crystalline minerals such as mullite, quartz, hematite and many others depending on the composition of the coal and the combustion conditions. The morphology of the fly ash particles is also varied, with the spherical shape of the particles occurring most often.

Power plant fly ash is a substance that has latent hydraulic properties. When hydrated in a mixture with Ca (OH) 2 resp. Portland cement produces hydrates similar to those formed by the reaction of Portland cement with water. These are the C-S-H phases, gehlenite hydrate, hydrogranates and others. This fact has been used since the 1930s, when concrete resp. it successfully adds power plant fly ash to mixed cements.

Extensive reviews of the current state of utilization of fly ash were published: in M. Ahmaruzzaman „A review on the utilization of flyash, Progress in Energy and Combustion Science, volume 36, No. 3, June 2010, pp. 327-363, in ZT Yao, XS Ji-, PK Sarker, J.Η. Tang ³ , LQ Ge, MS Xia, YQ Xi: A comprehensive review on the applications of coal fly ash, EarthScience Reviews Volume 141, February 2015, Pages 105-121 a v RS Blissett-, NA Rowson: A review of the multi- component utilization of coal fly ash, Fuel Volume 97, July 2012, Pages 123

Another product is fluid fly ash, which is formed during the fluid combustion of coal. In the Czech Republic and in some other countries, fluidised bed combustion is combined with flue gas desulphurisation by mixing ground coal with ground limestone. Fluid ash particles (according to ČSN 72 2080 „Fluid ash and fluid ash for construction purposes) are solid residues of fluid combustion of coal, mixtures of mineral fraction of coal and desulphurisation products formed by reactions of sorbent (eg limestone, dolomite) with sulfur dioxide (their formation temperature does not exceed 850 ° C). Fluid fly ash (according to ČSN 72 2080), unlike fly ash, contains CaSCU, and therefore the term calcium sulphate fly ash is more suitable for its marking. Fluid ash is composed of a chemically heterogeneous mixture. This mixture contains CaSCU in the form of high-temperature anhydrite Ah, CaO and partially sintered aluminosilicate particles formed from non-combustible parts of coal, which dehydrate or burn with combustion. they decarbonize and partially sinter. During combustion, no glassy (liquid) phase is formed as in the case of fly ash. It is converted into partially sintered products that contain Si, Al, Fe and other elements. Depending on the composition of the coal, the product may contain a number of other minerals such as quartz and hematite. Reaction products of CaO with non-combustible parts of coal which contain Si, Al minerals may also be present in the fluid calcium sulphate fly ash. Then limited formation of Ca silicates, aluminates and ferrites may occur. CaO has a similar morphology in fluid calcium sulphate fly ash as soft-burnt lime. There are also residues of layered structures of dehydrated and partially sintered clay minerals in fluid calcium sulphate fly ash. Their morphology and composition correspond to the metastable product in the firing of kaolinite - metakaolin.

Part of the calcium sulphate fluid ash falls onto the grate of the combustion boiler, where its particles agglomerate and a denser product is formed - fly ash.

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In contrast to silica fly ash, sulphated fly ash reacts with water. Hydration produces mainly acicular ettringite Ca ₆ Al ₂ (SO ₄ ) ₃ (OH) ₁₂ .26H ₂ O, gypsum CaSO ₄ .2H ₂ O. After solidification of the mixture of fluid ash with water, a material with measurable strengths (of the order of MPa) is formed. . However, the material is unstable in volume due to the further growth of ettringite crystals and cracks and destruction occur.

There are a number of standards for fly ash that define its composition. They define limits for SiO ₂ content, active SiO ₂ content (ČSN EN 197-1), CaO content (CSA A3001), SiO2 + AI ₂ 03 + Fe ₂ O ₃ content (ASTM C 618). All standards strictly limit the SO ₃ content to the maximum value

M.

3t-5%.

Fluid (calcium sulphate) fly ash does not meet these standards, and therefore its use for the production of concrete is still unacceptable.

The use of fluid fly ash as an additive in cements, mortars and concretes is associated with the risk of expansion reactions, reduction of strength and subsequent destruction. Therefore, fluid fly ash is used only to a small extent, mainly as a component of solidifying or reinforcing layers. Most of the fluid ash is deposited.

Research into the possibilities of preparing materials from fluid fly ash is the subject of ongoing research work, as evidenced by data from the literature.

· /

From CZ 299539 a mixture of binder and filler for the production of solid, water-stable and non-flammable building materials and products is known, which contains fluidized bed ash with the addition of natural bentonite, the predominant component of which is montmorillonite, in a weight ratio of 9: 1 . The mixture further comprises a filler selected from the group consisting of quartz sand from floating kaolin, crushed stone, blast furnace slag, steel slag, fine mica abrasion and natural shale, the specific surface area of the particles of this mixture without alkaline components ranging from 600 to 2000 m ^ g ¹ .

CN101643328 discloses a composition of a mixture of 15 to 50% fluid fly ash from desulphurisation processes, 44 to 83% Portland cement clinker and 2 to 6% gypsum.

A binder, in particular cement, is known from CZ 2008-662, characterized in that it contains /

based on the weight of the mixture up to 99% by weight of cement clinker, from 0.5 to 99% by weight.

fluid ash, up to 99% by weight, silica ash and / or calcium ash and / or other components selected from the group consisting of slag, pozzolans, tuffs, diatomaceous earth and the like, the remainder being impurities.

Furthermore, a dry binder composition for the production of mortars containing cement and / or lime hydrate is known from document number 20-316 U1, characterized in that it consists of up to 75% by weight of fluid fly ash, the remainder up to 100% by weight being cement or lime hydrate and or a suitable combination thereof. Furthermore, this mixture may contain fibrous reinforcement in an amount of up to 0.5% by weight, which is intended to prevent the formation of cracks due to volume changes (expansion).

A hydraulic binder based on fluid fly ash is known from CZ 22 ^ 922 U1, characterized in that it contains fluid fly ash and lime hydrate in a mutual weight ratio ranging from 2 ^ 6 fly ash: 75 ^ 6 lime hydrate to 65% fly ash. : 35 ^ 6 lime hydrate and has a hydraulic modulus in the range Mh = 3.0 to Mh = 1.0. Furthermore, a hydraulic binder with a specified ratio of fly ash: lime hydrate and a specified Mh. This binder shows volume changes (expansion) in the range of +3 to 3.9 percent (shown in the examples).

Thermal hydrothermal treatment of fluid fly ash at temperatures higher than 100 ° C, optimally at 175 to 230 ⁰ C in an autoclave from the works "Cementitious Materials Based on Fluidized Bed Coal Combustion by Havlica J., Odler 1., Brandštetr J., Mikulíková R ., Walther D. in Advances Cem. Res.16 (2004), no. 2, pp. 614s67 and „Durability of autoclaved aerated concrete produced from fluidized fly ash by Drábik M., Balkovic S., Peteja M. in Cement-Wapno-Gips p.29i33, no.7, 2011.

Furthermore, I know from CZ 305487 a method for processing energy products - fluid ash from the process of fluidized bed combustion of coal with ground limestone, wherein the fluid ash contains in addition to _______ τ *.

aluminosilicate materials also ^having at least 2 wt ^ of free CaO and at least 2 wt ^r) 6 CaSO4. A mixture of fluid ash with water containing a plasticizer, preferably based on carboxylates or phosphonate derivatives, is prepared to improve theological properties in a concentration of _0.2 to 3% by weight, based on the weight of the fluid ash, and further added 2 to 30% by weight, based on the weight of the fluid ash, of the lime hydrate, wherein the water / fluid ash ratio is 0.5 to 1.5. The prepared mixture is stored at 0 _; 5 to 4 hours at 15 to 25 ° C and then left for 2 to 36 hours in hot water vapor at 40 to 95 ° C, or allowed to freeze at normal temperature.

- 5 Summary of the Invention

Process for the preparation of a clinker-free hydraulic binder by mixing fluid ash from coal combustion with ground limestone, which contains, in addition to aluminosilicate, also at least 2 to 6 wt. of free CaO and at least wt. CaSCU, or mixtures thereof with substances selected from the group consisting of silica fly ash and Ca (OH) 2, with mixing water containing a plasticizer to improve theological properties in a concentration of 0.2 to 3% by weight, based on the weight of the fluid fly ash, consists in that the fluid ash from the combustion of coal with ground limestone is artificially ground to a specific surface area of 350 to 650 m ² / kg.

The mixing water is mixed with the ground fluid ash or a mixture thereof in a weight ratio of 0.2 to 0.65.

A maximum of 20% by weight can be added to the fluid ash before mixing with the mixing water. Ca (OH) 2, based on the mixture of fluid ash and Ca (OH) 2, or a maximum of 50 wt. of silica fly ash, based on the weight of the mixture of fluid fly ash and silica fly ash.

A maximum of 70% by weight of 6% by weight can also be added to the fluid ash before mixing with the mixing water. of silica fly ash and Ca (OH) 2, based on the weight of the mixture of silica fly ash and Ca (OH) 2 and fluid fly ash.

The fluid ash is artificially ground or mixed together with Ca (OH) 2 and / or silica fly ash prior to mixing with Ca (OH) 2 and / or silica fly ash.

The mixing water contains a plasticizer which is selected from the group consisting of sulfonated polymers of melamine with formaldehyde, the basic unit of which has the formula I,

polymers of polycarboxyether ethers containing basic units of general formulas II and III,

R

- _c -C - O o

I (EO) _a

Me

Ii QiiiJ <3 L where M = metal, Me = methyl group, E0 = oxyethylene group, R = methyl group or H, for example polyethylene glycol monomethyl ether, or polymers of phosphonates, where the basic unit is after ₃ h ₂ '''' CHj

for example polyoxyethylene aminodiphosphonate.

Based on extensive experiments, it has been found that a binder containing ground fluid fly ash from burning coal with ground limestone achieves significantly better properties than the known state of processing fluid fly ash from burning coal with limestone. The grinding of fluid fly ash is reflected in the improvement of the properties of the binder:

• The water coefficient (water to binder ratio) required to achieve acceptable workability of slurries, mortars and concretes is significantly lower than for mixtures of unground fluid ash. Reducing the water content and increasing the reactivity of the fluid fly ash by milling will result in a significant increase in the strength of the mixtures after hardening.

• The mixing time of slurries, mortars and concretes is shortened due to the reduced absorbency of ground fluid ash. The mixing time of the mixtures with unground fluid ash ranges from 10 to 45 minutes to achieve an acceptable consistency. Long mixing time of mixtures

with unground fluid ash is due to the fact that part of the water is soaked into the porous particles of the fluid ash and is lost due to the processability of the mixtures.

• Mixtures containing ground fluid fly ash achieve high strengths even during hardening in the iJi range.

temperatures of 15-25 ° C, thus eliminating the need for a hydrothermal process to achieve higher initial strengths.

• The grinding of fluid fly ash creates the potential possibility of processing the ground fluid fly ash itself without other mineral additives, in contrast to the hitherto known solution according to CZ 30 ^ 487.

For the processing of a binder containing ground fluid ash from the combustion of coal with ground limestone, it is necessary to use plasticizers, for example sulfonated melamine derivatives, polymers of polycarboxyether ethers, polymers of phosphonates.

The binder can be allowed to solidify freely at normal temperatures after processing, or it can be subjected to hydrothermal curing conditions, e.g., 12-24 hours at 60-80 ° C. Fluid ash from coal combustion with ground limestone and silica ash can be ground simultaneously before preparation of the binder, possibly also in a mixture with Ca (OH) 2. The binder can be used in the form of slurries, mortars and concretes.

Overview of pictures

Giant. 1a shows the pore size distribution in fluid fly ash from the combustion of coal with ground limestone, 1 ... unground fly ash, 2 ... ground fly ash. Hg porosimetry

Giant. Ib, c, d show particles of unground and ground fluid ash from the combustion of coal with ground limestone in electron microscope images.

Giant. 2 shows the dependence of the water coefficient at which the consistency of the liquid slurry is achieved on the specific surface of the ground fluid ash.

Giant. 3 shows the dependence of the compressive strength on the method of laying the mortar bodies prepared according to Example 3.

Giant. 4 shows the dependence of the compressive strength on the method of laying the mortar bodies prepared according to Example 5.

Giant. 5 shows the dependence of the volume change on beams measuring 4x4x16 cm in a time period of 10 to 560 days and on the method of storing beams prepared according to Example 7.

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*. » * · *> I ě *

Exemplary embodiments

Example 1

Fluid ash from coal combustion with ground limestone was ground in a ball mill to a specific surface area of 530 m ² / kg. The results from high-pressure Hg porosimetry show that the particles of these fly ash are porous and have the character of clusters - Fig. 1a. By grinding the fluid ashes from coal combustion with the ground ashes, the agglomerates are broken up, and thus the pore size distribution is changed. The scanning electron microscope images of Figs. 1b, c, d show a change in the character of the fluid ash before and after grinding.

Example 2

The fluid ash from burning coal with ground limestone was ground in a ball mill for various times. The ground fluid ash was slurried with the same rheological properties (liquid slurry). A plasticizer based on polycarboxy ether ethers in a concentration of wt. fly ash.

Giant. 2 shows the dependence of the water coefficient at which the fluidity of the slurry is achieved on the specific surface of the ground fluid ash from the combustion of coal with ground limestone. A plasticizer based on polycarboxy ether ethers was used. fluid ash.

Λ

The effect of grinding is manifested by the disruption of the porous particles of fluid ash from the combustion of coal with ground limestone and the reduction of the absorbency of the ash particles. Paradoxically, with increasing specific surface area (grinding time), the processability of ground fluid fly ash from ground coal with ground limestone improves, the water coefficient is significantly reduced, at which the fluidity of the fluid fly ash from coal combustion with ground limestone is achieved. The grinding of fluid ash from coal combustion with ground limestone allows the preparation of a binder with a low water content and thus with higher strengths.

Example 3

From the fluid ash from the combustion of coal with ground limestone ground to a specific surface of 620 m ² / kg, a mortar with a water coefficient w = 0.30 of liquid consistency was prepared, the ratio of fluid fly ash to continuous granulometry sand was 1: 2 wt. As an additive, a β-plasticizer based on polycarboxy ether ethers was added to the mixing water at a concentration of 2.5% by weight of the ash.

A part of the mortar bodies was then stored in water. The strength is shown in Fig. 3.

Example 4

Slurries with the same processability (liquid slurries) were prepared from ground fluid ash from coal combustion with ground limestone. The slurries were stored in test molds for 7 days in an atmosphere of 95% r.h. Table 1 shows the tensile strengths as a function of the specific surface area of the ground fluid ash.

Tab.l

Specific surface m ² / kg Compressive strength after 7 days (MPa) Unground fluid ash 2 370 20 500 40 540 60

Example 5

From the fluid ash from the combustion of coal with ground limestone ground to a specific surface area of 583 m 2 / kg, a mixture was prepared which contained 4 wt. of ground fluid ash + 4Š% wt. of silica fly ash + 10% by weight Ca (OH) 2. To this mixture was added in an amount of 2% by weight. polycarboxylic ether plasticizer, based on the weight of the mixture of ground fluid fly ash silica fly ash and Ca (OH) ₂ . Mortars with a water content of 0.25 and 0.30 were prepared. Compressive strengths as a function of time and method of deposition are shown in Fig. 4.

Examples 35 show that the binder according to the invention achieves high short-term and long-term strengths. Examples 3 A5 also show the stability of long-term strengths.

- 10 Example 6

Slurries with a composition of 8% by weight were prepared. of ground fluid ash from the combustion of coal with ground limestone with a specific surface area of 580 ml / kg, 10 ^ 6 wt. of fly ash and 10 wt. Ca (OH) ₂ with a water content of 0.41 (as an additive, a plasticizer based on polycarboxyether ethers was added to the mixing water in an amount of 1.5% by weight, based on the weight of the mixture of ground fluid fly ash, silica fly ash and Ca (OH) ₂ at free solidification in the laboratory at 20 DEG C. for 24 hours, after which the slurries were stored in air (square), in water (triangle) and in an environment with 95% relative humidity (cross), and after curing, volume changes were measured over time. on beams measuring 4x4x16 cm in a time period of 10 to 560 days.

These measurements show that the binder according to the invention is volumetrically stable for a long time, even when stored in water.

Example 7

From ground fluid ash from the combustion of coal with ground limestone with a specific surface area of 580 t in.

m ^ ykg with other ingredients were prepared slurries with a water coefficient of 0.30- <0.32 with the same consistency. A plasticizer based on polycarboxyether ethers was used as an additive in a concentration by weight, based on the weight of the ground fluid ash or a mixture of ground fluid ash, silica ash and Ca (OH) 2. The beginning of solidification of mixtures is given in tab. 2.

Tab. 2

Ingredients Beginning solidification Ground fluid ash, slurry w = 0.30 5 min 95% by weight ground fluid ash + 5 wt. Ca (OH) ₂ , slurry w = 0.30 15 min 35% by weight ground fluid ash + 50 wt. silica ash + 15% Ca (OH) ₂ w = 0.31 90 min 8Š% wt. ground fluid ash + 15 wt. Ca (OH) ₂ w = 0.3 50 min

- 11 tf • «<» »Tt

Example 8

From the ground fluid ash from the combustion of coal with ground limestone (specific surface area 520 m ² / kg), with the addition of 1, 1 wt. of a sulfonated condensate of melamine with formaldehyde, based on the weight of the fly ash, a slurry of w = 0.35 was prepared. The slurry had a liquid character and the onset of solidification was 30 minutes.

Example 9

A slurry was prepared from ground fluid ash from coal combustion with ground limestone with the addition of silica fly ash and Ca (OH) 2. The composition of the mixture was: 4% by weight. fluid ash, 45 ^ 6 wt. silica ash, 1φ6 wt. Ca (OH) 2. As a further additive, a plasticizer based on modified phosphonates was used in a concentration of 2.5% by weight, based on the weight of the mixture of ground fluid fly ash, silica fly ash and Ca (OH) ₂ . The plasticizer was added to the mixing water. The water coefficient of the slurry was 0.35, where the slurry had a liquid character.

Claims (8)

PATENT CLAIMS A process for the preparation of a clinker-free hydraulic binder by mixing fluid fly ash from coal combustion with ground limestone, which contains, in addition to aluminosilicate, also at least wt. of free CaO and at least 2 wt. CaSO ₄ , or mixtures thereof with substances selected from the group consisting of silica fly ash and Ca (OH) 2, with mixing water containing a plasticizer to improve the rheological properties in a concentration of 0.2 to 3% by weight, based on the weight of the fluid fly ash or mixture thereof , characterized in that the fluid ash from the combustion of coal with ground limestone is artificially ground to a specific surface area of 350 to 650 m ² / kg. 2. A process according to claim 1, characterized in that the mixing water is mixed with the ground fluid ash or a mixture thereof in a weight ratio of 0.2 to 0.65. 3. The preparation method according to claim 1 and 2. characterized in that a maximum of 20% by weight is added to the fluid ash before mixing with the mixing water. Ca (OH) 2, based on a mixture of fluid ash and Ca (OH) 2. Preparation process according to Claims 1 and 2, characterized in that a maximum of 50% by weight is added to the fluid ash before mixing with the mixing water. of silica fly ash, based on the weight of the mixture of fluid fly ash and silica fly ash. Preparation process according to Claims 1 to 4j, characterized in that a maximum of 70% by weight is added to the fluid ash before mixing with the mixing water. of silica fly ash and Ca (OH) 2, based on the weight of the mixture of silica fly ash and Ca (OH) 2 and fluid fly ash. Preparation process according to Claims 1 to 4, characterized in that the fluid ash is artificially ground before mixing with Ca (OH) 2 and / or silica fly ash. Preparation process according to Claims 1 to 5, characterized in that the fluid fly ash is ground together with Ca (OH) 2 and / or silica fly ash. The preparation process according to claims 1 to 7 _, characterized in that the plasticizer is selected from the group consisting of sulfonated polymers of melamine with formaldehyde, the basic unit of which has the formula I, α α »e • a v -O-CH 2 -fl NH I _> CH, -SO, fe e 3 polymers of polycarboxyether ethers which contain basic units of general formula II and III, r> - c -I c = o o (EO) _a Have where M = metal, Me = methyl group, E0 = oxyethylene group, R = methyl group or H., or phosphonate polymers, where the basic unit is after ₃ h ₂ ^ CHn