LT7167B - ASH PORTLAND CEMENT COMPOSITION - Google Patents

Abstract

The present invention is intended to obtain a special composition of fly ash Portland cement using a high purity inorganic calcium sulfoaluminate additive as a setting and hardening regulator. This additive contains >97.5% yelimite and was synthesized by a two-stage synthesis (hydrothermal and solid phase) from calcium carbonate, aluminum hydroxide and gypsum. The inorganic calcium sulfoaluminate additive differs from other additives for Portland cement in that it is high purity, environmentally friendly, non-toxic, alkali-free and suitable for fly ash Portland cement.

Description

TECHNICAL FIELD

The invention belongs to the field of cement compositions, and more specifically to fly ash Portland cement containing fly ash and setting time regulating additives.

STATE OF THE ART

Fly ash Portland cement is a special type of cement, which contains 65-94% clinker, 6-35% fly ash and up to 5% corrective additives. Fly ash is a secondary product formed in kilns and has pozzolanic properties. This type of cement is used because it reduces the amount of ash deposited in landfills and reduces CO2 emissions, due to the lower amount of Portland cement in concrete. In addition, fly ash improves sulfate resistance and lower heat release during hardening, which is important for the production of large structures. Finally, using fly ash reduces the cost of production, as expensive Portland cement is replaced by a cheap secondary product - fly ash. These cements are described in the EN 197-1 standard.

Setting time and compressive strength are two important indicators reflecting the properties of fresh and hardened cement samples. According to literature data, the addition of ash to Portland cement has a negative effect on setting time, i.e. as the ash content in the system increases, the setting time of the cement increases. In addition, the presence of ash in cement systems often leads to a decrease in compressive strength during early hydration.

During the production of Portland cement, clinker is ground, and usually the required amount of calcium sulfate or other additives are added to it to improve its properties. However, the setting and hardening time of Fly Ash Portland Cement is significantly extended, and the compressive strength is significantly reduced by increasing the ash content in the system, compared to pure Portland cement. Therefore, in order to ensure the appropriate setting time and compressive strength for practical applications, it is necessary to adjust the setting and hardening processes of cement mixtures containing fly ash.

The use of admixtures that modify the properties of cement and concrete in cements and cement mixtures is common practice. Setting retarders and accelerators adjust the setting time, which is useful for, for example, transportation, mixing, pumping, placing, smoothing or shaping, and ultimately for strength development. Meanwhile, hardening accelerators increase the early strength of concrete. The effect of individual admixtures on the cementitious system can only be determined experimentally and their effect varies depending on the phase composition of the admixture and the cement grade.

To shorten the setting time of Portland cement, calcium salts, triethanolamine, calcium formate and other salts can be used. Meanwhile, to extend the setting time, borax, sucrose, phosphates and other compounds can be used. As hardening accelerators, calcium and sodium salts, as well as calcium hydrosilicates or aluminates, which act as crystallization centers. The use of these additives can improve or worsen the rheological properties, and their influence on CEM type I cement has been widely studied. Unfortunately, additives that regulate the setting and hardening times and rheological properties of fly ash Portland cement have been little studied.

The disadvantage of the additives used is that by extending or shortening the setting time, the rheological properties and compressive strength of concrete also deteriorate.

U.S. Patent No. 7,326,920 discloses a Portland cement setting accelerator comprising calcium aluminate as an accelerator and additionally boric acid and/or its salt as a setting retarder. Unfortunately, the patent does not address the health and safety concerns associated with the use of boric acid. In addition, the use of calcium aluminate impairs the rheological properties.

International Patent Application No. PCT/US2008/051664, Publication No. WO 2008/089481, discloses a compound accelerator/retarder for cements of citric acid and boric acid salts. As in the previously discussed patent, health and environmental concerns are not addressed and additional pozzolans must be used.

U.S. Patent No. 4,257,815 discloses that inorganic additives such as calcium oxide or magnesium oxide can be used to adjust the properties of fresh mortar or concrete, such as the setting time of the mortar. This patent covers only cements with fly ash containing carbon and air-entraining agents.

U.S. Patent Nos. 5,110,362 and 5,654,352 disclose the possibility of air entrainment and retention in cementitious systems using organic additives, while U.S. Patent No. 6,136,089 discloses the effect of ozone oxidation of fly ash on cement properties.

US Patents No. 4,082,561 and 6,682,595 disclose the positive effect of potassium sulfate addition in shortening the setting time of mortar and improving strength in general purpose concrete structures: Patent No. 4,082,561 modifying the properties of pure Portland cement; Patent No. 4,082,561 replacing part of Portland cement with fly ash or slag. Unfortunately, these patents do not assess either the limit alkali content, which is permissible in CEMI/CEM type II cements up to 0.8%, or alkaline decomposition - especially in samples with fly ash.

International Patent Application No. PCT/FR2012/051172, Publication No. WO 2012/160319A1 discloses cement setting accelerators which consist of water-soluble salts such as: sodium silicate, sodium metasilicate, sodium and potassium silicates, potassium metasilicate, lithium silicate, lithium metasilicate and/or mixtures thereof. However, these alkali metal silicates can leach out of the cement stone, thereby impairing its long-term performance.

German patent No. DE 102005054190B3 discloses a suspension consisting of aluminum sulfate, amorphous aluminum hydroxide, carboxylic acid and/or their salts and sepiolite, which accelerates the hardening of concrete. However, a large amount of the suspension is required - 7% of the mass of cement, for the production of which at least four chemically pure and expensive reagents are used.

According to literature data, in addition to the previously listed additives, sulfoaluminate cements can be mixed into Portland cement cements. These cements can be considered environmentally friendly cements, since less carbon dioxide is emitted into the environment during their production. They are often used to reduce the problem of cracking of Portland cement concrete. Sulfoaluminate cements begin to form at a temperature of 900-950 °C. However, they are usually synthesized at a temperature of 1200-1250 °C, and at a temperature of 1350 °C they become metastable and begin to decompose. The main component of sulfoaluminate cements is jellite (Ca4Al6(SO4)Oi2), (c<50%). Together with the latter compound, sulfoaluminate cements form crotite (CaO^Al2Ū3), grossite (CaO (Al2Ū3)2), mayenite ((CaO)i2(Al2Ū3)/) and other high-temperature phases.

Limestone and raw materials containing aluminum and sulfur components are used for the production of sulfoaluminate cements. Raw materials containing sulfur and aluminum components can be of both natural origin and waste (ash, furnace slag, pond sludge, etc.).

Although fly ash Portland cement and sulfoaluminate cements, including their individual components, are well known, there is still a search for ways to improve the properties of fly ash Portland cement, such as setting time and rheology, without degrading other important characteristics.

ESSENCE OF THE INVENTION

The present invention discloses a fly ash Portland cement composition. The composition comprises Portland cement, fly ash and an environmentally friendly and non-toxic inorganic high purity inorganic calcium sulfoaluminate additive as a setting and hardening regulator. The additive improves the properties of fly ash Portland cement.

The invention describes the influence of a high-purity inorganic calcium sulfoaluminate additive on the setting and hardening properties of fly ash Portland cement. Using a high-purity inorganic calcium sulfoaluminate additive in a fly ash Portland cement composition allows the properties of fly ash Portland cement to be controlled during the preparation of mixtures.

The fly ash Portland cement composition can be used as conventional fly ash Portland cement, i.e. in the building materials and construction industry.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings and graphs are an integral part of the description of the invention and are provided as a reference to a possible implementation of the invention, but do not limit the implementation of the invention. The graphs are not necessarily to scale with the details of the invention. Details that are not necessary for explaining the operation of the invention and have no connection are not provided.

Fig. shows the X-ray diffraction analysis curve of a high-purity inorganic calcium sulfoaluminate additive precursor. Here: Ms12 calcium monosulfoaluminate, Cc - calcium carbonate.

Fig. shows the X-ray diffraction analysis curve of a high-purity inorganic calcium sulfoaluminate additive. Here: Y - yelimit, CO calcium oxide, A - anhydrite

DETAILED DESCRIPTION OF THE IMPLEMENTATION OF THE INVENTION

The present invention provides a fly ash Portland cement composition comprising:

from 65% to 94% Portland cement, preferably from 74% to 85%, for example about 80%, and which has the following oxide composition and physical properties:

1.1. Table. Oxide composition of Portland cement

Oxides Concentration, % SiO2 17-24 Al2O3 2-4 CaO 63-66 Fe2O3 2-4 Cl <0.1 K2O+Na2 O <1 SO3 <5 K. n.* <5.0

Note: * - heating losses, mass %

Table 1.2. Main properties of Portland cement

Particle size distribution (μm) Min 0.1 Max 70 d10 1.1 d 50 8.0 d 90 40.9 Color (m ² /kg) 430 Density (kg/ ^m3 ) 3100

from 5.75% to 30% fly ash, preferably from 14.75% to 25%, for example about 19.5%, and having the following oxide composition and physical properties:

Table 1.3. Oxide composition of fly ash

Oxides Concentration, % SiO2 40-50 Al2O3 28-31 CaO 6-9 Fe2O3 4-7 TiO2 1-3 P2O5 1-3 K2O+Na2O <2 SO3 <5 K. n. <5

Table 1.4. Main properties of fly ash

Particle size distribution (μm) Min <5 Max <250 d10 >5 <10 d 50 >20 <30 d 90 >80 <90 Color (m ² /kg) >400 <500 Density (kg/ ^m3 ) >2500 <2900

from 0.25% to 5% of a high purity inorganic calcium sulfoaluminate additive, preferably from 0.25% to 1%, for example 0.5%, which has the following oxide and phase composition and physical properties:

Table 1.5. Oxide composition of high-purity inorganic calcium sulfoaluminate additive

Oxides Concentration, % CaO 35-37 Al2O3 49-51 SO3 12-14 SiO2 <0.5 Mg <0.5 Fe2O3 <0.5 K2O+Na2O <1 K. n. <0.2

Table 1.6. Phase composition of high-purity inorganic calcium sulfoaluminate additive

Compound Concentration, % Yelimit >95 Anhydrite <0.5 Calcium oxide <0.5 Amorphous phase <3

Table 1.7. Physical properties of high purity inorganic calcium sulfoaluminate additive

Particle size Min <1

distribution (μm) Max <70 this >1 <5 d 50 >8 <20 C 90 >30 <50 Color (m ² /kg) >400 <500 Density (kg/ ^m3 ) >2500 <2800

According to one embodiment of the invention, a Portland cement composition comprises from 65% to 94% Portland cement, from 5.75% to 30% fly ash, and from 0.25% to 5% of a high purity inorganic calcium sulfoaluminate additive.

According to another embodiment of the invention, a Portland cement composition comprises from 74% to 85% Portland cement, from 14.75% to 25% fly ash, and from 0.25% to 1% of a high-purity inorganic calcium sulfoaluminate additive.

According to yet another embodiment of the invention, a Portland cement composition comprises 80% Portland cement, 19.5% fly ash, and 0.5% of a high purity inorganic calcium sulfoaluminate additive.

For all three examples mentioned, the compositions and properties of Portland cement, fly ash and high-purity inorganic calcium sulfoaluminate additive are as indicated in Tables 1.1 - 1.7.

Method for preparing a high-purity inorganic calcium sulfoaluminate additive. The starting raw materials of the high-purity inorganic calcium sulfoaluminate additive, such as calcium carbonate, aluminum hydroxide and dihydrate gypsum, are stored in raw material bunkers. Calcium carbonate and aluminum hydroxide weighed by weight dispensers from these bunkers are supplied to a furnace, such as a rotary kiln, where they are burned to calcium and aluminum oxides. The resulting oxides are stored in bunkers. Calcium and aluminum oxides and dihydrate gypsum are weighed by weight dispensers from the bunkers and supplied to a mill, such as a ball mill, for mechanochemical treatment. After treatment, the mixture obtained is stored in intermediate bunkers. The required amount of the mixture obtained is supplied to a periodic mixer, such as a propeller mixer, into which the required amount of water metered by a volumetric dispenser is added from the tank. The mixed starting materials are supplied to the autoclave by a pump. The synthesized material is poured into an intermediate tank, where excess liquid medium is decanted by a pump and fed to a furnace, such as a rotary kiln, for thermal treatment.

The high-purity inorganic calcium sulfoaluminate additive is obtained by a two-step process using:

calcium oxide CaO, which is prepared from reactive CaCO3 and additionally calcined in an environment at a temperature of 950 °C for 1 hour. The value of the specific surface area of the prepared calcium oxide Spav = 341 m ² /kg; CaOiasvas = 98.1%.

alumina AbŪ3, which is prepared from reactive Al(OH)3 and additionally calcined at 475 °C for 4 hours. The specific surface area of the prepared alumina is Spav = 1130 m ² /kg.

reagent gypsum CaSO2·2H2O. Surface area value Spav - 694 m ² /kg).

From these compounds, a starting mixture is prepared, the composition of which corresponds to the molar ratio CaO:Al2Ū3:SO4 = 4:3:1. This starting mixture is mechanochemically treated, for example, with a planetary mill or similar, with three 10-min. on-off cycles, at a speed of 900 rpm.

The treated mixture is added with distilled water to achieve a water-to-solids ratio (W/S) of 10 in the suspensions.

The synthesis was carried out without stirring, in 25 ml PTFE vessels of the suspension, placed in an autoclave or similar high-pressure reactor, when the saturated water vapor temperature is 110 °C, and the isothermal holding time is 8 hours. The temperature of 110 °C is reached within 2 hours. The synthesis products are washed with isopropanol, dried at 50 °C for 24 hours and sieved through a sieve with a mesh size of 315 μm. The phase composition of the product is shown in Fig. 1. The obtained precursor is placed in a ceramic crucible and fired in a muffle furnace at a temperature of 1150 °C for 1 hour. The properties and composition of the obtained high-purity inorganic calcium sulfoaluminate additive are disclosed in Tables 1.5-1.7 and Fig. 2.

Preferably, the resulting high purity inorganic calcium sulfoaluminate additive is composed of >97.5% yelimite, <0.35% calcium oxide, <0.2% anhydrite, and <1.9% amorphous phase.

Example of a method for obtaining a composition of Portland cement, fly ash and high purity calcium sulfoaluminate

Initial raw materials: Portland cement, grade CEM I 42.5N, fly ash, high-purity inorganic calcium sulfoaluminate additive and sand standardized by the European Committee for Standardization CEN (EN 196-1).

When preparing initial cement mixtures, the components are poured into sealed containers, 4 porcelain grinding bodies are placed in them to ensure the quality of homogenization. In one case, the mass % of the initial raw materials in the mixture is: Portland cement from 79.5% to 80%, fly ash from 19.5% to 20%, and high-purity inorganic calcium sulfoaluminate additive - 0.5%. The mixtures are homogenized for 1 h (at a speed of 34 rpm) in a material homogenization device. The prepared initial mixtures are used for normal consistency and setting time tests of cement paste according to the standard LST EN 196-3:2017, using an automatic Vicat apparatus EO44N (MATEST, Italy). The standard consistency is determined according to the scale readings, i.e. the distance between the piston and the base plate is 6 ± 2 mm. Meanwhile, the setting time is determined by the needle penetrating the dough every 5 minutes. The beginning of setting is determined when the distance between the needle and the base plate is 6 ± 2 mm, and the end of setting is determined when the needle first penetrates the sample by only 0.5 mm.

In the laboratory, the mechanical properties of cement mortar are determined according to the modified standard LST EN 196-1 and LST EN 197-1 methodology. For the preparation of three prisms (40 x 40 x 160 mm), 450 g of the composition, which includes a mixture of prepared Portland cement, fly ash and high-purity inorganic calcium sulfoaluminate additive, and 1350 g of standard CEN sand (EN 196-1), are weighed. The ratio of prepared binder to sand is 1:3. After that, 225 ml of distilled water is measured. The ratio of water to prepared binder V/K =

0.5. For the first 24 hours, the samples are cured in molds above water, then transferred to sealed containers with distilled water and kept for 2, 7 and 28 days at a temperature of 20 ± 1 °C. The compressive strength of the samples is determined using a MEGA 10400-50 press (FORM+TEST Seidner & Co. GmbH, Germany) at a speed of 2.4 kN/s.

The effect of high-purity inorganic calcium sulfoaluminate additive on the binding and hardening properties of fly ash Portland cement.

The normal cement paste consistencies, setting start and end times, and hardening properties of cement mortar when using only Portland cement, Portland cement with ash without high-purity inorganic calcium sulfoaluminate additive, and with high-purity inorganic calcium sulfoaluminate additive, the composition according to the invention, are presented in Tables 1.8 and 1.9.

Table 1.8. Setting time of ready-made cement pastes

Sample No. Mixture composition, % Setting time, min V/K Portland cement Fly ash High purity inorganic calcium sulfoaluminate additive Home The End 1 100 - - 160 400 0.290 2 80 20 - 267 440 0.306 3 80 19.5 0.5 137 302 0.310 4 79.5 20 0.5 174 289 0.310

Table 1.9. Compressive strength values of prepared cement mortars

Sample No. Mixture composition, % Compressive strength, MPa Portland cement Fly ash High purity calcium sulfoaluminate additive 2 days 7 days 28 days

1 100 - - 19.67 37.46 42.59 2 80 20 - 25.33 37.29 48.09 3 80 19.5 0.5 17.69 29.96 42.99 4 79.5 20 0.5 20.66 31.74 44.18

From the data presented in Tables 1.8 and 1.9 it can be seen that in order to achieve a normal consistency of the fly ash Portland cement paste, a higher ratio of water to prepared binder is required than for the pure Portland cement sample, and the initial and final setting times are extended by 107 min and 40 min, respectively. In addition, it was found that replacing Portland cement with fly ash (20%) improves the mechanical properties, i.e. after 28 days of hardening, the compressive strength values of sample 2 are 5.5 MPa higher compared to the values of sample 1.

When using cement mixtures with a high-purity inorganic calcium sulfoaluminate additive, the initial and final setting times of the cement paste are shortened, respectively: in sample 3 130 min and 138 min, and in sample 4 93 min and 151 min, compared to sample 2. It is worth noting that when using a high-purity inorganic calcium sulfoaluminate additive, an even higher ratio of water to prepared binder is required to obtain a normal consistency of the cement paste. Ash Portland cement mortars with a high-purity inorganic calcium sulfoaluminate additive are characterized by a slower development of strength growth during the first week, but after 28 days of hardening, the values determined for compressive strength are higher compared to the values of sample 1.

example

The preparation of initial cement mixtures, determination of the consistency and setting time of the cement paste, and the mechanical properties of the cement mortar are carried out as described in Example 1.

The difference is that different amounts of starting raw materials are used, with the Portland cement content in the mixture ranging from 79% to 80%, the fly ash content ranging from 19% to 20%, and the high-purity inorganic calcium sulfoaluminate additive content of 1%.

The indicators of the obtained results are presented in Tables 1.10 and 1.11.

.10. Table. Initial and final setting times of prepared cement pastes

Sample No. Mixture composition, % Setting time, min V/K Portland cement is Fly ash High purity calcium sulfoaluminate additive Home The End 5 80 19 1 97 177 0.313 6 79 20 1 107 186 0.313

Table 1.11. Compressive strength values of ready-mixed cement mortars

Sample No. Mixture composition, % Compressive strength, MPa Portland cement Fly ash High purity calcium sulfoaluminate additive 2 days 7 days 28 days 5 80 19 1 15.54 22.13 42.64 6 79 20 1 16.80 26.28 42.65

From the data presented in Tables 1.10 and 1.11 it can be seen that when using cement mixtures with a high-purity inorganic calcium sulfoaluminate additive, the initial and final setting times of the cement paste are shortened by 170 min and 263 min in sample 5, and by 160 min and 254 min in sample 6, respectively, compared to sample 2. It is worth noting that when using a larger amount of high-purity inorganic calcium sulfoaluminate additive, an even higher ratio of water to prepared binder is required to obtain a normal consistency of the cement paste. Ash Portland cement mortars with a high-purity inorganic calcium sulfoaluminate additive are characterized by a slower development of strength growth during the first week, but after 28 days of hardening, the values obtained in compressive strength are close to the values of sample 1.

example

Preparation of initial cement mixtures, determination of cement paste consistency and setting time are carried out as described in Example 1.

The difference is that the required amounts of starting raw materials were used, with the Portland cement content in the mixture varying from 78% to 80%, the fly ash content varying from 18% to 20%, and the high-purity inorganic calcium sulfoaluminate additive content being 2%.

The indicators of the obtained results are presented in Table 1.12.

Table 1.12. Setting time of ready-made cement pastes

Sample No. Mixture composition, % Setting time, min V/K Portland cement Fly ash High purity inorganic calcium sulfoaluminate additive Home The End 7 80 18 2 35 55 0.316 8 78 20 2 25 40 0.317

The data presented in Table 1.12 shows that when using cement mixtures with a high-purity inorganic calcium sulfoaluminate additive, the onset of cement paste setting was determined after 35 min in sample 7, and after 25 min in sample 8. According to the LST EN 197-1:2011 standard, the cement setting time must be no shorter than 60 min in order to ensure optimal performance properties of the cement paste, therefore the amount of high-purity inorganic calcium sulfoaluminate additive used is unsuitable for preparing cement mortars.

Claims (4)

DEFINITION OF THE INVENTION 1. A fly ash Portland cement composition comprising fly ash and high purity calcium sulfoaluminate, characterized in that the fly ash Portland cement composition comprises: from 65% to 94% Portland cement, from 5.75% to 30% fly ash, from 0.25% to 5% high-purity inorganic calcium sulfoaluminate additive. 2. A fly ash Portland cement composition according to claim 1, comprising: from 74% to 85% Portland cement, from 14.75% to 25% fly ash, from 0.25% to 1% high-purity inorganic calcium sulfoaluminate additive. 3. A fly ash Portland cement composition according to claim 1, comprising: about 80% Portland cement, about 19.5% fly ash, about 0.5% high-purity inorganic calcium sulfoaluminate additive. 4. A fly ash Portland cement composition according to any one of claims 1-3, wherein the high purity inorganic calcium sulfoaluminate additive comprises >97.5% yelimite, <0.35% calcium oxide, <0.2% anhydrite and <1.9% amorphous phase.