CN112608047A - Modified sulphoaluminate cement and preparation method and application thereof - Google Patents

Modified sulphoaluminate cement and preparation method and application thereof Download PDF

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CN112608047A
CN112608047A CN202011534500.5A CN202011534500A CN112608047A CN 112608047 A CN112608047 A CN 112608047A CN 202011534500 A CN202011534500 A CN 202011534500A CN 112608047 A CN112608047 A CN 112608047A
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cement
modified
lithium
sulphoaluminate cement
gypsum
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CN112608047B (en
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张文生
刘垒
任雪红
叶家元
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China Building Materials Academy CBMA
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B7/00—Hydraulic cements
    • C04B7/32—Aluminous cements
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B22/00—Use of inorganic materials as active ingredients for mortars, concrete or artificial stone, e.g. accelerators, shrinkage compensating agents
    • C04B22/08—Acids or salts thereof
    • C04B22/14—Acids or salts thereof containing sulfur in the anion, e.g. sulfides
    • C04B22/142—Sulfates
    • C04B22/143—Calcium-sulfate
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P40/00—Technologies relating to the processing of minerals
    • Y02P40/10—Production of cement, e.g. improving or optimising the production methods; Cement grinding

Abstract

The invention discloses a modified sulphoaluminate cement and a preparation method thereof, wherein the modified sulphoaluminate cement comprises 75-85% of lithium salt modified cement clinker by mass percent; 15 to 25 percent of gypsum. The preparation method comprises the steps of mixing lithium salt and the sulphoaluminate cement raw material, calcining at high temperature for 30-60 min, quickly cooling to room temperature to obtain lithium salt modified cement clinker, mixing the cement clinker with gypsum, and grinding to obtain the modified sulphoaluminate cement. The invention not only reduces the energy consumption and CO for preparing the sulphoaluminate cement clinker2The discharge amount is reduced, the setting time of the sulphoaluminate cement is greatly shortened by introducing the lithium oxide and the calcium sulfosilicate minerals into the cement clinker, the early strength is obviously improved, the stable and continuous development of the middle and later strength of the sulphoaluminate cement can be kept, and the problem of the backward shrinkage of the later strength is solved.

Description

Modified sulphoaluminate cement and preparation method and application thereof
Technical Field
The invention relates to the field of building materials, in particular to modified sulphoaluminate cement and a preparation method and application thereof.
Background
Compared with portland cement, the sulphoaluminate cement not only can reduce energy consumption and reduce CO in the preparation process2The cement has the characteristics of high condensation speed, rapid early-stage performance development, excellent corrosion resistance and the like, is the non-silicate cement with the largest output in China at present, and is widely used in the fields of rapid construction, low-temperature construction, ocean engineering, concrete products and the like. Although the sulphoaluminate cement taking the calcium sulphoaluminate as the main mineral has the characteristics of early strength and quick hardening, when the sulphoaluminate cement is applied to emergency projects such as waterproof leakage stoppage, quick repair and the like, the project requirements cannot be met only by virtue of early hydration and performance development of the sulphoaluminate cement, and an appropriate accelerating agent needs to be added for performance adjustment. Meanwhile, in the hydration process of the sulphoaluminate cement, the calcium sulphoaluminate mineral is hydrated in early stage to generate high-sulfur hydrated calcium sulphoaluminate (ettringite), but as the hydration reaction progresses, calcium sulfate is gradually consumed, and SO is in the pore solution of the cement hardening body4 2-The concentration of the sulphoaluminate cement is reduced, the strength contributor ettringite is gradually converted into low-sulfur hydrated calcium sulphoaluminate, and in addition, the hydration activity of belite minerals in the cement is low, so that the problems of strength increase and weakness in the middle and later periods of the sulphoaluminate cement and even the problem of strength retraction in the later period of the cement are caused. Therefore, further accelerating the early hydration of the sulphoaluminate cement and improving the stable development of the middle and later strength of the sulphoaluminate cement are problems to be solved in need of being adapted to the current construction which is increasingly diversified.
The research results show that the lithium salt can be used as an effective coagulant of sulphoaluminate cement, can play a role in promoting early hydration of the sulphoaluminate cement, reduce the setting time and improve the early strength. However, at present, the application process of accelerating early hydration of sulphoaluminate cement by using lithium salt is that the lithium salt is usually pre-dispersed in water and then mixed with cement, and the measure is difficult to fully mix the lithium salt with the cement, so that the time for the early hydration of the cement is not matched with the time for the action of the lithium salt, and the condition of unstable performance often occurs, and the lithium salt is used for accelerating the early hydration of the sulphoaluminate cementThe lithium salt promotes the rapid generation of ettringite crystals in the external environment of the cement particles, and a compact hydrated product layer is easily formed on the surfaces of the cement particles to wrap unhydrated minerals, so that the subsequent hydration process of the sulphoaluminate cement is hindered, and the later strength of the cement is reduced. In order to uniformly distribute lithium salt in cement, synchronously release the lithium salt in the hydration process of the cement, exert the effect to the maximum extent and not influence the subsequent hydration process of the cement, research attempts are currently made to prepare lithium salt modified sulphoaluminate cement clinker by uniformly mixing the lithium salt and cement raw materials in advance and then calcining the mixture at a high temperature, and finally prepare the fast hardening sulphoaluminate cement meeting the requirements. However, this study has the following technical problems: (1) part of lithium salt is easy to release SO in cement raw material by calcining2And harmful gases such as NO; (2) the firing range of the sulphoaluminate cement clinker is generally 1300-1400 ℃, and Li2O is easy to volatilize in a large amount at the temperature of more than 1250 ℃, and the loss of the lithium component in the clinker is easy to cause.
Disclosure of Invention
In view of the above-mentioned deficiencies of the prior art, the main object of the present invention is to provide a modified sulphoaluminate cement, a preparation method thereof and an application thereof, wherein the technical problem to be solved is to make a lithium salt which is thermally decomposed and does not release harmful gas dissolved in the prepared modified dicalcium silicate-calcium sulphoaluminate cement clinker, so as to exert the promoting effects of the lithium salt and calcium sulphoaluminate minerals in the sulphoaluminate cement to the maximum extent, further accelerate the early hydration process of the sulphoaluminate cement and improve the stable development of the middle and later strength of the cement.
The purpose of the invention and the technical problem to be solved are realized by adopting the following technical scheme. The invention provides modified sulphoaluminate cement, which comprises the following components in percentage by mass:
75 to 85 percent of lithium salt modified cement clinker;
15 to 25 percent of gypsum.
Further, in the modified sulphoaluminate cement, the content of lithium salt in the lithium salt modified cement clinker is 0.002-0.9 wt%.
Further, in the modified sulphoaluminate cement, the lithium salt is selected from one of lithium sulfate, lithium nitrate, lithium chloride, lithium slag, lithium-containing tailings and lithium carbonate.
Further, in the modified sulphoaluminate cement, the lithium salt is lithium carbonate.
Further, in the modified sulphoaluminate cement, the gypsum is selected from one of anhydrite, dihydrate gypsum and phosphogypsum.
Further, in the modified sulphoaluminate cement, the gypsum is selected from anhydrite.
Further, in the modified sulphoaluminate cement, the cement clinker comprises, by mass: 40-55% of anhydrous calcium sulphoaluminate; 20-40% of calcium sulfosilicate; 10-20% of dicalcium silicate; 3-8% of an iron aluminate mineral; 0-5% of free gypsum; 0-0.2% of free calcium oxide; 0.001-0.5% of lithium oxide, 0.1-1.2% of gehlenite and 0.05-0.8% of perovskite.
Further, in the modified sulphoaluminate cement, the initial setting time of the modified sulphoaluminate cement is 5-18 min, the final setting time is 9-25 min, the compressive strength of 4h is 18-31 MPa, the compressive strength of 6h is 32-40 MPa, the compressive strength of 1d is 40-50 MPa, the compressive strength of 3d is 45-55 MPa, the compressive strength of 28d is 75-85 MPa, and the compressive strength of 90d is 95-108 MPa.
The purpose of the invention and the technical problem to be solved are realized by adopting the following technical scheme. The preparation method of the modified sulphoaluminate cement provided by the invention comprises the following steps:
the cement raw materials and the lithium salt are ground and mixed according to the mass percentage, the lithium salt modified cement clinker is prepared by high-temperature calcination and quick cooling to room temperature, and then the cement clinker is mixed with the anhydrite and ground, and finally the modified sulphoaluminate cement is obtained.
Further, in the preparation method of the modified sulphoaluminate cement, the mass ratio of the cement raw material to the lithium salt is 100: (0.002-0.009).
Further, in the preparation method of the modified sulphoaluminate cement, the lithium salt is lithium sulfate, lithium nitrate, lithium chloride, lithium slag, lithium-containing tailings or lithium carbonate.
Further, in the preparation method of the modified sulphoaluminate cement, the lithium salt is lithium carbonate.
Further, in the preparation method of the modified sulphoaluminate cement, the cement raw material is at least one selected from limestone, alumina, dihydrate gypsum, red mud, phosphogypsum, chromium slag and fly ash.
Further, in the preparation method of the modified sulphoaluminate cement, when the cement raw meal consists of limestone, alumina, dihydrate gypsum, red mud, phosphogypsum, chromium slag and fly ash, the cement raw meal comprises the following components in percentage by mass:
35-55% of limestone; 15-20% of bauxite; 0-20% of dihydrate gypsum; 0-25% of red mud; 0-30% of phosphogypsum; 0-5% of chromium slag; 2-4% of fly ash.
Further, in the preparation method of the modified sulphoaluminate cement, the high-temperature calcination temperature is 1150-1250 ℃, and the heat preservation time is 30-60 min.
Further, in the preparation method of the modified sulphoaluminate cement, the quick cooling time is 2-5 min.
Further, in the preparation method of the modified sulphoaluminate cement, the specific surface area of the ground powder is 480-500 m2·kg-1。
The purpose of the invention and the technical problem to be solved are realized by adopting the following technical scheme. According to the building material provided by the invention, the building material comprises the modified sulphoaluminate cement.
Preferably, the building material is a mortar or a concrete.
By the technical scheme, the modified sulphoaluminate cement, the preparation method and the application thereof have the following beneficial effects:
1. according to the invention, Na is2O、K2O、P2O5、CaF2And Cr2O3The method can accelerate the effect of forming calcium sulphoaluminate minerals at low temperature, replaces part of the traditional raw materials such as limestone, alumina, dihydrate gypsum and the like with industrial solid wastes such as red mud, phosphogypsum, chromium slag and the like, mixes the industrial solid wastes with lithium salt such as lithium carbonate, and calcines the mixture at low temperature of 1150-1250 ℃ to prepare lithium salt modified dicalcium silicate-calcium sulphoaluminate cement clinker, and finally prepares the modified sulphoaluminate cement which meets the design requirements (the initial setting time is not higher than 18min, the compressive strength of cement paste for 4h is not lower than 15MPa, and the compressive strength after 28d of age can be continuously increased).
2. The preparation method provided by the invention expands the application of red mud, chromium slag and other industrial solid wastes in the preparation of the calcium sulfosilicate-sulphoaluminate cement clinker, simultaneously avoids the phenomenon that lithium oxide can be volatilized in large quantities at the temperature of more than 1250 ℃, and provides conditions for the effective solid solution of the lithium oxide in the cement clinker.
3. The modified sulphoaluminate cement prepared by the invention has the advantages of faster early hydration heat release rate, shorter setting time, obviously improved early strength and stable increase of middle and later strength of the cement. The initial setting time of the cement is 5-18 min, the final setting time is 9-25 min, the compressive strength of 18-31 MPa in 4h, the compressive strength of 32-40 MPa in 6h, the compressive strength of 40-50 MPa in 1d, the compressive strength of 45-55 MPa in 3d, the compressive strength of 75-85 MPa in 28d and the compressive strength of 95-108 MPa in 90d are achieved; this is because, on the one hand, solid solution of lithium oxide stabilizes the cubic form of calcium sulfoaluminate, which has a higher prehydration activity. On the other hand, in the process of mixing with water for hydration, lithium oxide dissolved in clinker minerals can be released along with the dissolution and hydration of the minerals, lithium hydroxide generated by reaction with the water improves the alkalinity of the hydration environment of the sulphoaluminate cement, promotes the dissolution of aluminum, accelerates the formation of hydration products, namely ettringite and alumina gel, simultaneously the alumina gel can participate in the hydration reaction of the sulphoaluminate minerals, promotes the sulphoaluminate minerals to generate hydration products, namely ettringite, hydrated mayenite, C-S-H gel and the like in the middle and later stages of the hydration reaction of the cement, promotes the further development of the middle and later stage strength of the sulphoaluminate cement, and avoids the phenomenon of retrogradation of the later stage strength.
4. Hair brushIn the prepared modified sulphoaluminate cement, the firing temperature of the dicalcium silicate-calcium sulphoaluminate cement clinker is 100-200 ℃ lower than that of the common sulphoaluminate cement clinker, the consumption of limestone is lower than that of the common sulphoaluminate cement, and the preparation energy consumption and CO are reduced2The emission amount is remarkably reduced.
5. The modified sulphoaluminate cement prepared by the invention can be suitable for waterproof plugging, rapid repair and other projects, and the later strength of the cement is not subjected to shrinkage.
The foregoing is a summary of the present invention, and in order to provide a clear understanding of the technical means of the present invention and to be implemented in accordance with the present specification, the following is a detailed description of the preferred embodiments of the present invention.
Drawings
FIG. 1 is a graph of hydration heat release rates for cements prepared in examples 1-3 and comparative examples.
FIG. 2 is an XRD analysis chart of hydration products of the cements prepared in example 2 and comparative examples 1-2 after 6h hydration.
FIG. 3 is a thermogram of hydration products of cement prepared in example 2 and comparative examples 1-2 after hydration for 28 d.
Detailed Description
To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description will be given to the modified sulfoaluminate cement and its preparation method and application, and its specific implementation, structure, characteristics and effects thereof according to the present invention in combination with the preferred embodiments. In the following description, different "one embodiment" or "an embodiment" refers to not necessarily the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
The following materials or reagents, unless otherwise specified, are all commercially available.
The invention provides modified sulphoaluminate cement, which comprises the following components in percentage by mass:
75 to 85 percent of lithium salt modified cement clinker;
15 to 25 percent of gypsum;
the content of lithium salt in the lithium salt modified cement clinker can be 0.002-0.9%, preferably 0.02 wt%, and the early 4-hour strength of the modified sulphoaluminate cement can reach the highest strength of 30.2MPa after the selection; the gypsum can be anhydrite, dihydrate gypsum or phosphogypsum, preferably anhydrite, and the anhydrite is selected to ensure that the strength of the cement is higher, and the 90d strength of the cement can reach 108MPa at most.
In specific implementation, the modified sulphoaluminate cement preferably comprises, by mass:
80% of lithium salt modified cement clinker;
20% of anhydrite;
thus, the cement is preferably made to have a higher strength than cement having other compositions.
In specific implementation, the cement clinker comprises the following components in percentage by mass: 40-55% of anhydrous calcium sulphoaluminate; 20-40% of calcium sulfosilicate; 10-20% of dicalcium silicate; 3-8% of an iron aluminate mineral; 0-5% of free gypsum; 0-0.2% of free calcium oxide; 0.001-0.5% of lithium oxide, 0.1-1.2% of gehlenite and 0.05-0.8% of perovskite; the preferred proportions are: 40.39% of calcium sulphoaluminate, 36.27% of calcium sulphoaluminate, 14.95% of dicalcium silicate, 7.93% of iron aluminate minerals, 0.24% of free gypsum, 0.05% of free calcium oxide, 0.01% of lithium oxide, 0.1% of gehlenite and 0.07% of perovskite; so that the strength of the cement is preferably higher.
Experiments prove that the initial setting time of the modified sulphoaluminate cement is 5-18 min, the final setting time is 9-25 min, the compressive strength of 4h is 18-31 MPa, the compressive strength of 6h is 32-40 MPa, the compressive strength of 1d is 40-50 MPa, the compressive strength of 3d is 45-55 MPa, the compressive strength of 28d is 75-85 MPa, and the compressive strength of 90d is 95-108 MPa.
The invention also provides a preparation method of the modified sulphoaluminate cement, which comprises the following steps:
the cement raw materials and the lithium salt are ground and mixed according to the mass ratio, the lithium salt modified cement clinker is prepared by high-temperature calcination and quick cooling to room temperature, and then the cement clinker is mixed with the anhydrite and ground, and finally the modified sulphoaluminate cement is obtained.
In specific implementation, the time of the quick cooling is 2-5min, preferably 2min, so that the strength of the cement is higher after the quick cooling is preferably performed.
In specific implementation, the specific surface area of the powder grinding is 480-500 m2·kg-1Preferably 490m2·kg-1The preferred effect is more stable development of cement strength.
In specific implementation, the preparation method can comprise the following steps:
grinding and mixing the cement raw material and the lithium salt according to a certain mass ratio to obtain raw material powder;
adding raw material powder into deionized water accounting for 6-10 wt% of the raw material powder, uniformly stirring, pressing into a raw material cake, and drying;
placing the raw meal cake in a high-temperature furnace, heating from room temperature to 1100-1200 ℃ at the heating rate of 4-6 ℃/min, preserving the heat for 50-70min, and quickly cooling to room temperature for 2-5min to obtain the lithium salt modified cement clinker;
mixing the cement clinker with anhydrite according to the proportion, and grinding the mixture to 480-500 m2·kg-1Finally obtaining the modified sulphoaluminate cement.
In specific implementation, the cement raw meal can be at least one selected from limestone, alumina, dihydrate gypsum, red mud, phosphogypsum, chromium slag and fly ash. When the cement raw material consists of limestone, alumina, dihydrate gypsum, red mud, phosphogypsum, chromium slag and fly ash, the cement raw material comprises the following components in percentage by mass: 35-55% of limestone; 15-20% of bauxite; 0-20% of dihydrate gypsum; 0-25% of red mud; 0-30% of phosphogypsum; 0-5% of chromium slag; 2-4% of fly ash; the preferred ratio in percentage by mass is as follows: 40% of limestone; 20 percent of alumina; 0% of dihydrate gypsum; 15% of red mud; 18% of phosphogypsum; 5% of chromium slag; 2% of fly ash; therefore, the optimized cement can ensure that the prepared cement has excellent mechanical property and can fully utilize various industrial solid wastes.
In specific implementation, the lithium salt may be selected from lithium sulfate, lithium nitrate, lithium chloride, lithium slag, lithium-containing tailings and lithium carbonateOne kind of the material is selected; in view of energy saving and environmental protection, lithium carbonate is preferred herein in the present invention because of the CO released by lithium carbonate2Greenhouse gases only, relative to SO2And NO has less environmental impact.
In specific implementation, the mass ratio of the cement raw material to the lithium salt may be 100: (0.002-0.009), preferably in a mass ratio of 100: 0.02%, so that the strength of the prepared cement in the early, middle and late stages can be highest, the strength in the early stage for 4 hours can reach 30.2MPa, the strength in the middle stage for 28d can reach 80.2MPa, and the strength in the later stage for 90d can reach 104.5 MPa.
In specific implementation, the high-temperature calcination temperature can be 1150-1250 ℃, and the heat preservation time can be 30-60 min; preferably, the high-temperature calcination temperature is 1200 ℃, the heat preservation time is 60min, so that the later strength of the cement prepared by the optimized post-calcined cement clinker is the highest, and the 90d strength can reach 108 MPa.
The invention also provides a building material, which comprises the modified sulphoaluminate cement; the building material is mortar or concrete.
The present invention will be described in detail with reference to examples. The following examples are given to illustrate the detailed embodiments and specific procedures, but the scope of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.
Example 1:
the embodiment provides modified sulphoaluminate cement, which comprises the following components in percentage by mass: 75% of lithium salt modified cement clinker and 25% of anhydrite;
the preparation method of the modified sulphoaluminate cement comprises the following steps:
(1) the cement raw material comprises the following components in percentage by mass: 51% of limestone, 19% of alumina, 28% of phosphogypsum and 2% of fly ash, and the specific components of the raw materials are shown in Table 1. Adding 0.002% lithium carbonate into cement raw material, and grinding into raw material powder (450 m) with laboratory ball mill2·kg-1)；
(2) Adding raw material powder into deionized water accounting for 8 wt% of the raw material powder, uniformly stirring, pressing into a raw material cake, and drying;
(3) and (3) placing the raw meal cake in a high-temperature furnace, heating from room temperature to 1150 ℃ at the heating rate of 5 ℃/min, preserving the heat for 60min, taking out, and quenching by blast air (3min) to room temperature to obtain the dicalcium silicate-calcium sulfoaluminate-calcium sulfosilicate cement clinker. Through detection and analysis, the cement clinker comprises the following main minerals in percentage by mass: 46.18 percent of calcium sulphoaluminate, 32.25 percent of calcium sulphosilicate, 12.36 percent of dicalcium silicate, 5.27 percent of iron aluminate mineral, 2.11 percent of free gypsum, 0.03 percent of free calcium oxide, 0.001 percent of lithium oxide, 1.1 percent of gehlenite and 0.7 percent of perovskite;
(4) adding 25 wt% of anhydrite (chemical composition of anhydrite is shown in table 1) into cement clinker, grinding for 30min by a ball mill to prepare the modified sulphoaluminate cement, and controlling the specific surface area to be (490 +/-10) m2·kg-1。
Table 1 raw material chemical composition (%)
Figure BDA0002852727400000081
Example 2:
the embodiment provides modified sulphoaluminate cement, which comprises the following components in percentage by mass: 80% of lithium salt modified cement clinker and 20% of anhydrite;
the preparation method of the modified sulphoaluminate cement comprises the following steps:
(1) the cement raw material comprises the following components in percentage by mass: 43% of limestone, 23% of red mud, 15% of alumina, 16% of dihydrate gypsum and 3% of fly ash, and the specific components of the raw materials are shown in Table 2. Adding 0.02% lithium carbonate into cement raw material, and grinding into raw material powder (470 m) with laboratory ball mill2·kg-1)；
(2) Adding raw material powder into deionized water accounting for 8 wt% of the raw material powder, uniformly stirring, pressing into a raw material cake, and drying;
(3) and (3) placing the raw meal cake in a high-temperature furnace, heating from room temperature to 1200 ℃ at the heating rate of 5 ℃/min, preserving the heat for 60min, taking out, and quenching by blast (2min) to room temperature to obtain the dicalcium silicate-calcium sulfoaluminate-calcium sulfosilicate cement clinker. Through detection and analysis, the cement clinker comprises the following main minerals in percentage by mass: 40.39% of calcium sulphoaluminate, 36.27% of calcium sulphoaluminate, 14.95% of dicalcium silicate, 7.93% of iron aluminate minerals, 0.24% of free gypsum, 0.05% of free calcium oxide, 0.01% of lithium oxide, 0.11% of gehlenite and 0.06% of perovskite;
(4) adding 20% anhydrite (chemical composition of anhydrite is shown in table 2) into cement clinker, grinding for 25min by a ball mill to obtain the modified sulphoaluminate cement, and controlling the specific surface area to be (490 +/-10) m2·kg-1。
Table 2 raw material chemical composition (%)
Figure BDA0002852727400000091
Example 3:
the embodiment provides modified sulphoaluminate cement, which comprises the following components in percentage by mass: 85% of lithium salt modified cement clinker and 15% of anhydrite;
a preparation method of modified sulphoaluminate cement comprises the following preparation steps:
(1) the cement raw material comprises the following components in percentage by mass: 40% of limestone, 15% of red mud, 20% of bauxite, 18% of phosphogypsum, 5% of chromium slag and 2% of fly ash, and the specific components of the raw materials are shown in Table 3. Adding 0.9 mass percent of lithium carbonate into the cement raw material, and finally grinding the lithium carbonate into raw material powder (430 m) by using a laboratory ball mill2·kg-1)；
(2) Adding raw material powder into deionized water accounting for 8 wt% of the raw material powder, uniformly stirring, pressing into a raw material cake, and drying;
(3) and (3) placing the raw meal cake in a high-temperature furnace, raising the temperature from room temperature to 1250 ℃ at the heating rate of 5 ℃/min, preserving the temperature for 30min, taking out the raw meal cake, and quenching the raw meal cake by blast for 5min to room temperature to obtain the dicalcium silicate-calcium sulfoaluminate-calcium sulfosilicate cement clinker. Through detection and analysis, the main mineral composition of the cement clinker is as follows: 47.64 percent of calcium sulphoaluminate, 20.68 percent of calcium sulphosilicate, 19.81 percent of dicalcium silicate, 6.41 percent of iron aluminate mineral, 3.22 percent of free gypsum, 0.03 percent of free calcium oxide, 0.5 percent of lithium oxide, 1.0 percent of gehlenite and 0.71 percent of perovskite.
(4) Adding 15% anhydrite (chemical composition of anhydrite is shown in table 3) into cement clinker, grinding for 35min by a ball mill to obtain the modified sulphoaluminate cement, and controlling the specific surface area to be (490 +/-10) m2·kg-1。
TABLE 3 raw material chemical composition (%)
Figure BDA0002852727400000101
Comparative example 1:
the cement clinker is prepared by mixing 34 wt% of limestone, 48 wt% of alumina and 18 wt% of dihydrate gypsum as raw materials, and is baked at 1350 ℃ for 30min to form the common sulphoaluminate cement clinker, wherein the mineral composition of the clinker comprises 69.17 wt% of calcium sulphoaluminate, 23.85 wt% of dicalcium silicate, 5.36 wt% of iron aluminate mineral, 1.20 wt% of free gypsum and 0.02 wt% of free calcium oxide. Then adding anhydrite which respectively accounts for 18wt percent of the mass of the cement into the cement clinker to prepare the common sulphoaluminate cement, and controlling the specific surface area of the cement to be (490 +/-10) m by ball mill grinding2·kg-1。
Comparative example 2:
30 wt% of limestone, 50 wt% of alumina and 20 wt% of dihydrate gypsum are used as raw materials to prepare cement raw materials, and the cement raw materials are subjected to heat preservation at 1350 ℃ for 30min to be fired into ordinary sulphoaluminate cement clinker, wherein the mineral composition of the clinker comprises 65.20 wt% of sulphoaluminate calcium, 25.38 wt% of dicalcium silicate, 8.21 wt% of aluminoferrite mineral, 1.16 wt% of free gypsum and 0.05 wt% of free calcium oxide. Then adding anhydrite accounting for 15 wt% of the cement mass and lithium carbonate accounting for 0.03 wt% of the cement mass into the cement clinker to prepare common sulphoaluminate cement, and controlling the specific surface area of the cement to be (490 +/-10) m through grinding by a ball mill2·kg-1。
The cement setting time and the compressive strength of the net paste were measured in examples 1 to 3 and comparative example, respectively, according to GB1346-2001 test method for water consumption, setting time and stability at standard consistency of cement and GB/T17671-1999 test method for cement strength, and the test results are shown in Table 4. The pH values of the cement 6h hydration products prepared in examples 1-3 and comparative example were measured using a METTLER TOLEDO FE20 pH meter, and the results are shown in Table 5. Hydration heat release curves of the cements prepared in examples 1 to 3 and comparative examples 1 to 2 were measured using a TAM-Air eight-channel isothermal calorimeter, and the results are shown in FIG. 1. The mineral phase compositions of the cement 6h hydration products prepared in example 2 and comparative examples 1-2 were measured using a D8X-ray diffractometer, and the results of the measurements are shown in fig. 2. The physicochemical changes of the cement 28d hydration products prepared in example 2 and comparative examples 1-2 during the temperature rise were measured by a simultaneous isothermal differential scanning calorimeter, and the test results are shown in fig. 3.
TABLE 4 results of physical Properties test of modified sulfoaluminate cements prepared in examples 1 to 3 of the present invention and sulfoaluminate cements of comparative examples 1 to 2
Figure BDA0002852727400000111
TABLE 5 pH values of modified sulfoaluminate cements prepared in examples 1 to 3 of the present invention and sulfoaluminate cements of comparative examples 1 to 2 after 6-hour hydration
Example 1 Example 2 Example 3 Comparative example 1 Comparative example 2
pH value 11.5 11.9 12.3 10.2 10.9
As can be seen from the data in Table 4 and FIG. 1, the modified sulphoaluminate cements prepared by the examples 1-3 of the invention have obviously accelerated early hydration heat release rate, obviously shortened initial setting and final setting time, obviously improved early compressive strength of 4h, 6h and 1d, continuously increased middle and later strength of the cement and no phenomenon of retrogradation of the later strength of the cement in the comparative examples 1-2 compared with the comparative example 1. The data in Table 5 show that the pH value of the early stage (hydration time 6h) hydration product of the modified sulphoaluminate cement prepared by the invention in the examples 1-3 is obviously higher than that of the modified sulphoaluminate cement prepared by the comparative examples 1-2, which shows that the lithium oxide dissolved in the cement clinker is released along with the dissolution and hydration of the mineral, and the alkalinity of the sulphoaluminate cement hydration environment is improved by the lithium hydroxide generated by the reaction with the water. Meanwhile, as can be seen from fig. 2, the diffraction peak intensities of ettringite and alumina gel in the cement hydration product prepared in example 2 are obviously higher than those in comparative examples 1-2, which shows that the generated lithium hydroxide further promotes the dissolution of aluminum and accelerates the formation of the hydration product ettringite and alumina gel. It can be seen from fig. 3 that, after the modified sulphoaluminate cement prepared in example 2 is cured for 28 days, the decomposition endothermic peak intensity of hydration products such as ettringite, hydrated gehlenite and C-S-H gel is obviously higher than that of the hydration products in comparative examples 1-2, which shows that the alumina gel formed in the early stage of hydration can participate in the hydration reaction of calcium sulphosilicate mineral, promotes the calcium sulphoaluminate mineral to generate products such as ettringite, hydrated gehlenite and C-S-H gel in the middle and later stages of the hydration reaction of the cement, promotes the further development of the middle and later stage intensity of the sulphoaluminate cement, and avoids the occurrence of the phenomenon of the later stage intensity retraction.
In conclusion, the measures adopted in the embodiments 1 to 3 of the invention are effective, and the modified sulphoaluminate cement prepared by the invention not only can accelerate the early hydration process of the cement, but also can improve the stable development of the middle and later strength of the cement, solve the problem of the retrogradation of the later strength of the cement and expand the application of the sulphoaluminate cement in more fields.
The recitation of numerical ranges herein includes all numbers subsumed within that range and includes any two numbers subsumed within that range. Different values of the same index appearing in all embodiments of the invention can be combined arbitrarily to form a range value.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and any simple modification, equivalent change and modification made to the above embodiment according to the technical spirit of the present invention are still within the scope of the technical solution of the present invention.

Claims (13)

1. The modified sulphoaluminate cement is characterized by comprising the following components in percentage by mass:
75 to 85 percent of lithium salt modified cement clinker;
15 to 25 percent of gypsum.
2. The modified sulphoaluminate cement of claim 1 wherein the lithium salt content of the lithium salt modified cement clinker is from 0.002 to 0.9 wt%.
3. The modified sulphoaluminate cement of claim 1 or claim 2 wherein the lithium salt is selected from one of lithium sulphate, lithium nitrate, lithium chloride, lithium slag, lithium containing tailings and lithium carbonate; the gypsum is selected from one of anhydrite, dihydrate gypsum and phosphogypsum.
4. The modified sulphoaluminate cement of claim 3 wherein the lithium salt is selected from lithium carbonate; the gypsum is selected from anhydrite.
5. The modified sulphoaluminate cement of claim 1 wherein the cement clinker comprises, in mass percent: 40-55% of anhydrous calcium sulphoaluminate; 20-40% of calcium sulfosilicate; 10-20% of dicalcium silicate; 3-8% of an iron aluminate mineral; 0-5% of free gypsum; 0-0.2% of free calcium oxide; 0.001-0.5% of lithium oxide; 0.1-1.2% of gehlenite; 0.05-0.8% of perovskite.
6. The modified sulphoaluminate cement of claim 1, wherein the initial setting time of the modified sulphoaluminate cement is 5-18 min, the final setting time is 9-25 min, the compressive strength at 4h is 18-31 MPa, the compressive strength at 6h is 32-40 MPa, the compressive strength at 1d is 40-50 MPa, the compressive strength at 3d is 45-55 MPa, the compressive strength at 28d is 75-85 MPa, and the compressive strength at 90d is 95-108 MPa.
7. A method for preparing a modified sulphoaluminate cement according to any of claims 1 to 6, comprising the steps of:
the cement raw materials and the lithium salt are ground and mixed according to the mass percentage, the lithium salt modified cement clinker is prepared by high-temperature calcination and quick cooling to room temperature, and then the cement clinker is mixed with gypsum and ground, and finally the modified sulphoaluminate cement is obtained.
8. The method for preparing modified sulphoaluminate cement of claim 7, wherein the mass ratio of the cement raw meal to the lithium salt is 100: (0.002-0.9); the lithium salt is selected from one of lithium sulfate, lithium nitrate, lithium chloride, lithium slag, lithium-containing tailings and lithium carbonate; the gypsum is selected from one of anhydrite, dihydrate gypsum and phosphogypsum.
9. The method for producing a modified sulfoaluminate cement of claim 8, wherein the cement raw material is at least one selected from the group consisting of limestone, alumina, dihydrate gypsum, red mud, phosphogypsum, chromium slag and fly ash; the lithium salt is selected from lithium carbonate; the gypsum is selected from anhydrite.
10. The method for preparing modified sulphoaluminate cement of claim 9, wherein when the cement raw meal consists of limestone, alumina, dihydrate gypsum, red mud, phosphogypsum, chromium slag and fly ash, the cement raw meal comprises, in mass percent:
35-55% of limestone; 15-20% of bauxite; 0-20% of dihydrate gypsum; 0-25% of red mud; 0-30% of phosphogypsum; 0-5% of chromium slag; 2-4% of fly ash.
11. The method for preparing the modified sulphoaluminate cement of claim 7, wherein the high temperature calcination is carried out at 1150-1250 ℃ for 30-60 min; the quick cooling time is 2-5 min; the specific surface area range of the powder grinding is 480-500 m2·kg-1。
12. A building material, characterized in that it comprises a modified sulphoaluminate cement according to any of claims 1 to 6.
13. The building material of claim 12, wherein the building material is mortar or concrete.
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