CN112608047B - Modified sulphoaluminate cement and preparation method and application thereof - Google Patents
Modified sulphoaluminate cement and preparation method and application thereof Download PDFInfo
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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
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- 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
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- C04B22/143—Calcium-sulfate
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Abstract
The invention discloses modified sulphoaluminate cement and a preparation method thereof, wherein the modified sulphoaluminate cement comprises lithium in percentage by mass75% -85% of salt modified cement clinker; 15-25% of gypsum. The preparation method comprises the steps of mixing lithium salt with a sulphoaluminate cement raw material, calcining at high temperature for 30-60 min, rapidly 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 clinker 2 The discharge amount, and the setting time of the sulphoaluminate cement is greatly shortened and the early strength is remarkably improved by introducing lithium oxide and calcium sulphosilicate minerals into the cement clinker, so that the stable and continuous development of the middle and later strengths of the sulphoaluminate cement can be maintained, and the problem that the later strengths of the sulphoaluminate cement are inverted is solved.
Description
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 silicate cement, the sulphoaluminate cement not only can reduce energy consumption and CO in the preparation process 2 The method has the characteristics of high setting speed, rapid early performance development, excellent corrosion resistance and the like, is non-silicate cement with the largest yield in China at present, and is widely used in the fields of quick construction, low-temperature construction, ocean engineering, concrete products and the like. Although the sulfoaluminate cement taking calcium sulfoaluminate as a main mineral has the characteristic of early strength and quick hardening, when the sulfoaluminate cement is applied to emergency projects such as waterproof plugging, quick repair and the like, the engineering requirements cannot be met only by virtue of the early hydration and performance development of the sulfoaluminate cement, and a proper accelerator is required to be doped for performance adjustment. Meanwhile, in the hydration process of the sulphoaluminate cement, calcium sulphoaluminate minerals are hydrated in early stage to generate high-sulfur hydrated calcium sulphoaluminate (ettringite), but with the progress of hydration reaction, calcium sulfate is gradually consumed, SO in the cement hardening body pore solution 4 2- The strength contributor ettringite is gradually converted into low-sulfur hydrated calcium sulfoaluminate, and the hydration activity of belite minerals in the cement is low, so that the strength of the sulfoaluminate cement is increased and weakened in the middle and later stages, and even the problem of shrinkage of the cement in the later stages occurs. Therefore, the method for further accelerating the early hydration of the sulphoaluminate cement and improving the stable development of the middle and later strengths of the sulphoaluminate cement is suitable for the increasingly diversified and urgent problems to be solved in the current construction.
The current research results show that the lithium salt can be used as an effective coagulant for the sulphoaluminate cement, can promote 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 the sulphoaluminate cement by using lithium salt is to disperse the lithium salt in water in advance and mix the lithium salt with cement, so that the lithium salt is difficult to be fully mixed with the cement, the action time of the early hydration of the cement and the lithium salt is not matched, the situation of unstable performance is often caused, and because the lithium salt promotes rapid generation of ettringite crystals under the external environment of cement particles, a compact hydration product layer is easily formed on the surfaces of the cement particles to wrap unhydrated minerals of the cement particles, 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 cement hydration process, furthest exert the effect of the lithium salt, and not influence the subsequent hydration process of the cement, researches are currently carried out to try to prepare lithium salt modified sulphoaluminate cement clinker by pre-uniformly mixing the lithium salt with cement raw materials and calcining the mixture at a high temperature, and finally, the rapid hardening sulphoaluminate cement meeting the requirements is prepared. However, this study has the following technical problems: (1) Part of lithium salt is easy to release SO after calcination in cement raw material 2 And NO and other harmful gases; (2) The firing range of the sulphoaluminate cement clinker is generally 1300-1400 ℃, and Li 2 O is easy to volatilize in a large amount at the temperature of more than 1250 ℃ and easily causes the loss of lithium components in clinker.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention mainly aims to provide modified sulphoaluminate cement, a preparation method and application thereof, and aims to solve the technical problems that lithium salt released by pyrolysis without harmful gas is dissolved in the prepared modified dicalcium silicate-calcium sulphoaluminate-calcium sulphosilicate cement clinker, so that the promotion effect of lithium salt and calcium sulphosilicate mineral is exerted in the sulphoaluminate cement to the greatest extent, the early hydration process of the sulphoaluminate cement is further accelerated, and the stable development of the middle-late strength of the cement is improved.
The aim and the technical problems of the invention are realized by adopting the following technical proposal. The invention provides modified sulphoaluminate cement, which comprises the following components in percentage by mass:
75% -85% of lithium salt modified cement clinker;
15-25% 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 the following components in percentage by mass: 40-55% of anhydrous calcium sulfoaluminate; 20-40% of calcium sulfosilicate; 10-20% of dicalcium silicate; 3-8% of ferroaluminate minerals; free gypsum 0-5%; free calcium oxide 0-0.2%; 0.001 to 0.5 percent of lithium oxide, 0.1 to 1.2 percent of gehlenite and 0.05 to 0.8 percent 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 of the modified sulphoaluminate cement is 9-25 min, the 4h compressive strength is 18-31 MPa, the 6h compressive strength is 32-40 MPa, the 1d compressive strength is 40-50 MPa, the 3d compressive strength is 45-55 MPa, the 28d compressive strength is 75-85 MPa, and the 90d compressive strength is 95-108 MPa.
The aim and the technical problems of the invention are realized by adopting the following technical proposal. The preparation method of the modified sulphoaluminate cement provided by the invention comprises the following steps:
and grinding and mixing the cement raw material and lithium salt according to the mass percentage, calcining at high temperature, rapidly cooling to room temperature to obtain lithium salt modified cement clinker, mixing the cement clinker with anhydrite, and grinding to obtain the modified sulphoaluminate cement.
Further, the preparation method of the modified sulphoaluminate cement comprises the following steps of: (0.002-0.009).
Further, the preparation method of the modified sulphoaluminate cement comprises the step of preparing lithium salt, wherein the lithium salt is lithium sulfate, lithium nitrate, lithium chloride, lithium slag, lithium-containing tailings or lithium carbonate.
Further, the preparation method of the modified sulphoaluminate cement comprises the step of preparing the modified sulphoaluminate cement, wherein the lithium salt is lithium carbonate.
Further, according to the preparation method of the modified sulphoaluminate cement, the cement raw material is at least one selected from limestone, bauxite, dihydrate gypsum, red mud, phosphogypsum, chromium slag and fly ash.
Further, in the preparation method of the modified sulphoaluminate cement, when the cement raw material consists of limestone, bauxite, 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; phosphogypsum 0-30%; 0-5% of chromium slag; 2-4% of fly ash.
Further, the preparation method of the modified sulphoaluminate cement comprises the steps of calcining at the high temperature of 1150-1250 ℃ and preserving heat for 30-60 min.
Further, in the preparation method of the modified sulphoaluminate cement, the rapid cooling time is 2-5 min.
Further, in the preparation method of the modified sulphoaluminate cement, the specific surface area of the grinding is 480-500 m 2 ·kg -1 。
The aim and the technical problems of the invention are realized by adopting the following technical proposal. According to the invention, the building material comprises the modified sulphoaluminate cement.
Preferably, the building material is mortar or concrete.
By means of the technical scheme, the modified sulphoaluminate cement and the preparation method and application thereof have the following beneficial effects:
1. the invention is based on Na 2 O、K 2 O、P 2 O 5 、CaF 2 And Cr (V) 2 O 3 And the effect of forming calcium sulfoaluminate minerals at low temperature can be accelerated, the industrial solid wastes such as red mud, phosphogypsum, chromium slag and the like are utilized to replace part of the traditional raw materials such as limestone, alumina, dihydrate gypsum and the like, and are mixed with lithium salt such as lithium carbonate to be calcined at 1150-1250 ℃ to prepare lithium salt modified dicalcium silicate-calcium sulfoaluminate-calcium sulfosilicate cement clinker, and finally the modified sulfoaluminate 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 age can be continuously increased) is prepared.
2. The preparation method expands the application of red mud, chromium slag and other industrial solid wastes in the preparation of calcium silicate-sulphoaluminate cement clinker, avoids the phenomenon that lithium oxide volatilizes in a large amount at the temperature of over 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 stably increased middle and later strengths. The initial setting time of the cement is 5-18 min, the final setting time is 9-25 min, the compressive strength for 4h is 18-31 MPa, the compressive strength for 6h is 32-40 MPa, the compressive strength for 1d is 40-50 MPa, the compressive strength for 3d is 45-55 MPa, the compressive strength for 28d is 75-85 MPa, and the compressive strength for 90d is 95-108 Mpa; this is because, on the one hand, solid solution of lithium oxide stabilizes calcium sulfoaluminate in the cubic crystal form, which has higher early hydration 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 mineral dissolution and hydration, lithium hydroxide generated by reaction with water can improve the alkalinity of the hydration environment of the sulphoaluminate cement, promote the dissolution of aluminum, accelerate the formation of ettringite and alumina gel which are hydration products, simultaneously, the alumina gel can participate in the hydration reaction of calcium sulphosilicate minerals, promote the calcium sulphosilicate minerals to generate hydration products such as ettringite, hydrated gehlenite and C-S-H gel in the middle and later stages of the cement hydration reaction, promote the further development of the middle and later stage strength of the sulphoaluminate cement, and avoid the occurrence of the phenomenon of later-stage strength collapse.
4. The firing temperature of the dicalcium silicate-calcium sulfoaluminate-calcium sulfosilicate cement clinker is 100-200 ℃ lower than that of the common sulfoaluminate cement clinker, the consumption of limestone is lower than that of the common sulfoaluminate cement, and the energy consumption and CO are prepared 2 The discharge amount is significantly reduced.
5. The modified sulphoaluminate cement prepared by the invention can be suitable for projects such as waterproof plugging, quick repair and the like, and the later strength of the cement is not inverted.
The foregoing description is only an overview of the present invention, and is intended to provide a more thorough understanding of the present invention, and is to be accorded the full scope of the present invention.
Drawings
FIG. 1 is a graph showing the hydration heat release rate of cements produced 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 6 hours of hydration.
FIG. 3 is a thermal analysis chart of hydration products of the cement 28d prepared in example 2 and comparative examples 1-2.
Detailed Description
In order to further illustrate the technical means and effects adopted by the invention to achieve the preset aim, the following is a detailed description of a modified sulphoaluminate cement, a preparation method thereof, a specific implementation mode, a structure, characteristics and effects thereof, which are provided by the invention, in combination with a preferred embodiment. In the following description, different "an embodiment" or "an embodiment" do not necessarily refer to the same embodiment. Furthermore, the particular features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.
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% -85% of lithium salt modified cement clinker;
15% -25% of gypsum;
the lithium salt content in the lithium salt modified cement clinker can be 0.002-0.9%, preferably 0.02wt%, and the early 4h strength of the modified sulphoaluminate cement can reach the highest value after the preference, and is 30.2MPa; the gypsum can be anhydrite or dihydrate gypsum or phosphogypsum, preferably anhydrite, and the anhydrite is selected so that the cement strength is higher, and the 90d strength of the cement can reach 108MPa at most.
In specific implementation, the modified sulphoaluminate cement preferably comprises the following components in percentage by mass:
80% of lithium salt modified cement clinker;
20% of anhydrite;
this is preferred to give the cement a higher strength than cements of other proportions.
In specific implementation, the cement clinker comprises the following components in percentage by mass: 40-55% of anhydrous calcium sulfoaluminate; 20-40% of calcium sulfosilicate; 10-20% of dicalcium silicate; 3-8% of ferroaluminate minerals; free gypsum 0-5%; free calcium oxide 0-0.2%; 0.001 to 0.5 percent of lithium oxide, 0.1 to 1.2 percent of gehlenite and 0.05 to 0.8 percent of perovskite; the preferable proportion is: 40.39% of calcium sulfoaluminate, 36.27% of calcium sulfosilicate, 14.95% of dicalcium silicate, 7.93% of aluminoferrite mineral, 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; this is preferred because the strength of the post-cement is 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 for 4h is 18-31 MPa, the compressive strength for 6h is 32-40 MPa, the compressive strength for 1d is 40-50 MPa, the compressive strength for 3d is 45-55 MPa, the compressive strength for 28d is 75-85 MPa, and the compressive strength for 90d is 95-108 MPa.
The invention also provides a preparation method of the modified sulphoaluminate cement, which comprises the following steps:
grinding and mixing the cement raw material and lithium salt according to the mass ratio, calcining at high temperature, rapidly cooling to room temperature to obtain lithium salt modified cement clinker, mixing the cement clinker with anhydrite, and grinding to obtain the modified sulphoaluminate cement.
In specific implementation, the rapid cooling time is 2-5min, preferably 2min, so that the cement strength is higher after the rapid cooling is preferred.
In specific implementation, the specific surface area of the grinding is 480-500 m 2 ·kg -1 Preferably 490m 2 ·kg -1 The preferable effect is that the cement strength is more stable.
In specific implementation, the preparation method can comprise the following steps:
grinding and mixing cement raw materials and lithium salt according to a certain mass ratio to obtain raw material powder;
adding deionized water accounting for 6-10wt% of the raw material powder into the raw material powder, uniformly stirring, pressing into a raw material cake, and drying;
placing the raw material cake into a high temperature furnace, heating from room temperature to 1100-1200 ℃ at a heating rate of 4-6 ℃/min, preserving heat for 50-70min, and cooling to room temperature for 2-5min to obtain lithium salt modified cement clinker;
mixing the cement clinker and the anhydrite according to the proportion, and grinding to 480-500 m 2 ·kg -1 Finally, the modified sulphoaluminate cement is obtained.
In particular, the cement raw material may 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, bauxite, 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; phosphogypsum 0-30%; 0-5% of chromium slag; 2-4% of fly ash; the preferred ratios in mass percent are: 40% of limestone; 20% of alumina; gypsum dihydrate 0%; 15% of red mud; phosphogypsum 18%; 5% of chromium slag; 2% of fly ash; after the optimization, the prepared cement has excellent mechanical properties and can fully utilize various industrial solid wastes.
In specific implementation, the lithium salt can be selected from one of lithium sulfate, lithium nitrate, lithium chloride, lithium slag, lithium-containing tailings and lithium carbonate; in view of energy saving and environmental protection, the present invention is preferably lithium carbonate here because of the CO released by lithium carbonate 2 Greenhouse gases only, relative to SO 2 And NO has less environmental impact.
In specific implementation, the mass ratio of the cement raw material to the lithium salt can be 100: (0.002-0.009), the preferable mass ratio is 100:0.02%, so that the prepared cement has the highest early, middle and later strength, the early 4h strength can reach 30.2MPa, the middle 28d strength can reach 80.2MPa, and the later 90d strength can reach 104.5MPa.
In the concrete 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 ℃, and the heat preservation time is 60min, so that the cement prepared from the cement clinker which is preferably post-calcined has the highest post-strength and the 90d strength of 108MPa.
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. Examples the following examples give detailed embodiments and specific procedures on the premise of the technical solution of the present invention, but the scope of the present invention is not limited to the following examples. The methods used in the examples described below 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. The lithium carbonate is externally mixed into cement raw material in the mass ratio of 0.002%, and finally the cement raw material is ground into raw material powder (450 m) by using a laboratory ball mill 2 ·kg -1 )；
(2) Adding deionized water accounting for 8 weight percent of the raw material powder into 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 a heating rate of 5 ℃/min, preserving heat for 60min, taking out the raw meal cake, and carrying out blast quenching (3 min) 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 mineral components in percentage by mass: 46.18% of calcium sulfoaluminate, 32.25% of calcium sulfosilicate, 12.36% of dicalcium silicate, 5.27% of aluminoferrite mineral, 2.11% of free gypsum, 0.03% of free calcium oxide, 0.001% of lithium oxide, 1.1% of gehlenite and 0.7% of perovskite;
(4) Adding 25wt% of anhydrite (the chemical composition of the anhydrite is shown in Table 1) into cement clinker, grinding by a ball mill (30 min) to obtain modified sulphoaluminate cement, and controlling the specific surface area to be (490+/-10) m 2 ·kg -1 。
TABLE 1 chemical composition of raw materials (%)
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. The lithium carbonate is externally mixed into cement raw material in the mass ratio of 0.02%, and finally the cement raw material is ground into raw material powder (470 m) by a laboratory ball mill 2 ·kg -1 )；
(2) Adding deionized water accounting for 8 weight percent of the raw material powder into 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 a heating rate of 5 ℃/min, preserving heat for 60min, taking out the raw meal cake, and carrying out blast quenching (2 min) 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 mineral components in percentage by mass: 40.39% of calcium sulfoaluminate, 36.27% of calcium sulfosilicate, 14.95% of dicalcium silicate, 7.93% of aluminoferrite mineral, 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 by ball mill (25 min) to obtain modified sulphoaluminate cement, controlling specific surface area to be (490+ -10) m 2 ·kg -1 。
TABLE 2 chemical composition of raw materials (%)
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;
the preparation method of the 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 alumina, 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. The lithium carbonate is externally mixed into cement raw material in the mass ratio of 0.9%, and finally the cement raw material is ground into raw material powder (430 m) by a laboratory ball mill 2 ·kg -1 )；
(2) Adding deionized water accounting for 8 weight percent of the raw material powder into the raw material powder, uniformly stirring, pressing into a raw material cake, and drying;
(3) Placing the raw meal cake in a high temperature furnace, heating from room temperature to 1250 ℃ at a heating rate of 5 ℃/min, preserving heat for 30min, taking out the raw meal cake, and carrying out blast quenching (5 min) to room temperature to obtain 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% of calcium sulfoaluminate, 20.68% of calcium sulfosilicate, 19.81% of dicalcium silicate, 6.41% of aluminoferrite minerals, 3.22% of free gypsum, 0.03% of free calcium oxide, 0.5% of lithium oxide, 1.0% of gehlenite and 0.71% of perovskite.
(4) Adding 15% anhydrite (the chemical composition of the anhydrite is shown in Table 3) into cement clinker, grinding by a ball mill (35 min) to obtain modified sulphoaluminate cement, and controlling the specific surface area to be (490+/-10) m 2 ·kg -1 。
TABLE 3 chemical composition of raw materials (%)
Comparative example 1:
34 weight percent of limestone, 48 weight percent of bauxite and 18 weight percent of dihydrate gypsum are used as raw materials to prepare cement raw materials, and the cement raw materials are heat-preserved for 30 minutes at 1350 ℃ to be burned into common sulphoaluminate cement clinker, wherein the mineral composition of the cement raw materials comprises 69.17 weight percent of calcium sulphoaluminate, 23.85 weight percent of dicalcium silicate, 5.36 weight percent of aluminoferrite mineral, 1.20 weight percent of free gypsum and 0.02 weight percent of free calcium oxide. Then the cement is cookedAdding anhydrite accounting for 18wt% of the cement mass into the material to prepare common sulphoaluminate cement, and grinding the common sulphoaluminate cement by a ball mill to control the specific surface area of the cement to be (490+/-10) m 2 ·kg -1 。
Comparative example 2:
30wt% of limestone, 50wt% of bauxite and 20wt% of dihydrate gypsum are used as raw materials to prepare cement raw materials, and the cement raw materials are heat-preserved for 30min at 1350 ℃ to be burned into common sulphoaluminate cement clinker, wherein the mineral composition of the sulphoaluminate cement clinker comprises 65.20wt% of calcium sulphoaluminate, 25.38wt% of dicalcium silicate, 8.21wt% of aluminoferrite mineral, 1.16wt% of free gypsum and 0.05wt% of free calcium oxide. Adding anhydrite accounting for 15wt% of the cement mass and lithium carbonate accounting for 0.03wt% of the cement mass into the cement clinker to prepare common sulphoaluminate cement, and grinding the common sulphoaluminate cement by a ball mill to control the specific surface area of the cement to be (490+/-10) m 2 ·kg -1 。
According to GB1346-2001 "cement Standard consistency Water consumption, setting time, stability test method" and GB/T17671-1999 "Cement Strength test method", examples 1-3 and comparative examples were tested for setting time and net-slurry compressive Strength, respectively, 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 determined using a METTLER TOLEDO FE pH value of METTLER TOLEDO FE pH value, respectively, and the test results are shown in Table 5. The hydration exotherms of the cements prepared in examples 1-3 and comparative examples 1-2 were measured using a TAM-Air eight-channel isothermal calorimeter, respectively, 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 by using a D8X-ray diffractometer, respectively, and the test results are shown in FIG. 2. The physicochemical changes of the hydration products of cement 28d prepared in example 2 and comparative examples 1-2 during the temperature rising process were measured by a synchronous isothermal differential scanning calorimeter, respectively, and the test results are shown in fig. 3.
TABLE 4 physical Property test results of modified sulphoaluminate cements prepared in examples 1 to 3 of the present invention and sulphoaluminate cements of comparative examples 1 to 2
TABLE 5 pH after hydration of the modified sulphoaluminate cements prepared in examples 1 to 3 of the present invention and the sulphoaluminate cements of comparative examples 1 to 2 for 6 hours
| Example 1 | Example 2 | Example 3 | Comparative example 1 | Comparative example 2 | |
| pH value of | 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 in examples 1 to 3 of the present invention have significantly faster early hydration heat release rate, significantly shorter initial setting and final setting times, significantly improved early compressive strength at 4h, 6h and 1d, and continuously increased middle and later strengths of the cement, without the occurrence of late strength scaling phenomenon of the cement in comparative examples 1 to 2. The data in Table 5 shows that the pH value of the early (hydration 6 h) hydration product of the modified sulphoaluminate cement prepared in the embodiment 1-3 is obviously higher than that of the comparative example 1-2, which shows that lithium oxide dissolved in cement clinker is released along with mineral dissolution and hydration, lithium hydroxide generated by reaction with water is generated, and the alkalinity of the hydration environment of the sulphoaluminate cement is improved. Meanwhile, as can be seen from fig. 2, the diffraction peak intensity of ettringite and alumina gel in the cement hydration product prepared in example 2 is obviously higher than that of comparative examples 1-2, which shows that the generated lithium hydroxide further promotes the dissolution of aluminum and accelerates the formation of ettringite and alumina gel as hydration products. As can be seen from FIG. 3, 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 comparative examples 1-2, which shows that alumina gel formed in early stage of hydration can participate in hydration reaction of calcium sulphosilicate mineral, products such as ettringite, hydrated gehlenite and C-S-H gel are promoted to be generated in the middle and later stages of cement hydration reaction, further development of the middle and later stage intensity of the sulphoaluminate cement is promoted, and the phenomenon of late stage intensity collapse is avoided.
In conclusion, the measures taken in the embodiments 1-3 of the invention are effective, and the modified sulphoaluminate cement prepared by the invention not only can accelerate the early hydration process of cement, but also can improve the stable development of the middle and later strengths of cement, solve the problem of shrinkage of the later strengths of cement, and expand the application of the sulphoaluminate cement in more fields.
The numerical ranges recited herein include all numbers within the range and include any two of the range values within the range. The 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 of the preferred embodiments of the present invention, and is not intended to limit the present invention in any way, but any simple modification, equivalent variation and modification made to the above embodiments according to the technical substance of the present invention still fall within the scope of the technical solution of the present invention.
Claims (4)
1. The modified sulphoaluminate cement is characterized by comprising the following components in percentage by mass:
75% -85% of lithium salt modified cement clinker;
15% -25% of gypsum;
the lithium salt modified cement clinker comprises the following components in percentage by mass: 40-55% of anhydrous calcium sulfoaluminate; 20-40% of calcium sulfosilicate; 10-20% of dicalcium silicate; 3-8% of ferroaluminate minerals; free gypsum 0-5%; free calcium oxide 0-0.2%; 0.001-0.5% of lithium oxide; 0.1-1.2% of gehlenite; 0.05-0.8% of perovskite;
the initial setting time of the modified sulphoaluminate cement is 5-18 min, the final setting time is 9-25 min, the compressive strength for 4h is 18-31 MPa, the compressive strength for 6h is 32-40 MPa, the compressive strength for 1d is 40-50 MPa, the compressive strength for 3d is 45-55 MPa, the compressive strength for 28d is 75-85 MPa, and the compressive strength for 90d is 95-108 MPa;
the lithium salt is selected from lithium carbonate; the gypsum is selected from anhydrite;
the content of lithium salt in the lithium salt modified cement clinker is 0.002-0.9wt%;
grinding and mixing cement raw materials and lithium salt according to mass percent, calcining at high temperature, rapidly cooling to room temperature to obtain lithium salt modified cement clinker, mixing the cement clinker with gypsum, and grinding to obtain modified sulphoaluminate cement;
the mass ratio of the cement raw material to the lithium salt is 100: (0.002 to 0.9);
the cement raw material comprises the following components in percentage by mass:
35-55% of limestone; 15-20% of alumina; 0-20% of dihydrate gypsum; 0-25% of red mud; 0-30% of phosphogypsum; 0-5% of chromium slag; 2-4% of fly ash.
2. The modified sulphoaluminate cement of claim 1, wherein the high-temperature calcination temperature is 1150-1250 ℃ and the heat preservation time is 30-60 min; the rapid cooling time is 2-5 min; the specific surface area of the grinding machine ranges from 480 m to 500m 2 ·kg -1 。
3. A building material comprising the modified sulfoaluminate cement of claim 1.
4. A building material according to claim 3, wherein the building material is mortar or concrete.
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