WO2015007226A1 - Dolomite composite admixture preparation method and novel application - Google Patents

Abstract

A dolomite composite admixture preparation method and novel application; the dolomite composite admixture preparation method comprising: levigating dolomite to particles basically the same as silicate concrete; adding a specific proportion of dolomite powder by mass of silicate concrete; adding a specific equivalent amount of alkali-containing substance of sodium oxide by mass of dolomite powder, and mixing uniformly to prepare concrete composite admixture having impermeability performance. Concrete having anti-freezing and impermeability features and high flexural strength can be prepared by adding a dolomite composite admixture by mass of silicate concrete when preparing high durability concrete.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing a concrete composite admixture, and more particularly to a method for preparing a dolomite composite admixture and a novel application thereof. BACKGROUND OF THE INVENTION It is well known that if dolomite is used as an aggregate in a concrete mix, the dolomite aggregate will react with the alkali in the cement, i.e., alkali-carbonate reaction. The alkali-carbonate reaction is a reaction between the alkali in the cement and the dolomite in the coarse aggregate under the condition of water, and causes the local volume expansion of the concrete, which may even cause cracking of the concrete, which is caused by the concrete alkali aggregate. One of the reasons for the reaction, so far, the purpose of studying the alkali aggregate reaction is mostly to prevent and inhibit the alkali aggregate reaction from causing damage to concrete engineering. On the other hand, during the hardening process of cast-in-place concrete, ordinary concrete will produce large volume shrinkage due to moisture volatilization, physical and chemical reactions, changes in ambient temperature and humidity, etc., and even cracks may occur due to volume shrinkage. , adversely affecting the load carrying capacity, workability, durability and the like of concrete. Therefore, in the project, it is usually used to increase the reinforcement, reduce the water-cement ratio, strengthen the maintenance, incorporate some high-quality mineral fine aggregates, shrinkage reducer, expansion agent, etc. to solve the impact of concrete volume shrinkage. Although the volume shrinkage and cracking of concrete are reduced to some extent, there are still some shortcomings such as high cost slump loss and high speed. Feng Xiaoxin et al. introduced the "alkali-carbonate reaction (also known as de-dosphing reaction) in the Journal of the Chinese Academy of Ceramics 2005, "Expansion Mechanism of Alkali Carbonate Reaction". The mechanism is as follows: CaMg (C0 ₃ ) ₂ + 2MOH = CaC0 ₃ + Mg(OH) ₂ + M ₂ C0 ₃ where M is an alkali metal ion: Na ⁺ , K ⁺ , Li ⁺ . In addition to calcite and brucite, the product layer of the de-Dolomitization reaction There are K ⁺ , Na ⁺ and C0 ₃ ² _ ions, that is, the reaction products K ⁺ , Na ⁺ and C0 ₃ ^{2 of the} de-Dovamitization reaction do not return to the pore solution, but remain in the product layer to occupy a certain space. Therefore, the space occupied by the dolomitization reaction product is larger than the space occupied by the dolomite participating in the reaction, thereby causing expansion. Tang Mingshu also introduced the alkali carbonate expansion mechanism in the third phase of the China Science Foundation in 1995. The Mg ²⁺ ions on the dolomite surface combine with the 011_ ions to form brucite. The calcium carbonate at the original surface layer forms calcite and swells. By Due to local reaction and crystallization pressure, the free energy G298 of the dolomite reaction is negative, about -12.19kJ, that is, the reaction can be carried out at room temperature, which is also the driving force for ions to enter the confined space. The essence is the process by which magnesium carbonate in dolomite reacts with hydroxide ions in an environmental solution to form magnesium hydroxide. Moreover, a large number of experimental results show that the alkali carbonate reaction is different from the alkali-silicic acid reaction, and the alkali-carbonate reaction cannot be effectively inhibited even with a low alkali cement or a common admixture. However, this provides a convenient way to prepare dolomite impervious concrete composite admixture, that is, the amount of dolomite expansion can be controlled by controlling the alkali content. Impervious concrete can generally be made of concrete mixed with an appropriate amount of expansion agent or expanded cement. According to the common types of expansion agents can be divided into: calcium sulphoaluminate, calcium sulphoaluminate - calcium oxide, calcium oxide expansion agent, light burnt magnesium oxide, light burnt dolomite. Although such a swelling agent can effectively solve the problem that concrete shrinkage improves the impermeability of concrete, the production process is complicated, high-temperature sintering is required, and the amount of expansion is difficult to control, and the storage time is too long, which causes a decrease in activity and is generally expensive.

CN102180613A discloses "a steel slag composite powder and a preparation method thereof", which comprises the following raw materials by weight ratio: hot slag steel slag micropowder 30-45, refining slag micropowder 5-10, slag micropowder 30-45, polycarboxylic acid 3-3.5 , triethanolamine 3-3.5, calcium sulfate 5-6, polyaluminum sulfate 4-5 and dolomite powder 2-3. The steel slag composite powder can be used in raw materials of cement, concrete and the like to reduce the manufacturing cost of cement, concrete and the like.

CN101016198 discloses an ultrafine carbonate rock concrete composite admixture and a preparation method thereof, which are composed of ultrafine carbonate rock powder and mineral powder according to 20%-90%: 10%-80% by weight. The carbonate rock used is mainly composed of calcite, dolomite or both. The carbonate rock is ground into an ultrafine powder and mixed with other mineral powders in proportion. The prepared composite admixture can replace 20%-80% cement, reduce the water consumption of concrete, greatly reduce the amount of cement, and formulate high-performance concrete. In addition, eight copies of the patent literature on dolomite and concrete were found on the website of the State Intellectual Property Office:

CN1176231 discloses a method for producing "micro-expansion type Portland cement" to produce a fired cement, and dolomite is only one of the raw materials;

CN1175559 discloses a "micro-expansion, waterproof, crack-resistant colored cement" made of expanded cement mixed with calcined dolomite;

CN1224633 discloses a "desulfurization method for fluidized bed furnace flue gas" as a desulfurizing agent for a combustion boiler;

CN1631830 discloses a "coal gangue active mixed material, a preparation method thereof and a high performance cement" high temperature calcined dolomite to prepare a coal gangue mixed material; CN101040017 discloses a "aqueous epoxy resin system" dolomite as a filler for waterborne epoxy resin, which is used for concrete protection;

CN102776388 A discloses a "Pijiang method for smelting magnesium and application of rare earth oxide as mineralizer" in the form of calcined dolomite, which is mixed into concrete and reacts with water to form a volume expansion effect of magnesium hydroxide. ;

CN101987761A discloses that "a concentric structure latent flow landscape green space system for deep treatment of small-scale dispersed domestic sewage" is related to sewage treatment, and has nothing to do with building materials such as concrete;

CN102050614A discloses "a dolomite magnesium cement concrete and a manufacturing method thereof": dolomite magnesia cement, that is, calcined dolomite and magnesium chloride form magnesium cement; CN102092976A discloses an "ecological bulk concrete expansion agent and preparation method" Calcined dolomite is used as an early expansion of concrete to compensate for shrinkage of concrete. The above patent documents mostly use dolomite as a raw material to produce calcined dolomite by heating, and use the volume expansion of MgO+H ₂ 0→Mg(OH) ₂ to achieve the action of the expansion agent. In the prior art, it is customary to think that the alkali-carbonate reaction is one of the important types of alkali-aggregate reaction, which causes the concrete to expand in volume, causing cracking of the concrete, causing serious damage to the concrete project and visually It is called "cancer" of concrete. So far, the purpose of studying alkali aggregate reaction is to prevent the alkali aggregate reaction from happening, how to effectively inhibit the alkali aggregate reaction, and how to reduce the alkali aggregate reaction caused by concrete engineering. damage. The invention is creative in that it overcomes the existing technical prejudice, adopts a technical means that people have abandoned by technical prejudice, and utilizes the volume expansion generated by the alkali carbonate reaction to compensate for the volume shrinkage of the concrete, and obtains a high volume compactness. Durable concrete with good antifreeze, impermeability and carbonization resistance. SUMMARY OF THE INVENTION The object of the present invention is to provide a method for preparing a dolomite composite admixture for the deficiencies of the above prior art for improving the durability of concrete. Another object of the present invention is to provide a dolomite composite admixture. New applications for ingredients. The object of the present invention is achieved by the following technical solutions: The preparation method of the dolomite composite admixture mainly comprises the following steps: a. grinding the dolomite to a particle size substantially the same as that of the Portland cement; b. When preparing the dolomite composite admixture, mix 2%-20% of dolomite powder according to the quality of the Portland cement, and mix the alkali matter containing <1.5% equivalent of sodium oxide according to the mass of dolomite powder. Preparation of dolomite concrete composite admixture. New application of dolomite composite admixture: In the preparation of concrete, 2%-20% alkali dolomite composite admixture is blended according to the quality of Portland cement, which is formulated to have high impermeability, antifreeze and anti-carbonization properties. High durability concrete. Specific experiment: The cement is the Yatai Group P042.5R ordinary Portland cement produced by Yatai Group. The equivalent alkali content of the tested cement is about 1.16%, which can be regarded as high alkali cement. Dolomite is produced in Shandong. The chemical composition of dolomite is: Ca031.41%, Mg021.86%, C0247.73%, and the ratio of Ca ^{2+ to} Mg ²⁺ is 1:0.69. The ratio of Ca ²⁺ and Mg ^{2+ was} actually measured to be 1:0.67. It was confirmed by X-ray diffractometry to be dolomite, and the dolomite was ground to a particle size by a planetary rapid grinder. According to the provisions of GB/T17671-1999 "Cement mortar strength test method", the test piece is made. Each group of test blocks was filled with different levels of dolomite powder, the odd array was cured in air at a temperature of 20 ° C, and the even array was cured in water at a temperature of 20 ° C. After the cement test piece was removed for 24 hours, the amount of change of the test piece was measured on the second day, the fifth day, the tenth day, the seventeenth day, and the twenty-eighth day, and the experimental values are shown in Table 1. Schedule 1, the variation of the age of the cement specimens mixed with different dolomite under different curing conditions mm

13# 10.0 +0.902 +0.865 +0.773 +0.700 +0.512 20°C空气中

13# 10.0 +0.902 +0.865 +0.773 +0.700 +0.512 20°C in the air

14# 10.0 +0.913 +0.870 +0.785 +0.703 +0.519 20°C water

15# 20.0 +0.918 +0.862 +0.789 +0.752 +0.633 20°C in the air

16# 20.0 +0.922 +0.885 +0.823 +0.737 +0.654 20°C water Note: “+” in the table indicates the expansion of the test piece, “-” indicates the shrinkage of the test piece, and the base length of the test piece is 160mm. °C air curing test specimen strength test results

 Schedule 3, 20 ° C water curing cement test piece strength test results

 Schedule 4, concrete 28-day compression and flexural strength

7-day flexural strength 7-day compressive strength 28-day flexural strength 28-day compressive strength Test No.

 MPa MPa MPa MPa

20% common mineral admixture 30. 46.7

 20% dolomite compound blending

28.9 9.8 46.9 Experimental results, as can be seen from the attached table 1, the dolomite-doped samples mixed with high-alkali cement have undergone health maintenance, and the specimens are slightly expanded. The amount of specimens cured in water is larger than that in air. For ease of analysis and comparison, see Figure 1, Figure 2. From the microstructural analysis of scanning electron microscopy, it can be seen that the microscopic cracks of cement stone added with dolomite See Figure 3 and Figure 4 for details. Figure 5 is a schematic diagram of the results of adding 5% dolomite test piece and blank test piece after 150 freeze-thaw cycles. The addition of 5% dolomite test piece is not damaged. However, the blank sample showed obvious freezing damage after 150 freeze-thaw cycles. Advantageous Effects: After testing, the composite admixture concrete member prepared by the invention does not produce cracks, and at the same time improves the impermeability and flexural strength of the concrete, and the actual impermeability level of 28 days reaches the requirement of P14, the process is simple, and the cost is low. It not only improves the performance of the concrete, but also increases the function of the concrete, and the effect is remarkable, which is an unexpected effect. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in FIG. In the drawings: Figure 1 is a schematic diagram showing the trend of the linear expansion of the test piece during the curing in air with time; Figure 2 is a schematic diagram showing the trend of the linear expansion of the test piece during the maintenance of water in time; Schematic diagram of the scanning electron microscope test results of adding dolomite and curing the test piece in the air, wherein the microscopic crack is visible; Fig. 4 is a schematic diagram of the scanning electron microscope test results of adding 5% dolomite and curing the test piece in the air, wherein no obvious Micro-cracks; Figure 5 is a schematic diagram of the results of adding 5% dolomite specimens and blank specimens after 150 freeze-thaw cycles, in which 5% dolomite specimens were not damaged, and the blanks were frozen at 150 times. Figure 6 is a schematic diagram of the results of scanning electron microscopy of the sample numbered 1# in Schedule 5, showing microscopic cracks; Figure 7 is the sample numbered 11# in Schedule 5. Scanning electron microscopy test results, no obvious micro cracks; Figure 8A is a schematic diagram of the test results after 200 freeze-thaw tests, showing that the blank test piece has obvious frost damage; and Figure 8B is added 6% A schematic diagram of the test results of dolomite specimens after 200 freeze-thaw cycles, which showed that the specimens with 6% dolomite were not damaged. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS It should be noted that the embodiments in the present application and the features in the embodiments may be combined with each other without conflict. The invention will be described in detail below with reference to the drawings in conjunction with the embodiments. The preparation method of the dolomite composite admixture comprises the following steps: a. grinding the dolomite to a particle size substantially the same as that of the Portland cement; b. in the preparation of the dolomite composite admixture, according to the Portland cement The mass is blended with 2%-20% of dolomite powder, and the alkali-containing substance of <1.5% equivalent of sodium oxide is mixed uniformly according to the mass of dolomite powder to prepare a concrete composite admixture with high durability. The new application of dolomite composite admixture, in the preparation of micro-expansion or compensation shrinkage concrete, according to the quality of Portland cement, 2%-20% dolomite composite admixture is blended to prepare it with high impermeability and anti-freeze. High durability concrete resistant to carbonization. Another object of the present invention is to provide a dolomite composite admixture for Portland cement, the dolomite composite admixture comprising dolomite powder and an alkali metal compound, and the fineness of the dolomite powder satisfies the Portland cement The fineness standard, the molar ratio of the alkali metal ion of the alkali metal compound to the dolomite powder is <2:1. The particle size of the dolomite powder in the above dolomite composite admixture is equivalent to the particle size of the Portland cement. Therefore, when it is used as a composite admixture of Portland cement, dolomite powder and alkali generate so-called alkali aggregate in the art. reaction:

CaMg (C0 ₃ ) ₂ + 2MOH = CaC0 ₃ +Mg(OH) ₂ +M ₂ C0 ₃ wherein M is an alkali metal ion: Na ⁺ , K ⁺ , Li ⁺ . The hydroxide ions consumed in the above reaction are from Portland cement, and the corresponding alkali metal ions may be derived from alkali metal compounds or from Portland cement. When the Portland cement contains less alkali metal oxides. The amount of the alkali metal compound in the dolomite composite admixture of the present invention can be appropriately adjusted; it will be apparent to those skilled in the art that the alkali metal ion (M ⁺ ) can be reused and dolomite in the above alkali aggregate reaction. The action of MgC0 ₃ , and its content will affect the progress of the alkali aggregate reaction, so those skilled in the art can use the above reaction principle according to the actual needs, the molar ratio of alkali metal ions to dolomite powder is less than 2:1. The amount of the alkali metal compound is adjusted. The expansion effect of the reaction is used to compensate the volume shrinkage of the concrete, so that the concrete having the volume is high in density; in addition, the magnesium hydroxide formed by the above reaction, that is, the brucite, can make the micropores of the Portland cement. The filling is dense, which increases the resistance of the cement to the liquid flow. Because the brucite colloid has a large specific surface area and good hydrophilicity, it preferentially adsorbs the OH-ion to make the brucite colloid negatively charged and can The hydrated counterion in the molecule and the solution is bound in the colloidal flocculation structure. At this time, the water in the pore is no longer the free water of common nature, but the water molecules are arranged in an orderly manner. According to the capillary, the capillary is finer. The principle that the freezing point of water is larger, and the freezing point of the cationic solution containing Na ⁺ , K ⁺ and the like is lower, so that the water in the inner hole of the concrete and the cement product having the above dolomite composite admixture is at a low temperature condition. It will not freeze underneath, which will improve the impermeability, frost resistance and carbonation resistance of concrete and cement products, thus fundamentally solving the problem of the current low durability of Portland cement. Moreover, the above dolomite powder Used to solve the current use of conventional calcium sulphoaluminate, calcium sulphoaluminate-calcium oxide, calcium oxide, light burnt magnesia, light burnt dolomite, etc. Expansion agent as the cement admixture of complex, high cost problem requires high temperature firing prior to use thereof. The above dolomite powder is a powder of C _a Mg(C0 ₃ ) ₂ which is understood by those skilled in the art, and may be derived from a dolomite chemical product obtained by purification treatment or a dolomite containing dolomite directly, regardless of The dolomite products are also dolomite, which can all achieve the above effects. The alkali metal compound which can be used in the present invention may be an inorganic alkali metal compound which is commonly used in the art, for example, the alkali metal compound is selected from the group consisting of sodium oxide, sodium hydroxide, sodium silicate, sodium carbonate, sodium hydrogencarbonate, sodium sulfate, potassium oxide, One or more of the group consisting of potassium hydroxide, potassium silicate, potassium carbonate, potassium sulfate, lithium oxide, lithium hydroxide, lithium silicate, lithium carbonate, and lithium sulfate. The above alkali metal compounds are capable of forming MOH in the environment of Portland cement, and further providing alkali ions for the alkali aggregate reaction of dolomite. Another object of the present invention is to provide a cement comprising Portland cement and dolomite powder. The amount of dolomite powder is 2-28% by weight, preferably 2-20% by weight of the Portland cement, and the fineness of the dolomite powder is satisfied. The fineness standard of Portland cement. The Portland cement of the present application is the same as the Portland cement in the prior art, and generally has an alkali metal compound. According to the above description, the alkali ions corresponding to the alkali metal ions in the dolomite powder and the Portland cement occur. The alkali aggregate reaction increases the compactness of the concrete and improves the impermeability, frost resistance and carbonation resistance of concrete and cement products. Similarly, the dolomite powder used in the above cement is a powder of CaMg(C0 ₃ ) ₂ which is understood by those skilled in the art, and may be derived from a dolomite chemical product obtained by purification treatment, or may be directly used to contain dolomite. Dolomite, whether using dolomite products or dolomite, can achieve the above effects. In a preferred embodiment of the present invention, the dolomite powder is taken from dolomite having a dolomite content of 70 to 99% by weight, and the dolomite powder is used in an amount of 3 to 12% by weight of the Portland cement. In order to make the above-mentioned cement convenient to use and to make the dolomite therein sufficiently react with the alkali aggregate, it is preferable that the above cement further includes an alkali metal compound, and a part of the alkali metal compound is carried by the acid salt cement to control the alkali of the alkali metal compound. The molar ratio of the metal ion to the dolomite powder is <2: 1, as described above, the alkali metal ion can repeatedly react with the residual dolomite alkali aggregate, and therefore, the amount of the alkali metal compound in the cement of the present invention is controlled as described above. The scope can meet the requirements of enhancing the impermeability, frost resistance and carbonization resistance of cement products. In order to further optimize various performance indexes of the cement, it is preferred that the molar ratio of the above alkali metal ion to dolomite powder is <1:1, more preferably <1:3, more preferably <1:10. The alkali metal compound used in the present invention may be an inorganic alkali metal compound commonly used in the art, such as an alkali metal compound selected from the group consisting of sodium oxide, sodium hydroxide, sodium silicate, sodium carbonate, sodium hydrogencarbonate, sodium sulfate, potassium oxide, One or more of the group consisting of potassium hydroxide, potassium silicate, potassium carbonate, potassium sulfate, lithium oxide, lithium hydroxide, lithium silicate, lithium carbonate, and lithium sulfate. The above alkali metal compounds are capable of forming MOH in the environment of Portland cement, and further providing alkali ions for the alkali aggregate reaction of dolomite. The above-mentioned Portland cement as one of the raw materials is selected from pure cement Portland cement, ordinary Portland cement, slag Portland cement, pozzolan Portland cement, fly ash Portland cement and composite silicate. One or more of the group consisting of cement. Still another object of the present invention is to provide an application of the above cement in mortar or concrete. When the cement of the present invention is applied to mortar or concrete, the anti-freezing, impermeability and anti-carbonization properties of the mortar and concrete can be effectively optimized. Example 1 Anti-cracking mortar: The plaster was composed of PC 32.5 cement: medium sand of 1:3 and an appropriate amount of water, and incorporated 10% by weight of dolomite powder and 0.2% sodium carbonate. Specifically: 370 kg of cement, 1350 kg of medium sand, 37 kg of dolomite powder, 0.037 kg of sodium carbonate. On the red brick clear water wall, the surface of the square was 1 square meter with mortar, and after 7 days, no crack was found in the mortar surface. Also on the red brick clear water wall, the comparative plastering mortar without the dolomite powder is also coated with three pieces of 1 square meter in size. After 7 days, there are fine mortar cracks. Example 2 Impervious concrete: C30P6 pumped impervious concrete reference ratio: P042.5 strength grade cement, cement alkali content 0.85%, cement dosage 275kg, fly ash 80kg, medium sand 840kg, gravel 5~31.5mm The particle size is 1010kg, water is 170kg, and naphthalene-based water reducing agent is 9kg. The 28-day actual detection of the impermeability level reached the P8 requirement. C30P6 pumped impervious concrete test ratio: P042.5 strength grade cement, cement dosage 275kg, fly ash 40kg, dolomite concrete composite admixture 40kg, including sodium hydroxide 0.24 kg, sand 836kg, gravel 5~ 31.5mm particle size 1008 kg, water 170kg, water reducing agent 9kg. The 28-day actual impermeability rating is up to P10. Example 3 Reference composite mineral admixture: composed of 60% fly ash and 40% slag powder. Experimental dolomite composite mineral admixture: composed of 40% fly ash, 39.5% dolomite powder, 0.5% sodium hydroxide and 20% slag powder.

C30 concrete reference mix ratio: P042.5 strength grade cement, cement dosage 278kg, reference compound blending 1450 kg, sand 830kg, gravel 5~31.5mm particle size 1080 kg, water 168kg, water reducing agent 5.4kg.

C30 concrete experimental mix ratio: P042.5 strength grade cement, cement dosage 278kg, dolomite composite admixture 50 kg, sand 830kg, gravel 5~31.5mm particle size 1080 kg, water 168kg, water reducing agent 5.4kg. The 28-day compressive and flexural strength of concrete is shown in Table 4. From the experimental results, it can be seen that the dolomite composite admixture also has the effect of improving the flexural strength of concrete. Example 4 Reference composite mineral admixture: consisting of 60% fly ash and 40% slag powder. Dolomite composite mineral admixture: 40% of fly ash, 39.5% of dolomite powder, 1.2% of sodium dolomite powder, 20% of slag powder.

1) C30P6 pumped impervious concrete blank test mix ratio: P042.5 strength grade cement, cement alkali content 0.85%, cement dosage 278kg, reference composite admixture 80 kg, sand 830kg, gravel (5-31.5mm) 1080 Kg, water 168kg, naphthalene high-efficiency water reducing agent 9kg. After 28 days, the slow freezing method was used to detect freezing and thawing 100 times.

2) C30P6 pumped impervious concrete verification experiment mix ratio: P042.5 strength grade cement, cement alkali content 0.88%, cement dosage 278kg, dolomite composite admixture 80 kg, sand 830kg, gravel (5-31.5mm)

1080 kg, water 168kg, naphthalene high-efficiency water reducing agent 9.2kg. After 28 days, the slow freezing method was used to detect freezing and thawing 200 times. Example 5 Cement is the Dinglu P042.5R ordinary Portland cement produced by Yatai Group. The equivalent alkali content of the tested cement is about 1.16%, which can be regarded as high alkali cement. The fineness of the cement is 0.045mm square hole. The sieve residue of the sieve was 15% by weight. The dolomite production in Shandong Province, the actual detection of Ca ²⁺ and Mg ²⁺ ratio of 1:0.67, X-ray diffractometry confirmed dolomite (CaMg (C0 ₃ ) ₂ ), dolomite content of about 99wt%, rapid grinding by planetary The machine will grind the dolomite to the fineness and the fineness of the cement to obtain the dolomite powder. According to the provisions of GB/T17671-1999 "Cement mortar strength test method", the test piece is made. Each group of test blocks was filled with different content of dolomite powder, the odd array was cured in air at a temperature of 20 ° C, and the even array was cured in water at a temperature of 20 ° C. The cement specimens were demolished after 24 h, and the age-intensity changes of the cement specimens mixed with different amounts of dolomite under different curing conditions were determined on the 2nd, 5th, 10th, 17th and 28th days respectively. The amount of the experiment is shown in the attached table 5. Schedule 5

The experimental results can be seen from the attached table 5. The dolomite-doped samples mixed with high-alkali cement are cured, and the specimens are slightly expanded. The number of specimens cured in water is larger than that in air. Analytical comparison, scanning electron microscopy detection of two samples of dolomite air-free curing test piece and adding 5wt% dolomite air-maintenance test piece, the test results are shown in Figure 6 and Figure 7, from Figure 6 and Figure The microstructure analysis of the scanning electron microscope of 7 shows that the micro-cracks of the cement stone added with dolomite are significantly reduced; FIG. 8A and FIG. 8B show the 200 pieces of slow freezing and freezing of the blank test piece and the test piece added with 6wt% dolomite. A schematic diagram of the subsequent test results, FIG. 8A shows that the blank sample showed significant freezing damage after 200 freeze-thaw cycles, and FIG. 8B showed that the test piece added with 6% dolomite was not damaged. It can be seen that the composite admixture concrete member prepared by the invention does not produce cracks, and at the same time improves the impermeability and flexural strength of the concrete. In addition, the actual impermeability level of the 28-day test reaches the requirement of P14. Example 6 and Example 7 The test of applying the cement of the present invention to a mortar:

Example 6 Anti-cracking mortar: The plaster is composed of PC32.5 cement and medium sand in a ratio of 1:3, and is doped with 10% by weight of dolomite powder (dolomite content 99wt%) and 0.2% sodium carbonate. For: 370 kg of cement, 1350 kg of medium sand, 37 kg of dolomite powder, 0.037 kg of sodium carbonate. On the red brick clear water wall, use a mortar to wipe the surface of 1 square meter and see three pieces. After 7 days, the mortar was tested and no cracks were found. Also on the red brick clear water wall, the comparative plastering mortar without dolomite powder (the same as the dolomite powder is the same as the plastering mortar). It also covers three square meters of 1 square meter. After 7 days, you can see the fine mortar crack. . Example 7 Raw materials: Liaoyuan Jingang Cement Group produces cement clinker, tested for 3 days strength 27.6MPa, 28 days strength 57.6MPa, cement clinker equivalent alkali content 1.2 wt%; Jilin Tonghua Liuhe gypsum, S0 ₃ content 25%; The Changchun Thermal Power Plant II produces fly ash; Tonggang produces slag powder, Liaoning dolomite, which is confirmed by energy spectrometer and X-ray diffractometer to be dolomite, and the effective dolomite content is 96wt%. Dolomite 12wt%, clinker 53wt%, gypsum 6wt%, fly ash 16wt%, slag 12%, sodium sulfate 1%. It was finely ground by cement test, and the fineness was 21% of the sieve with a 0.045 square sieve, and the compressive strength after 28 days of detection was 38.7 MPa. The waterproof mortar mortar prepared by the above cement is mixed according to the ratio of cement to medium sand = 1:3. Specifically: 350 kg of cement, 1350 kg of medium sand, 200 kg of water, a pool of 0.75 cubic meters of water can be built with red bricks, and the surface is covered with the above mortar on the inside. After 20 days of curing, water is retained, and no leakage occurs for 3 months. . Example 8 to Example 12 The test of applying the cement of the present invention to concrete: The dolomite powder is from the dolomite produced in Liaoning, and is confirmed to be dolomite by energy spectrometer and X-ray diffractometer, and the content of dolomite is 96wt%. Example 8 Reference composite mineral admixture: composed of 60% fly ash and 40% slag powder; dolomite composite mineral admixture: 40% from fly ash, 39.5% from dolomite powder, 1.2% from dolomite powder Sodium sulphate, 20% slag powder.

C30P6 pumped impervious concrete 1: P042.5 strength grade cement, cement alkali content 0.85%, cement dosage 278kg, reference composite admixture 80 kg, sand 830kg, crushed stone (particle size 5~31.5mm) 1080 kg, water 168kg, naphthalene-based high-efficiency water reducing agent 9kg After 28 days of standard maintenance, the freeze-thaw method of GB/T50082-2009 is used to test the freezing and thawing 100 times. After 28 days of standard curing, the actual impermeability level can reach P8.

C30P6 pumped impervious concrete II: P042.5 strength grade cement, cement alkali content 0.88%, cement dosage 278kg, dolomite composite admixture 80 kg, sand 830kg, particle size 5~31.5mm gravel 1080 kg, 168kg of water, 9.2kg of naphthalene-based high-efficiency water reducing agent. After standard maintenance, the freeze-thaw method was tested for 200 times after 28 days, and the actual impermeability level after 28 days was up to P14. Example 9

C20 concrete reference ratio: PC32.5 general Portland cement, cement alkali content 1.1%, cement dosage 302kg, particle size 5~31.5mm gravel 1238kg, sand 625 kg water 175kg, naphthalene water reducer 9.1 Kg. After standard maintenance, the actual impermeability level is up to P6 after 28 days.

C20 concrete test ratio: PC32.5 high durability cement (12% by weight of dolomite, 53wt% of sputum, 17wt% of gypsum, 17wt% of fly ash, 12wt% of slag powder, lwt% of sodium sulphate), 302kg of cement, 625kg of sand , 1238 kg of gravel with a particle size of 5~31.5mm, 175kg of water, and 9.1kg of naphthalene-based water reducing agent. After standard maintenance, the actual impermeability level is up to P12 after 28 days. Example 10

C30P6 pumped antifreeze concrete foundation mix ratio: general silicate P042.5 strength grade cement, cement dosage 325kg, medium sand 835kg, particle size 5~31.5mm gravel 1010kg, water 170kg, naphthalene water reducer 9 kg, made of 100 X 100 X 100mm cubic concrete specimens, after 28 days of standard curing, the concrete specimens were tested for freeze-thaw resistance up to 100 times. C30P6 pumped antifreeze concrete test mix ratio: P042.5 high durability cement (Dolomite 8wt%, dip

81wt%, gypsum 7wt% fly ash 2wt%, slag powder 2wt%), cement dosage 325kg, sand 835kg, particle size 5~31.5mm gravel 1010 kg, water 170kg, naphthalene water reducing agent 9 kg, After 28 days of standard curing, the concrete was tested for antifreeze and thawing for 200 times. Example 11 C30 concrete reference ratio: P042.5 strength grade cement, cement alkali content 0.88%, cement dosage is

278kg, fly ash 50kg, slag 30kg medium sand 840kg, particle size 5~31.5mm gravel 1010kg, water 175kg, naphthalene water reducing agent 7.1kg. The concrete carbonation test method of GB/T50082-2009 is used in the test method for long-term performance and durability test of ordinary concrete. The actual carbonization depth of concrete specimens after standard curing for 28 days is 8.7 mm. C30 concrete test ratio: P042.5 strength grade cement, cement alkali content 0.88%, cement dosage 278kg, Example 12 dolomite composite admixture 80kg, sand 840kg, particle size 5~31.5mm gravel 1010 kg , 170kg of water and 7.2kg of water reducing agent. The concrete carbonation test method of GB/T50082-2009 is used in the test method for long-term performance and durability of ordinary concrete. The average carbonization depth of concrete specimens after 28 days of standard curing is 4.5 mm. Example 12

C20 concrete reference ratio: PC32.5 general Portland cement, cement alkali content 1.1%, cement dosage 302kg, particle size 5~31.5mm gravel 1238kg, sand 625 kg water 175kg, naphthalene water reducer 9.1 Kg. 28 Tianjing carbonization box carbonization experiment, the actual detection of the average carbonization depth of 9.3mm. C20 concrete test ratio: PC32.5 high durability cement (Dolomite 12wt%, 53 53wt%, gypsum

6wt% fly ash 17wt%, slag powder 12wt%, sodium sulfate lwt%), cement dosage 302kg, sand 625kg, particle size 5~31.5mm gravel 1238 kg, water 175kg, naphthalene water reducer 9.1kg . The carbonization test of the carbonization box for 28 days actually measured the average carbonization depth of 5.4 mm. The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes can be made to the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and scope of the present invention are intended to be included within the scope of the present invention.

Claims

claims 1. A method for preparing dolomite composite admixture, characterized in that it includes the following steps: a. Grind the dolomite to basically the same particle size as Portland cement; b. When preparing dolomite composite admixture, add 2%-20% dolomite powder based on the mass of Portland cement, and add <1.5% equivalent of sodium oxide alkali-containing substances based on the mass of dolomite powder and mix them evenly. Dolomite composite admixture is prepared. 2. A new application of dolomite composite admixture, which is characterized in that when preparing concrete, 2%-20% dolomite composite admixture is added according to the mass of Portland cement, and is formulated to have high impermeability , high durability concrete with anti-freeze and anti-carbonation properties. 3. A dolomite composite admixture for Portland cement, characterized in that the dolomite composite admixture includes: Dolomite powder, the fineness of the dolomite powder meets the fineness standard of the Portland cement; alkali metal compound, the molar ratio of the alkali metal ions of the alkali metal compound to the dolomite powder is <2:1. 4. The dolomite composite admixture according to claim 3, characterized in that the dolomite powder is obtained from dolomite. 5. The dolomite composite admixture according to claim 3, wherein the alkali metal compound is selected from the group consisting of sodium oxide, sodium hydroxide, sodium silicate, sodium carbonate, sodium bicarbonate, sodium sulfate, and potassium oxide. One or more from the group consisting of , potassium hydroxide, potassium silicate, potassium carbonate, potassium sulfate, lithium oxide, lithium hydroxide, lithium silicate, lithium carbonate and lithium sulfate. 6. A cement, characterized in that the cement includes: Portland cement; Dolomite powder, the dosage of the dolomite powder is 2 to 28 wt% of the Portland cement, preferably 2 to 20 wt%, and the fineness of the dolomite powder meets the fineness standard of the Portland cement. The cement according to claim 6, characterized in that the dolomite powder is obtained from dolomite. 8. The cement according to claim 7, characterized in that the dolomite powder is taken from dolomite with a dolomite content of 70 to 99wt%, and the dosage of the dolomite powder is 3 to 12wt of the Portland cement. %. 9. The cement according to claim 6, characterized in that, the cement further includes an alkali metal compound, part of the alkali metal compound is brought in by the Portland cement, and the alkali metal ions of the alkali metal compound are The molar ratio of the dolomite powder is <2:1. 10. The cement according to claim 9, characterized in that the alkali metal compound is selected from the group consisting of sodium oxide, sodium hydroxide, sodium silicate, sodium carbonate, sodium bicarbonate, sodium sulfate, potassium oxide, potassium hydroxide, One or more from the group consisting of potassium silicate, potassium carbonate, potassium sulfate, lithium oxide, lithium hydroxide, lithium silicate, lithium carbonate and lithium sulfate. 11. The cement according to claim 6, characterized in that the Portland cement is selected from the group consisting of pure clinker Portland cement, ordinary Portland cement, slag Portland cement, pozzolanic Portland cement, powder One or more of the group consisting of fly ash Portland cement and composite Portland cement. 12. The application of the cement according to any one of claims 6 to 11 in mortar or concrete.