A dolomite recyclable cementitious material and its preparation method and application

Abstract

The present invention relates to a dolomite recyclable cementitious material and a preparation method and application thereof, which comprises, by mass percentage, 10-50% of partially calcined dolomite and 50-90% of auxiliary cementitious materials; the partially calcined dolomite comprises MgO and CaO. The present invention partially calcines dolomite to obtain a partially calcined dolomite having a gradient structure of active calcium oxide and active magnesium oxide. The porous calcium oxide / magnesium oxide on the surface of the material excites a variety of silicon-aluminum raw materials and industrial waste at different hydration periods, and the internal calcium carbonate provides nucleation sites and micro-aggregate filling effects. The surface calcium oxide / magnesium oxide is generated by low-temperature calcination, and its activity is significantly improved compared with the existing calcium oxide / magnesium oxide, which effectively makes up for the strength development defects of the calcium system excitation and the early strength defects of the magnesium system excitation.

Description

Technical Field

[0001] The invention belongs to the field of green building materials, and particularly relates to a dolomite recyclable cementitious material and a preparation method and application thereof. Background Art

[0002] The foundation of human modernization, especially in the field of construction, is built on the consumption of large amounts of raw materials and the generation of large amounts of waste. At present, the main materials consumed by the construction industry are carbonate rock minerals, such as limestone, magnesite, dolomite, etc. Their structural formation is formed through thousands of years of geological deposition and ion transfer. However, rapid urbanization has formed a serious imbalance in its reserves and consumption. For example, nearly 400 million tons of construction and demolition waste are disposed of in landfills each year, of which waste concrete accounts for about 20-30%. In addition, carbon dioxide emissions generated by cement and concrete production account for about 8% of total emissions, which will cause a serious greenhouse effect and accelerate global warming. Therefore, there is an urgent need to develop low-carbon utilization of waste concrete and corresponding high value-added technologies.

[0003] As a Ca and Mg carbonate raw material with abundant reserves, dolomite is currently widely used in industries such as refractory materials, glass, and cement production. Due to the urgent demand for limestone raw materials and the shortage of high-quality raw materials, recycled aggregate substitution has been driven, and dolomite aggregate has gradually been developed and often used as concrete aggregate. However, dolomite can react with cement binders under certain unclear conditions, and the reaction is physically expansive, and the practical application of dolomite in recycled aggregate recovery is limited by shortcomings such as impure residual binders. In addition, due to its multi-phase composition and complex composition that is difficult to control, the traditional complete calcination process also limits its application and development in the construction field. Summary of the invention

[0004] The purpose of the present invention is to overcome the above technical deficiencies, provide a dolomite recyclable cementitious material and a preparation method and application thereof, and solve the technical problem in the prior art that waste dolomite aggregates are difficult to recycle and reuse.

[0005] In order to achieve the above technical objectives, in the first aspect, the technical solution of the present invention provides a dolomite recyclable cementitious material:

[0006] Calculated by mass percentage, the invention comprises 10-50% of partially calcined dolomite and 50-90% of auxiliary cementitious materials; the partially calcined dolomite comprises MgO and CaO.

[0007] Furthermore, the content of MgO in the partially calcined dolomite is 30-37%, and the content of CaO in the partially calcined dolomite is 40-55%.

[0008] Furthermore, the auxiliary cementitious material includes mineral powder, fly ash or calcined clay.

[0009] Furthermore, the specific surface area of ​​the auxiliary gelling material is ≥380m 2 / kg.

[0010] In a second aspect, the technical solution of the present invention provides a method for preparing a dolomite recyclable cementitious material, comprising the following steps:

[0011] The dolomite is crushed and ground, and partially calcined, and after the calcination, it is cooled to obtain partially calcined dolomite;

[0012] The auxiliary cementitious material is added to part of the calcined dolomite and mixed evenly.

[0013] Furthermore, the dolomite comprises waste dolomite aggregate or low-grade dolomite with an effective content of ≥50%; the particle size of the dolomite after crushing and grinding is in the range of 1 μm to 100 μm.

[0014] Furthermore, in the partial calcination treatment, the calcination temperature is 800-1000° C., and the calcination time is 3-60 min.

[0015] Further, the cooling is quenched under a fan.

[0016] In a third aspect, the technical solution of the present invention provides an application of a dolomite recyclable cementitious material in preparing concrete.

[0017] Furthermore, during the preparation process, the dolomite recyclable cementitious material is mixed with water to form a material with a gradient core-shell structure, wherein the core layer comprises partially calcined dolomite and the shell layer comprises a hydration product of the auxiliary cementitious material.

[0018] Compared with the prior art, the beneficial effects of the present invention include:

[0019] (1) The present invention partially calcines dolomite to obtain a partially calcined dolomite with active calcium oxide and active magnesium oxide having a gradient structure. The porous calcium oxide / magnesium oxide on the surface of the material excites a variety of siliceous and aluminum raw materials and industrial waste at different hydration periods, and the internal calcium carbonate provides nucleation sites and micro-aggregate filling effects. The surface calcium oxide / magnesium oxide is generated by low-temperature calcination, and its activity is significantly improved compared with the existing calcium oxide / magnesium oxide, which effectively makes up for the strength development defects of the calcium system excitation and the early strength defects of the magnesium system excitation.

[0020] (2) The present invention further improves the application range of the dolomite gradient cementitious material by controlling the calcination system to regulate the activity of the surface calcium oxide / magnesium oxide, and can be applied to different ranges of silicon-aluminum raw material systems.

[0021] (3) Low-temperature calcination has a simple process flow and can use low-grade dolomite for calcination. Compared with the traditional complete calcination preparation method, it can save a lot of resources and reduce unnecessary carbon emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the process of the present invention;

[0023] Figure 2 The 3d and 7d compressive strengths of the early strength gelling materials prepared in Examples 1 to 3 and Comparative Examples 1 to 5 of the present invention;

[0024] Figure 3 This is a SEM image of Example 1 of the present invention after hydration. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] Dolomite itself is a commonly used cement-based material admixture and aggregate, which has the function of physical filling and inducing nucleation.

[0027] After calcination and decomposition, dolomite will generate a large amount of active CaO and MgO, both of which can efficiently excite mineral admixtures such as ore powder, fly ash, and calcined clay. The present invention adopts a low temperature and controlled heating process to prepare partially calcined dolomite, and controls the activity of surface calcium oxide / magnesium oxide and the gradient structure of dolomite by controlling the calcination system. This preparation method greatly improves the resource utilization rate of low-grade dolomite and can be applied to the excitation of a variety of silicon-aluminum raw materials and industrial waste. The process is simple and reliable, the production cost is low, and the application range of the activator can be effectively improved.

[0028] The recyclable cementitious material prepared from waste dolomite aggregates of the present invention comprises, by mass percentage, 10-50% of partially calcined dolomite and 50-90% of auxiliary cementitious materials; further comprises 10-30% of partially calcined dolomite and 70-90% of auxiliary cementitious materials; and further comprises 15-25% of partially calcined dolomite and 75-85% of auxiliary cementitious materials.

[0029] Measured by mass percentage, the partially calcined dolomite includes 30-37% MgO and 40-55% CaO; further, the partially calcined dolomite includes 30-35% MgO and 40-50% CaO, further includes 33-35% MgO and 40-45% CaO, and optimally includes 34% MgO and 43% CaO.

[0030] After the recyclable cementitious material is mixed with water and hardened, it has a gradient core-shell structure, wherein the core layer includes a portion of calcined dolomite; and the shell layer includes a hydration product of the auxiliary cementitious material.

[0031] The auxiliary cementitious material includes mineral admixtures such as mineral powder, fly ash or calcined clay, preferably mineral powder.

[0032] The specific surface area of ​​the auxiliary cementitious material is ≥380m 2 / kg.

[0033] See also Figure 1 The method for preparing a recyclable cementitious material from waste dolomite aggregate of the present invention comprises the following steps:

[0034] The dolomite is crushed and ground, then uniformly calcined, and a low-temperature partial calcination treatment is performed to obtain a calcined sample, and after the calcination, rapid cooling is performed to obtain partially calcined dolomite;

[0035] The auxiliary cementitious material is added to part of the calcined dolomite and mixed evenly.

[0036] The particle size of the dolomite after crushing and grinding is in the range of 1 μm to 100 μm.

[0037] The partial calcination treatment is performed by calcining the sample in a drum calcination furnace at a temperature of 800 to 1000°C for 3 to 60 minutes, followed by rapid cooling under a fan. Further, the calcination treatment is performed at 800 to 900°C but not equal to 900°C for 3 to 60 minutes, or at 900 to 1000°C for 3 to 30 minutes; further, the calcination treatment is performed at 900 to 1000°C for 10 minutes.

[0038] The dolomite raw material has an effective content of ≥50%, and can be sourced from waste dolomite aggregate or low-grade dolomite.

[0039] The invention obtains dolomite aggregate from waste concrete by grinding and calcining, and uses it as one of the raw materials of cementitious material. The cementitious material prepared by mixing with mineral admixture can partially or completely replace cement and be used for preparing concrete, thus realizing the recycling of raw materials.

[0040] The present invention also provides an application of a recyclable cementitious material, wherein water and an appropriate amount of a water reducing agent are added to the recyclable cementitious material, the slurry is quickly stirred evenly to obtain a slurry, the slurry is cast into shape, and the slurry is removed from the mold for curing after solidification.

[0041] Furthermore, the amount of water reducing agent used is 0.3% to 1% of the mass of the recyclable cementitious material; most preferably 0.5%.

[0042] Furthermore, the water-to-binder ratio is 0.4 to 0.6.

[0043] The recyclable cementitious material of the present invention has a core structure composed of partially calcined dolomite and a gradient core-shell structure composed of hydration products covering the partially calcined outer layer. The dolomite has a wide range of sources and can be recycled waste concrete aggregate or low-grade dolomite.

[0044] The present invention conducts rapid partial calcination (3 to 60 minutes) of dolomite at a certain temperature (800 to 1000°C) to obtain a partially calcined dolomite with active calcium oxide and active magnesium oxide having a gradient structure. The porous calcium oxide / magnesium oxide on the surface of the material excites a variety of silicon-aluminum raw materials and industrial waste at different hydration periods, and the internal calcium carbonate provides nucleation sites and micro-aggregate filling effects. The surface calcium oxide / magnesium oxide is generated by low-temperature calcination, and its activity is significantly improved compared with the existing calcium oxide / magnesium oxide, which effectively makes up for the strength development defects of the calcium system excitation and the early strength defects of the magnesium system excitation, greatly improving the resource utilization rate and application scope of low-grade dolomite.

[0045] In order to make the purpose, technology / solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0046] The polycarboxylate water-reducing agent used in the embodiment is produced by Guizhou Qianqian Building Materials Co., Ltd., and its solid content is 45%. The dolomite powder used in the embodiment is obtained by grinding and crushing waste dolomite aggregate, wherein the effective percentage of dolomite is 91.26%. The chemical composition of the dolomite used in the embodiment is measured by X-ray fluorescence spectrometer (Zetium, Malvern Panalytics), and the test results are shown in Table 1.

[0047] Table 1 Physical and chemical analysis of dolomite

[0048]

[0049] Example 1

[0050] A method for preparing a recyclable cementitious material from waste dolomite aggregate, comprising the following steps:

[0051] Select abandoned dolomite aggregate, crush and grind it into powder with a particle size of 200 mesh, calcine the powder in a drum calciner at a temperature of 950°C for 10 min, and then quench; take 51.67g of the cooled sample (of which the MgO content after calcination is 34% and the CaO content is 43%), add 200g of mineral powder, stir slowly for two minutes in a stirring pot to mix well, then add 96g of water (water-cement ratio is 0.4) and an appropriate amount of water reducer (0.5% of the total mass of recyclable cementitious material), stir quickly for 3 minutes to obtain a slurry, and cast it into shape. After solidification, remove the mold and maintain it, which is recorded as k1.

[0052] Example 2

[0053] A method for preparing a recyclable cementitious material from waste dolomite aggregate, comprising the following steps:

[0054] Select waste dolomite aggregate, crush and grind it into powder with a particle size of 200 mesh, calcine the powder in a drum calcining furnace at a temperature of 950°C for 10 min, and then cool it with the furnace; take 51.67g of the cooled sample (of which the MgO content after calcination is 34% and the CaO content is 43%), add 200g of calcined clay, stir slowly for two minutes in a stirring pot to mix well, then add 144g of water (water-cement ratio is 0.6) and an appropriate amount of water reducer (0.5% of the total mass of recyclable cementitious material), stir quickly for 3 minutes to obtain a slurry, and cast it into shape. After solidification, remove the mold and maintain it, which is recorded as k2.

[0055] Example 3

[0056] A method for preparing a recyclable cementitious material from waste dolomite aggregate, comprising the following steps:

[0057] Select abandoned dolomite aggregate, crush and grind it into powder with a particle size of 200 mesh, calcine the powder in a drum calcining furnace at a temperature of 950°C and a calcination time of 10 min, and then cool it with the furnace; take 51.67g of the cooled sample (of which the MgO content after calcination is 34% and the CaO content is 43%), add 200g of fly ash, stir slowly for two minutes in a stirring pot to mix well, then add 96g of water (water-cement ratio is 0.4) and an appropriate amount of water reducer (0.5% of the total mass of recyclable cementitious material), stir quickly for 3 minutes to obtain a slurry, and cast it into shape. After solidification, remove the mold and maintain it, which is recorded as k3.

[0058] Comparative Example 1

[0059] Select abandoned dolomite aggregate, crush and grind it into powder with a particle size of 200 mesh, and completely calcine the powder in a drum calcining furnace at a temperature of 950°C for 30 minutes, and then cool it with the furnace; take 43.32g of the cooled sample (of which the MgO content after calcination is 37% and the CaO content is 55%), add 200g of mineral powder, stir slowly for two minutes in a stirring pot to mix well, then add 96g of water (water-cement ratio is 0.4) and an appropriate amount of water reducer (0.5% of the total mass of recyclable cementitious material), stir quickly for 3 minutes to obtain a slurry, and cast it into shape. After solidification, remove the mold and maintain it, which is recorded as k4.

[0060] Comparative Example 2

[0061] Select 17.58g of chemically pure magnesium oxide powder with the same MgO mass as in Example 1, 22.42g of chemically pure calcium oxide powder with the same CaO mass, and 11.67g of chemically pure calcium carbonate powder with the same CaCO3 mass, add 200g of mineral powder, premix for two minutes, then add 96g of water and an appropriate amount of water reducer (0.5% of the total mass of the recyclable cementitious material) to ensure working performance, stir quickly for 3 minutes to obtain a slurry, and cast it into shape. After solidification, remove the mold and maintain it, which is recorded as k5.

[0062] Comparative Example 3

[0063] Select 17.58g of chemically pure magnesium oxide powder with the same MgO mass as in Example 2, 22.42g of chemically pure calcium oxide powder with the same CaO mass, and 11.67g of chemically pure calcium carbonate powder with the same CaCO3 mass, add 200g of calcined clay, premix for two minutes, then add 144g of water and an appropriate water reducer (0.5% of the total mass of the recyclable cementitious material) to ensure working performance, stir quickly for 3 minutes to obtain a slurry and shape it, remove the mold and maintain after solidification, which is recorded as k6.

[0064] Comparative Example 4

[0065] Select 17.58g of chemically pure magnesium oxide powder with the same MgO mass as in Example 3, 22.42g of chemically pure calcium oxide powder with the same CaO mass, and 11.67g of chemically pure calcium carbonate powder with the same CaCO3 mass, add 200g of fly ash, premix for two minutes, then add 96g of water and an appropriate amount of water reducer (0.5% of the total mass of the recyclable cementitious material) to ensure working performance, stir quickly for 3 minutes to obtain a slurry and shape it. After solidification, remove the mold and maintain it, which is recorded as k7.

[0066] Comparative Example 5

[0067] Select abandoned dolomite aggregate, crush and grind it into powder with a particle size of 200 mesh, and completely calcine the powder in a drum calcining furnace at a temperature of 800°C for 60 minutes, and then cool it with the furnace; take 138.55g of the cooled sample (the MgO content after calcination is 26%, and it does not contain CaO), add 200g of mineral powder, stir slowly for two minutes in a stirring pot to mix, then add 96g of water (water-cement ratio is 0.4) and an appropriate amount of water reducer (0.5% of the total mass of recyclable cementitious material) and stir quickly for 3 minutes to obtain a slurry, which is then cast and formed. After solidification, the mold is removed and maintained, which is recorded as k8.

[0068] Figure 2 The 3d and 7d compressive strength comparison diagram of Examples 1 to 3 and Comparative Examples 1 to 5 shows that, compared with Comparative Examples 1 to 4, Examples 1 to 3 have better strength development. K1 to 3 are partially calcined dolomite with a calcination degree of 77%, respectively, compounded with mineral powder, calcined clay, and fly ash. Compared with fully calcined dolomite K4 and analytical pure reagent K5 to 7, they show higher 3d and 7d strengths, indicating that partially calcined dolomite has a better stimulating effect on mineral admixtures. On the one hand, due to the high reactivity of low-temperature incompletely calcined dolomite, magnesium oxide and calcium oxide can efficiently stimulate the hydration of mineral powder. On the other hand, the partially calcined dolomite forms hydration products that wrap inert products such as calcium carbonate that do not participate in the reaction, making the matrix more compact. Since group K4 is completely calcined, there is no micro-aggregate effect produced by inert calcium carbonate, resulting in lower strength than partially calcined ones; but the auxiliary cementitious material composited in K4 is mineral powder, and its effect is better than that of composites with other auxiliary cementitious materials. It can be seen that group K1 uses partially calcined dolomite combined with mineral powder, which can produce a synergistic effect.

[0069] In addition, the calcined dolomite used in Comparative Example 5 only decomposed magnesium carbonate into magnesium oxide, and calcium carbonate did not begin to decompose. Figure 1 It can be seen that the 3d strength of k8 (containing only MgO) is much lower than that of k1 (containing MgO and CaO), that is, calcium oxide provides better early strength for the system.

[0070] At the same time, relative to analytically pure reagents k5-7, k1-3 of the present invention have better performance, indicating that other substances exist in the partially calcined dolomite and cooperate with the known components to play a synergistic role, thereby improving its 3d and 7d strengths; the specific strengths are shown in Table 1 below.

[0071] Table 1 Compressive strength test of the test pieces of the embodiments of the present invention and the comparative examples

[0072] Compressive strength 3d(MPa) 7d(MPa) k1 15.1 19.7 k2 7.7 12.7 k3 4.7 10.7 k4 11.0 16.9 k5 10.6 15.7 k6 4.6 8.7 k7 2.8 5.5 k8 3.2 14.5

[0073] It can be seen from Table 1 that the 3d strength of the recyclable cementitious material of the present invention can reach 4.7-15.1 MPa, and the 7d strength can reach 10.7-19.1 MPa.

[0074] Figure 3 This is the SEM image of Example 1 after hydration for 7 days. It can be seen that a large amount of amorphous hydration products, namely gel, are formed between the interface transition zone between the mineral powder and the partially calcined dolomite. This is also the reason for its high 7d strength. In addition, the hydration product is tightly connected with the partially calcined dolomite that has not reacted completely and has high compatibility, thereby making the matrix denser, which fully illustrates the advantages of the calcination scheme of this invention.

[0075] Compared with the prior art, the present invention discloses a recyclable cementitious material prepared from waste dolomite aggregate and a preparation method thereof. The waste dolomite aggregate is crushed and ground, then uniformly calcined, and a low-temperature partial calcination treatment is performed to obtain a calcined sample. After the calcination is completed, it is rapidly cooled and compounded with a specific auxiliary cementitious material to obtain a dolomite recyclable cementitious material; the present invention obtains dolomite aggregate from waste concrete by grinding and calcining, thereby realizing the recycling of raw materials. The partially calcined dolomite has active calcium oxide and active magnesium oxide with a gradient structure. The active calcium oxide enables the system to obtain good early strength, and the magnesium oxide slowly hydrates and plays an stimulating role in the subsequent curing process, so that the system has excellent strength development. At the same time, the internal calcium carbonate provides nucleation sites and micro-aggregate filling effects. The preparation method of the stimulant greatly improves the resource disposal problem of low-grade dolomite, can be applied to the treatment of a variety of silicon-aluminum raw materials and industrial solid waste, has a simple and reliable process, and has a low production cost. At the same time, the activity and gradient structure of dolomite are regulated by controlling the calcination system, which greatly improves the application range of the material.

[0076] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A dolomite recyclable cementitious material, characterized in that: The invention comprises, by mass percentage, 20.5-25% of partially calcined dolomite and 75-79.5% of auxiliary cementitious materials; the partially calcined dolomite comprises 33-35% of MgO and 40-45% of CaO; The auxiliary gelling material is mineral powder; The preparation steps of partially calcined dolomite include: The dolomite is crushed and ground, then uniformly calcined, and a low-temperature partial calcination treatment is performed to obtain a calcined sample, and after the calcination, rapid cooling is performed to obtain partially calcined dolomite; In the partial calcination treatment, the calcination temperature is 900-1000° C. and the calcination time is 10 min.

2. The dolomite recyclable cementitious material according to claim 1, characterized in that: The specific surface area of ​​the auxiliary cementitious material is ≥380m 2 / kg.

3. The method for preparing a dolomite recyclable cementitious material according to any one of claims 1 to 2, characterized in that: The following steps are involved: The dolomite is crushed and ground, and partially calcined, and after the calcination, it is cooled to obtain partially calcined dolomite; The auxiliary cementitious material is added to part of the calcined dolomite and mixed evenly.

4. The method for preparing a dolomite recyclable cementitious material according to claim 3, characterized in that: The dolomite comprises waste dolomite aggregate or low-grade dolomite with an effective content of ≥50%; the particle size of the dolomite after crushing and grinding is in the range of 1 μm to 100 μm.

5. The method for preparing a dolomite recyclable cementitious material according to claim 3, characterized in that: Cooling is rapid cooling under a fan.

6. Use of the dolomite recyclable cementitious material according to any one of claims 1 to 2 in preparing concrete.

7. The use according to claim 6, characterized in that: During the preparation process, the dolomite recyclable cementitious material is mixed with water to form a material with a gradient core-shell structure, wherein the core layer includes part of the calcined dolomite and the shell layer includes the hydration product of the auxiliary cementitious material.

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