Carbon sequestration type ultra-high pumping concrete and preparation method thereof

Abstract

The application provides a preparation method of carbon sequestration type super high pumping concrete, comprising the following steps: firstly, cement, mineral powder, type I cement waste slurry and polycarboxylate superplasticizer are mixed, CO2 is introduced, and carbon sequestration type cementitious material slurry is obtained through reaction; sand, gravel and type II cement waste slurry are mixed, CO2 is introduced, and then the mixture is filtered and naturally air-dried, and carbon sequestration type aggregate is obtained through reaction; secondly, polycarboxylate slump retaining agent, defoaming agent and water are mixed to obtain rheological modifier; thirdly, the fluidized bed-chemical vapor deposition method is adopted to cover the atomized rheological modifier on the surface of a mixture of silica fume and fly ash to obtain rheological modifier admixture; finally, the carbon sequestration type cementitious material slurry, the carbon sequestration type aggregate, the rheological modifier admixture and the air entraining agent are weighed according to proportions, and are stirred and mixed uniformly to obtain the carbon sequestration type super high pumping concrete. The carbon sequestration type super high pumping concrete prepared by the application has the dual advantages of CO2 solidification and excellent pumping performance, and is beneficial to the development of the building material industry.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, specifically relating to a carbon-fixing type ultra-high pumpable concrete and its preparation method. Background Technology

[0002] The CO2 greenhouse effect is considered a major cause of global warming, making carbon emission reduction and CO2 recycling and reuse efforts of great significance.

[0003] my country's building materials industry is enormous, accounting for a very high percentage of CO2 emissions. Looking at the proportion of CO2 emissions related to building materials production, transportation, construction, demolition, and operation, carbon emissions from the building materials production stage exceed those from the building operation stage.

[0004] Invention patent CN201811297984.9 discloses a processing method for carbon fixation of precast concrete products. The specific implementation steps are as follows: the prepared precast concrete products are soaked in a calcium-based alkaline solution. After soaking for a period of time, the precast concrete products after alkaline soaking are taken out and placed in a carbonation curing kiln. Waste heat flue gas containing CO2 is introduced into the carbonation curing kiln. After the precast concrete products are carbonized and cured for a period of time, they are taken out from the carbonation curing kiln, thus completing the carbon fixation of the precast concrete products.

[0005] Invention patent CN202111434838.8 discloses a fully solid waste-based carbonated non-burning lightweight aggregate and its preparation method. The method involves grinding and mixing active component type solid waste (blast furnace slag, steel slag or furnace slag), lightweight filling type solid waste (fly ash, river silt or red mud) and alkali-activated type solid waste (carbide slag) to obtain mixed solid waste powder. Then, the mixed solid waste powder is granulated with water to obtain particulate matter. After pre-curing the particulate matter, it is subjected to CO2 mineralization curing to obtain fully solid waste-based carbonated non-burning lightweight aggregate.

[0006] Invention patent CN201610104078.7 discloses a method for preparing building material products with high carbon content. The method involves mixing a cementitious material containing components such as dicalcium silicate, tricalcium silicate, and calcium hydroxide with water at a certain water-cement ratio, and then mixing and stirring it in a CO2 atmosphere according to a certain procedure to absorb a certain amount of CO2, thereby producing a building material product blank. Then, the blank is carbonized and cured to absorb CO2 again to produce building material products.

[0007] As can be seen from the aforementioned domestic patents, researchers have already used carbonation reactions to solidify CO2 during the building materials preparation stage in order to achieve carbon emission reduction in the building materials industry.

[0008] Ultra-high-speed pumped concrete (UHQPC) effectively solves the concrete construction problems of super-tall and super-large buildings. Its vertical pumping height is generally greater than 200m, which accelerates construction speed and reduces construction costs compared to ordinary concrete, resulting in significant technical and economic benefits in engineering projects. To meet the requirements of long-distance pumping, UHQPC must possess good rheological properties to avoid problems such as excessive pumping resistance or pipeline blockage. However, conventionally cured CO2-generated concrete mixtures lack rheological property control measures, exhibiting problems such as high viscosity and poor pumpability, thus failing to meet the application requirements of UHQPC.

[0009] Based on this, a carbon-fixing ultra-high pumpable concrete and its preparation method are provided, which is of great significance for broadening the application scenarios of carbon-fixing building materials and realizing the development of the building materials industry. It is also a technical problem that researchers urgently need to solve. Summary of the Invention

[0010] One of the objectives of this invention is to provide a method for preparing carbon-fixed ultra-high pumpability concrete that combines the advantages of CO2 solidification and easy pumping.

[0011] The second objective of this invention is to provide a carbon-fixing type ultra-high pumpable concrete that combines the advantages of CO2 curing and easy pumping, and has high mechanical strength.

[0012] One of the technical solutions adopted to achieve the objective of this invention is: to provide a method for preparing carbon-fixing ultra-high pumpability concrete, comprising the following steps:

[0013] S1. Mix P·O 52.5 cement, mineral powder, type I cement waste slurry and polycarboxylate superplasticizer, and simultaneously introduce CO2 to react and obtain carbon-fixed cementitious material slurry;

[0014] S2. Mix sand, gravel and type II cement waste slurry, and simultaneously introduce CO2, then filter and air dry to obtain carbon-fixed aggregate.

[0015] S3. Mix polycarboxylate slump retainer, defoamer and water to obtain rheology modifier;

[0016] S4. Using fluidized bed chemical vapor deposition, the atomized rheology modifier is coated onto the surface of the mixture of silica fume and fly ash to obtain a rheology modifier admixture;

[0017] S5. Weigh out 582-607 parts by weight of carbon-fixing cementitious material slurry, 1673-1742 parts by weight of carbon-fixing aggregate, 102-115 parts by weight of rheology modifier and 0.020-0.045 parts by weight of air-entraining agent, stir and mix evenly to obtain carbon-fixing ultra-high pumpable concrete.

[0018] The overall concept of a carbon-fixing ultra-high pumpable concrete provided by this invention is as follows: First, under the condition of introducing CO2, the raw materials are prepared into carbon-fixing cementitious slurry and carbon-fixing aggregate, respectively. This step can consume CO2 in the waste gas and exhaust gas of industrial production, achieving the effect of carbon reduction and carbon fixation. The preparation of carbon-fixing cementitious slurry and carbon-fixing aggregate can also consume a certain amount of cement waste slurry, realizing the reuse of cement waste slurry from commercial concrete plants; Second, a rheology modifier is prepared by mixing polycarboxylate slump retainer, defoamer and water. Atomization and coating on the surface of the silica fume and fly ash mixture, and efficient dispersion in concrete using silica fume and fly ash as carriers, can enhance the effects of polycarboxylate-based slump retainers and defoamers. At the same time, the "ball effect" of silica fume and fly ash can improve the rheological properties of concrete and increase pumpability. Finally, by mixing carbon-fixing cementitious material slurry, carbon-fixing aggregate, rheology modifier admixture and air-entraining agent, and optimizing the dosage ratio, a carbon-fixing ultra-high pumpability concrete with the advantages of CO2 solidification and easy pumping is obtained.

[0019] Furthermore, the solid content of the polycarboxylate superplasticizer is 8-12%, and the solid content of the polycarboxylate slump retainer is 8-12%. Preferably, the solid content of both the polycarboxylate superplasticizer and the polycarboxylate slump retainer is 10%.

[0020] Furthermore, both Type I and Type II cement waste slurry are cement-containing wastewater generated from the cleaning of mixing equipment and pump trucks at commercial concrete mixing plants; preferably, the solid content of Type I cement waste slurry is 8% to 12%, and the solid content of Type II cement waste slurry is 20% to 30%.

[0021] Furthermore, in step S1, the mass ratio of P·O 52.5 cement, mineral powder, type I cement slurry and polycarboxylate superplasticizer is (56-60):(11.0-14.0):(26.0-28.0):(1.0-1.5).

[0022] Furthermore, in step S1, the CO2 purity is greater than or equal to 85%, the CO2 pressure is 0.3 to 0.6 MPa, and the CO2 introduction time is 45 to 50 min.

[0023] In step S1 of this invention, low-solids-content cement waste slurry is mixed with P·O 52.5 cement to form a solution containing a large amount of Ca(OH)2. The introduced CO2 reacts with the Ca(OH)2 to achieve solidification, solving the problem that CO2 does not readily undergo carbonation on the surface of powdered cement. Furthermore, the reuse of cement waste slurry from commercial concrete mixing plants can be achieved while the CO2 is being solidified. In addition, the incorporation of polycarboxylate superplasticizer reduces the cement hydration rate, ensuring the stability of the cement slurry during the 45-50 minute period after CO2 introduction, and also improving the workability and pumpability of the final concrete material.

[0024] Furthermore, in step S2, the mass ratio of sand, gravel, and type II cement waste slurry is (36-40):(50-54):(8-12).

[0025] Furthermore, in step S2, the purity of CO2 is greater than or equal to 85%, the pressure of CO2 is 0.3 to 0.6 MPa, and the CO2 introduction time is 10 to 18 hours.

[0026] In step S2 of the present invention, calcium oxides and Ca(OH)2 in cement waste slurry are covered on the surface of sand and gravel, and then reacted with CO2 to generate products such as calcium carbonate. CO2 is then solidified on the surface of sand and gravel particles to achieve the preparation of carbon-fixed aggregate.

[0027] In this invention, the CO2 introduction time is set according to the difference between carbon-fixing slurry and carbon-fixing aggregate: the liquid phase of carbon-fixing slurry in step S1 contains more calcium ions, which makes it easier to undergo carbonization reaction, while the object of CO2 introduction in step S2 is a mixture of aggregate and waste slurry, with a lower proportion of waste slurry. By extending the CO2 introduction time, the carbonization reaction can be carried out more fully, thereby improving the carbon fixation efficiency and ensuring the mechanical properties of the product.

[0028] Furthermore, in step S3, the mass ratio of polycarboxylate slump retainer, defoamer and water is (16-18):(1-2):(80-83); preferably, the mass ratio of polycarboxylate slump retainer, defoamer and water is 17:1:82.

[0029] Furthermore, in step S4, the mass ratio of the rheology modifier to the mixture of silica fume and fly ash is (1-2):(8-9), preferably 1:9. In the mixture, the mass ratio of silica fume to fly ash is (40-45):(55-60), preferably 45:55.

[0030] In steps S3 and S4 of this invention, polycarboxylate-based slump retainers and defoamers, which are beneficial to the workability of concrete, are attached to the surface of silica fume and fly ash particles to prepare a rheology-modifying mineral admixture. This improves the workability of pumped concrete in two ways: firstly, the polycarboxylate-based slump retainers and defoamers are efficiently dispersed in concrete using silica fume and fly ash as carriers, enhancing their effectiveness; secondly, the "ball effect" of silica fume and fly ash improves the rheological properties of concrete and increases its pumpability. Furthermore, to facilitate vapor deposition of the polycarboxylate-based slump retainers and defoamers, they are diluted with water. However, this added water will gradually evaporate in the mineral admixture, so it can be disregarded when calculating the concrete mix proportions.

[0031] Furthermore, in step S5, the carbon-fixing cementitious material slurry, carbon-fixing aggregate, rheology modifier and water are first stirred for 30-60 seconds, and then an air-entraining agent is added and stirred for another 60-90 seconds to obtain a carbon-fixing ultra-high pumpable concrete.

[0032] By adopting the above technical solutions, large air bubbles in the concrete are reduced, significantly improving the density of the hardened concrete and ensuring its high mechanical strength. Simultaneously, the air-entraining agent is added post-processed, introducing small air bubbles beneficial to workability and improving the pumpability of the concrete.

[0033] The second technical solution adopted by the present invention is to provide a carbon-fixing type ultra-high pumpable concrete prepared by the preparation method described in the first objective of the present invention.

[0034] The carbon-fixing ultra-high pumpable concrete has an initial spread of 620–660 mm, an initial inverted slump cone emptying time of 5–12 s, a 1-hour spread of 600–645 mm, and a 1-hour slump of 6–14 s. It exhibits good fluidity and easy pumping performance, while also possessing a 28-day compressive strength of 72.5–75.6 MPa, demonstrating excellent mechanical properties and better meeting the needs of building construction.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] (1) The present invention provides a method for preparing carbon-fixed ultra-high pumpable concrete, which utilizes cement waste slurry from commercial concrete plants to solve the problem that CO2 is difficult to undergo carbonation reaction on the surface of powder cement and sand and gravel, and prepares carbon-fixed cementitious material slurry and carbon-fixed aggregate. While achieving carbon reduction and carbon fixation, it solves the problem that cement waste slurry from commercial concrete plants is difficult to reuse.

[0037] (2) The present invention provides a method for preparing carbon-fixed ultra-high pumpable concrete, which uses spherical mineral admixtures as carriers to carry polycarboxylate slump retainers and defoamers into the concrete, thereby improving the dispersion uniformity and effect of the two in the concrete. In addition, the "ball effect" of the mineral admixtures enables the concrete to have pumpability.

[0038] (3) The present invention provides a method for preparing carbon-fixed ultra-high pumpable concrete, which uses cementitious materials and sand to solidify CO2 and uses rheology-modified mineral admixtures to improve the workability of concrete. The carbon-fixed ultra-high pumpable concrete has the dual advantages of CO2 solidification and excellent pumping performance, and has high mechanical strength. It has the potential for promotion and application in the construction of ultra-high and ultra-large buildings. Attached Figure Description

[0039] Figure 1This is a schematic flowchart illustrating a method for preparing carbon-fixing ultra-high pumpable concrete according to an embodiment of the present invention. Detailed Implementation

[0040] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0041] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0042] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0043] All substances used in the embodiments of this invention are commercially available. The specifications of the samples used in the embodiments of this invention are shown in Table 1.

[0044] Table 1

[0045] Raw material name Specification factory P·O 52.5 cement P·O 52.5 Huaxin Cement Co., Ltd. Mineral powder S95 Wuhan Huashen Intelligent Technology Co., Ltd. Type I cement waste slurry Solid content 8%–12% Sedimentation tank of commercial concrete mixing plant Polycarboxylate superplasticizer Water reduction rate: 32% (10% solids content) Sika (China) Co., Ltd. sand Fineness modulus 2.5 commercial concrete mixing plant stone 5-20mm continuous gradation commercial concrete mixing plant Type II cement waste slurry Solid content 20%–30% Sedimentation tank of commercial concrete mixing plant Polycarboxylate slump retainer 10% solids Sika (China) Co., Ltd. Defoamer silicone defoamer Dow Corning silica ash SF-93 Wuhan Xinbida fly ash Level I Wuhan Yangluo Power Plant Entraining agent AE-2 Klein

[0046] The raw materials and dosages used in various embodiments of the present invention are shown in Table 2 below.

[0047] Table 2

[0048]

[0049] The preparation methods of carbon-fixing ultra-high pumpability concrete in the above embodiments are as follows:

[0050] Step 1: According to the proportions shown in Table 2, mix and stir P·O 52.5 cement, mineral powder, type I cement waste slurry and polycarboxylate superplasticizer (10% solid content), and simultaneously introduce CO2 to react and obtain carbon-fixed cementitious material slurry;

[0051] Step 2: According to the proportions shown in Table 2, mix sand, crushed stone and type II cement waste slurry, and simultaneously introduce CO2. Then filter and air dry naturally to obtain carbon-fixed aggregate.

[0052] Step 3: According to the proportions shown in Table 2, mix the polycarboxylate slump retainer (10% solid content), defoamer and water to obtain the rheology modifier;

[0053] Step 4: Using fluidized bed chemical vapor deposition, the atomized rheology modifier is coated onto the surface of the silica fume and fly ash mixture to obtain a rheology modifier admixture;

[0054] Step 5: Weigh out the carbon-fixing cementitious material slurry, carbon-fixing aggregate and rheology modifier according to the proportions shown in Table 2, mix and stir for 30 seconds, then add part of air-entraining agent according to the proportions shown in Table 2, stir for 60 seconds, and obtain carbon-fixing ultra-high pumpable concrete.

[0055] Performance testing

[0056] According to GB / T50080 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures", the carbon-fixing ultra-high pumpable concrete prepared in Examples 1-4 was subjected to spread test and inverted slump cone evacuation test, and cured for 28 days at 20±2℃ and 95% humidity. The compressive strength of each sample was tested according to GB / T50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete". The test results are shown in Table 3 below.

[0057] Table 3

[0058] Performance test results Example 1 Example 2 Example 3 Example 4 Initial expansion / mm 650 635 620 660 Initial inverting time / s 7 9 12 5 1h expansion / mm 635 615 600 645 1 hour of rewinding time / s 8 12 14 6 28-day compressive strength / MPa 73.2 74.8 72.5 75.6

[0059] As can be seen from the above table,

[0060] The carbon-fixing ultra-high pumpable concrete prepared in Examples 1-4 exhibited a 28-day compressive strength of 72.5–75.6 MPa, all meeting the mechanical performance requirements. The initial spread of all concrete groups was greater than 600 mm, indicating that their flowability met pumping requirements. Among these, Example 3 had the longest slump cone emptying time and the highest concrete viscosity among all examples; Example 4 had the largest spread and the shortest slump cone emptying time. This indicates that the concrete prepared in Example 4 possesses advantages of good workability and low viscosity, exhibiting excellent pumpability and meeting the construction requirements of ultra-high pumpable concrete, making it the best among all examples.

[0061] Furthermore, based on the comparative results of Examples 1-3, it is evident that increasing CO2 purity and pressure and extending the CO2 introduction time excessively during the preparation of carbon-fixing cementitious slurry and carbon-fixing aggregate can lead to a deterioration in the workability of concrete. This is primarily because excessive calcium carbonate is generated, and the small particle size of calcium carbonate crystals increases the slurry viscosity, resulting in poor rheological properties. In this invention, controlling the CO2 introduction rate and time within a reasonable range helps improve the rheological properties of the slurry.

[0062] Furthermore, based on the comparison results of Examples 1 and 4, it can be seen that when preparing carbon-fixing cementitious material slurry, appropriately increasing the dosage of polycarboxylate superplasticizer can increase the spreadability of concrete. This is mainly because polycarboxylate superplasticizer inhibits cement hydration during CO2 curing process on the one hand, and plays a good dispersing role in concrete on the other hand.

[0063] In summary, the carbon-fixing ultra-high pumpable concrete preparation method provided by this invention produces carbon-fixing ultra-high pumpable concrete that meets the requirements for workability and mechanical properties of ultra-high pumpable concrete, and also has the advantages of CO2 solidification and easy pumping. It has broad prospects for promotion and application in the construction of ultra-high and ultra-large buildings.

[0064] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for preparing carbon-fixing ultra-high pumpability concrete, comprising the following steps: S1. P·O 52.5 cement, mineral powder, type I cement waste slurry, and polycarboxylate superplasticizer are mixed and stirred at a mass ratio of 56-60:11-14:26-28:1-1.5, while CO2 is introduced simultaneously to react and obtain a carbon-fixing cementitious material slurry; the type I cement waste slurry is cement-containing wastewater generated from the cleaning of mixing equipment and pump trucks in commercial concrete plants, with a solid content of 8%-12%; the CO2 purity is greater than or equal to 85%, the CO2 pressure is 0.3-0.6 MPa, and the CO2 introduction time is 45-50 min; S2. Sand, crushed stone, and Type II cement waste slurry are mixed and stirred at a mass ratio of 36-40:50-54:8-12, while CO2 is introduced. The mixture is then filtered and air-dried to obtain carbon-fixed aggregate. The Type II cement waste slurry is cement-containing wastewater generated from the cleaning of mixing equipment and pump trucks at commercial concrete mixing plants, with a solid content of 20%-30%. The purity of the CO2 is greater than or equal to 85%, the pressure of the CO2 is 0.3-0.6 MPa, and the CO2 introduction time is 10-18 h. S3. Mix polycarboxylate slump retainer, defoamer and water to obtain rheology modifier; S4. Using fluidized bed chemical vapor deposition, the atomized rheology modifier is coated onto the surface of the mixture of silica fume and fly ash to obtain a rheology modifier admixture. S5. Weigh 582-607 parts by weight of carbon-fixing cementitious slurry, 1673-1742 parts by weight of carbon-fixing aggregate, 101-103 parts by weight of rheology modifier and 0.020-0.045 parts by weight of air-entraining agent, mix them evenly to obtain carbon-fixing ultra-high pumpable concrete; the initial spread of the carbon-fixing ultra-high pumpable concrete is greater than 600 mm, the initial slump tube emptying time is 5-12 s, and the 28-day compressive strength is 72.5-75.6 MPa.

2. The preparation method according to claim 1, characterized in that, In step S3, the mass ratio of polycarboxylate slump retainer, defoamer and water is 16-18:1-2:80-83.

3. The preparation method according to claim 1, characterized in that, In step S4, the mass ratio of the rheology modifier to the mixture of silica fume and fly ash is 1-2:8-9; and the mass ratio of silica fume to fly ash in the mixture is 40-45:55-60.

4. The preparation method according to claim 1, characterized in that, In step S5, the carbon-fixing cementitious material slurry, carbon-fixing aggregate, rheology modifier and water are first stirred for 30-60 seconds, and then an air-entraining agent is added and stirred for another 60-90 seconds to obtain a carbon-fixing ultra-high pumpable concrete.

Images