A high-magnesium and low-carbon cement concrete and its preparation method

Abstract

The present invention discloses a high-magnesium, low-carbon cement concrete. The raw materials and their weight percentages include: 70-90 parts high-magnesium, low-carbon cement, 10-30 parts ordinary Portland cement, 150-200 parts fine aggregate, 180-250 parts coarse aggregate, 30-50 parts water, 1-3 parts fiber, 0.5-1.5 parts water reducer, and 0.3-1.0 parts reinforcing agent. The high-magnesium, low-carbon cement contains C2MS2 as the main mineral. The present invention, based on high-magnesium, low-carbon cement obtained by using low-grade limestone and aggregate waste in large dosages, further introduces a reinforcing agent and a gradient carbonation curing system, which can effectively improve the mechanical properties of the resulting concrete, etc., and has significant economic and environmental benefits.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and particularly relates to high-magnesium low-carbon cement concrete and a preparation method thereof. Background Art

[0002] Concrete is a common building material, known for its high volume, low price, and widespread application. However, traditional concrete is associated with high carbon emissions, 60% of which comes from the calcination of limestone. Low-carbon cement, primarily composed of the low-calcium minerals C3S2, CS, β-C2S, and γ-C2S, has been a hot topic of research in recent years. Compared to Portland cement, which is primarily composed of C3S minerals, low-carbon cement requires less limestone, has a lower calcination temperature, and can absorb significant amounts of CO2. This reduces carbon emissions from the cement industry in many ways while also enabling the production of building materials with excellent physical properties. Furthermore, its rapid carbonation curing time and high strength make it particularly suitable for precast concrete building materials.

[0003] Low-grade limestone, due to its low CaO content and high MgO and SiO2 contents, is difficult to formulate with other conventional raw materials into high-KH Portland cement clinker. Furthermore, the high calcination temperature and low eutectic point of the clinker can lead to severe melt scaling in equipment, resulting in a limited range of applications and limited effective utilization. Aggregate plants inevitably discharge large amounts of waste slag containing stone dust during sand and gravel production. The stone dust in this aggregate slag is primarily calcite and dolomite, with a MgO content generally ranging from 5% to 15%. It also contains clay minerals, resulting in a complex composition and making it difficult to utilize. Therefore, it is of great significance to effectively utilize this low-grade limestone and aggregate slag, which have low CaO and high MgO contents, as a resource.

[0004] By using low-grade limestone and aggregate waste with low CaO content and high MgO content, and increasing the MgO content in the ingredients, high-magnesium low-carbon cement clinker with C2MS2 (calcium magnesium feldspar) as the main mineral can be produced. Its calcination temperature is lower than that of low-carbon cement clinker, and its grindability is good, which can significantly reduce the preparation cost and energy consumption; however, compared with low-carbon cement clinker, its carbon fixation rate and carbonization strength are lower, and the strength after carbonization is about 70-80% of the low-carbon cement clinker with C3S2 as the main mineral.

[0005] Since high-magnesium low-carbon cement is lower in strength than low-carbon cement with C3S2 as the main mineral, using it to prepare concrete will lead to problems such as insufficient strength. How to improve the strength of concrete made with high-magnesium low-carbon cement has become a technical problem that needs to be solved urgently. Summary of the Invention

[0006] The purpose of the present invention is to address the problems and shortcomings of the existing technology and provide a high-magnesium low-carbon cement concrete, which realizes the preparation of high-strength concrete based on the high-magnesium low-carbon cement prepared by large-scale utilization of low-grade limestone and aggregate waste.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The invention discloses a high-magnesium low-carbon cement concrete. The raw materials and their weight proportions include: 70-90 parts of high-magnesium low-carbon cement, 10-30 parts of ordinary Portland cement, 150-200 parts of fine aggregate, 180-250 parts of coarse aggregate, 30-50 parts of water, 1-3 parts of fiber, 0.5-1.5 parts of water reducer, and 0.3-1.0 parts of reinforcing agent.

[0009] According to the above solution, the strength grade of the ordinary Portland cement is above 42.5.

[0010] According to the above solution, the fine aggregate is machine-made sand with a particle size of less than 4.75 mm, a fineness modulus of 2.3-3.2, and a crushing value of ≤20%.

[0011] According to the above scheme, the coarse aggregate is crushed stone with a particle size of 5-31.5 mm, which meets the requirements of continuous grading, needle-shaped and flake-shaped particle content ≤5%, crushing value ≤15%, and water absorption rate ≤1.5%.

[0012] According to the above solution, the water reducing agent is a polycarboxylic acid water reducing agent with a water reduction rate of 10-25%.

[0013] According to the above solution, the fibers are one or more of glass fibers, basalt fibers, carbon fibers, steel fibers, pulp fibers, etc., with a fiber diameter of not less than 6 μm and a length of 10-30 mm.

[0014] According to the above scheme, the mineral composition of the high-magnesium low-carbon cement includes, by percentage, C2MS2 (calcite-magnesium feldspar) 40-80%, C3S2 20-40%, CS+C2S 0-20%;

[0015] According to the above solution, the 80 μm sieve residue rate of the high-magnesium low-carbon cement is ≤10%.

[0016] According to the above scheme, the high-magnesium low-carbon cement is obtained by using low-grade limestone, aggregate waste slag and coal gangue as main raw materials, which are proportioned, mixed, ground and calcined.

[0017] According to the above scheme, the mass ratio of the low-grade limestone, aggregate waste slag and coal gangue is 50-70:0-20:20-30.

[0018] Furthermore, the main chemical components and contents of the low-grade limestone include: CaO 40-48%; MgO3-10%; SiO2 4-10%; Al2O3 0-3%; Fe2O3 0-2%; and a loss on ignition of 35-42%; the main chemical components and contents of the aggregate waste include: CaO 20-40%; MgO 5-15%; SiO2 15-25%; Al2O3 3-6%; Fe2O3 2-5%; and a loss on ignition of 25-40%; the main chemical components and contents of the coal gangue include: CaO 0-5%; MgO 0-5%; SiO2 60-90%; Al2O3 0-8%; Fe2O3 0-5%; and a loss on ignition of 0-8%.

[0019] According to the above scheme, further control indicators in the batching process include: MgO 6-8wt%, KH 0.3-0.4, SM 4-7, and a total CaO to total SiO2 mass ratio of 1.1-1.3.

[0020] According to the above scheme, the calcination temperature is 1200-1250°C.

[0021] According to the above scheme, the enhancer is one or more of polyethylene glycol, glycerol, ethylene glycol, etc.

[0022] The above-mentioned method for preparing high-magnesium low-carbon cement concrete comprises the following steps:

[0023] (1) Weighing the raw materials according to the proportion, placing high magnesium low carbon cement, ordinary Portland cement, fine aggregate, coarse aggregate, and fiber into a mixer and mixing them evenly, then adding water, a water reducer, and a reinforcing agent and stirring to obtain a concrete mixture;

[0024] (2) Pour the mixture into a mold and vibrate to form a mold with a thickness not exceeding 200 mm;

[0025] (3) Demolding after natural curing in a dry environment;

[0026] (4) After demoulding, gradient carbonization curing is carried out to obtain high-magnesium low-carbon cement concrete.

[0027] According to the above scheme, the natural curing time is 24-48 hours.

[0028] According to the above scheme, the gradient step carbonization curing adopts a CO2 concentration of 20-100%, an air pressure of 0.1-0.3 MPa, a temperature of 25-55°C, and a total carbonization time of 12-24 hours.

[0029] According to the above scheme, in the gradient step carbonization curing, more than two carbonization curing steps are adopted, and the CO2 concentration and gas pressure used are increased in sequence.

[0030] Furthermore, in the gradient step-by-step carbonization curing, the CO2 concentration used in the first carbonization curing step is 20-30%, the air pressure is 0.1-0.2 MPa, and the time is 5-40% of the total carbonization time; when the temperature is set to 25-40°C, the CO2 concentration used in the last carbonization curing step is 50-100%, the air pressure is 0.2-0.3 MPa, and the time is 30-70% of the total carbonization time; when the temperature is set to 40-55°C, the CO2 concentration used in the last carbonization curing step is 30-100%, the air pressure is 0.1-0.3 MPa, and the time is 30-70% of the total carbonization time.

[0031] Furthermore, between the adjacent carbonization curing steps, the increase in CO2 concentration is 10-40% (absolute value), the increase in gas pressure is 0-0.1 MPa, and the time change is 0-30% of the total carbonization time.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1) The present invention uses high-magnesium, low-carbon cement with C2MS2 (calcium magnesium feldspar) as the main mineral to prepare concrete, which has lower cost and energy consumption, and has good economic and environmental benefits;

[0034] 2) The calcination temperature of the high magnesium low carbon cement clinker obtained by the present invention is lower than that of the low carbon cement clinker, and the grindability is good, which can significantly reduce the preparation cost and energy consumption, but the carbonization activity is lower than that of the low carbon cement; the reinforcing agent introduced by the present invention can promote the Mg 2+ It is easier to dissolve, thereby effectively stimulating the carbonization activity of C2MS2; secondly, the generated MgCO3 can play the role of filling, connecting, and interface strengthening between silica gel and traditional carbonization product CaCO3; in addition, the present invention further combines the optimized C2MS2 mineral gradient carbonization curing conditions to further effectively improve the strength of concrete made with high-magnesium low-carbon cement, which can provide a new idea for the preparation of low-cost, high-strength concrete. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the 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.

[0036] In the following examples, the fine aggregate used is machine-made sand with a particle size of less than 4.75 mm, a fineness modulus of 2.7, and a crushing value of 14%;

[0037] The coarse aggregate used is crushed stone with a particle size of 5-31.5mm, meeting the requirements of continuous grading, with a needle and flake particle content of 3%, a crushing value of 12%, and a water absorption rate of 0.8%;

[0038] The actual chemical composition and content (mass percentage) of the low-grade limestone, aggregate waste and coal gangue used are shown in Table 1.

[0039] Table 1 Chemical composition (%)

[0040] name Loss on ignition <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO MgO <![CDATA[SO3]]> <![CDATA[K2O]]> <![CDATA[Na2O]]> Low-grade limestone 39.84 5.66 1.29 1.02 45.33 5.64 0.05 0.29 0.15 Aggregate waste 31.5 20.99 4.64 3.13 28.29 8.76 0.93 0.12 0.71 coal gangue 4.63 79.3 4.62 3.64 2.08 2.31 0.48 1.34 0.55

[0041] Example 1

[0042] A high-magnesium low-carbon cement concrete, the preparation method of which comprises the following steps:

[0043] (1) Weigh the raw materials, and the weight proportions of the raw materials are as follows: 85 parts of high magnesium low carbon cement (C2MS2=71.4%, C3S2=20.5%, C2S=6.7%, 80 μm sieve residue ≤10%), 15 parts of ordinary Portland cement (42.5 grade), 184 parts of fine aggregate, 245 parts of coarse aggregate, 37 parts of water, 1.5 parts of fiber (glass fiber), 0.8 parts of water reducer (polycarboxylate water reducer, water reduction rate 20%), and 0.7 parts of reinforcing agent (polyethylene glycol);

[0044] The high-magnesium low-carbon cement is prepared by mixing low-grade limestone, aggregate waste, and coal gangue in a mass ratio of 56:20:24, while controlling the MgO content to 7.776%, KH to 0.352, SM to 5.466, and the total CaO to SiO2 mass ratio to 1.195; mixing and grinding the mixed raw materials, and then calcining them at 1210°C to obtain the cement.

[0045] The weighed high magnesium low carbon cement, ordinary Portland cement, fine aggregate, coarse aggregate and fiber are put into a mixer and mixed evenly, and then water, a water reducing agent and a reinforcing agent are added and stirred to obtain a concrete mixture;

[0046] (2) Pour the mixture into a mold and vibrate to form a mold with a thickness not exceeding 200 mm;

[0047] (3) De-mould after natural curing in a dry environment for 1 day;

[0048] (4) After demoulding, the concrete was placed in a carbonization kettle and first carbonized for 2 h at a CO2 concentration of 20%, an air pressure of 0.1 MPa, and a temperature of 25°C; then the CO2 concentration was adjusted to 50%, an air pressure of 0.2 MPa, and a temperature of 25°C for a further 8 h; finally, the CO2 concentration was adjusted to 80%, an air pressure of 0.3 MPa, and a temperature of 25°C for a further 14 h; a total of 24 h of carbonization was performed under this gradient curing to obtain high-magnesium low-carbon cement concrete.

[0049] Example 2

[0050] A high-magnesium low-carbon cement concrete, the preparation method of which comprises the following steps:

[0051] (1) Weigh the raw materials and their weight proportions: 88 parts of high magnesium low carbon cement (C2MS2 = 71.4%, C3S2 = 20.5%, C2S = 6.7%, 80 μm sieve residue ≤ 10%), 12 parts of ordinary Portland cement (52.5), 175 parts of fine aggregate, 242 parts of coarse aggregate, 34 parts of water, 2 parts of fiber (basalt fiber), 1 part of water reducer (polycarboxylate water reducer, water reduction rate 20%), and 0.8 parts of reinforcing agent (glycerol);

[0052] The high-magnesium low-carbon cement is prepared by mixing low-grade limestone, aggregate waste, and coal gangue in a mass ratio of 56:20:24, while controlling the MgO content to 7.776%, KH to 0.352, SM to 5.466, and the total CaO to SiO2 mass ratio to 1.195; mixing and grinding the mixed raw materials, and then calcining them at 1210°C to obtain the cement.

[0053] Put high magnesium low carbon cement, ordinary Portland cement, fine aggregate, coarse aggregate and fiber into a mixer and mix them evenly, then add water, water reducing agent and reinforcing agent and mix to obtain a concrete mixture;

[0054] (2) Pour the mixture into a mold and vibrate to form a mold with a thickness not exceeding 200 mm;

[0055] (3) De-mould after natural curing in a dry environment for 1 day;

[0056] (4) After demoulding, the concrete was placed in a carbonization kettle and carbonized for 3 h at a CO2 concentration of 30%, an air pressure of 0.1 MPa, and a temperature of 25°C; then the CO2 concentration was adjusted to 60%, an air pressure of 0.2 MPa, and a temperature of 25°C for a further 9 h; finally, the CO2 concentration was adjusted to 70%, an air pressure of 0.3 MPa, and a temperature of 25°C for a further 12 h; a total of 24 h of carbonization was performed under this gradient curing to obtain high-magnesium low-carbon cement concrete.

[0057] Comparative Example 1

[0058] A low-carbon cement concrete, the preparation method of which is substantially the same as that of Example 1, except that:

[0059] The high-magnesium low-carbon cement in step (1) is replaced by low-carbon cement whose mineral composition is mainly C3S2 (C3S2=75.4%, CS=23.5%, 80μm sieve residue rate ≤10%) without adding a reinforcing agent;

[0060] The carbonization curing in step (4) was changed to carbonization for 24 h at a CO2 concentration of 80%, an air pressure of 0.3 MPa, and a temperature of 25°C.

[0061] Comparative Example 2

[0062] A low-carbon cement concrete, the preparation method of which is substantially the same as that of Example 1, except that:

[0063] No enhancer is added in step (1);

[0064] The carbonization curing in step (4) was changed to carbonization for 24 h at a CO2 concentration of 80%, an air pressure of 0.3 MPa, and a temperature of 25°C.

[0065] Comparative Example 3

[0066] A low-carbon cement concrete, the preparation method of which is substantially the same as that of Example 1, except that no reinforcing agent is added in step (1).

[0067] Comparative Example 4

[0068] A low-carbon cement concrete, the preparation method of which is substantially the same as that of Example 1, except that the carbonation curing in step (4) is changed to carbonization for 24 hours at a CO2 concentration of 80%, an air pressure of 0.3 MPa, and a temperature of 25°C.

[0069] The physical properties and carbon sequestration of the low-carbon cement concrete measured in each embodiment and comparative example are shown in Table 2.

[0070] Table 2 Physical properties and carbon sequestration

[0071] project Compressive strength (MPa) <![CDATA[Carbon sequestration amount (kg / m 3 )]]> Example 1 63.6 126 Example 2 62.7 123 Comparative Example 1 60.4 122 Comparative Example 2 48.2 95 Comparative Example 3 52.6 107 Comparative Example 4 59.3 118

[0072] From the above results we can see that:

[0073] In Comparative Examples 2 and 3, without adding a reinforcing agent, the physical properties of the concrete prepared using high-magnesium low-carbon cement are worse than those of the concrete prepared using low-carbon cement (C3S2=75.4%, CS=23.5%) whose mineral composition is mainly C3S2 as described in Comparative Example 1.

[0074] The physical properties of the concrete prepared in Comparative Example 4 using high CO2 concentration and pressure conditions throughout the process are still inferior to those of the carbonized concrete obtained in Example 1 of the present invention and the concrete prepared with the low-carbon cement in the comparative example.

[0075] The present invention is based on the high-magnesium low-carbon cement produced by extensively utilizing low-grade limestone and aggregate waste, and by adding a reinforcing agent and performing gradient curing, can effectively improve the physical properties of carbonized concrete, and in particular can produce a low-carbon cement having performance superior to that produced by low-carbon cement mainly based on C3S2 minerals such as Comparative Example 1.

[0076] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A high-magnesium low-carbon cement concrete, characterized in that: The raw materials and their weight proportions include: 70-90 parts of high magnesium low carbon cement, 10-30 parts of ordinary Portland cement, 150-200 parts of fine aggregate, 180-250 parts of coarse aggregate, 30-50 parts of water, 1-3 parts of fiber, 0.5-1.5 parts of water reducer, and 0.3-1.0 parts of reinforcing agent; The enhancer is one or more of polyethylene glycol, glycerol, and ethylene glycol; The mineral composition of the high magnesium low carbon cement includes, by percentage, C2MS2 40-80%, C3S2 20-40%, CS+C2S 0-20%; The high-magnesium low-carbon cement is prepared by mixing, grinding and calcining low-grade limestone, aggregate waste and coal gangue as main raw materials in a certain proportion; the calcination temperature is 1200-1250°C; the main chemical components and their contents in the low-grade limestone include: CaO 40-48%; MgO 3-10%; SiO2 4-10%; Al2O3 0-3%; Fe2O3 0-2%; The high-magnesium low-carbon cement concrete is subjected to gradient carbonation curing after demoulding. In the gradient carbonization curing, more than two carbonization curing steps are adopted, and the CO2 concentration and gas pressure used are increased in sequence.

2. The high-magnesium low-carbon cement concrete according to claim 1, characterized in that: The 80μm sieve residue rate of the high-magnesium low-carbon cement is ≤10%.

3. The high-magnesium low-carbon cement concrete according to claim 1, characterized in that: The fine aggregate is machine-made sand with a particle size of less than 4.75 mm, a fineness modulus of 2.3-3.2, and a crushing value ≤20%; the coarse aggregate is crushed stone with a particle size of 5-31.5 mm, meeting continuous grading, with a needle- and flake-shaped particle content ≤5%, a crushing value ≤15%, and a water absorption rate ≤1.5%.

4. The high-magnesium low-carbon cement concrete according to claim 1, characterized in that The water reducing agent is a polycarboxylic acid water reducing agent with a water reducing rate of 10-25%.

5. The high-magnesium low-carbon cement concrete according to claim 1, characterized in that: The fibers are one or more of glass fibers, basalt fibers, carbon fibers, steel fibers, and pulp fibers, and have a fiber diameter of no less than 6 μm and a length of 10-30 mm.

6. The method for preparing high-magnesium low-carbon cement concrete according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Weigh all raw materials according to the proportion, put high magnesium low carbon cement, ordinary Portland cement, fine aggregate, coarse aggregate and fiber into a mixer and mix them evenly, then add water, water reducer and reinforcing agent and stir to obtain a concrete mixture; (2) pouring the mixture into a mold and vibrating it into shape; (3) Demolding after natural curing in a dry environment; (4) After demolding, gradient carbonization curing is carried out to obtain high-magnesium low-carbon cement concrete.

7. The preparation method according to claim 6, characterized in that The gradient carbonization curing adopts a CO2 concentration of 20-100%, an air pressure of 0.1-0.3 MPa, a temperature of 25-55°C, and a total carbonization time of 12-24 hours.