High-early-strength quick-hardening cement-based material used in low-temperature environment and preparation method thereof

Abstract

The invention discloses a high-early-strength quick-hardening cement-based material for a low-temperature environment and a preparation method of the high-early-strength quick-hardening cement-based material. The cement-based material is prepared from the following components in parts by weight: 400 parts of sulphate aluminium cement, 100 parts of coal ash, 150 parts of water, 0.05-10 parts of lithium carbonate and 2 parts of a water reducing agent. According to the invention, high-purity lithium carbonate (gt; the early-stage hydration activity of the sulphoaluminate cement in a low-temperature (-5 DEG C) environment is remarkably improved, and good workability and compactness of slurry are ensured by combining an optimized mixing ratio and a polycarboxylic acid high-efficiency water reducing agent, so that a foundation is laid for early-stage strength development; the preparation method of the cement-based material provided by the invention is simple to operate, does not need complex pretreatment, and does not affect the construction period. Meanwhile, the industrial by-product fly ash is utilized, the resource utilization trend is met, energy is remarkably saved through the simplified maintenance process, and carbon emission is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to a high-early-strength and fast-hardening cement-based material for low-temperature environment and a preparation method thereof, and belongs to the technical field of building materials. BACKGROUND

[0002] With the rapid development of infrastructure construction in China, especially major projects such as high-speed railways and bridges, higher requirements are put forward for the construction and service performance of building materials in harsh environments. However, in the vast northwest, northeast and part of the central region of China, winter construction of concrete faces severe challenges. Low-temperature environment not only greatly reduces construction efficiency, but also poses a serious threat to the long-term durability of building structures. Traditional solutions mainly include:

[0003] External insulation measures (such as electric blankets and warm shed method) aim to maintain concrete temperature and ensure hydration. However, this method has huge energy consumption, high carbon emissions, poor economy and environmental protection; the use of Portland cement, although widely used, has inherent slow setting and hardening, low early strength characteristics, which is weak in winter construction in cold regions and has limited development.

[0004] Under this background, sulphoaluminate cement is considered as an ideal low-carbon cementitious material to solve the problem of winter construction in cold regions due to its high early strength, fast hydration heat release, good frost resistance, and micro-expansibility, as well as its low calcination temperature (100-200℃ lower than Portland cement) and low CO2 emissions. However, its inherent potential cannot be fully realized in-5℃ environment, and the core bottleneck is the lack of effective low-temperature activation technology. In particular, in the context of emergency repair, rapid access construction and other scenarios with strict requirements on construction period in cold regions, the setting and hardening speed of concrete directly determines the project progress and early safety guarantee capability of the structure.

[0005] Therefore, it is of extremely urgent engineering demand and great strategic significance to develop a new type of high-efficiency activator system specially suitable for-5℃ low-temperature environment, which can precisely control the setting time of sulphoaluminate cement (especially significantly shorten the initial and final setting time to meet the repair requirements), and fully activate its early strength development. This will not only directly solve the core pain points of winter construction of infrastructure in cold regions, guarantee the engineering quality and progress, but also fully utilize the green and low-carbon advantages of sulphoaluminate cement. SUMMARY

[0006] Invention purposes: The first purpose of the present application is to provide a high early strength and fast hardening cement-based material for low temperature environment, and the second purpose of the present application is to provide a preparation method of the high early strength and fast hardening cement-based material for low temperature environment. The high early strength and fast hardening cement-based material developed in the present application has high early strength and fast hydration speed compared with a portland cement system, and has stable late strength growth speed compared with an aluminate cement system, can continuously hydrate under negative temperature conditions, and significantly improves the applicability of the material in winter construction, repair and other projects.

[0007] Technical scheme: The high early strength and fast hardening cement-based material for low temperature environment comprises the following components in parts by weight: sulphoaluminate cement: fly ash: water: lithium carbonate: water reducing agent = 400: 100: 150: (0.05-10): 2.

[0008] Further, the components include the following components in parts by weight: sulphoaluminate cement: fly ash: water: lithium carbonate: water reducing agent = 400: 100: 150: (0.8-3.2): 2. Most preferably, the components include sulphoaluminate cement: fly ash: water: lithium carbonate: water reducing agent = 400: 100: 150: 0.8: 2. The sulphoaluminate cement meets the national standard “Sulphoaluminate Cement” GB20472-2006. The fly ash is F-class 1st grade fly ash. The purity of the lithium carbonate is more than 99%. The water reducing agent is a polycarboxylic acid superplasticizer, and the effective solid content of the water reducing agent is more than 20%. The temperature of the low temperature environment is generally -5-0℃.

[0009] The preparation method of the high early strength and fast hardening cement-based material for low temperature environment comprises the above steps.

[0010] (1) mixing sulphoaluminate cement and fly ash, and stirring until uniform to obtain a composite cementitious material;

[0011] (2) dispersing lithium carbonate and a water reducing agent in water to obtain a mixed solution containing additives;

[0012] (3) mixing the mixed solution containing additives and the composite cementitious material, low-speed stirring, and then high-speed stirring to obtain a high early strength and fast hardening cement-based material slurry.

[0013] Further, in step (3), the speed of low-speed stirring is 80 r / min or less, and the time of low-speed stirring is 60-120 s. After low-speed stirring, stopping for 15 s or more, and scraping off the cement slurry adhered to the machine, high-speed stirring is performed at a speed of 120-180 r / min and a time of 60-90 s.

[0014] Technical mechanism: In the early hydration stage, Li +The protective film formed during the hydration process of sulphoaluminate cement can be penetrated to shorten the induction period and improve the early hydration degree of cement minerals. The addition of Li2CO3 reduces the liquidus freezing point of sulphoaluminate cement to -4.3℃, which provides a longer hydration time at the early stage of hydration. Secondly, the addition of Li2CO3 increases the alkalinity of the hydration reaction in the sulphoaluminate cement system, accelerates the dissolution of Al + 3+ The addition of Li2CO3 increases the alkalinity of the hydration reaction in the sulphoaluminate cement system, accelerates the dissolution of Al 3+ The addition of Li2CO3 increases the alkalinity of the hydration reaction in the sulphoaluminate cement system, accelerates the dissolution of Al

[0015] Advantages: Compared with the prior art, the present application has the following remarkable advantages: (1) The present application significantly improves the early hydration activity of sulphoaluminate cement at low temperature or even negative temperature environment by introducing a specific amount of high-purity lithium carbonate (>99%), combined with optimized mix proportion and polycarboxylate superplasticizer, which ensures good workability and compactness of the paste, laying a foundation for early strength development; (2) The material components in the cement-based material of the present application have a significant synergistic effect. Sulphoaluminate cement itself has early strength characteristics. The addition of fly ash (F-class I-grade) improves the paste performance and participates in the later reaction. The superplasticizer ensures good fluidity and water-reducing effect at low water-binder ratio. High-purity lithium carbonate is the key low-temperature activator and early strength agent. (3) The preparation method of the cement-based material provided by the present application is simple to operate and does not require complex pretreatment, which will not affect the construction period. At the same time, the use of industrial by-product fly ash conforms to the trend of resource utilization, and the simplified curing process significantly saves energy and reduces carbon emissions. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is the microstructure diagram of the sample hydrated for 28d in Comparative Example 1 and Example 4;

[0017] Figure 2 is the XRD diagram of the cement-based materials obtained from Example 4, Example 8 and Comparative Example 1 at -5℃ at 1d and 7d in Example 9;

[0018] Figure 3 is the TG-DTG curve diagram of the cement-based materials of Example 4, Example 8 and Comparative Example 1 at -5℃ at 1d and 7d. DETAILED DESCRIPTION

[0019] The technical solutions of the present application will be further described below in conjunction with the drawings.

[0020] In the following examples, the sulphoaluminate cement is a fast hardening composite sulphoaluminate cement (R·SAC) of 42.5 strength grade produced by Tangshan Polar Bear Building Material Co., Ltd., the chemical composition of which is shown in Table 1. The fly ash is a Class I fly ash of F type, the important chemical composition of which is shown in Table 2. The lithium carbonate is produced by Shanghai Sinopharm Chemical Reagent Co., Ltd., with a purity of more than 99%. The polycarboxylate superplasticizer has an effective solid content of 28%, a pH value of 13.19, a specific gravity of 36.39, and a water solubility of 0.38. The water is Wahaha pure water.

[0021] Table 1 Chemical composition of cement (mass ratio wt. %)

[0022]

[0023] Table 2 Chemical composition of fly ash (mass ratio wt. %)

[0024]

[0025] Example 1:

[0026] The raw material components are taken in the following weight parts: sulphoaluminate cement 400 parts, fly ash 100 parts, water 150 parts, lithium carbonate 0.05 parts, and polycarboxylate superplasticizer 2 parts.

[0027] Preparation method:

[0028] (1) The raw material components are weighed in mass parts and prepared for use;

[0029] (2) The sulphoaluminate cement and fly ash are added to a mixer and stirred until uniform, to obtain a composite cementitious material;

[0030] (3) The lithium carbonate and the superplasticizer are uniformly dispersed in water to obtain a mixed solution containing admixtures;

[0031] (4) The mixed solution in step (3) and the composite cementitious material in step (2) are added to a NJ-160 type cement paste stirrer, stirred at low speed (60 r / min) for 120 s, and after stopping for 15 s while scraping the cement paste on the blade and the wall of the pot into the middle of the pot, stirred at high speed (120 r / min) for 120 s, to obtain the high early strength fast hardening cement-based material paste.

[0032] Example 2:

[0033] The raw material components are taken in the following weight parts: sulphoaluminate cement 400 parts, fly ash 100 parts, water 150 parts, lithium carbonate 0.1 parts, and polycarboxylate superplasticizer 2 parts.

[0034] The preparation method is the same as in Example 1.

[0035] Example 3:

[0036] The raw material components were taken by weight parts as follows: sulphoaluminate cement 400 parts, fly ash 100 parts, water 150 parts, lithium carbonate 0.2 parts, polycarboxylate superplasticizer 2 parts.

[0037] The preparation method was the same as in Example 1.

[0038] Example 4:

[0039] The raw material components were taken by weight parts as follows: sulphoaluminate cement 400 parts, fly ash 100 parts, water 150 parts, lithium carbonate 0.8 parts, polycarboxylate superplasticizer 2 parts.

[0040] The preparation method was the same as in Example 1.

[0041] Example 5:

[0042] The raw material components were taken by weight parts as follows: sulphoaluminate cement 400 parts, fly ash 100 parts, water 150 parts, lithium carbonate 1.6 parts, polycarboxylate superplasticizer 2 parts.

[0043] The preparation method was the same as in Example 1.

[0044] Example 6:

[0045] The raw material components were taken by weight parts as follows: sulphoaluminate cement 400 parts, fly ash 100 parts, water 150 parts, lithium carbonate 3.2 parts, polycarboxylate superplasticizer 2 parts.

[0046] The preparation method was the same as in Example 1.

[0047] Example 7:

[0048] The raw material components were taken by weight parts as follows: sulphoaluminate cement 400 parts, fly ash 100 parts, water 150 parts, lithium carbonate 5 parts, polycarboxylate superplasticizer 2 parts.

[0049] The preparation method was the same as in Example 1.

[0050] Example 8:

[0051] The raw material components were taken by weight parts as follows: sulphoaluminate cement 400 parts, fly ash 100 parts, water 150 parts, lithium carbonate 10 parts, polycarboxylate superplasticizer 2 parts.

[0052] The preparation method was the same as in Example 1.

[0053] Comparative Example 1:

[0054] The raw material components were taken by weight parts as follows: sulphoaluminate cement 400 parts, fly ash 100 parts, water 150 parts, polycarboxylate superplasticizer 2 parts.

[0055] Preparation method:

[0056] (1) Each raw material component was weighed by mass parts, and was ready for use;

[0057] (2) The sulphoaluminate cement and fly ash were added into a mixer, and were stirred until uniform to obtain a composite cementitious material;

[0058] (3) The water reducing agent was uniformly dispersed in water to obtain a mixed solution containing an additive;

[0059] (4) The mixed solution in step (3) and the composite cementitious material in step (2) were added into a NJ-160 type cement paste stirrer, and were stirred at a low speed (60 r / min) for 120 s, and after stopping for 15 s while scraping the cement paste on the blade and the pot wall into the middle of the pot, the stirring was carried out at a high speed (120 r / min) for 120 s, and thus the high early strength and fast hardening cement-based material paste was obtained.

[0060] Performance detection:

[0061] The cement-based materials in the above examples 1-8 and comparative example 1 were directly placed into a curing temperature of -5℃ for curing, and then were tested and determined, and the initial setting time, the final setting time, the 1d, 3d and 7d compressive strength were mainly determined. The test results are shown in Tables 3 and 4.

[0062] Table 3 Test results of setting time of cement-based materials in examples 1-8 and comparative example 1 at -5℃ (unit: min)

[0063]

[0064] The results in Table 3 show that by adding Li2CO3 in examples 1-8, the initial and final setting times can be significantly shortened, and the time difference between the initial setting and the final setting can also be obviously shortened. For example, the initial setting time in example 4 is shortened to 53% of that in comparative example 1, the final setting time is reduced to 57.2%, and the time difference between the initial setting and the final setting is also shortened by 64%. With the change of the Li2CO3 content in the total amount of solid raw materials in the examples, it can be found that the setting accelerating effect is more significant when the content in examples 4-6 is in the range of 0.16% to 0.64%, and the setting time is prolonged when the content is further increased. However, it should be noted that too short setting time is not conducive to the normal construction of concrete. Therefore, the content of Li2CO3 in sulphoaluminate cement should be strictly controlled or be used in combination with a suitable retarder to achieve the combination of early strength and good construction performance.

[0065] Table 4 Test results of compressive strength of cement-based materials in examples 1-8 and comparative example 1 at -5℃ (unit: MPa)

[0066]

[0067]

[0068] As can be seen from the results of Table 4, when the curing temperature is -5℃, the early strength of Comparative Example 1 is low and develops slowly under the negative temperature condition, and the 1d strength is only 6.38 MPa. With the increase of the Li2CO3 content in Examples 1-8, the 3d strength is increased by 8.7%, 20.5%, 63.2%, 127%, 86.2%, 74.2%, 31.2% and 34.3% respectively. Therefore, in general, the improvement effect of Examples 3-6 is more significant, and in particular, Example 4 has the best mechanical properties. It can be found that when the Li2CO3 content in the examples is relatively large in the total amount of solid raw materials, which is more than 0.98% of Example 7, the strength loss is large, which is due to the fact that the early hydration reaction is too fast, resulting in that the surface of the cement particles is wrapped by the early generated cement hydration products, thereby delaying the increase of the cement strength.

[0069] The cement-based material paste prepared from Example 4 and Comparative Example 1 was cured at -5℃ for 28d to obtain a cement-based material, and the scanning electron microscope analysis results are shown in Figure 1 . Figure 1 The microstructure of the samples hydrated for 28d in Comparative Example 1 and Example 4 is shown in Figure 2, wherein a is Comparative Example 1, and b is Example 4. As can be seen from Figure 1 , a large number of needle-like and densely overlapped AFt crystals exist in the high-early-strength and fast-hardening cement-based material for cold region environment prepared in Example 4, and no obvious holes and cracks are observed in the electron micrographs of the same sample, and the structure of the sulphoaluminate cement stone in Figure b is compact. This is related to the freezing of the cement sample under negative temperature. In Comparative Example 1, the size of the hydration product AFt crystal is obviously reduced, and there are black holes in the matrix, so the strength is relatively low.

[0070] The XRD analysis results of the cement-based paste prepared from Example 4, Example 8 and Comparative Example 1 cured at -5℃ for 1d and 7d respectively are shown in Figure 2 . Figure 2 The XRD patterns of the cement-based materials obtained from Example 4, Example 8 and Comparative Example 1 under the condition of -5℃ in Example 9 for 1d and 7d are shown in Figure 3, wherein a is 1d, and b is 7d; by comparing the influence of the change of Li2CO3 content on the diffraction peak intensity of the crystalline phase material in the cement system, it can be found that the incorporation of Li2CO3 has a significant influence on the content of ettringite (AFt), and the diffraction peak intensity of ettringite in Example 4 is significantly increased, and the diffraction peak of unhydrated calcium sulphoaluminate is also the smallest. The low reactant peak intensity and high product peak intensity indicate that Example 4 has a higher hydration degree.

[0071] The cement-based pastes prepared in Example 4, Example 8 and Comparative Example 1 were subjected to thermogravimetric analysis, and the results are shown in FIGS. 8A and 8B. Figure 3 Figure 3 FIGS. 8A and 8B are TG-DTG curves of the cement-based materials obtained in Example 4, Example 8 and Comparative Example 1 at -5°C for 1 day and 7 days, respectively, where a is 1 day and b is 7 days. As can be seen from the weight loss peaks in the curves, the results are consistent with the XRD diffraction patterns, which mainly contain the hydration products AFt, amorphous C-S-H gel and AH3, etc., with a small amount of CH appearing only in the later stage. The total weight loss of the TG curve of Example 4 at -5°C is the lowest, indicating that the addition of 0.16% Li2CO3 produces the most hydration products among the three dosage groups to fill the pores of the sulfoaluminate cement, making the pore structure more compact.​

Claims

1. A high early strength and fast hardening cement-based material for low temperature environment, characterized in that: The composition comprises the following components in proportion by weight: sulphoaluminate cement: fly ash: water: lithium carbonate: water reducing agent = 400:100:150:(0.05-10):

2.

2. The high early strength and fast hardening cement-based material for low temperature environment according to claim 1, characterized in that: The composition comprises the following components in proportion by weight: sulphoaluminate cement: fly ash: water: lithium carbonate: water reducing agent = 400:100:150:(0.8-3.2):

2.

3. The high early strength and fast hardening cement-based material for low temperature environment according to claim 1, characterized in that: Sulphoaluminate cement complies with the national standard "Sulphoaluminate Cement" GB20472-2006.

4. The high early strength and fast hardening cement-based material for low temperature environment according to claim 1, characterized in that: The fly ash is Class F, Grade 1 fly ash.

5. The high early strength and fast hardening cement-based material for low temperature environment according to claim 1, characterized in that: The purity of lithium carbonate is above 99%.

6. The high early strength and rapid hardening cement-based material for low temperature environment according to claim 1, characterized in that: The water reducer is a polycarboxylic acid high-efficiency water reducer.

7. The high early strength and rapid hardening cement-based material for low temperature environment according to claim 1, characterized in that: The effective solid content of the water reducer is more than 20%.

8. The method for preparing the high early strength and fast hardening cement-based material for low temperature environment according to any one of claims 1 to 7, characterized in that: Including the above steps: (1) mixing sulphoaluminate cement and fly ash and stirring until uniform to obtain a composite cementitious material; (2) dispersing lithium carbonate and a water reducing agent in water to obtain a mixed solution containing an admixture; (3) The mixed solution containing the admixture is mixed with the composite cementitious material, stirred at a low speed, and then stirred at a high speed to obtain a high early strength and fast hardening cement-based material slurry.

9. The method of preparation according to claim 8, characterized in that: In step (3), the speed of low-speed stirring is below 80 r / min, and the time of low-speed stirring is 60 to 120 s.

10. The preparation method according to claim 8, characterized in that: In step (3), the speed of high-speed stirring is 120-180 r / min, and the time of low-speed stirring is 60-90 s.

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