A concrete frost-resistant aggregate, a frost-resistant concrete and a preparation method thereof

Abstract

This application relates to a frost-resistant aggregate for concrete, frost-resistant concrete, and a preparation method thereof. By weight, it comprises 1 part reinforcing agent, 3-4 parts modified oak fine aggregate, and 1-2 parts water. The modified oak fine aggregate is at least partially hydroxylated oak fine aggregate. By weight fraction, the reinforcing agent comprises 20%-40% sodium nitrite, 45%-55% calcium oxide powder, 0-2% powder water-reducing agent, 8%-15% early-strength agent, and 2%-10% soluble carbonate. The pre-wetted modified oak fine aggregate releases the reinforcing agent aqueous solution into the capillaries of the concrete, maintaining internal humidity, which is beneficial for setting and hardening, lowering the freezing point of water in the concrete, and preventing frost heave damage under negative temperatures, thus exhibiting strong crack resistance. Oak has a low thermal conductivity and good insulation properties, preventing heat loss from the concrete interior, increasing the initial placement temperature and maintaining it in cold climates, effectively improving the early mechanical properties of the concrete.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete, in particular to a concrete anti-freezing aggregate, an anti-freezing concrete and a preparation method. BACKGROUND

[0002] Due to the influence of special geographical environment, the climate in plateau areas has the characteristics of large diurnal temperature difference and dryness. Under the extreme environment conditions of plateau and alpine regions, the bearing capacity of infrastructure such as railway engineering is reduced due to freeze-thaw damage, the durability is reduced, and the structural safety is threatened. Therefore, improving the durability of concrete structures, especially the frost resistance, has become a key and difficult problem in the research of infrastructure in plateau and alpine regions.

[0003] In winter, the natural environment temperature in plateau and alpine regions is generally negative, and the minimum temperature can reach-15℃. Under low temperature conditions, the hydration speed of cement will slow down, thereby prolonging the time of concrete setting and hardening. Construction in winter harsh environment will cause low early strength of concrete, easy damage to internal structure, and cause irreversible damage.

[0004] The thermal conductivity coefficient of present C40 concrete is 2.5W / (m·K), and the thermal conductivity coefficient of fine aggregate sand is 0.58W / (m·k). The higher the thermal conductivity coefficient, the faster the heat loss. The hydration heat of present medium and low grade C40 concrete is low and the heat preservation effect is poor, which is easy to be affected by low temperature environment, and even can cause concrete freezing and freeze damage. In addition, under the construction in plateau and alpine environment, due to the influence of large diurnal temperature difference, strong wind and dryness and other adverse weather factors, the early internal humidity of concrete will decrease rapidly, and the mechanical properties develop slowly, which is easy to produce microcracks, resulting in poor durability of concrete.

[0005] At present, the measures such as heating raw materials, building steam curing shed and electric heating are taken to ensure that the concrete is in a positive temperature environment in the early stage (0-7 days) during winter construction, instead of improving the performance of concrete materials. SUMMARY

[0006] The present application provides a concrete anti-freezing aggregate, an anti-freezing concrete and a preparation method, which improves the heat preservation and anti-freezing performance of concrete, and has the advantages of high early strength, high toughness and anti-cracking.

[0007] In a first aspect, a concrete anti-freezing aggregate is provided, which comprises 1 part of a reinforcing agent, 3-4 parts of a modified oak fine aggregate and 1-2 parts of water in terms of mass fraction.

[0008] The modified oak fine aggregate is an oak fine aggregate at least partially esterified with hydroxyl groups.

[0009] The reinforcing agent, by mass fraction, comprises 20%–40% sodium nitrite, 45%–55% calcium oxide powder, 0%–2% powder water-reducing agent, 8%–15% early strength agent, and 2%–10% soluble carbonate.

[0010] In some embodiments, the reinforcing agent comprises, by mass fraction, 30% sodium nitrite, 50% calcium oxide powder, 2% powder water-reducing agent, 10% early strength agent and 8% soluble carbonate.

[0011] In some embodiments, the early strength agent is calcium formate;

[0012] The soluble carbonates include one or more of lithium carbonate and sodium carbonate;

[0013] The powder water-reducing agent is a polycarboxylate high-efficiency powder water-reducing agent;

[0014] The calcium oxide powder has a mesh size of 600-800 mesh;

[0015] The gradation of the oak fine aggregate is as follows: 19.3% of particles larger than 2.36 mm, 19.7% of particles between 2.36 and 1.18 mm, 15.6% of particles between 1.18 and 0.60 mm, 36.8% of particles between 0.60 and 0.30 mm, 8.0% of particles between 0.3 mm and 0.15 mm, and 0.6% of fine oak powder with a particle size below 0.15 mm.

[0016] Secondly, a method for preparing concrete antifreeze aggregate as described in any of the above-mentioned methods is provided, comprising the following steps:

[0017] Mix 1 part reinforcing agent and 3-4 parts modified oak fine aggregate, then add 1-2 parts water and stir to form a saturated oak fine aggregate reinforced suspension, which is the concrete antifreeze aggregate.

[0018] In some embodiments, the modified oak fine aggregate is prepared as follows:

[0019] The dried oak fine aggregates are soaked in a hydroxyl esterifying agent and then subjected to a hot water bath heating treatment.

[0020] After being removed, it is rinsed with clean water and dried to obtain modified oak fine aggregate.

[0021] In some embodiments, the hydroxyl esterifying agent is acetic anhydride;

[0022] The insulated water bath heating treatment includes: treatment at 100℃ for 10 to 24 hours.

[0023] Thirdly, a freeze-resistant concrete is provided, comprising fine aggregate, wherein 5% to 10% of the volume of the fine aggregate is replaced by an equal amount of the freeze-resistant concrete aggregate as described above.

[0024] In some embodiments, the frost-resistant concrete includes C40 concrete, which includes the fine aggregate.

[0025] Fourthly, a freeze-resistant concrete is provided, comprising the freeze-resistant aggregates as described in any of the above.

[0026] Fifthly, a method for preparing frost-resistant concrete as described in any of the above-mentioned methods is provided, comprising the following steps:

[0027] Finally, add the concrete antifreeze aggregate, mix well, and you will get antifreeze concrete.

[0028] The beneficial effects of the technical solution provided in this application include:

[0029] This application provides a concrete antifreeze aggregate, antifreeze concrete, and a preparation method. The pre-wetted modified oak fine aggregate releases a reinforcing agent aqueous solution into the capillaries of the concrete, maintaining internal moisture, which is beneficial for setting and hardening, and lowers the freezing point of water in the concrete. In sub-zero temperatures, the concrete is less prone to freezing and frost heave damage, exhibiting strong crack resistance. Furthermore, oak has a low thermal conductivity and good heat insulation properties, preventing heat loss from the concrete interior, thus increasing the initial placement temperature and maintaining it in cold climates, effectively improving the early mechanical properties of the concrete. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 A flowchart illustrating the preparation process of modified oak fine aggregate provided in this application embodiment. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] This application provides a concrete antifreeze aggregate, which, by mass fraction, comprises 1 part reinforcing agent, 3-4 parts modified oak fine aggregate, and 1-2 parts water; wherein the modified oak fine aggregate is at least partially hydroxylated oak fine aggregate; the reinforcing agent, by mass fraction, comprises 20%-40% sodium nitrite, 45%-55% calcium oxide powder, 0-2% powder water-reducing agent, 8%-15% early strength agent, and 2%-10% soluble carbonate.

[0034] Oak is a type of hardwood made from oak trees. It possesses low thermal conductivity and good insulation properties, and its water absorption rate is higher than sand, allowing it to release water within concrete, promoting secondary hydration of the adhesive. Furthermore, it is rich in wood fibers, giving it high toughness and increasing the crack resistance of concrete. For example, the oak fine aggregate with a specific gradation shown in Table 1 below has a measured water absorption rate of 8%, a thermal conductivity of 0.2 W / (m·K), and a density of 0.8 g / cm³. 3 Furthermore, its microstructure is characterized by porosity.

[0035] If oak fine aggregate is directly used to replace part of the fine aggregate in ordinary concrete, the oak may absorb moisture from the fresh concrete and oxidize and rot, ultimately resulting in defects that lead to low mechanical strength and failure to meet design standards. Therefore, oak fine aggregate is modified to induce partial hydroxyl esterification of the wood cells.

[0036] The purpose of the above modification treatment is to reduce the water absorption rate of oak particles and block some of the internal pore structures, which can effectively improve the dimensional stability and durability of wood and achieve better bonding between oak fine aggregate and cementitious materials.

[0037] Meanwhile, reinforcing agents are also added, among which sodium nitrite can combine with water to form hydrated ions. These hydrated ions will hinder the formation of hydrogen bonds between water molecules, thereby lowering the freezing point of free water and bound water in concrete. Finely ground calcium oxide reacts with water to generate calcium carbonate, which can fill the pore structure in concrete, making the concrete more compact. At the same time, the heat released by the reaction is absorbed and stored by oak, which plays a heating role on the raw materials. Early strength agent can accelerate the hydration of cement and improve the early strength of concrete. Soluble carbonate can react with aluminates in cement to generate aluminum carbonate, which compensates for shrinkage through expansion reaction, improving the durability and crack resistance of concrete. It can be seen that the main functions of this reinforcing agent added to concrete include: (1) improving the early strength of concrete and shortening the curing time; (2) effectively lowering the freezing point of water in concrete, and cementitious materials can be hydrated under negative temperature conditions; (3) destroying the structure of ice, which is flocculent in capillary pores, reducing the risk of frost heave damage.

[0038] Oak has a low density and is classified as a lightweight fine aggregate. Directly adding it to concrete will cause it to float, resulting in uneven concrete mass distribution and segregation. Mixing the reinforcing agent powder with the dried modified oak fine aggregate allows sufficient fine powder to be absorbed onto the oak surface. Upon adding water, the reinforcing agent dissolves, forming a slurry that coats the surface of the modified oak fine aggregate and even penetrates into the oak, creating a saturated oak fine aggregate reinforcing suspension. This provides overall reinforcement and effectively prevents the lightweight aggregate from floating during later molding.

[0039] Pre-wetted modified oak fine aggregate releases a reinforcing agent solution into the capillaries of the concrete, maintaining internal moisture and promoting setting and hardening. It also lowers the freezing point of water in the concrete, preventing frost heave damage and cracking in sub-zero temperatures. Furthermore, oak's low thermal conductivity and good insulation properties prevent heat loss from the concrete, increasing the initial placement temperature and maintaining it in cold climates, effectively improving the early mechanical properties of the concrete.

[0040] As a preferred example, the reinforcing agent comprises, by mass fraction, 30% sodium nitrite, 50% calcium oxide powder, 2% powder water-reducing agent, 10% early strength agent and 8% soluble carbonate.

[0041] As a preferred example, the gradation and sieving of the oak fine aggregate are shown in Table 1 below:

[0042] Table 1

[0043]

[0044]

[0045] In this application, the early strength agent may be calcium formate or the like.

[0046] In this application, the soluble carbonate includes one or more of lithium carbonate and sodium carbonate;

[0047] In this application, the powder water-reducing agent is a polycarboxylate high-efficiency powder water-reducing agent, such as Sika's powder water-reducing agent product 540P;

[0048] In this application, the calcium oxide powder has a mesh size of 600 to 800 mesh, preferably 800 mesh.

[0049] This application also provides a method for preparing concrete antifreeze aggregate, which includes the following steps: mixing 1 part of reinforcing agent and 3-4 parts of modified oak fine aggregate, and then adding 1-2 parts of water and stirring to form a saturated oak fine aggregate reinforced suspension, thereby obtaining concrete antifreeze aggregate.

[0050] Among them, see Figure 1As shown, the preparation method of the modified oak fine aggregate is as follows:

[0051] 101: Soak the dried oak fine aggregate in a hydroxyl esterifying agent and then heat it in a hot water bath.

[0052] Specifically, the oak fine aggregate was dried in an oven for 24 hours at a temperature of 50°C.

[0053] Oak fine aggregate is soaked in a certain amount of acetic anhydride and heated in a hot water bath at 100°C. After 10–24 hours, it is removed from the acetic anhydride solution. The oak fine aggregate will show a significant increase in weight after this process. Preferably, it can be removed after 24 hours of hot water bath heating.

[0054] 102: After removal, rinse with clean water and dry to obtain modified oak fine aggregate.

[0055] The oak fine aggregate was rinsed with clean water and dried naturally. The water absorption rate of the modified oak fine aggregate was measured to be reduced to about 5%.

[0056] The concrete antifreeze aggregate provided in this application can be used as an internal admixture in concrete, replacing a portion of the fine aggregate in the original concrete formula to obtain new concrete and improve its antifreeze properties. It can also be used as an external admixture, directly added to the original concrete formula to obtain new concrete and improve its antifreeze properties.

[0057] The specific method of addition can be determined based on actual needs, and the amount added can also be determined based on actual needs.

[0058] For example, as an example, this application provides an antifreeze concrete comprising fine aggregate, wherein 5% to 10% of the volume of the fine aggregate is replaced by the aforementioned antifreeze concrete aggregate.

[0059] Furthermore, the frost-resistant concrete includes C40 concrete, which includes the fine aggregate; the water-cement ratio of the frost-resistant concrete is equal to that of the C40 concrete. That is, the water-cement ratio remains constant. 5% to 10% of the volume of the fine aggregate in the original C40 concrete is replaced by the aforementioned frost-resistant concrete aggregate.

[0060] For example, as an example, an embodiment of this application provides an antifreeze concrete, which includes the above-mentioned antifreeze concrete aggregate.

[0061] This application also provides a method for preparing antifreeze concrete, which includes the following steps: after other materials are added and mixed, antifreeze concrete aggregate is added last, and after stirring evenly, antifreeze concrete is obtained.

[0062] Comparative Example 1:

[0063] A C40 concrete, calculated per cubic meter, comprises: 344 kg cement, 86 kg fly ash, 763 kg fine aggregate, 1054 kg stone, 4.3 kg water-reducing agent, and 159 kg water.

[0064] The water-to-binder ratio is 159kg / (344kg+86kg)=0.37.

[0065] The preparation steps include: weighing cement, fly ash, fine aggregate, and stone, mixing them in a mixing pot for 2 minutes, then adding the weighed water and water-reducing agent, mixing for 2 minutes, and then forming concrete.

[0066] Example 1:

[0067] Compared to Comparative Example 1, Example 1 uses concrete frost-resistant aggregate to replace 10% of the fine aggregate volume in Comparative Example 1, while the remaining 90% of the fine aggregate volume remains unchanged. Specifically:

[0068] A C40 antifreeze concrete, calculated per cubic meter of concrete, comprises: 344 kg cement, 86 kg fly ash, 686.7 kg fine aggregate, 38.8 kg antifreeze aggregate for concrete, 1054 kg stone, 4.7 kg water-reducing agent, and 149 kg water.

[0069] The 38.8 kg concrete antifreeze aggregate includes 7 kg of reinforcing agent, 21.8 kg of modified oak fine aggregate, and 10 kg of water.

[0070] The water-to-binder ratio is (10kg+149kg) / (344kg+86kg)=0.37.

[0071] The preparation steps include:

[0072] Step 1, Premixing: Pour 7 kg of reinforcing agent and 21.8 kg of modified oak fine aggregate into a mixer and mix for 5 minutes. Then add 10 kg of water and mix for another 5 minutes to form a saturated oak fine aggregate reinforcing suspension, thus obtaining concrete antifreeze aggregate.

[0073] The second step is to weigh out cement, fly ash, fine aggregate, and stone, mix them in a mixing pot for 2 minutes, then add the weighed water and water-reducing agent, mix for 2 minutes, add the concrete antifreeze aggregate, and finally mix for 5 minutes to form concrete.

[0074] Examples of combinations are shown in Table 2 below:

[0075] Table 2

[0076]

[0077] Comparative Example 2:

[0078] The difference between Comparative Example 2 and Example 1 is that the first step of premixing the reinforcing agent and modified oak fine aggregate is not performed; instead, the reinforcing agent and modified oak fine aggregate are directly added during the concrete mixing in the second step.

[0079] Comparative Example 3:

[0080] The difference between Comparative Example 3 and Example 1 is that oak fine aggregate was used directly instead of modified oak fine aggregate, that is, the oak fine aggregate was not modified. The water absorption rate of the oak fine aggregate was measured to be 8%.

[0081] Comparative Example 4:

[0082] The difference between Comparative Example 4 and Example 1 is that concrete antifreeze aggregate was used instead of 15% of the volume of fine aggregate in Comparative Example 1.

[0083] The following tests were performed on Comparative Examples 1 to 4 and Example 1:

[0084] Compressive strength test: The compressive strength test was conducted according to the "GB / T50081 Standard for Test Methods of Mechanical Properties of Concrete". The molded concrete blocks were all 150mm×150mm×150mm in size. Three blocks were molded for each case at each age, and the average value was taken. The test design differed from the standard in that the molded blocks were not cured in a temperature- and humidity-controlled indoor environment, but rather under the natural climate conditions of a construction site in a high-altitude region during winter. During this period, the lowest temperature reached -10℃ and the highest temperature reached 12℃, accompanied by winds of up to 10m / s. The test results can accurately reflect the changes in the mechanical strength of concrete under complex and deteriorating conditions, closely matching the actual application effects.

[0085] Flexural strength and fracture energy testing: 150mm×150mm×550mm molded specimens were tested. After 28 days of standard curing, a four-point bending test was conducted according to the "GBT 50081-2019 Standard for Test Methods of Physical and Mechanical Properties of Concrete" to test the flexural strength and fracture energy.

[0086] Freeze-thaw resistance test: The rapid freeze-thaw method in GB / T 50082-2009 was adopted, and the specimen size was 100mm×100mm×400mm. After the specimen was cured in the standard curing room for 24 days, it was taken out of the standard curing room and immersed in water at (20±2)℃ for 4 days. During immersion, the water level should be (20~30)mm higher than the specimen. The freezing temperature was set to -10℃ and the thawing temperature was set to 10℃. The test can be stopped when one of the following two conditions occurs: (1) the dynamic elastic modulus of the specimen drops below 60%; (2) the weight loss rate of the specimen reaches 5%.

[0087] The test results are shown in Table 3 below:

[0088] Table 3

[0089]

[0090] As can be seen from the table above, if the reinforcing agent is not premixed with the modified oak fine aggregate (Comparative Example 2), if the oak fine aggregate is not modified (Comparative Example 3), or if the amount of antifreeze aggregate in the concrete is too high (Comparative Example 4), the mechanical properties of the formed concrete are lower than expected (Example 1). Therefore, the steps that this application seeks to protect play a crucial role in the preparation of antifreeze concrete.

[0091] Example 1 and Comparative Example 1 were also tested for flexural strength and fracture energy, further demonstrating that the flexural and crack resistance of concrete formed using the high toughness of oak is further improved. Regarding frost resistance, Example 1 achieved a frost resistance grade of F600 under extreme freeze-thaw cycles, significantly higher than that of the Comparative Example.

[0092] To reveal the reaction mechanism and products of antifreeze aggregates in concrete, samples from Example 1 and Comparative Example 1 were subjected to QXRD (quantum X-ray fluorescence spectrometry). The results are shown in Table 4 below.

[0093] Table 4:

[0094]

[0095] Note: C3S is Ca3SiO5; C2S is Ca2SiO4; C4AF is calcium iron aluminum stone.

[0096] Quantitative analysis of hydration products by QXRD (Quantitative X-ray Fluorescence Spectroscopy) revealed that, compared with Comparative Example 1, the total amount of C2S, C3S, and Ca(OH)2 generated in Example 1 was higher. This further proves that the addition of antifreeze aggregate can react with cement, promote the hydration of cementitious materials, generate more and stronger hydration products, improve the early strength of concrete, and ensure that the mechanical properties of concrete structures can develop normally under low temperature conditions.

[0097] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A concrete antifreeze aggregate, characterized in that: The raw materials, by weight, include 1 part reinforcing agent, 3 to 4 parts modified oak fine aggregate, and 1 to 2 parts water; The modified oak fine aggregate is at least partially hydroxylated oak fine aggregate; The reinforcing agent, by mass fraction, comprises 20%–40% sodium nitrite, 45%–55% calcium oxide powder, 0%–2% powder water-reducing agent, 8%–15% early strength agent, and 2%–10% soluble carbonate.

2. The concrete antifreeze aggregate as described in claim 1, characterized in that: The reinforcing agent comprises, by mass fraction, 30% sodium nitrite, 50% calcium oxide powder, 2% powder water-reducing agent, 10% early strength agent and 8% soluble carbonate.

3. The concrete antifreeze aggregate as described in claim 1, characterized in that: The early-strength agent is calcium formate; The soluble carbonates include one or more of lithium carbonate and sodium carbonate; The powder water-reducing agent is a polycarboxylate high-efficiency powder water-reducing agent; The calcium oxide powder has a mesh size of 600-800 mesh; The gradation of the oak fine aggregate is as follows: 19.3% of the particles are larger than 2.36 mm, 19.7% are between 2.36 and 1.18 mm, 15.6% are between 1.18 and 0.60 mm, 36.8% are between 0.60 and 0.30 mm, 8.0% are between 0.3 mm and 0.15 mm, and 0.6% are fine oak powder with a particle size of less than 0.15 mm.

4. A method for preparing concrete antifreeze aggregate as described in any one of claims 1 to 3, characterized in that, It includes the following steps: Mix 1 part reinforcing agent and 3-4 parts modified oak fine aggregate, then add 1-2 parts water and stir to form a saturated oak fine aggregate reinforced suspension, which is the concrete antifreeze aggregate.

5. The method for preparing concrete antifreeze aggregate as described in claim 4, characterized in that, The preparation method of the modified oak fine aggregate is as follows: The dried oak fine aggregates were soaked in a hydroxyl esterifying agent and then subjected to a hot water bath heating treatment. After being removed, it is rinsed with clean water and dried to obtain modified oak fine aggregate.

6. The method for preparing concrete antifreeze aggregate as described in claim 5, characterized in that: The hydroxyl esterifying agent is acetic anhydride; The insulated water bath heating treatment includes: treatment at 100℃ for 10 to 24 hours.

7. A frost-resistant concrete comprising fine aggregate, characterized in that: The volume of the fine aggregate is replaced by an equal amount of the concrete antifreeze aggregate as described in any one of claims 1 to 3.

8. The frost-resistant concrete as described in claim 7, characterized in that: The antifreeze concrete is C40 concrete, which includes the fine aggregate.

9. A type of frost-resistant concrete, characterized in that: It includes concrete antifreeze aggregate as described in any one of claims 1 to 3.

10. A method for preparing frost-resistant concrete as described in any one of claims 7 to 9, characterized in that, It includes the following steps: Finally, add the concrete antifreeze aggregate, mix well, and you will get antifreeze concrete.

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