Concrete thermal damage inhibiting material for high-geothermal environment and preparation method and application thereof

Abstract

The application belongs to the technical field of functional additives for building materials, and particularly discloses a concrete thermal damage inhibiting material for high-geothermal environments and a preparation method thereof.The concrete thermal damage inhibiting material comprises a plurality of components, such as mineral admixtures, quartz sand, metakaolin, nanomaterials, thickening agents, and retarders, which are uniformly mixed in predetermined mass percentages.The concrete thermal damage inhibiting material uses conventional components in building materials, and through reasonable collocation, comprehensively considers the performance improvement in cement hydration, hydration product distribution, and density improvement when applied to concrete, and comprehensively guarantees the application effect.The concrete thermal damage inhibiting material can be applied to concrete construction in high-geothermal environments, improves the density of concrete, guarantees the uniform development of strength, reduces the water evaporation rate, avoids structure degradation under high geothermal temperature, avoids the problems of reduced late strength and uneven early hydration product distribution of concrete under high-geothermal action, and improves the durability.

Description

Technical Field

[0001] This invention belongs to the technical field of functional additives for building materials. Specifically, it discloses a material for inhibiting thermal damage to concrete in high geothermal environments, its preparation method, and its application. Background Technology

[0002] Currently, transportation infrastructure construction in western my country is experiencing a new boom. However, this region has a high altitude and is dominated by mountains and hills. Due to factors such as geological lithology, some areas have high geothermal and rock temperature environments. Generally, rock temperatures exceeding 30℃ are considered high rock temperatures, and some tunnel construction processes will encounter temperatures of around 80℃.

[0003] High geothermal temperatures make it difficult to guarantee the mechanical and durability properties of concrete in tunnel engineering. In such environments, the workability of concrete changes significantly, with increased slump loss and reduced workable time, causing construction difficulties and increasing the likelihood of defects such as insufficient compaction. After pouring, the rapid evaporation rate of water in concrete leads to increased initial hydration, earlier initial and final setting, and significant changes in the microstructure of hydration products. This results in increased early strength but decreased later strength, along with reduced internal density and increased porosity, all of which reduce the concrete's durability. Shotcrete is most significantly affected by high geothermal environments. From the moment it hits the rock surface, high geothermal temperatures affect the hydration properties and strength development of the cementitious materials, thus impacting the bond strength and rebound of the shotcrete. In high geothermal environments, the rebound of ordinary shotcrete increases significantly, bond strength is severely lost, and even debonding and cracking occur, rendering the concrete ineffective in supporting the surrounding rock. This becomes a key factor affecting the performance of shotcrete in high geothermal conditions.

[0004] Improving the geothermal resistance of concrete hinges on ensuring uniform strength development under high geothermal conditions and preventing excessively rapid early hydration, which can lead to stagnation or even regression in later strength development. Furthermore, due to the low early density of concrete, the mixing water evaporates under high temperatures, reducing the available water for cement hydration and further inhibiting strength development. Therefore, suppressing water evaporation is also a measure to improve the mechanical properties of concrete under high geothermal conditions.

[0005] Current research focuses on concrete for high geothermal environments, including a high-temperature resistant concrete and its preparation method. This method utilizes the synergistic effect of attapulgite, polybutylene terephthalate (PET), polyphenylene ether (PPE), nano-ferric oxide (Fe3O4), and organosilicon to minimize the increase in cement hydration rate and water evaporation rate under high-temperature conditions, thus slowing down the decrease in cement paste strength and resulting in concrete with excellent impact resistance and high-temperature resistance. However, the incorporation of PET and organosilicon can negatively impact the workability of the concrete.

[0006] Another report on high-strength shotcrete for high-temperature tunnels and its preparation method uses cement, fly ash, slag powder, sand, coarse aggregate, vitrified microspheres, PVA fiber, steel fiber, modified rubber, water-reducing agent, accelerator, and water to prepare the concrete. Water glass is used for curing; the water glass reacts with the calcium hydroxide generated during cement hydration to form calcium silicate gel, preventing moisture loss during curing. However, the curing process using water glass is complex, leading to increased construction costs.

[0007] Another example is a type of shotcrete material specifically designed for high-temperature, dry, and hot tunnel environments. By incorporating nano-silica, it utilizes the micro-aggregate effect, pozzolanic effect, and nucleation effect to promote rapid hydration and setting of the shotcrete under severe conditions of rapid water loss in high-temperature environments, thereby improving early-age strength and reducing rebound. However, the application of nanomaterials can negatively impact the workability of concrete, leading to a decrease in flowability during construction and pouring. Furthermore, nanomaterials are prone to agglomeration and have poor dispersibility, easily forming clumps when incorporated into concrete, thus affecting their effectiveness.

[0008] In addition, a technique for using concrete for initial support in high-stress, high-temperature tunnel excavation also improves the workability of concrete by using basalt fibers and redispersible latex powder, giving the concrete strong adhesion and enabling it to bond well with the surrounding rock. However, the main purpose of this method is to improve the crack resistance of shotcrete; it does not provide relevant research results on maintaining compressive strength under high temperature conditions or inhibiting moisture evaporation.

[0009] It is evident that the technical problems that concrete is prone to encounter in high geothermal environments have not yet been adequately resolved, and further research is needed to improve the performance of concrete in this application environment. Summary of the Invention

[0010] To overcome the shortcomings of existing technologies, this invention provides a concrete thermal damage inhibition material for use in high geothermal environments. This concrete thermal damage inhibition material exhibits excellent geothermal resistance; concrete using this material shows significant improvement in mechanical properties under high geothermal conditions, and a reduced moisture evaporation rate.

[0011] To achieve the above objectives, the present invention specifically adopts the following technical solution:

[0012] A concrete thermal damage inhibition material for high geothermal environments, comprising the following components mixed uniformly in mass percentages:

[0013]

[0014]

[0015] Among them, the mineral admixture is any one or a mixture of two of fly ash and mineral powder, and its performance meets the requirements of relevant national standards, such as GB T 1596 "Fly Ash for Cement and Concrete" and GB T 18046 "Granulated Blast Furnace Slag Powder for Cement and Concrete", etc.

[0016] The nanomaterials are selected from any one or a mixture of at least two of nano-silica, nano-calcium carbonate, and nano-titanium dioxide, with the particle size controlled between 50 nm and 300 nm. The nanomaterials, when incorporated into concrete, act as nucleation sites, facilitating the crystallization and nucleation of CSH gel. Through uniformly dispersed nanomaterials, CSH gels are uniformly nucleated and grown within the concrete during cement hydration, avoiding uneven distribution of CSH gels within the concrete due to high temperatures, which can lead to unbalanced strength development and reduced density.

[0017] The fineness of the quartz sand can be controlled between 1500 and 2000 mesh, and the particle size of the metakaolin can be controlled between 10 μm and 50 μm. Quartz sand and metakaolin possess potential alkali reactivity. Under the influence of high temperature and calcium hydroxide generated during cement hydration, the alkali reactivity of quartz sand and metakaolin is activated, generating CSH gel, which can increase the density of the matrix and compensate for the subsequent reduction in strength of concrete at high temperatures.

[0018] The retarder is selected from any one or a mixture of at least two of molasses retarder, lignin sulfonate, and hydroxycarboxylic acid retarder. Retarders slow down the cement hydration rate. Under high temperatures, the cement hydration rate is rapid, resulting in hydration products that cannot be distributed effectively and promptly, leading to reduced concrete density and uneven density distribution at different locations. Using a retarder slows down the cement hydration rate at high temperatures, which is beneficial for the distribution of hydration products, thereby improving the uniformity and density of the concrete.

[0019] The thickener is selected from any one or a mixture of at least two of methyl cellulose ether, polyacrylamide, and polyvinyl alcohol. The molecular weight of the methyl cellulose ether is preferably controlled above 100,000, and the molecular weights of the polyacrylamide and polyvinyl alcohol are preferably controlled above 5 million; higher molecular weights generally result in better performance. The thickener can adsorb and fix free water molecules through its hydrophilic groups and long side chains, causing its apparent volume to continuously increase under swelling. Simultaneously, the side chains of the thickener molecules attract each other, promoting the formation and entanglement of a gel network structure, preventing the migration of free water. Furthermore, the thickener undergoes surface adsorption with cement particles in the slurry, increasing the viscosity of the concrete matrix, thereby preventing the movement and evaporation of water at high temperatures, ensuring sufficient moisture for cement hydration under high temperatures, and contributing to further strength improvement.

[0020] Another objective of this invention is to provide a method for preparing the above-mentioned concrete thermal damage inhibition material for high geothermal environments, wherein the material is added in a quantity ranging from high to low and stirred evenly.

[0021] For example, the following steps can be taken: First, add mineral admixtures, quartz sand and metakaolin to a mixer and stir evenly; then, add nanomaterials and continue stirring evenly; finally, add thickener and retarder to the mixer and stir evenly, then discharge the material to prepare a concrete thermal damage inhibition material for high geothermal environments.

[0022] Generally, during the above stirring process, stirring at a rate of 1500r / min to 2000r / min for about 3 to 5 minutes is sufficient to achieve uniform mixing.

[0023] The concrete heat damage inhibitory material provided by this invention can be applied to concrete. Specifically, during the concrete mixing process, the concrete heat damage inhibitory material is used to replace an equal amount of the cementitious material used in concrete mixing, and the two materials are mixed together to prepare concrete. Generally, when the concrete heat damage inhibitory material for tunnels in high geothermal environments is used in concrete, the dosage is 10% to 30% of the mass of the cementitious material.

[0024] The concrete heat damage inhibitor provided by this invention uses conventional components from building materials. Through reasonable combination, it comprehensively considers the performance improvement effects of these components on cement hydration, distribution of hydration products, and density enhancement when applied to concrete, thus comprehensively ensuring the performance improvement of concrete in high geothermal environments. This concrete heat damage inhibitor can be applied to concrete construction in high geothermal environments. By increasing the density of concrete in high geothermal environments, it ensures uniform strength development and reduces the rate of moisture evaporation, avoiding structural deterioration under high geothermal temperatures. Furthermore, this concrete heat damage inhibitor can effectively avoid the problems of reduced strength in the later stages of concrete and uneven distribution of early hydration products under high geothermal conditions (which can easily lead to weak points inside the concrete, thus manifesting as a reduction in strength macroscopically), while also improving the durability of concrete. Detailed Implementation

[0025] The embodiments of the present invention will now be described in detail. However, the present invention can be implemented in many different forms, and should not be construed as being limited to the specific embodiments set forth herein. Rather, these embodiments are provided to explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the various embodiments of the invention and various modifications suitable for particular intended applications.

[0026] The embodiments of the present invention provide specific compositions and proportions of various concrete thermal damage inhibition materials, as shown in Table 1 below.

[0027] Table 1. Composition (wt%) of the concrete thermal damage inhibition materials provided in Examples 1 to 8

[0028]

[0029] The specific compositions of the mineral admixtures, nanomaterials, thickeners and retarders in each embodiment are shown in Table 2 below.

[0030] Table 2 shows the specific composition (wt%) of each component in the concrete thermal damage inhibition materials provided in each embodiment.

[0031]

[0032] The concrete thermal damage inhibition materials provided in the above embodiments are all prepared using the following methods:

[0033] Step 1) Add the mineral admixture, quartz sand and metakaolin to the mixer and stir at a speed of 2000 r / min for about 3 minutes until uniform.

[0034] Step 2) After stirring, add the nanomaterial and continue stirring at a rate of about 1500 r / min for about 3 minutes until uniform.

[0035] Step 3) After mixing evenly again, add the thickener and retarder to the mixer and stir at a speed of about 2000 r / min for 5 minutes until uniform, then discharge the material to prepare various concrete heat damage inhibition materials.

[0036] To demonstrate the necessity of each component and its content in the aforementioned concrete thermal damage inhibition material, several comparative experiments were conducted, as shown in Table 3 below.

[0037] Table 3 shows the composition (wt%) of the comparative materials provided in Comparative Examples 1 to 4.

[0038]

[0039] The specific compositions of mineral admixtures, nanomaterials, thickeners, and retarders in each comparative example are shown in Table 4 below.

[0040] Table 4 and Table 3 provide the specific composition (wt%) of each component in the comparative materials provided for each comparative example.

[0041]

[0042] To demonstrate the effectiveness of the concrete thermal damage inhibition materials provided in each embodiment, the following application examples are provided.

[0043] Application Examples

[0044] The concrete was fixed according to the mix proportion of C30 concrete in Table 5 below as the benchmark mix proportion. Concrete heat damage inhibitors with different specific compositions were added to the concrete in proportions shown in Table 6, replacing the cementitious materials in the concrete in equal amounts. The water evaporation rate and compressive strength changes of the obtained concrete under high temperature were measured.

[0045] Specifically, during the incorporation of the aforementioned concrete heat damage inhibitors and comparative materials into the concrete, the concrete powder and aggregates were first mixed evenly during molding, followed by the addition of water, water-reducing agent, and water-retaining material. After stirring for 2 minutes, the concrete was poured out of the mixing pot and then placed into molds. Each group of concrete specimens was used for moisture evaporation testing and compressive strength testing. After molding, each group of compressive strength specimens underwent standard curing and 60℃ heat curing until the specified age, followed by compressive strength testing. The concrete compressive strength was tested according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". A high-temperature drying environment was simulated using an electrically heated blast constant-temperature drying oven to test the moisture evaporation rate of the concrete at 60℃. The concrete moisture evaporation test is carried out according to the following steps: After the concrete is formed, the initial mass of the specimen is tested and the specimen is placed in an oven (60℃) along with the mold; the concrete mass is tested at different times after forming; after the concrete is cured at 60℃ for 24 hours, the mold is removed and the specimen is placed in the oven again.

[0046] Table 5 C30 Concrete Mix Proportions (kg / m³) 3 )

[0047]

[0048] To demonstrate the deficiencies of the comparative materials provided in the above comparative examples, the comparative materials of each comparative example were also incorporated into the concrete according to the mix proportions in Table 5, as described in the above application examples. The dosages are also listed in Table 6 below.

[0049] Table 6 shows the dosage of concrete heat damage inhibition materials provided in each embodiment and comparative materials provided in each comparative example in concrete.

[0050]

[0051] The combination ratios provided in Table 5 above were also used as a blank control group for the same tests.

[0052] Results Analysis

[0053] The water loss of concrete under 60℃ curing conditions was tested according to the experimental method, and the test results are shown in Table 7.

[0054] Table 7 Water Loss of Concrete under Various Curing Methods at 60℃

[0055]

[0056]

[0057] As shown in Table 7, under curing conditions at 60℃, the water loss of the concrete in the control group gradually increased. After 1 day, the water loss was 1.46%, after 3 days it was 2.14%, and after 28 days of curing at 60℃, the water loss reached 3.93%. This is because the evaporation of water reduces the water used for cement hydration within the concrete, preventing some cement particles from hydrating. Simultaneously, the channels formed by water evaporation lead to a decrease in the strength and density of the concrete.

[0058] After using the concrete heat damage inhibition materials provided by this invention (the concrete corresponding to Examples 1 to 8), a comparison showed that under the same age conditions, the water loss of the concrete was significantly reduced. After 28 days, the water loss was in the range of 2.8% to 3.1%, which was more than 20% lower than the control group. The reduction in water loss after incorporating the concrete heat damage inhibition materials effectively inhibits the rate of water evaporation in concrete under high geothermal conditions, proving the effectiveness of this invention.

[0059] The comparative experiments revealed that the water loss of concrete in Comparative Examples 1 to 4 increased rapidly, exceeding 3.5% at 28 days, significantly greater than the water loss in the other examples and similar to that in the control group. This indicates that the water evaporation pattern of the concrete in the comparative examples did not change significantly. The comparative comparison shows that the concrete heat damage inhibition material of this invention effectively inhibits water loss from concrete under thermal conditions through the combined action of different components. The absence of any component would prevent the reduction of water loss; all components are essential.

[0060] The compressive strength of concrete under standard curing conditions and 60℃ curing conditions was tested according to the test method. The test results are shown in Table 8 below.

[0061] Table 8 Compressive strength of concrete under different curing methods

[0062]

[0063] As shown in Table 8, the compressive strength of concrete in the control group at 3 days under heat curing conditions was significantly greater than that of concrete at the same age under standard curing conditions. At this age, the ratio of heat-cured strength to standard-cured strength was 1.80. With increasing concrete age, the compressive strength of standard-cured concrete increased rapidly, but the compressive strength of heat-cured concrete increased slowly, showing a reversal at 28 days, falling below the compressive strength of heat-cured concrete at 7 days. A comparison reveals that at 7 days, the compressive strength of standard-cured concrete was already close to that of 60℃ heat-cured concrete, while at 28 days, the compressive strength of standard-cured concrete was significantly greater than that of 60℃ heat-cured concrete, at which point the ratio of heat-cured strength to standard-cured strength was only 0.74.

[0064] After using the concrete heat damage inhibition materials provided by this invention (the concrete corresponding to Examples 1 to 8), the compressive strength of the concrete at 60°C was greater than that under standard curing conditions at both 3-day and 7-day curing ages. Furthermore, at 28-day curing, the compressive strength of the concrete under both curing methods was essentially the same. These results demonstrate that using the concrete heat damage inhibition materials provided by this invention effectively improves the long-term compressive strength of concrete under geothermal conditions, avoiding strength degradation caused by geothermal factors. This results in the compressive strength of concrete under high geothermal conditions being essentially close to that under standard curing conditions, proving that this invention can effectively ensure the strength development and stability of concrete under high geothermal conditions.

[0065] The comparative experiments revealed that the ratio of the 60℃ heat-cured strength to the standard-cured strength at 1 day of age in Comparative Examples 1–4 was initially quite high. This indicates that the concrete hydrated rapidly under high-temperature curing conditions, leading to a rapid increase in strength. This suggests that the materials used in the concrete in these comparative examples did not inhibit the rapid hydration process. At 7 days of age, the strength of the concrete cured at 60℃ was close to that of the standard-cured concrete. At 28 days of age, the strength of the concrete cured at 60℃ was lower than that of the standard-cured concrete and also lower than that of the concrete in the examples under the same conditions. This is partly due to the continuous evaporation of moisture from the concrete in the comparative examples, leaving no moisture for the cement to continue the hydration reaction in the later stages. It is also because the rapid early hydration in the concrete in the comparative examples resulted in a large amount of hydration products that inhibited further hydration. The strength variation patterns of the concrete in Comparative Examples 1–4 were basically consistent with those of the control group, exhibiting a pattern of rapid early strength increase followed by a slower and even regressive increase in later strength. The results show that the absence of any component in the comparative examples prevents the achievement of the purpose of the present invention—to ensure the strength stability of concrete under thermal conditions—in the concrete thermal damage inhibition material.

[0066] Although the invention has been shown and described with reference to specific embodiments, those skilled in the art will understand that various changes in form and detail may be made herein without departing from the spirit and scope of the invention as defined by the claims and their equivalents.

Claims

1. A concrete thermal damage inhibition material for high geothermal environments, characterized in that, It consists of the following components, which are mixed evenly in parts by mass, and the total of all components is 100%: Mineral admixtures: 30%~60%; Quartz sand 15%~30%; Metakaolinite 10%~30%; Nanomaterials 3%~5%; Thickener 0.1%~2%; Retarder 0.1%~1%; The fineness of the quartz sand is between 1500 mesh and 2000 mesh, and the particle size of the metakaolin is between 10 μm and 50 μm.

2. The concrete thermal damage inhibition material according to claim 1, characterized in that, The mineral admixture is selected from any one or a mixture of two of fly ash and mineral powder.

3. The concrete thermal damage inhibition material according to claim 1, characterized in that, The nanomaterial is selected from any one or a mixture of at least two of nano-silica, nano-calcium carbonate, and nano-titanium dioxide.

4. The concrete thermal damage inhibition material according to claim 3, characterized in that, The particle size of the nanomaterial is between 50 nm and 300 nm.

5. The concrete thermal damage inhibition material according to claim 1, characterized in that, The retarder is selected from any one or a mixture of at least two of molasses retarder, lignin sulfonate and hydroxycarboxylic acid retarder.

6. The concrete thermal damage inhibition material according to claim 1, characterized in that, The thickener is selected from any one or a mixture of at least two of methylcellulose ether, polyacrylamide, and polyvinyl alcohol.

7. The concrete thermal damage inhibition material according to claim 6, characterized in that, The molecular weight of the methylcellulose ether is above 100,000, and the molecular weights of the polyacrylamide and polyvinyl alcohol are both above 5 million.

8. The method for preparing the concrete thermal damage inhibition material according to any one of claims 1 to 7, characterized in that, The process includes the following steps: dividing the mineral admixtures, quartz sand, metakaolin, nanomaterials, thickeners, and retarders into three categories—high, medium, and low—based on their content. These components are then mixed step by step in order of quantity, from highest to lowest, and stirred until homogeneous. The high-content components include mineral admixtures, quartz sand, and metakaolin; the medium-content components are nanomaterials; and the low-content components include thickeners and retarders.

9. The application of the concrete thermal damage inhibition material as described in any one of claims 1 to 7, characterized in that, The steps include: during the concrete mixing process, replacing the concrete mixing cementitious material with the concrete heat damage inhibitor at a dosage of 10% to 30% by mass, and mixing it with the remaining cementitious material to prepare concrete.

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