Nano rubber cement-based composite material and preparation method thereof

Abstract

The invention discloses a nano rubber cement-based composite material and a preparation method thereof, and belongs to the technical field of building materials. The raw materials of the composite material comprise cement and nano rubber powder, and the weight of the nano rubber powder is 1%-4% of the weight of the cement. The durability of the nano rubber cement-based composite material is greatly improved compared with that of neat cement paste. The nano rubber has a hydrophobic characteristic, so that the water absorption rate of the cement matrix is reduced by the modification of the nano rubber on the cement matrix, and meanwhile, the pore connectivity of the cement matrix modified by the nano rubber is reduced, so that the carbonization resistance and freeze-thaw resistance of the cement-based material are greatly improved compared with those of cement paste; the permeability of erosion ions such as chloride ions and sulfate ions is greatly reduced, and long-term safe operation of cement-based buildings is facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and in particular relates to a nano rubber cement-based composite material and a preparation method thereof. Background Art

[0002] Cement-based materials are composite materials based on cement. They are the most widely used and largest-volume man-made materials in engineering construction. However, the physical structure of cement-based materials is porous and hydrophilic. When cement-based materials are used in the field of hydraulic construction, corrosive substances in the water penetrate into the materials through the pores, changing the internal environment of the materials. As they age, ion erosion causes steel bars to corrode and rust, resulting in cracking and falling off of the surface of cement-based materials, loosening of the overall structure, and a significant decrease in the strength of building materials. In addition, existing cement-based materials used in marine construction projects are prone to carbonization reactions, alkali-aggregate reactions, freeze-thaw damage, and other problems, which pose a safety hazard to the long-term use of hydraulic structures and greatly limit the service life of the buildings. Improving the durability of cement-based materials has always been a hot topic in the research field.

[0003] At present, the main measures to improve the durability of cement-based materials include: ① improving aggregate grading, achieving dense filling, and reducing material defects, but this method cannot completely eliminate macroscopic defects; ② compounding organic matter to form an organic-inorganic cross-linked network to block the transmission channel of harmful media, but the introduction of most organic matter will lead to a decrease in the strength of cement-based materials, and the organic matter is prone to aging and failure; ③ using third-party media such as waterproof membranes to isolate harmful media from contact with the cement matrix, but this method causes greater environmental pollution, and the third-party medium is prone to aging and failure.

[0004] In recent years, the research on nano-modified cement-based materials has attracted much attention. Nanomaterials have small particle size and high surface activity, which can provide nucleation sites to promote cement hydration and fill the pores and cracks inside cement-based materials. Some nanomaterials have volcanic ash activity and can absorb calcium hydroxide to form hydration products during cement hydration, thereby improving the interface transition zone and microscopic pore structure of cement-based materials, making their structure more compact, and enhancing the mechanical properties and durability of cement-based materials. For example, Chinese patent CN118479811A discloses a cement-based material and its preparation method and application, including the following raw materials by mass: 100 parts of cement; 80 parts to 100 parts of quartz sand; 0.5 parts to 3.5 parts of nano-silicon dioxide; 0.5 parts to 1.5 parts of polycarboxylic acid water reducer; 0 parts to 1 part of dispersant; 20 parts to 35 parts of water. The invention uses nano-silicon dioxide to fill the internal pores of cement-based materials, improve the microstructure of cement-based materials, and improve the mechanical properties of cement-based materials. However, commonly used nanomaterials such as nano-silica and nano-titanium dioxide will accelerate the early hydration of cement, resulting in excessive early hydration heat and temperature stress, which will cause cracking of cement-based materials.

[0005] On the other hand, given the good chemical resistance of polymers, it has been widely used to improve the corrosion resistance of cement-based materials by adding polymers, among which rubber is often used to modify cement mortar and concrete. Compared with ordinary concrete, rubber concrete with rubber particles partially replacing natural aggregates has higher strain capacity, lower cracking tendency and stronger corrosion resistance. However, due to the non-polarity and low strength of rubber, the high bubble phenomenon in the mixing process of rubber concrete with rubber particles as aggregates will lead to porous interface transition zone, thereby reducing the mechanical properties of concrete. In terms of the feasibility of engineering applications, in order to ensure the connectivity with the cement matrix, large-particle rubber often needs to be treated by sulfonation process, silane coupling agent surface modification and other methods to treat the rubber surface, which has higher time cost and raw material cost.

[0006] Therefore, it is of great significance to develop a cement-based material with low pore connectivity and good durability. Summary of the invention

[0007] In view of the above deficiencies in the prior art, one of the purposes of the present invention is to provide a nano-rubber cement-based composite material. The nano-rubber cement-based composite material of the present invention has low internal pore connectivity, low water absorption, and excellent impermeability and anti-carbonization properties.

[0008] To achieve the above purpose, the specific technical solutions of the present invention are as follows:

[0009] A nano rubber cement-based composite material, characterized in that its raw materials include cement and nano rubber powder, and the weight of the nano rubber powder is 1% to 4% of the weight of the cement.

[0010] Preferably, the weight of the nano rubber powder is 2% of the weight of the cement.

[0011] Preferably, the average particle size of the nano rubber powder is 20-100 nm. More preferably, the average particle size of the nano rubber powder is 20-30 nm.

[0012] Preferably, the nano rubber powder comprises at least one of nitrile rubber, styrene butadiene rubber and butadiene rubber. More preferably, the nano rubber powder is nitrile butadiene rubber.

[0013] Preferably, the cement is 42.5 Portland cement and / or 52.5 Portland cement.

[0014] Another object of the present invention is to provide a method for preparing the nano-rubber cement-based composite material, which comprises the following steps: uniformly mixing the nano-rubber powder, cement and water to obtain the nano-rubber cement-based composite material.

[0015] More preferably, the method comprises the following specific steps: firstly, the nano rubber and cement are uniformly stirred in a dry powder state to obtain a mixed powder, and then water is added to the mixed powder and stirred uniformly to obtain the nano rubber cement-based composite material.

[0016] Preferably, the stirring time when preparing the mixed powder is 8 to 15 minutes, and the stirring time of the mixed powder and water is less than 4 minutes.

[0017] Compared with the prior art, the present invention is beneficial in that:

[0018] (1) The present invention changes the pore structure inside the cement-based material by adding nano rubber powder. The proportion of macropores (pore size greater than 10 μm) in the nano rubber cement-based composite material of the present invention is greatly reduced compared with general cement paste, and the critical pore size (the minimum pore size for forming a continuous network inside the material) in the nano rubber cement-based composite material is significantly larger than that in general cement paste, indicating that the internal connectivity of the nano rubber cement-based composite material is significantly lower than that of general cement paste, which provides a fundamental structural guarantee for reducing the permeability of cement-based materials and improving their durability.

[0019] (2) The durability of the nano-rubber cement-based composite material of the present invention is greatly improved compared with cement paste. Nano-rubber itself has hydrophobic properties, so the modification of the cement matrix by nano-rubber reduces the water absorption rate of the cement matrix. At the same time, due to the reduction of the pore connectivity of the cement matrix after the modification by nano-rubber, the carbonization resistance and freeze-thaw resistance of the cement-based material of the present invention are greatly improved compared with cement paste, and the permeability of corrosive ions such as chloride ions and sulfate ions is greatly reduced, which is conducive to the long-term safe operation of cement-based buildings.

[0020] (3) Compared with the accelerated hydration effect of conventional nanomaterials such as nano-silicon dioxide and nano-titanium dioxide, the nano-rubber used in the present invention has the effect of delaying the early hydration of the cement matrix, and can effectively reduce the early hydration heat of cement-based composite materials. The effect increases with the increase of the nano-rubber dosage, avoiding the situation where the early hydration heat is too high and the temperature stress is generated during the construction. Compared with other conventional nanomaterials, it is more beneficial to actual construction.

[0021] (4) The preparation method of the nano-rubber cement-based composite material of the present invention is easy to operate. In terms of feasibility of engineering application, the nano-rubber powder does not need to be chemically pretreated, and the mixing method is simpler, which is convenient for engineering construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a scanning electron microscope image of a sample obtained by molding the nano-rubber cement-based composite material of Comparative Example 1 of the present invention;

[0023] Figure 2This is a scanning electron microscope image of a sample obtained by molding the nano-rubber cement-based composite material according to Example 3 of the present invention. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The invention provides a nano rubber cement-based composite material, the raw materials of which include cement and nano rubber powder, wherein the weight of the nano rubber powder is 1% to 4% of the weight of the cement.

[0026] The average particle size of the nano rubber powder is 20-100 nm, for example, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc.

[0027] The nano rubber powder includes at least one of nitrile rubber, styrene butadiene rubber and butadiene rubber.

[0028] The cement is 42.5 silicate cement and / or 52.5 silicate cement.

[0029] The preparation method of the nano rubber cement-based composite material comprises the following steps: uniformly mixing the nano rubber powder, cement and water to obtain the nano rubber cement-based composite material.

[0030] For illustration only, in the following examples and comparative examples, the cement is 42.5 silicate cement; the nano rubber powder is nitrile rubber with an average particle size of 30 nm.

[0031] The raw materials used in the examples and comparative examples can all be obtained commercially.

[0032] Example 1

[0033] The present embodiment provides a nano-rubber cement-based composite material, which is prepared by the following steps: taking 1 part by weight of nano-rubber powder and 100 parts by weight of cement powder, stirring and mixing them in a dry powder state for 10 minutes to obtain a mixed powder, then adding 33 parts by weight of mixing water to the mixed powder, stirring slowly for 2 minutes and then stirring quickly for 2 minutes, and stirring evenly to obtain a nano-rubber cement-based composite material.

[0034] Example 2

[0035] The present embodiment provides a nano-rubber cement-based composite material, which is prepared by the following steps: 2 parts by weight of nano-rubber powder and 100 parts by weight of cement powder are stirred and mixed in a dry powder state for 10 minutes to obtain a mixed powder, and then 33 parts by weight of mixing water are added to the mixed powder, slowly stirred for 2 minutes and then quickly stirred for 2 minutes, and the nano-rubber cement-based composite material is obtained after stirring evenly.

[0036] Example 3

[0037] The present embodiment provides a nano-rubber cement-based composite material, which is prepared by the following steps: 4 parts by weight of nano-rubber powder and 100 parts by weight of cement powder are stirred and mixed in a dry powder state for 10 minutes to obtain a mixed powder, then 33 parts by weight of mixing water are added to the mixed powder, slowly stirred for 2 minutes and then quickly stirred for 2 minutes, and the nano-rubber cement-based composite material is obtained after stirring evenly.

[0038] Comparative Example 1

[0039] This comparative example provides a silicate cement paste material, which is prepared by the following steps: 100 parts by weight of cement powder and 33 parts by weight of mixing water are slowly stirred for 2 minutes and then quickly stirred for 2 minutes, and the silicate cement paste material is obtained after stirring evenly.

[0040] Comparative Example 2

[0041] The comparative example provides a nano-rubber cement-based composite material, which is prepared by the following steps: 0.5 parts by weight of nano-rubber and 100 parts by weight of cement powder are stirred and mixed in a dry powder state for 10 minutes to obtain a mixed powder, and then 33 parts by weight of mixing water are added to the mixed powder, slowly stirred for 2 minutes and then quickly stirred for 2 minutes, and the nano-rubber cement-based composite material is obtained after stirring evenly.

[0042] Comparative Example 3

[0043] The method of this comparative example is basically the same as that of Example 2, except that 2 parts by weight of nano-SiO 2 Replace 1 part by weight of nano rubber powder.

[0044] Test example

[0045] (1) A high-performance fully automatic mercury intrusion instrument was used to perform mercury intrusion experiments on the cement-based composite materials of Examples 1-3 and Comparative Examples 1-3. The pore size distribution parameters of each material were measured as shown in Table 1.

[0046] Table 1 Pore size distribution parameters inside cement-based materials

[0047] The data in Table 1 show the effect of different nano-rubber addition amounts on the pore structure of the prepared nano-rubber cement-based composite material. According to the widely accepted pore structure theory, the size and density of the pores inside the material have an important influence on the macroscopic properties of the material, among which the three-dimensional size of the macropores (pore size>10μm) is closely related to the physical strength and permeability of the cementitious material. Compared with Comparative Example 1, in terms of pore size distribution, the introduction of nano-rubber significantly reduces the proportion of macropores, and the critical pore size (the minimum pore size for forming a continuous network inside the material) is significantly increased when the nano-rubber addition amount is greater than 1% of the cement mass, which reduces the connectivity inside the material and provides a fundamental structural guarantee for reducing the permeability of cement-based materials and improving their durability. By comparing Example 2 and Comparative Example 3, it can be seen that under the same dosage, the improvement of the pore structure by nano-rubber is more obvious than that by nano-silicon dioxide.

[0048] (2) Scanning electron microscope imaging was performed on the samples obtained by molding the nano-rubber cement-based composite materials of Example 3 and Comparative Example 1. Figure 1 This is a scanning electron microscope image of the sample of Comparative Example 1, with a magnification of 12300 times; Figure 2 The scanning electron microscope image of the sample of Example 3 is 9800 times magnified. It can be seen from the figure that in the sample of Comparative Example 1, calcium silicate hydrate (CSH) mainly appears as amorphous aggregates, and a large number of cluster structures are widely distributed on the surface of the sample. It can be observed that there are a large number of micropores and microcracks in the microstructure. The sample of Example 3 shows that the nano rubber particles are distributed on the surface of the hydration products and crystals, providing a place for the deposition of new hydration products and forming the characteristic needle-like microstructure characteristics of the cement-elastomer composite material. At the same time, the microstructure of the sample of Example 3 is more compact, the large pores are relatively reduced, the connection between the crystals is closer, the crystal structure is transformed from a brittle and easily broken rod-like structure to a flat structure, and the pore volume is significantly reduced.

[0049] (3) The overall water absorption rate and capillary water absorption rate of the cement-based composite materials of Examples 1-3 and Comparative Examples 1-3 were tested in the following steps: the cement-based composite material samples were cured until the age reached 28 days, 6 samples were taken from each group and dried for 48 hours, the mass was recorded, and then half of them were immersed in pure water for an overall water absorption test, with the water surface 2 cm above the top of the sample; the other half was immersed in tap water at a depth of 2 mm for a capillary water absorption test. During the test, the mass change of the sample was recorded and the mass change rate was calculated to represent the water absorption rate. The test results are shown in Table 2.

[0050] Table 2 Capillary water absorption and overall water absorption results of cement-based materials

[0051]

[0052] The data in Table 2 show the effect of different nano-rubber additions on the water absorption of the prepared nano-rubber cement-based composites. The test shows that the overall water absorption of Comparative Example 1 is 6.78%, and the water absorption of Examples 1-3 is 3.93%, 1.90% and 1.30%, respectively, which is reduced by 42%, 71.9%, and 80.8%; the capillary water absorption of Comparative Example 1 is 5.19%, and the capillary water absorption of Examples 1-3 is 3.06%, 2.17% and 1.13%, respectively, which is reduced by 41.0%, 58.3% and 78.2%. By comparing Examples 1 to 3, it can be seen that the water absorption of cement-based composites shows a law of decreasing with the increase of nano-rubber addition. This is because the cyano group in the nano-rubber has a strong hydrophobicity, and the addition of nano-rubber leads to a reduction in the proportion of macropores larger than 10μm in the sample. The experimental results show that the addition of nano-rubber significantly reduces the water absorption of cement paste. By comparing Example 2 and Comparative Example 3, it can be seen that, under the same dosage, the improvement effect of nano rubber on water absorption is more obvious than that of nano silicon dioxide.

[0053] (4) The chloride ion permeability of the cement-based composite materials of Examples 1-3 and Comparative Examples 1-3 was tested in accordance with GB / T 42272-2022 "Test Method for Chloride Ion Diffusion Coefficient of Cement Mortar". A cylindrical specimen with a diameter of 100 mm and a height of 50 mm was prepared for chloride ion penetration test in each specific embodiment. The 28-day-old specimen was placed under negative pressure in a vacuum saturated salt device for 18 hours, and the saturated salt solution was a 4 mol / L NaCl solution. The specimen was then clamped between the test fixtures, the solution tank of the test fixture was filled with a 4 mol / L sodium chloride solution and connected to the wiring port, and the chloride ion diffusion coefficient automatic detection device was used for detection, and the calculated chloride ion diffusion coefficient of the specimen was used as an indicator of the anti-chloride ion penetration performance. The test results are shown in Table 3.

[0054] (5) The carbonation resistance of the cement-based composite materials of Examples 1-3 and Comparative Examples 1-3 was tested in accordance with GB / T 42277-2022. A cement paste specimen of 40*40*40 mm was prepared for each specific example. After curing for 28 days, the specimen was dried in a 60°C oven for 48 hours, cooled for 2 hours, and placed in a carbonization box. During the test, the carbon dioxide concentration in the box was maintained at 20%, the relative humidity was controlled at 70%, and the temperature was controlled at 20°C. After the specimen was carbonized for 14 days, it was taken out for testing. The carbonization depth was used as an indicator of the carbonation resistance performance. The test results are shown in Table 3.

[0055] (6) The freeze-thaw resistance of the cement-based composite materials of Examples 1-3 and Comparative Examples 1-3 was tested in accordance with GB / T 41060-2021. A 40*40*40 mm cement paste specimen was prepared for each specific embodiment, cured for 28 days, and then immersed for 4 days. Before the freeze-thaw experiment, 3 samples were taken from each group for compressive strength test and the initial compressive strength value was recorded. Subsequently, a programmable constant temperature and humidity test chamber was used for freeze-thaw cycle test. The sample was placed in a plastic container (50 mm×50 mm×50 mm), immersed in water, and then the sealed sample container was placed in a freeze-thaw chamber containing ethylene glycol (antifreeze). The strength loss rate of each group of samples before and after 70 freeze-thaw cycles was used as the freeze-thaw resistance performance index. The test results are shown in Table 3.

[0056] Table 3 Chloride ion penetration resistance, carbonization resistance, and freeze-thaw resistance performance indicators of cement-based materials

[0057]

[0058] The data in Table 3 show the effects of different nano-rubber addition amounts on the chloride ion penetration resistance, carbonization resistance and freeze-thaw resistance of the prepared nano-rubber cement-based composites:

[0059] According to the experimental results of the anti-chloride ion penetration performance test, the chloride ion permeability coefficient of comparative example 1 is 0.654, and the chloride ion permeability coefficients of embodiments 1-3 are 0.358, 0.217, and 0.377, respectively, which are reduced by 45.3%, 66.8%, and 42.3%, respectively. The chloride ion penetration experimental results show that the anti-chloride ion penetration performance of the nano-rubber cement-based composite material is affected by the amount of nano-rubber added. When the amount of nano-rubber added is 2% of the cement mass, the anti-chloride ion penetration performance is the best. According to the experimental results of the anti-carbonization performance test, the carbonization depth of comparative example 1 is 3.88, and the carbonization depths of embodiments 1-3 are 2.06, 1.58, and 2.4, respectively, which are reduced by 46.9%, 59.3%, and 38.1%, respectively; the carbonization experimental results show that the anti-carbonization performance of the nano-rubber cement-based composite material is affected by the amount of nano-rubber added. When the amount of nano-rubber added is 2% of the cement mass, the anti-carbonization performance is the best. In actual engineering applications, reinforced concrete is a very commonly used building material in the engineering field. Carbonation and chloride salt erosion can lead to a decrease in the pH value of the cementitious material, which in turn causes the steel bar passivation film to fail. The steel bar is corroded and expanded, which in turn causes excessive stress inside the concrete, reducing the strength and bearing capacity of the reinforced concrete. From the data in Table 3, it can be seen that the nano-rubber cement-based composite material proposed in the present invention has good anti-carbonation performance and anti-chloride ion penetration performance, and has good engineering application prospects.

[0060] According to the experimental results of the freeze-thaw resistance test, the strength loss rate before and after the freeze-thaw cycle of comparative example 1 is 36.7%, and the strength loss rates before and after the freeze-thaw cycle of embodiments 1-3 are 26.9%, 22.6% and 18.4% respectively. The freeze-thaw resistance test experimental results show that the carbonization resistance of nano rubber cement-based composites is affected by the amount of nano rubber added, showing a law that the strength loss rate gradually decreases with the increase of nano rubber addition, which is consistent with the law obtained by the water absorption experiment. Under the repeated freeze-thaw cycles caused by temperature fluctuations in high-cold areas, moisture penetrates into concrete through micropores, crystallizes and expands in the concrete micropores, causing severe cracking of concrete. Therefore, water absorption and permeability are closely related to the frost resistance of concrete. From the microscopic experimental results, nano rubber cement-based composites improve the pore structure of cement-based by adding nano rubber, and then improve the freeze-thaw resistance of cement-based materials. From the macroscopic experimental results, nano rubber cement-based composites reduce the water absorption of cement-based materials by adding nano rubber, and then directly reduce the direct harm caused by water freezing and thawing.

[0061] By comparing Example 2 and Comparative Example 3, it can be seen that when the same mass fraction of nanomaterials is added, the nano-rubber cement-based composite material exhibits better durability than the nano-silicon dioxide cement-based composite material.

[0062] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A nano rubber cement-based composite material, characterized in that: The raw materials include cement and nano rubber powder, and the weight of the nano rubber powder is 1% to 4% of the weight of the cement.

2. A nano rubber cement-based composite material according to claim 1, characterized in that: The weight of the nano rubber powder is 2% of the weight of the cement.

3. The nano rubber cement-based composite material according to claim 1, characterized in that: The average particle size of the nano rubber powder is 20-100 nm.

4. The nano rubber cement-based composite material according to claim 1, characterized in that: The average particle size of the nano rubber powder is 20-30 nm.

5. The nano rubber cement-based composite material according to claim 1, characterized in that: The nano rubber powder includes at least one of nitrile rubber, styrene butadiene rubber and butadiene rubber.

6. The nano rubber cement-based composite material according to claim 1, characterized in that: The cement is 42.5 silicate cement and / or 52.5 silicate cement.

7. The method for preparing the nano-rubber cement-based composite material according to any one of claims 1 to 6, characterized in that: The steps are as follows: the nano rubber powder, cement and water are mixed evenly to obtain the nano rubber cement-based composite material.

8. The method for preparing the nano rubber cement-based composite material according to claim 7, characterized in that: The specific steps are as follows: firstly, the nano rubber and cement are stirred evenly in a dry powder state to obtain a mixed powder, and then water is added to the mixed powder and stirred evenly to obtain the nano rubber cement-based composite material.

9. The method for preparing the nano rubber cement-based composite material according to claim 8, characterized in that: The stirring time for preparing the mixed powder is 8 to 15 minutes, and the stirring time for the mixed powder and water is less than 4 minutes.

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