Micro-expansive cement mortar capable of degrading nitrogen oxides under natural light and preparation method thereof

Abstract

The invention discloses a micro-expanding cement mortar capable of degrading nitrogen oxides under natural light. The mortar comprises the following components, in parts by weight: 0.01-0.03 parts of amphoteric graphite-phase carbon nitride, 0.04-0.08 parts of desulfurized gypsum, 0.05-0.1 parts of coal gangue powder, 0.1-0.2 parts of steel slag powder, 0.001-0.005 parts of plastic expansion agent, 0.001-0.005 parts of defoaming agent, 0.001-0.002 parts of powdered polycarboxylate water reducer, 0.001-0.003 parts of mineral activity stimulator, 0.001-0.005 parts of perlite, 0.5-0.7 parts of ordinary silicate cement, 2-4 parts of building sand and 0.4 parts of water. The total amount of the components, excluding water and building sand, is 1 part. The present invention utilizes the efficient photocatalytic performance of amphoteric graphite phase carbon nitride under visible light to effectively degrade harmful nitrogen oxides in the air, playing a positive role in purifying the environment; the micro-expansion performance generated by the expansion component can reduce the occurrence of mortar shrinkage cracks, improve the durability and aesthetics of the material, and at the same time, the large-scale use of industrial solid waste such as desulfurization gypsum, coal gangue and steel slag is conducive to resource recycling and reduction of environmental pollution.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and particularly relates to a micro-expansive cement mortar capable of degrading nitrogen oxides under natural light and a preparation method thereof. Background Art

[0002] With the acceleration of industrialization, environmental pollution has become one of the greatest challenges facing humanity. Nitrogen oxides, a major harmful component in the atmosphere, are produced through a wide range of pathways, including industrial furnaces, chemical raw material production, motor vehicles, and the oxidation of nitrogen-containing organic matter in fuels. Their harmful effects primarily include damage to the human respiratory system, the generation of photochemical smog, acid rain, and ozone layer depletion. To improve this situation, scientists are actively exploring various methods to reduce atmospheric nitrogen oxide levels.

[0003] As a foundational material in the construction industry, cement plays an irreplaceable role due to its superior performance, wide range of applications, and enormous volume. Shrinkage is an inherent property of cement-based materials. Its root cause is the volume reduction of cement upon hydration. Furthermore, shrinkage due to factors such as drying shrinkage, temperature shrinkage, and carbonization shrinkage significantly influences the formation and development of cracks. The formation of cracks not only affects the aesthetics of buildings but also increases the erosion of materials by harmful substances, significantly reducing their durability. Research has shown that adding an appropriate amount of micro-expanding components to cement-based materials can effectively reduce the occurrence of cracks.

[0004] Titanium dioxide (TiO2) is the most widely used photocatalyst in cement-based composites. Leveraging the redox activity of semiconductor TiO2 under sunlight, it can degrade or purify pollutants while also achieving a self-cleaning effect on building surfaces. Consequently, the introduction of photocatalysts into cement-based materials to remove harmful nitrogen oxides from the atmosphere is gaining increasing attention. However, research has shown that TiO2 is only excited by ultraviolet light and cannot effectively utilize visible light and solar energy. Therefore, the search for more suitable photocatalysts for the effective removal of atmospheric pollutants is crucial.

[0005] Graphitic carbon nitride, as a star material in the field of photocatalysis in this century, is highly sought after because it can effectively utilize the visible light portion of sunlight. However, the bulk material has shortcomings such as low specific surface area and high photogenerated electron-hole recombination rate, which greatly limits its application. Therefore, improving the photocatalytic performance of this material and combining it with cement-based materials to remove nitrogen oxides from the atmosphere is an important measure to improve the human living environment.

[0006] Mortar is a common rigid waterproof material in concrete structures. Photocatalytic materials are combined with cement mortar to prepare environmentally friendly cement mortar, which not only has a waterproof effect, but also can effectively eliminate nitrogen oxides in the atmosphere and improve the air environment.

[0007] For example, CN 108609930A discloses a graphite-phase carbon nitride photocatalytic cement mortar, which is composed of 1 part cement, 0.01-0.05 parts graphite-phase carbon nitride, 0.03-0.07 parts polymer, 2-5 parts building sand, and 0.025-0.035 parts admixture. The graphite-phase carbon nitride is prepared by calcining and grinding urea, cyanamide, dicyandiamide, and melamine in a weight ratio of 1:1:1:1. Its application in cement mortar has a single function and low photocatalytic efficiency under visible light. For example, CN 115259768A discloses a modified graphite-phase carbon nitride photocatalytic cement mortar, which comprises mixing the modified graphite-phase carbon nitride with cement mortar in a weight ratio of 1-20 / 1000. The graphite-phase carbon nitride is modified by heat treatment, resulting in low photocatalytic efficiency.

[0008] Therefore, the key to the present invention is to prepare a cement mortar that can efficiently degrade nitrogen oxides in the air under natural light and has high crack resistance and good economic benefits. Summary of the Invention

[0009] The purpose of the present invention is to provide a micro-expansive cement mortar capable of degrading nitrogen oxides under natural light and a preparation method thereof in response to the problems existing in the prior art.

[0010] To achieve the above object, the technical solution adopted by the present invention is:

[0011] A slightly expansive cement mortar capable of degrading nitrogen oxides under natural light, characterized in that it comprises the following components in parts by weight: 0.01-0.03 parts of amphoteric graphite phase carbon nitride, 0.04-0.08 parts of desulfurized gypsum, 0.05-0.1 parts of coal gangue powder, 0.1-0.2 parts of steel slag powder, 0.001-0.005 parts of plastic expansion agent, 0.001-0.005 parts of defoaming agent, 0.001-0.005 parts of powdered polycarboxylate water reducer, 0.001-0.003 parts of mineral activity stimulator, 0.001-0.005 parts of perlite, 0.5-0.7 parts of ordinary Portland cement, 2-4 parts of building sand and 0.4 parts of water. Among the above components, excluding water and building sand, the total amount of other components is 1 part.

[0012] Furthermore, the preparation method of the amphoteric graphite phase carbon nitride is as follows: Step 1: The raw material is selected from one of melamine, dicyandiamide or cyanamide, which is heated to 520°C at a rate of 5°C / min in a muffle furnace, kept warm for 240 minutes, and then cooled to room temperature in the furnace to obtain blocky graphite phase carbon nitride, which is ground into powder for later use.

[0013] The second step is: weighing a certain amount of the graphite phase carbon nitride obtained above, placing the graphite phase carbon nitride in a 5-15 mol / L sulfuric acid solution according to a mass ratio of the graphite phase carbon nitride to the sulfuric acid solution of 1:5 to 1:10, stirring for 20-30 hours under ultrasonic dispersion conditions, and then rotating the obtained mixed system with a centrifugal separator to obtain a lower layer of precipitate; washing the lower layer of precipitate with water, dispersing and centrifuging in sequence, and repeating the process several times, and repeatedly collecting the upper layer of colloid; placing the obtained upper layer of colloid in an oven at 70-90°C to dry and grind to obtain amphoteric graphite phase carbon nitride.

[0014] Furthermore, the sulfur trioxide content in the desulfurized gypsum is 40-43%.

[0015] Furthermore, the coal gangue after being ground by air flow mill has a specific surface area of ​​600-700 kg / m 2 .

[0016] Furthermore, the steel slag is ground by air jet mill to a specific surface area of ​​400-500 kg / m 2 .

[0017] Furthermore, the mineral activity stimulant is composed of polyacrylamide and polyglycerol fatty acid ester in a mass ratio of 1:1 to 1:3.

[0018] Furthermore, the main component of the plastic expansion agent is azodicarbonamide, and the bulk density is 400-500kg / m 3 .

[0019] Furthermore, the defoaming agent is propylene glycol block polyether.

[0020] Furthermore, the water reduction rate of the powdered polycarboxylic acid water-reducing agent is 25-30%.

[0021] Furthermore, the perlite has a particle size of 100 mesh.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention utilizes acid modification and ultrasonic treatment exfoliation technology, combined with colloidal pH control technology to prepare amphoteric graphite phase carbon nitride nanosheet colloid, the maximum thickness of which does not exceed 10nm. The modified material is then used in the form of powder in micro-expanding cement mortar. Compared with block materials and graphite phase carbon nitride prepared by a single exfoliation method, the photocatalytic effect of the modified material using visible light is significantly improved, which can effectively reduce nitrogen oxides in the air and improve air quality. The micro-expanding components, namely coal gangue, desulfurized gypsum and plastic expansion agent azodicarbonamide, are then introduced. When the hydration reaction occurs, a large amount of ettringite crystals can be produced. , which in turn causes the cement stone to expand, which can compensate for the shrinkage of the cement-based material itself, reduce the risk of mortar cracking, and solve the problem of plastic cracking of the mortar; the introduction of a mineral active stimulant (a mixture of polyacrylamide and polyglycerol fatty acid ester) can increase the hydration activity of industrial solid waste, improve the mechanical properties of the mortar, and cooperate with the defoamer propylene glycol block polyether to increase the density of the mortar, further improving the mechanical properties; and the introduction of a water-retaining component, namely perlite powder, can effectively store water, weaken the internal shrinkage of the mortar, reduce drying shrinkage, and promote the secondary hydration of the cementitious material, improve the mechanical properties of the mortar and reduce the risk of cracking. Among them, the present invention uses a large amount of industrial solid waste steel slag, coal gangue and desulfurization gypsum, which can bring obvious economic benefits while reducing environmental pollution. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0025] In the following embodiments, the sulfur trioxide content in the desulfurized gypsum is 40-43%; the coal gangue powder is obtained by grinding coal gangue by air flow mill, and the specific surface area is 600-700 kg / m 2 The steel slag powder is obtained by grinding steel slag by air flow mill, and the specific surface area is 400-500kg / m 2 The perlite particle size is 100 mesh; the water reducing rate of the powdered polycarboxylic acid water reducer is 25-30%; the plastic expansion agent is azodicarbonamide, and the bulk density is 400-500kg / m 3 ; The defoaming agent is propylene glycol block polyether.

[0026] In the following embodiment, the preparation method of the amphoteric graphite phase carbon nitride includes the following two steps: the first step: selecting melamine as the raw material, heating it to 520°C at a rate of 5°C / min in a muffle furnace, keeping it warm for 240 minutes, and then cooling it to room temperature in the furnace to obtain bulk graphite phase carbon nitride (the bulk graphite phase carbon nitride is also used in Comparative Example 1), and grinding it into powder for later use;

[0027] The second step: weigh a certain amount of the above-obtained graphite phase carbon nitride powder and place it in a 10 mol / L sulfuric acid solution, stir it under ultrasonic dispersion conditions for 24 hours, and then separate the obtained liquid with a centrifugal separator at high speed to obtain a lower precipitate; the lower precipitate is washed with water, dispersed and centrifuged in sequence, and repeated several times, and the upper colloid, i.e., the amphoteric graphite phase carbon nitride nanosheet colloid, is repeatedly collected. The lower precipitate remaining after collecting the upper colloid is used for comparative example 2; the colloid is placed in an 80°C oven for drying and grinding to obtain amphoteric graphite phase carbon nitride powder.

[0028] The amphoteric graphite phase carbon nitride nanosheet colloid has been verified to have Tyndall effect by illumination experiments and is a colloid; and AFM (atomic force microscope) characterization shows that the thickness of the nanosheet is 5 to 10 nm and the length is 50 to 100 nm.

[0029] In the following embodiment, the preparation method of the micro-expanding cement mortar that can degrade nitrogen oxides under natural light is as follows: according to the weight proportions of the raw materials in the embodiment, amphoteric graphite phase carbon nitride, desulfurized gypsum, coal gangue powder, plastic expansion agent, defoaming agent, steel slag powder, powdered polycarboxylic acid water reducer, mineral activity stimulator, perlite, ordinary silicate cement, construction sand and water are fully mixed in proportion to obtain the micro-expanding cement mortar that can degrade nitrogen oxides under natural light.

[0030] Example 1

[0031] The invention discloses a micro-expanding cement mortar capable of degrading nitrogen oxides under natural light. The mortar is prepared by uniformly mixing the following components in parts by weight: 0.01 part of amphoteric graphite-phase carbon nitride powder, 0.05 part of desulfurized gypsum, 0.08 part of coal gangue powder, 0.2 part of steel slag powder, 0.001 part of plastic expansion agent, 0.003 part of defoaming agent, 0.001 part of powdered polycarboxylic acid water reducer, 0.001 part of polyacrylamide, 0.001 part of polyglycerol fatty acid ester, 0.003 part of perlite, 0.65 part of ordinary silicate cement, 2.8 parts of building sand and 0.4 part of water.

[0032] Example 2

[0033] The invention discloses a micro-expanding cement mortar capable of degrading nitrogen oxides under natural light. The mortar is prepared by uniformly mixing the following components in parts by weight: 0.03 parts of amphoteric graphite-phase carbon nitride powder, 0.05 parts of desulfurized gypsum, 0.06 parts of coal gangue powder, 0.2 parts of steel slag powder, 0.001 parts of plastic expansion agent, 0.003 parts of defoaming agent, 0.001 parts of powdered polycarboxylic acid water reducer, 0.001 parts of polyacrylamide, 0.001 parts of polyglycerol fatty acid ester, 0.003 parts of perlite, 0.65 parts of ordinary silicate cement, 2.8 parts of building sand and 0.4 parts of water.

[0034] Example 3

[0035] The invention discloses a micro-expanding cement mortar capable of degrading nitrogen oxides under natural light. The mortar is prepared by uniformly mixing the following components in parts by weight: 0.02 parts of amphoteric graphite-phase carbon nitride powder, 0.05 parts of desulfurized gypsum, 0.07 parts of coal gangue powder, 0.2 parts of steel slag powder, 0.002 parts of plastic expansion agent, 0.002 parts of defoaming agent, 0.001 parts of powdered polycarboxylic acid water reducer, 0.001 parts of polyacrylamide, 0.001 parts of polyglycerol fatty acid ester, 0.003 parts of perlite, 0.65 parts of ordinary silicate cement, 2.8 parts of building sand and 0.4 parts of water.

[0036] Comparative Example 1

[0037] The raw materials and composition of the slightly expansive cement mortar capable of degrading nitrogen oxides under natural light provided in this comparative example are substantially the same as those of Example 1, except that the amphoteric graphite-phase carbon nitride powder in the raw materials is replaced by blocky graphite-phase carbon nitride.

[0038] Comparative Example 2

[0039] The raw materials and composition of the micro-expanding cement mortar capable of degrading nitrogen oxides under natural light provided in this comparative example are basically the same as those in Example 1, except that the amphoteric graphite phase carbon nitride powder is replaced by graphite phase carbon nitride prepared by collecting and drying the remaining lower layer precipitate after collecting the amphoteric graphite phase carbon nitride nanosheet colloid.

[0040] Comparative Example 3

[0041] The raw materials and composition of the micro-expansive cement mortar capable of degrading nitrogen oxides under natural light provided in this comparative example are basically the same as those in Example 1, except that the plastic expansion agent is replaced by an inorganic calcium expansion agent, which meets the Type II technical index requirements in GB / T 23439 "Concrete Expansion Agents".

[0042] Comparative Example 4

[0043] The raw materials and composition of the slightly expansive cement mortar capable of degrading nitrogen oxides under natural light provided in this comparative example are substantially the same as those of Example 1, except that the mineral activity stimulant is replaced by triethanolamine.

[0044] Comparative Example 5

[0045] The raw materials and composition of the slightly expansive cement mortar capable of degrading nitrogen oxides under natural light provided in this comparative example are substantially the same as those of Example 1, except that the perlite is replaced by stone powder, which is an inert material.

[0046] The photocatalytic performance of the mortar was evaluated by the following methods:

[0047] The photocatalytic reactor uses a closed ventilation duct filled with cement mortar test blocks. A simulated sunlight light source is installed on the top of the device. Nitric oxide is used to simulate nitrogen oxide pollutants in the atmosphere. The gas flow rate is 0.3 L / min. The test environment temperature is 20°C and the humidity is 60±5%. Gas samples are collected at the inlet and outlet every one hour, and the concentration of the target pollutant is analyzed. The photocatalytic efficiency of the cement mortar is calculated according to the following formula:

[0048] η=(C0-Cx) / C0

[0049] Where C0 is the concentration of nitric oxide at the inlet; C x is the concentration of nitric oxide at the outlet; η is the photocatalytic efficiency (%)

[0050] The benchmark group is ordinary building mortar, which meets the technical index requirements of dry-mixed plaster mortar strength grade M20 in the standard JG / T230-2007 "Ready-mixed Mortar".

[0051] The compressive strength of mortar specimens was tested according to the industry standard JGJ 70-2009 "Test Method for Basic Properties of Building Mortar".

[0052] The expansion performance of mortar was tested according to the national standard GB / T 23439-2017 "Concrete Expansion Agent", and the curing conditions were constant temperature water curing at 20°C.

[0053] The early crack resistance of mortar was tested with reference to the national standard GB / T 50082-2009 "Standard for test methods of long-term performance and durability of ordinary concrete". The flat plate cracking performance test used a flat thin plate mold with dimensions of 800mm×600mm×100mm, containing 7 crack inducers, and maintained the wind speed at the center of the specimen surface at not less than 5m / s.

[0054] The test results of compressive strength, limited expansion rate, crack resistance and photocatalytic performance of different micro-expansion mortar samples are shown in Table 1.

[0055] Table 1 Mortar performance test results

[0056]

[0057] The test results show that Example 3 has the best comprehensive effect, with the mortar's 28-day compressive strength reaching an optimal 36.4 MPa. Under 20°C water curing conditions, the mortar's limited expansion rates at 7 and 28 days are 0.011% and 0.026%, respectively. The photocatalytic efficiency is 18.6%, and the crack area reduction rate is 80.7%. It can also be found that the use of amphoteric graphite phase carbon nitride in Example 3 greatly improves the degradation efficiency of nitrogen oxides compared to Comparative Examples 1 and 2; the composite mineral active activator can significantly improve the mechanical properties of the mortar compared to a single early strength agent; perlite can improve the late compressive strength and crack resistance of the mortar; the plastic expansion agent has a significant effect on inhibiting early cracking in the mortar compared to the inorganic calcium expansion agent, and there is a good synergistic effect between the components. It is foreseeable that, given the current government's strict management of the atmospheric environment and the rapid development of the construction industry, the micro-expansive cement mortar capable of degrading nitrogen oxides under natural light described in the present invention has broad application prospects.

[0058] While 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 these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A micro-expansive cement mortar capable of degrading nitrogen oxides under natural light, characterized in that: The invention comprises the following components in parts by weight: 0.01-0.03 parts of amphoteric graphite phase carbon nitride, 0.04-0.08 parts of desulfurized gypsum, 0.05-0.1 parts of coal gangue powder, 0.1-0.2 parts of steel slag powder, 0.001-0.005 parts of plastic expansion agent, 0.001-0.005 parts of defoaming agent, 0.001-0.005 parts of powdered polycarboxylate water reducer, 0.001-0.003 parts of mineral activity stimulator, 0.001-0.005 parts of perlite, 0.5-0.7 parts of Portland cement, 2-4 parts of building sand and 0.4 parts of water. Except for water and building sand, the other components are all powders and the total amount is 1 part; wherein the mineral activity stimulator is composed of polyacrylamide and polyglycerol fatty acid ester in a mass ratio of 1:1 to 1:3; The preparation method of the amphoteric graphite phase carbon nitride is divided into two steps as follows: Step 1: The raw material is selected from melamine, dicyanamide or cyanamide, which is heated to 500-550°C at a rate of 2-10°C / min in a muffle furnace, kept warm for 200-300 minutes, and then cooled to room temperature in the furnace to obtain blocky graphite phase carbon nitride, which is then ground into graphite phase carbon nitride powder for later use; Step 2: Weigh a certain amount of graphite carbon nitride powder, place the graphite carbon nitride powder in a 5-15 mol / L sulfuric acid solution at a mass ratio of 1:5 to 1:10, stir for 20-30 hours under ultrasonic dispersion conditions, and then separate the resulting mixture by centrifugation to obtain a lower precipitate; The lower precipitate is sequentially washed with water, dispersed and centrifuged, and the process is repeated several times, and the upper colloid, i.e., amphoteric graphite phase carbon nitride nanosheet colloid, is repeatedly collected; the colloid is placed in an oven at 70-90° C. and dried, and ground to obtain amphoteric graphite phase carbon nitride.

2. The micro-expansive cement mortar capable of degrading nitrogen oxides under natural light according to claim 1, characterized in that: The thickness of the nanosheets in the amphoteric graphite phase carbon nitride nanosheet colloid is less than 10 nm, and the length is less than 100 nm.

3. The micro-expansive cement mortar capable of degrading nitrogen oxides under natural light according to claim 1, characterized in that: The sulfur trioxide content in the desulfurization gypsum is 40-43%.

4. The micro-expansive cement mortar capable of degrading nitrogen oxides under natural light according to claim 1, characterized in that: Gangue powder is obtained by grinding gangue by air jet mill, with a specific surface area of ​​600-700 m 2 / kg; the steel slag powder is obtained by grinding steel slag by jet mill, and the specific surface area is 400-500 m 2 / kg.

5. The micro-expansive cement mortar capable of degrading nitrogen oxides under natural light according to claim 1, characterized in that: The plastic expansion agent is azodicarbonamide, and the bulk density is 400-500 kg / m 3 .

6. The micro-expansive cement mortar capable of degrading nitrogen oxides under natural light according to claim 1, characterized in that: The defoaming agent is propylene glycol block polyether.

7. The micro-expansive cement mortar capable of degrading nitrogen oxides under natural light according to claim 1, characterized in that: The water reducing rate of the powdered polycarboxylate water reducer is 25-30%; the particle size of the perlite is 80-120 meshes.

8. The method for preparing a micro-expansive cement mortar capable of degrading nitrogen oxides under natural light according to any one of claims 1 to 7, characterized in that: Amphoteric graphite phase carbon nitride, desulfurized gypsum, coal gangue powder, plastic expansion agent, defoaming agent, steel slag powder, powdered polycarboxylic acid water reducer, mineral activity stimulator, perlite, silicate cement, building sand and water are fully mixed in proportion to obtain the micro-expansive cement mortar that can degrade nitrogen oxides under natural light.

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