Cellulose modified water purification type pervious concrete and preparation method thereof

Abstract

The present application relates to a kind of cellulose modified water purification type pervious concrete and preparation method, comprising: microcrystalline cellulose modification, with diabase as aggregate, with cement, fly ash, modified microcrystalline cellulose and water are mixed, forming, demolding, it is obtained.The present application, modified microcrystalline cellulose and fly ash form synergistic effect, the cement paste of pervious concrete is improved, and water retention can inhibit the phenomenon of slurry bleeding hole appears, and the structure performance of pervious concrete skeleton and paste is stable.Pervious concrete compressive strength, flexural strength increases, and because slurry bleeding hole phenomenon reduces, the water permeability of pervious concrete increases.Modified microcrystalline cellulose makes the purification capacity of pervious concrete further improve, and C-S-H gel in modified pervious concrete cement paste and modified microcrystalline cellulose ligand are coordinated to realize the adsorption of Cu (II), Cr (III), Zn (II), Pb (II) ion in water.Modified microcrystalline cellulose makes cement paste early hydration process slow down, and it is beneficial to reduce the generation of early surface crack of pervious concrete paste.

Description

Technical Field

[0001] This invention belongs to the field of concrete materials technology, and relates to a cellulose-modified permeable concrete and its preparation method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Permeable concrete is an important material for municipal road construction. Due to its unique interconnected pore structure, surface water from urban roads can be systematically drained into the ground through these interconnected pores, forming a water-reducing film and runoff. However, water flowing through permeable concrete can carry heavy metal pollutants such as Cr, Cu, and Pb generated on the road surface into the runoff, thus polluting groundwater systems. Therefore, improving the permeability and water purification functions of permeable road materials has significant economic and social implications. The cement paste layer on the outer wall of the internal pores of permeable concrete has a certain adsorption effect on harmful substances such as heavy metal ions in rainwater runoff. The composition and properties of the cement paste layer between aggregates have a significant impact on the purification characteristics of permeable concrete.

[0004] Due to its unique physical structure, fly ash has a certain ability to adsorb heavy metals and other pollutants from water. Adding fly ash to the mix design of permeable concrete can give it a certain heavy metal purification function. However, increasing the amount of fly ash can affect the fullness of the cement paste in permeable concrete, causing slurry flow and peeling, resulting in poor uniformity of paste distribution and even a decrease in strength. Because the amount of fly ash added is limited, the purification effect of fly ash permeable concrete is also quite limited. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes a cellulose-modified permeable concrete and its preparation method.

[0006] To achieve the above-mentioned technical objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a cellulose-modified permeable concrete, wherein the cellulose-modified permeable concrete comprises the following components: cement, fly ash, aggregate, modified microcrystalline cellulose (MCCPA), and water; by mass parts, cement 400-500, fly ash 75-85, water 150-170, and aggregate 1500-1600; the modified microcrystalline cellulose is added externally according to the mass percentage of the cementitious materials, and the external addition ratio is 0.05-0.25%.

[0008] Furthermore, the external doping ratio is 0.05% to 0.15%.

[0009] Furthermore, the cement is P·O 42.5 grade ordinary Portland cement.

[0010] Furthermore, the aggregate is diabase crushed stone with a particle size of 4.75-9.50 mm.

[0011] Furthermore, the modified microcrystalline cellulose is microcrystalline cellulose modified by crosslinking microcrystalline cellulose and organic amines with epichlorohydrin; preferably, the microcrystalline cellulose has a diameter of 20-70 μm and a length of 100-400 μm.

[0012] In a second aspect of the present invention, a method for preparing the above-mentioned cellulose-modified permeable concrete is provided. The preparation method includes the following steps:

[0013] (1) Modification of microcrystalline cellulose: Add NaOH solution to microcrystalline cellulose and stir evenly, then add organic amine, stir in an ice water bath for a period of time, then add epichlorohydrin and continue stirring until the reaction is complete; after the reaction, wash the product with distilled water until the solution is neutral, dry, pulverize and sieve.

[0014] (2) Preparation of cellulose-modified permeable concrete: Modified microcrystalline cellulose is added to water in proportion and soaked and dispersed; according to the mix proportion, aggregate, cement, fly ash and water with dispersed modified microcrystalline cellulose are mixed, molded and demolded to obtain cellulose-modified permeable concrete.

[0015] Furthermore, in step (1), the NaOH solution has a mass percentage concentration of 14%.

[0016] Furthermore, in step (1), every 10g of microcrystalline cellulose is dissolved in 100mL of 14% NaOH solution.

[0017] Furthermore, in step (1), the mass ratio of microcrystalline cellulose, organic amine, and epichlorohydrin is 1:5:10 to 1:10:20.

[0018] Furthermore, in step (1), the organic amine is selected from one or more of tetraethylenepentamine (TEPA), triethylenetetramine (TETA), diethylenetriamine (DETA), and diethylenetriaminepentaacetic acid (DTPA).

[0019] Furthermore, after adding the organic amine, stir for 3-8 minutes.

[0020] Further, after adding epichlorohydrin, stir for 12-24 hours.

[0021] The present invention has the following beneficial effects:

[0022] The incorporation of modified microcrystalline cellulose in this invention makes the slurry structure of permeable concrete more compact and stable, and enhances the cement hydration reaction to a certain extent. In cement slurry incorporating modified microcrystalline cellulose, the hydration product Ca(OH)2 participates more in the pozzolanic reaction, generating more hydrated calcium silicate gel. This improves the micropore state of the hardened cement slurry, inducing the formation process of the cement slurry microstructure and the growth of CSH gel. While enhancing the hydration reaction, it also disperses and transfers the internal stress of the cement slurry, making the slurry microstructure more compact and stable.

[0023] The incorporation of modified microcrystalline cellulose can synergistically enhance the performance of permeable concrete with fly ash, improving the cohesiveness and water retention of the cement paste, inhibiting grout leakage and pore blockage, and stabilizing the skeleton and paste structure of the permeable concrete. The compressive and flexural strengths of the permeable concrete increase, and the permeability increases due to reduced grout leakage and pore blockage.

[0024] After the incorporation of modified microcrystalline cellulose, the purification capacity of permeable concrete is further improved. The CSH gel and modified microcrystalline cellulose ligand in the cement paste of modified permeable concrete synergistically adsorb and reduce the concentration of Cu(II), Cr(III), Zn(II), and Pb(II) ions.

[0025] The incorporation of modified microcrystalline cellulose slows down the early hydration process of cement paste, which helps to reduce the generation of early surface cracks in permeable concrete paste, improves the heat release rate in the second half, and ensures that the overall heat release from hydration is the same. Attached Figure Description

[0026] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings, wherein:

[0027] Figure 1 These are Fourier transform infrared spectra of the MCC before and after modification according to this invention;

[0028] Figure 2 These are scanning electron microscope images of the MCC and MCCPA of this invention;

[0029] Figure 3 This is the demolding bottom surface of the permeable concrete test block of the present invention;

[0030] Figure 4 The compressive and flexural strengths of permeable concrete specimens with different MCCPA admixtures according to the present invention;

[0031] Figure 5 The porosity and permeability coefficient of permeable concrete with different MCCPA admixtures according to the present invention;

[0032] Figure 6 This invention relates to the water purification performance of permeable concrete with different MCCPA dosages.

[0033] Figure 7 This is a graph showing the hydration heat release curves of different cement pastes according to the present invention;

[0034] Figure 8 XRD patterns of 7-day permeable concrete cement paste with different MCCPA dosages according to the present invention;

[0035] Figure 9 This is a SEM image of the cement paste of permeable concrete with different MCCPA dosages at 28 days, according to the present invention. Detailed Implementation

[0036] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0037] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0038] Cement: Produced by Guangxi Huarun Cement Co., Ltd., P·O 42.5 grade ordinary Portland cement, specific properties are shown in Table 1.

[0039] Table 1 Chemical composition and physical and mechanical properties of cement

[0040]

[0041] Fly ash: The main properties of the Class II fly ash produced by a power plant in Guangxi are shown in Table 2.

[0042] Table 2 Main Properties of Fly Ash

[0043]

[0044] Aggregate: Use diabase crushed stone with a particle size of 4.75-9.50mm. The physical properties of the aggregate are shown in Table 3.

[0045] Table 3 Physical property indicators of aggregates

[0046]

[0047] Microcrystalline cellulose (MCC): Produced by Zhejiang Yinuo Biotechnology Co., Ltd., with a diameter of 20-70μm and a length of 100-400μm.

[0048] Epichlorohydrin, produced by Shanghai Maclean Biochemical Technology Co., Ltd., analytical grade.

[0049] Tetraethylenepentamine, chromium nitrate, copper sulfate, zinc nitrate, lead nitrate, and sodium hydroxide, produced by Shanghai Sinopharm Chemical Reagent Co., Ltd., analytical grade.

[0050] Example 1

[0051] Cellulose modification: Microcrystalline cellulose (MCC) was weighed and placed in a plastic beaker. A 14% NaOH solution was added and stirred until homogeneous. Tetraethylenepentamine (TEPA) was then added, and the beaker was placed in an ice-water bath. Using a top-mounted stirrer, the mixture was stirred for five minutes before epichlorohydrin (ECH) was added. The mass ratio of MCC, TEPA, and ECH was 1:5:10. After stirring and reacting the raw materials in the beaker for 12 hours, MCC and TEPA crosslinked into a solid via ECH, and stirring was stopped. The crosslinked solid was washed with distilled water until the solution was neutral. The washed solid particles were placed in a forced-air drying oven and dried at 90°C to constant weight. The particles were then pulverized, sieved, and sealed for storage. The modified cellulose was labeled MCCPA. The FTIR spectrum of the sample was tested using the KBr pellet method to verify the changes in surface groups of the microcrystalline cellulose before and after modification.

[0052] Preparation of permeable concrete specimens: Modified MCCPA was added to the water required for the permeable concrete mix design according to the proportions (0%, 0.05%, 0.10%, 0.15%, 0.20%, and 0.25% of the total cementitious materials) for immersion and dispersion. The permeable concrete was prepared using the cement slurry method and mixed evenly according to the mix design (as shown in Table 4, the reference mix design for permeable concrete is m(cement):m(fly ash):m(water):m(aggregate) = 451:80.5:159.5:1572.5, with MCCPA added according to the mass percentage of the cementitious materials). After mixing, the permeable concrete was placed in two layers into a standard cubic mold with a side length of 100 mm. After tamping and vibration, the surface was sealed with polyethylene film and cured at room temperature for 24 hours. The mold was then removed, and the specimens were transferred to a standard curing chamber for curing to the corresponding age.

[0053] Table 4. Mix Proportions for Permeable Concrete

[0054]

[0055] Mechanical and permeability properties of permeable concrete: Mechanical properties were tested according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". After sealing the four sides of the test block with grease and plastic wrap, the porosity and permeability coefficient were determined according to CJJ / T135-2009 "Technical Specification for Permeable Cement Concrete Pavement".

[0056] Water purification performance of permeable concrete: Simulated heavy metal wastewater was prepared by dissolving copper sulfate, chromium nitrate, zinc nitrate, and lead nitrate in distilled water. A 50 mg / L solution of heavy metals Cu(II), Cr(III), Zn(II), and Pb(II) was prepared, and the pH of the solution was corrected to 6-7 to reduce the error caused by precipitation of heavy metal ions in an alkaline environment. The prepared permeable concrete specimens were placed in a storage tank, and 8 L of simulated wastewater was poured in. The tank opening was covered with plastic wrap and sealed for a certain period of time. Samples were taken after standing at 0h, 6h, 12h, 18h, 24h, and 30h. 2 mL of the supernatant was extracted, filtered, and the heavy metal content was tested using atomic absorption spectrometry. The adsorption and solidification performance of permeable concrete specimens for Cu(II), Cr(III), Zn(II), and Pb(II) heavy metal ions was compared through heavy metal adsorption tests at different time points.

[0057] from Figure 1 Fourier transform infrared (FTIR) spectra of MCC before and after modification show that TEPA was successfully bonded to the MCC surface using a chemical modification method. The FTIR spectra of MCC at 1057 cm⁻¹ are shown in the graphs. -1 2902cm -1 3446cm -1 Characteristic peaks of (-COC), (-CH), and (-OH) appeared at 1640 cm⁻¹. Compared to MCC, the spectrum of the modified MCCPA showed better performance at 1640 cm⁻¹. -1 and 3356cm -1 The new characteristic peaks appearing at 2000-3400 cm⁻¹ correspond to the stretching vibration peaks of (-NH₃) and (-NH₂) amino groups, respectively. -1 A broad absorption peak appears at [a certain point], which is caused by the superposition of NH bond absorption peaks in NH / NH2, indicating that the modified fiber contains a large number of amino groups. Furthermore, the modified MCCPA spectrum also shows the characteristic absorption peak of MCC, indicating that amino group monomers have been successfully introduced into the MCC fiber matrix. The cellulose chains in microcrystalline cellulose contain a large number of hydroxyl groups. The chlorine atoms on epichlorohydrin can react not only with the hydroxyl groups on microcrystalline cellulose but also with the amino groups on tetraethylenepentamine. The epoxy group at the other end of epichlorohydrin can react with the amino groups on tetraethylenepentamine, thus epichlorohydrin acts as a crosslinking agent. When microcrystalline cellulose is grafted onto the surface of small molecule amines through crosslinking, the Fourier spectra of the resulting chemically modified product differ significantly from those of the unmodified microcrystalline cellulose.

[0058] Figure 2 Scanning electron microscopy images of MCC and MCCPA show that some microcrystalline cellulose surfaces are covered by solid amine products after modification, while a certain number of amino and hydroxyl groups appear on the surface. Therefore, it can be concluded that the specific surface area of ​​the modified MCCPA particles is reduced to some extent, and the hydrophilicity is improved compared with the original MCC. It is speculated that the MCC may have been encapsulated and formed MCCPA particles with a certain heavy metal adsorption capacity based on a cellulose skeleton, further indicating that the experimental modification method is effective.

[0059] Depend on Figure 3 As seen on the demolded bottom surface of the above-mentioned permeable concrete test blocks, the bottom surface of the permeable concrete in the blank control group was partially filled with slurry, and slurry flow occurred due to the large amount of fly ash added to the cement paste in the basic mix proportion. However, after adding MCCPA, the pore blockage gradually decreased, and the higher the dosage, the better the fullness and uniformity of the slurry coating, and the more uniform the pores. This indicates that the addition of MCCPA can make the workability and permeability of permeable concrete more balanced, make the slurry structure more compact and stable, enhance the hydration reaction to a certain extent, effectively prevent slurry flow and early compressive strength reduction caused by fly ash alone in the blank group, and form a synergistic effect with fly ash in terms of mechanical strength, making the performance of permeable concrete even better.

[0060] Figure 4The figures show the compressive and flexural strength test results of permeable concrete specimens with different MCCPA dosages and a blank control group. As can be seen from the figures, the compressive strengths of the permeable concrete without modified cellulose MCCPA at 3d, 7d, and 28d were 17.31 MPa, 19.52 MPa, and 26.89 MPa, respectively, while the flexural strength at 28d was 3.59 MPa. At 3d, the compressive strength of the specimen with 0.20% MCCPA was 18.67 MPa, an increase of 7.93% compared to the blank control group. At 7d, the compressive strength of the specimen with 0.15% MCCPA was 22.48 MPa, an increase of 15.16% compared to the blank control group. At 28d, the compressive strength of the specimen with 0.15% MCCPA was 29.52 MPa and the flexural strength was 4.16 MPa, increases of 9.49% and 15.87% respectively compared to the control group. An appropriate amount of modified fiber MCCPA fills the pores in the cement paste matrix of permeable concrete and promotes the hydration of the cementitious material, thereby enhancing the mechanical properties of the permeable concrete. However, when the MCCPA dosage exceeds 0.15%, the compressive strength at 7 days and 28 days begins to decrease, and the decrease increases with the increase of MCCPA dosage. When the MCCPA dosage is 0.25%, the compressive strength of the permeable concrete at 7 days and 28 days is only 18.30 MPa and 24.61 MPa, respectively, which are 6.25% and 8.71% lower than the control specimen. Excessive MCCPA dosage leads to increased water absorption in the early stages of hydration of the modified permeable concrete, increasing the viscosity of the cement paste during mixing. This results in more air bubbles being introduced into the cementitious material, forming more defective pores, reducing the paste density, and ultimately decreasing the strength of the permeable concrete. In summary, within the range of 0.05-0.15%, the addition of MCCPA significantly improves the mechanical strength of permeable concrete. However, with further increases in dosage, the compressive strength begins to decrease. Therefore, the optimal mechanical properties are achieved when the dosage is within the range of 0.05-0.15%.

[0061] Depend on Figure 5The changes in effective porosity and permeability coefficient of permeable concrete are shown. Within the MCCPA dosage range of 0.05-0.25%, the porosity of the MCCPA specimens ranged from 17.23% to 18.25% with minimal variation. This is because, during the mix design of the permeable concrete, a consistent target porosity and a fixed paste-aggregate ratio were set, and the porosity design was based on the skeleton structure parameters. Furthermore, the added modified cellulose MCCPA did not affect the skeleton structure characteristics of the formed permeable concrete. As shown in the figure, with the increase of MCCPA dosage, the porosity and permeability coefficient of the specimens initially showed a slow increasing trend, and began to decrease after the dosage exceeded 0.25%. When the MCCPA dosage was 0.20%, the permeability coefficient of the permeable concrete reached a maximum of 3.79 mm / s, which was 15.92% higher than the 3.27 mm / s permeability coefficient of the blank control group without MCCPA. The blank control group of permeable concrete did not include modified fiber MCCPA in its base mix proportion. The cement paste had high fluidity, leading to partial slurry flow and pore blockage during molding. After incorporating modified fiber MCCPA, it synergistically interacts with fly ash, improving the cohesiveness and water retention of the cement paste, suppressing slurry flow and pore blockage. This stabilizes the skeleton and paste structure of the permeable concrete, resulting in corresponding improvements in effective porosity and permeability coefficient.

[0062] Figure 6The static adsorption performance of different permeable concretes for heavy metals Cu(II), Cr(III), Zn(II), and Pb(II) ions was investigated. The interconnected pore structure of permeable concrete allows heavy metal ions from wastewater to float on the surface of the internal aggregate and cementitious layer, where they are adsorbed and solidified by the cement silicate phase and micropores. Taking the results of a 24-hour static test as an example, the removal rates of heavy metals Cu(II), Cr(III), Zn(II), and Pb(II) ions in the blank control group of permeable concrete were 56.52%, 53.53%, 52.62%, and 45.26%, respectively, indicating that the structure of permeable concrete itself has a certain removal effect on heavy metals Cu(II), Cr(III), Zn(II), and Pb(II) in wastewater. After adding modified cellulose MCCPA, the purification capacity of permeable concrete was further improved. The experimental group with the best water purification effect at a dosage of 0.25% achieved removal rates of heavy metals Cu(II), Cr(III), Zn(II), and Pb(II) of 69.37%, 76.54%, 66.51%, and 57.9%, respectively, which were 16.95%, 37.83%, 13.88%, and 12.71% higher than those in the blank control group. This is because the modified MCCPA contains a large number of positively charged functional groups (amino groups) that adsorb Cu(II), Cr(III), Zn(II), and Pb(II), and its incorporation into cement paste promotes the multi-site adsorption performance of the paste. Some Cu(II), Cr(III), Zn(II), and Pb(II) are adsorbed from the wastewater solution to the surface via electrostatic attraction. The Cu(II), Cr(III), Zn(II), and Pb(II) adsorbed to the surface provide empty orbitals, and the N atoms in the amino groups provide lone pairs of electrons, causing the heavy metal ions to chelate and reduce with the N atoms on the amino groups. They are then adsorbed onto the MCCPA, thus achieving a better solidification effect on the heavy metals. Simultaneously, as the amount of modified cellulose added increases, the micropores on the surface of the permeable concrete cement paste increase, which also enhances its adsorption and chelation fixation of Cu(II), Cr(III), Zn(II), and Pb(II) to a certain extent.

[0063] The longer the test blocks were soaked in the wastewater solution, the better the removal effect of permeable concrete on Cu(II), Cr(III), Zn(II), and Pb(II). The removal rates of Cu(II), Cr(III), Zn(II), and Pb(II) were relatively fast in the early stage of settling, but the rate of increase slowed significantly in the later stage. In the initial stage of permeable concrete entering the water, various ions in the wastewater diffuse, and Cu(II), Cr(III), Zn(II), and Pb(II) are initially adsorbed on the surface of the permeable concrete slurry through physical action, leading to a decrease in the concentration of Cu(II), Cr(III), Zn(II), and Pb(II) in the wastewater solution. With the extension of the settling time, some unhydrated tricalcium silicate and dicalcium silicate in the water can continue to react, generating hydrated calcium silicate gel and other substances, which also adsorb and coat Cu(II), Cr(III), Zn(II), and Pb(II), promoting a continuous decrease in the concentration of heavy metal ions in the wastewater. However, when the permeable concrete slurry is saturated with the reaction sites of Cu(II), Cr(III), Zn(II), and Pb(II), the rate of decrease of heavy metal ions in the wastewater solution slows down significantly.

[0064] Figure 7 This study investigated the effects of different MCCPA dosages and cement water-cement ratios on the hydration rate and heat release of cement. Cement paste with a blank control of 0.30%, cement paste with 0.10% MCCPA and a water-cement ratio of 0.30%, cement paste with 0.20% MCCPA and a water-cement ratio of 0.30%, and cement paste with 0.20% MCCPA and a water-cement ratio of 0.35 were selected, and the hydration rate and heat release were measured, generating corresponding curves. The graph shows that the addition of MCCPA slows down the early hydration process of the cement paste, resulting in a decrease in the hydration rate. Furthermore, at the same water-cement ratio, the 0.20% MCCPA dosage has a greater impact on the early hydration rate of the cement paste than the 0.10% MCCPA dosage. This may be because MCCPA absorbs some free water in the early stages of cement hydration, reducing the actual water-cement ratio within the cement paste and affecting the rate and heat release of the early hydration reaction. As time progresses and the reaction develops, this moisture is gradually released, thereby stimulating secondary hydration of the cement paste and generating heat of hydration. Therefore, the heat release rate in the latter half of the reaction is improved, and the overall heat release during hydration remains the same. At the same MCCPA dosage, the MCCPA-modified cement paste with a water-cement ratio of 0.35 exhibits a greater heat release rate and a greater heat release than that with a ratio of 0.30. With a higher water-cement ratio, sufficient moisture in the paste is provided for both early and later hydration reactions, making the hydration-inducing and promoting effect of MCCPA more pronounced.

[0065] Figure 8The X-ray diffraction (XRD) patterns and phase composition of cement paste in permeable concrete specimens with different MCCPA dosages are shown in the figures. It can be seen that the main hydration products of both the blank control cement sample and the MCCPA-modified material are Ca(OH)₂, CSH hydrated calcium silicate gel, CaCO₃, and ettringite. After the addition of MCCPA, the CaCO₃ content in the specimens increased, and the Ca(OH)₂ diffraction peak in the MCCPA-modified material showed a certain weakening trend. The 0.10% dosage specimen contained even less Ca(OH)₂, which is detrimental to the mechanical properties of the matrix, indicating that MCCPA has a certain modifying effect on the cement paste. Simultaneously, the modified fibers, after grinding and pulverizing, contain some submicron particles. Under their induction, more Ca(OH)₂ participates in the pozzolanic reaction, generating more hydrated calcium silicate gel. The reaction consumption of the hydration product Ca(OH)₂ improves the porosity of the hardened cement paste, resulting in the permeable concrete having a superior compressive strength compared to the blank specimen. Furthermore, the modified MCCPA particles have a certain promoting effect on the hydration of cement paste, while the smaller particle size of the modified cellulose has a greater inducing effect on the hydration reaction, thus affecting both the initial and subsequent time periods of the hydration reaction. Meanwhile, due to... Figure 8 The XRD pattern of the cement paste shows that the addition of MCCPA has no significant effect on the diffraction peaks of the hydration product ettringite. The absence of new diffraction peaks after the addition of MCCPA also proves that no new crystalline phase is formed during the hydration process, meaning that the modified cellulose MCCPA itself does not directly participate in the hydration reaction of the cement paste.

[0066] SEM images of cement paste from permeable concrete specimens with different MCCPA dosages are shown below. Figure 9As shown in Figure (a), the microstructure of the control group sample is compared with that of the sample containing 0.10% MCCPA in Figure (b) and the sample containing 0.20% MCCPA in Figure (c). It can be seen that the modified cellulose can coexist and fuse with the hydration products of cement paste, and the surface of MCCPA is completely covered with cement hydration products. After 28 days of hydration, the CSH crystals gradually grow, and the cement paste structure becomes increasingly dense, making it difficult to find clear outlines of the modified cellulose fibers. The modified cellulose MCCPA, after grinding and pulverizing, contains a variety of modified fibers of different scales, including submicron scale. These fibers can bind with cement hydration products and water through some free -OH groups, inducing the production of more CSH gel hydration products from C3S in ordinary silicate cement, which then adhere to the surface of the MCCPA and grow. MCCPA, embedded in the gaps of cement paste, optimizes the structure, reducing the consumption of hexagonal plate-shaped Ca(OH)2 crystals, a hydration product. A large amount of amorphous hydration products and flocculents are generated inside the cement paste, covering the surface and strengthening the interface between the adhering substances and hydration products, further filling the internal micropores. MCCPA acts as a bridge and filler in the cement paste. Together with CSH gel, it not only controls the bonding between cement particles but also fills microcracks, thus achieving a certain degree of balanced distribution of microscopic internal forces, resisting primary microcracks, and improving the crack resistance and durability of the cement paste's microstructure. On one hand, under the induction of sufficient water for the hydration reaction provided by modified cellulose, the hydration products of the cement paste generate more CSH crystals along the axis of the MCCPA fibers, forming a three-dimensional structure within the paste, improving the thixotropic properties and anti-sagging properties of the cement paste. On the other hand, the certain number of hydroxyl and amino groups on the surface of the chemically modified MCCPA fibers can form many hydrogen bonds with water molecules in the paste. The formation of hydrogen bonds reduces the association degree of water, and the water demand in cement paste is reduced accordingly. Under the induction of MCCPA fibers, hydrated cement particles can better form a more uniform and compact microstructure, resulting in a denser structure and a significant reduction in surface pores of the cement paste.

[0067] Figure (b) shows that some MCCPA contains fiber cavities. During the initial mixing stage, it absorbs water and swells slightly. During cement hydration, if segregation occurs and insufficient water is available, it can release more water to provide the necessary moisture for later cement hydration. This reduces the probability of early drying shrinkage cracks in the cement paste, thus improving the early strength of permeable concrete and making the cement paste denser. Some incompletely modified microcrystalline cellulose loses water at the end of hydration, shrinking and collapsing, leaving voids around the fibers. Therefore, excessive dosage can affect the volume stability of the cement paste material and the later strength of permeable concrete.

[0068] Results and Discussion

[0069] (1) Infrared spectroscopy analysis confirmed that TEPA was successfully bonded to the MCC surface using a chemical modification method. The spectrum of the modified MCCPA was at 1640 cm⁻¹. -1 and 3356cm -1 The new characteristic peaks appearing at 2000-3400 cm⁻¹ correspond to the stretching vibration peaks of (-NH₃) and (-NH₂) amino groups, respectively. -1 The broad absorption peak at this point is caused by the superposition of NH bond absorption peaks in NH / NH2, indicating that the modified cellulose contains a large number of amino groups, which may be encapsulated and form hydrophilic particles with certain heavy metal adsorption properties based on cellulose as the skeleton.

[0070] (2) The incorporation of MCCPA can balance the workability and permeability of permeable concrete, make the slurry structure more compact and stable, and enhance the cement hydration reaction to a certain extent, effectively preventing the slurry flow phenomenon caused by the single adsorption of fly ash in the blank group. With the increase of MCCPA dosage, the compressive and flexural strengths of permeable concrete specimens first increase and then decrease. When the dosage is 0.15%, the compressive and flexural strengths of the specimens at 7d and 28d are the best, which are 22.48MPa, 29.52MPa and 4.16MPa, respectively, which are 15.16%, 9.49% and 15.87% higher than those of the control group.

[0071] (3) The addition of modified cellulose MCCPA did not affect the structural characteristics of the permeable concrete skeleton after molding, and the measured effective porosity of the permeable concrete fluctuated slightly. The permeability coefficient of the permeable concrete with MCCPA added reached a maximum of 3.79 mm / s, which was 15.92% higher than the permeability coefficient of 3.27 mm / s of the blank control group without MCCPA. After the addition of modified fiber MCCPA, the cohesiveness and water retention of the cement paste of the permeable concrete were improved, the phenomenon of grout flow and pore blockage was suppressed, and the structural performance of the permeable concrete skeleton and paste was stable.

[0072] (4) After adding modified cellulose MCCPA, the purification capacity of permeable concrete was further improved. The best water purification effect was achieved in the 0.25% dosage group, where the removal rates of heavy metals Cu(II), Cr(III), Zn(II), and Pb(II) were 69.37%, 76.54%, 66.51%, and 57.9%, respectively, which were 16.95%, 37.83%, 13.88%, and 12.71% higher than those in the blank control group. The synergistic adsorption of CSH gel and MCCPA ligands in the modified permeable concrete cement paste reduced the concentration of heavy metal ions. The longer the permeable concrete was soaked in the wastewater solution, the better the removal effect of heavy metal ions.

[0073] (5) The hydration heat test results show that adding MCCPA slows down the early hydration process of cement paste, which helps to reduce the generation of early surface cracks in permeable concrete paste. Under the same water-cement ratio, the higher the MCCPA dosage, the greater the impact on the early hydration rate. The heat release rate in the second half is improved, and the total heat release of hydration is the same in the end.

[0074] (6) XRD diffraction patterns show that the addition of MCCPA has no significant effect on the diffraction peaks of ettringite, and the modified cellulose itself does not directly participate in the hydration reaction of cement. In the cement paste modified with MCCPA, Ca(OH)2 participates more in the pozzolanic reaction, generating more hydrated calcium silicate gel. The reaction consumption of the hydration product Ca(OH)2 improves the pore state of the hardened cement paste.

[0075] (7) SEM electron microscopy revealed that MCCPA has good compatibility with cement hydration products and has surface hydrophilicity and water retention properties. It can play a certain inducing role in the formation process of cement paste microstructure and CSH gel growth, enhance the hydration reaction, disperse and transfer the internal stress of cement paste, and make the paste microstructure more compact and stable.

[0076] Example 2

[0077] Cellulose modification: Microcrystalline cellulose (MCC) was weighed and placed in a plastic beaker. A 14% NaOH solution was added and stirred until homogeneous. Tetraethylenepentamine (TEPA) was then added, and the beaker was placed in an ice-water bath. Using a top-mounted stirrer, the mixture was stirred for five minutes before epichlorohydrin (ECH) was added. The mass ratio of MCC, TEPA, and ECH was 1:10:20. After stirring and reacting the raw materials in the beaker for 12 hours, MCC and TEPA crosslinked into a solid via ECH, and stirring was stopped. The crosslinked solid was washed with distilled water until the solution was neutral. The washed solid particles were placed in a forced-air drying oven and dried at 90°C until constant weight. The particles were then pulverized, sieved, and sealed for storage. The resulting modified cellulose was labeled MCCPA.

[0078] Preparation of permeable concrete specimens: Modified MCCPA was added to the water required for the permeable concrete mix design at a ratio of 0.15% of the total cementitious material. The permeable concrete was prepared using the cement slurry method and mixed evenly according to the mix design (the reference mix design for permeable concrete is m(cement):m(fly ash):m(water):m(aggregate) = 400:75:150:1500). After mixing, the permeable concrete was placed in two layers into a standard cubic mold with a side length of 100 mm. After tamping and vibration, the surface was sealed with polyethylene film and cured at room temperature for 24 hours. The molds were then removed, and the specimens were transferred to a standard curing chamber for curing to the appropriate age.

[0079] Example 3

[0080] Cellulose modification: Microcrystalline cellulose (MCC) was weighed and placed in a plastic beaker. A 14% NaOH solution was added and stirred until homogeneous. Tetraethylenepentamine (TEPA) was then added, and the beaker was placed in an ice-water bath. Using a top-mounted stirrer, the mixture was stirred for five minutes before epichlorohydrin (ECH) was added. The mass ratio of MCC, TEPA, and ECH was 1:5:10. After stirring and reacting the raw materials in the beaker for 12 hours, MCC and TEPA crosslinked into a solid via ECH, and stirring was stopped. The crosslinked solid was washed with distilled water until the solution was neutral. The washed solid particles were placed in a forced-air drying oven and dried at 90°C until constant weight. The particles were then pulverized, sieved, and sealed for storage. The resulting modified cellulose was labeled MCCPA.

[0081] Preparation of permeable concrete specimens: Modified MCCPA was added to the water required for the permeable concrete mix design at a ratio of 0.15% of the total cementitious material. The permeable concrete was prepared using the cement slurry method and mixed evenly according to the mix design (the reference mix design for permeable concrete is m(cement):m(fly ash):m(water):m(aggregate) = 500:85:170:1600). After mixing, the permeable concrete was placed in two layers into a standard cubic mold with a side length of 100mm. After tamping and vibration, the surface was sealed with polyethylene film and cured at room temperature for 24 hours. The molds were then removed, and the specimens were transferred to a standard curing chamber for curing to the appropriate age.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cellulose-modified permeable concrete, characterized in that, The cellulose-modified permeable concrete is composed of the following components: cement, fly ash, aggregate, modified microcrystalline cellulose (MCCPA), and water; by weight, cement 400-500, fly ash 75-85, water 150-170, and aggregate 1500-1600; the modified microcrystalline cellulose is added externally according to the mass percentage of the cementitious materials, with an external addition ratio of 0.05-0.25%. The modified microcrystalline cellulose is a modified microcrystalline cellulose that is cross-linked with microcrystalline cellulose and organic amines via epichlorohydrin; The organic amine is selected from one or more of tetraethylenepentamine, triethylenetetramine, diethylenetriamine, and diethylenetriaminepentaacetic acid; The cellulose-modified permeable concrete is used to adsorb Cu(II), Cr(III), Zn(II), and Pb(II) ions in water.

2. The cellulose-modified permeable concrete according to claim 1, characterized in that, The external doping ratio is 0.05%~0.15%.

3. The cellulose-modified permeable concrete according to claim 1, characterized in that, The aggregate is diabase crushed stone with a particle size of 4.75-9.50 mm.

4. The cellulose-modified permeable concrete according to claim 1, characterized in that, The cement is P·O42.5 grade ordinary Portland cement.

5. The cellulose-modified permeable concrete according to claim 1, characterized in that, The microcrystalline cellulose has a diameter of 20-70 μm and a length of 100-400 μm.

6. The method for preparing cellulose-modified permeable concrete according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: (1) Modification of microcrystalline cellulose: Add NaOH solution to microcrystalline cellulose and stir evenly, then add organic amine, stir in an ice water bath for a period of time, then add epichlorohydrin and continue stirring until the reaction is complete; after the reaction, wash the product with distilled water until the solution is neutral, dry, pulverize and sieve. (2) Preparation of cellulose-modified permeable concrete: Add modified microcrystalline cellulose to water in proportion and soak and disperse it; mix aggregate, cement, fly ash and water containing modified microcrystalline cellulose according to the mix proportion, form and demold to obtain cellulose-modified permeable concrete.

7. The preparation method according to claim 6, characterized in that, In step (1), the NaOH solution has a mass percentage concentration of 14%.

8. The preparation method according to claim 6, characterized in that, In step (1), 10g of microcrystalline cellulose is dissolved in 100mL of 14% NaOH solution.

9. The preparation method according to claim 6, characterized in that, In step (1), the mass ratio of microcrystalline cellulose, organic amine, and epichlorohydrin is 1:5:10 to 1:10:

20.

10. The preparation method according to claim 6, characterized in that, After adding the organic amine, stir for 3-8 minutes; after adding the epichlorohydrin, stir for 12-24 hours.

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