An alkali-activated crack-resistant mortar coating for ductile iron pipes and its preparation method

Abstract

This invention discloses an alkali-activated crack-resistant mortar coating for ductile iron pipes and its preparation method. The alkali-activated crack-resistant mortar coating for ductile iron pipes is composed of a precursor, an activator, sand, water, fiber, and additives. The proportions of each component in the alkali-activated crack-resistant mortar coating are as follows: 90-110 parts precursor, 9-17 parts activator, 120-150 parts sand, 5-15 parts fiber, and a water-cement ratio of 0.25-0.50. This alkali-activated crack-resistant mortar coating prolongs the setting time of alkali-activated cementitious materials and inhibits cracking. Simultaneously, the preparation process is simple, it exhibits good mechanical properties, early strength, and rapid hardening, resulting in high production efficiency. Furthermore, the alkali-activated crack-resistant mortar coating of this invention does not use cement clinker, but uses industrial solid waste such as blast furnace slag powder, steel slag powder, and fly ash as the main raw materials. This significantly improves the mechanical and corrosion resistance of buried ductile iron pipelines while achieving comprehensive utilization of multiple solid wastes.

Description

Technical Field

[0001] This invention belongs to the field of ductile iron pipe production, specifically relating to an alkali-activated crack-resistant mortar coating for ductile iron pipes and its preparation method. Background Technology

[0002] Ductile iron pipes, used as buried and exposed pipelines, possess excellent mechanical and corrosion-resistant properties. However, current technologies for external corrosion protection of ductile iron pipes primarily focus on high-chlorinated polyethylene finishing layers under general corrosion conditions, epoxy coatings or polyethylene sheaths wrapped around high-chlorinated polyethylene finishing layers under more corrosive conditions, and polyurethane coatings under heavy-duty corrosion conditions. Organic coatings such as epoxy and polyurethane coatings have relatively poor mechanical properties, and their mechanical and corrosion-resistant performance is thickness-dependent. When applied to buried pipe laying construction, localized wear and scratches are inevitable in underground construction scenarios, creating weak points in the pipe's corrosion protection, which then lead to corrosion and reduce the pipe's service life. Furthermore, during long-distance transportation and installation of ductile iron pipes, scratches, collisions, and abrasions inevitably occur, damaging the coating and its external anti-corrosion layer. Therefore, to ensure corrosion resistance in corrosive environments and mechanical performance under construction conditions, it is necessary to increase the coating thickness, resulting in increased costs.

[0003] Currently, there are ductile iron pipe products on the market that use external concrete or mortar as a coating. These pipes are made by using ordinary silicate cement concrete or mortar, which is cured through spraying or direct molding to obtain the outer concrete or mortar layer. However, cement is generally produced through a process of "two grindings and one firing," which consumes a large amount of natural resources and energy, and emits a large amount of carbon dioxide, contributing to the greenhouse effect. All of these factors cause irreversible damage to the environment. Because concrete prepared with ordinary silicate cement has a long setting time, it requires a long curing period, which seriously affects the production efficiency of ductile iron pipes. On the other hand, steam curing is used to reduce curing time, but this results in high production costs.

[0004] Existing alkali-activated mortars, when directly applied to 3-5mm thick cement linings, suffer from problems such as easy peeling and surface hardening cracks. Figure 1 and Figure 2 As shown.

[0005] Alkali-activated cementitious materials are cementitious materials prepared by mixing finely ground water-quenched blast furnace slag, fly ash, or other potentially active industrial solid wastes with alkali components. Their production process effectively utilizes industrial by-products, resulting in significant environmental benefits. Alkali-activated cementitious materials not only possess high early strength but also advantages such as low energy consumption and strong corrosion resistance, making them suitable for use in the ductile iron pipe industry. In particular, the water-quenched blast furnace slag used in the alkali-activation precursor is an industrial by-product of the ductile iron pipe industry, further reducing energy consumption and costs associated with loading, unloading, and transportation. Simultaneously, the application of alkali-activated cementitious materials can significantly reduce carbon emissions.

[0006] However, the shrinkage of alkali-activated cementitious materials can be 2 to 3 times that of ordinary silicate cement hardened materials. High shrinkage easily leads to cracks and seriously affects their service life. Furthermore, the hydration and hardening of alkali-activated slag cementitious materials differs from that of ordinary silicate cement. Its essence lies in the breaking and recombination process of Ca-O, Si-O, and Al-O bonds in the slag glass, a process that is relatively concentrated. Therefore, the application of alkali-activated cementitious materials with their short setting time in the field of ductile iron pipes also needs to be considered. Summary of the Invention

[0007] The technical problem to be solved by this invention is to overcome the problems of low mechanical strength, poor corrosion resistance and high production cost of the outer protective layer of ductile iron pipes, while extending the setting time of alkali-activated cementitious materials and inhibiting cracking of alkali-activated cementitious materials, so as to provide an alkali-activated crack-resistant mortar coating for ductile iron pipes and its preparation method.

[0008] An alkali-activated crack-resistant mortar coating for ductile iron pipes is disclosed. The alkali-activated crack-resistant mortar coating for ductile iron pipes is composed of a precursor, an activator, sand, water, fiber, and additives. The precursor is one or a mixture of several of the following materials: blast furnace slag powder, steel slag powder, and fly ash. The weight proportions of the alkali-activated crack-resistant mortar coating are as follows: 90-110 parts precursor, 9-17 parts activator, 120-150 parts sand, 5-15 parts fiber, and the mass ratio of water to precursor is 0.25-0.50.

[0009] Furthermore, the activator is one or a mixture of several of the following three activators: alkali metal hydroxide, water glass, and alkali metal carbonate.

[0010] Furthermore, the fiber is a synthetic fiber or a natural fiber, with a length of 3-20 mm.

[0011] Furthermore, the additive comprises 0.5%-5% by weight of redispersible latex powder as a precursor.

[0012] Furthermore, the admixture also includes a water-reducing agent at a precursor mass of 0.05%-3%.

[0013] Furthermore, the admixture also includes 0.01-0.5% of a retarder by mass of the precursor.

[0014] Furthermore, the thickness of the alkali-activated crack-resistant mortar coating for the ductile iron pipe is 3-5 mm.

[0015] The preparation method of alkali-activated crack-resistant mortar coating for ductile iron pipes includes the following steps:

[0016] A. Material 1 and Material 2 are uniformly mixed to obtain a precursor mixture, wherein Material 1 is a uniform mixture of one or more of the following three materials: blast furnace slag powder, steel slag powder and fly ash, and fiber; Material 2 is a uniform mixture of redispersible latex powder, water-retaining agent, water-reducing agent and sand.

[0017] B. After uniformly mixing the precursor mixture with material 3, an alkali-activated crack-resistant mortar is obtained. Material 3 is a mixture of activator, water and retarder. The order of addition is to first mix the activator and water with the precursor mixture, and then add the retarder.

[0018] C. Apply alkali-activated crack-resistant mortar to the outer surface of the ductile iron pipe;

[0019] D. Perform maintenance.

[0020] Further, in step C, the coating is one of extrusion coating, spraying, and mold grouting; wherein, extrusion coating involves placing alkali-activated crack-resistant mortar in the hopper of an extrusion pump, pumping the alkali-activated crack-resistant mortar to an extrusion device, and using pressure to extrude the alkali-activated crack-resistant mortar onto the outer surface of the ductile iron pipe to form a coating; spraying involves placing alkali-activated crack-resistant mortar in the hopper of a spraying pump, and using compressed air assisted by a spraying pump to uniformly spray the alkali-activated crack-resistant mortar onto the outer surface of the ductile iron pipe to form a coating; mold grouting involves placing the ductile iron pipe body in a pre-processed mold, and pouring the alkali-activated crack-resistant mortar into the mold to form a coating;

[0021] In step D, the curing method is steam curing or natural curing. The steam curing conditions are relative humidity above 95%, temperature 40-80℃, curing time 1-4 hours, curing with film and watering for 1-7 days.

[0022] The beneficial effects of this invention are as follows: Extensive testing has shown that dispersible latex powder enhances the bonding strength of alkali-activated crack-resistant mortar, effectively solving the aforementioned problem of easy detachment. By pre-mixing fibers with precursors in a dry-mixing process, followed by mixing with sand, additives, and other materials, the fibers are gradually and evenly dispersed in the alkali-activated mortar, reducing fiber agglomeration and better utilizing their anti-cracking properties, thus solving the problem of dry-hardening cracks in existing alkali-activated mortars. This alkali-activated crack-resistant mortar coating, used as an external anti-corrosion layer for ductile iron pipes, offers advantages such as high mechanical strength, excellent corrosion resistance, and a simple preparation process. Furthermore, this alkali-activated crack-resistant mortar does not use cement clinker, achieving comprehensive utilization of multiple solid wastes. Simultaneously, it features early strength and rapid hardening; compared to the 4-8 hours of steam curing required for ordinary silicate cement preparation, this alkali-activated crack-resistant mortar requires only 1-4 hours, significantly improving production efficiency.

[0023] 1. Compared with traditional external anti-corrosion coatings, such as epoxy coatings, polyurethane coatings and other organic coatings, the alkali-activated crack-resistant mortar coating of the present invention has better wear resistance and higher mechanical strength, and is better able to adapt to various complex environments in underground construction, preventing local wear and scratches, thereby improving the service life of ductile iron pipes.

[0024] 2. Compared with existing ductile iron pipe products with external concrete or mortar coatings on the market, the alkali-activated crack-resistant mortar coating of the present invention for ductile iron pipes has high early strength, rapid and stable strength development, and superior durability, which significantly reduces early curing time and improves the production rhythm and efficiency of ductile iron jacking pipes.

[0025] 3. This invention uses industrial solid wastes such as blast furnace slag powder, steel slag powder and fly ash as the main raw materials to achieve comprehensive utilization of multiple solid wastes, and does not use cement clinker, which greatly reduces carbon emissions and meets the goal of green and low-carbon development.

[0026] 4. Solve the problems of short setting time and easy cracking of alkali-activated mortar in the field of ductile iron pipe, and expand the application field of alkali-activated mortar. Attached Figure Description

[0027] Figure 1 This is a photograph of the actual surface-bonded object for Comparative Example 2;

[0028] Figure 2 This is a photograph of the actual surface-bonded object for Comparative Example 3;

[0029] Figure 3 This is a diagram showing the impact test results of Example 1;

[0030] Figure 4 This is a diagram showing the impact test results of Example 2;

[0031] Figure 5This is a diagram showing the results of the impact test for Comparative Example 1. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] In this embodiment, 70 parts of slag powder, 20 parts of fly ash (consisting of a precursor), and 10 parts of fiber are weighed and poured into a mixer, and slowly stirred for 30 seconds to obtain material 1; 3 parts of redispersible latex powder, 0.15 parts of water-reducing agent, and 120 parts of sand are poured into the mixer, and slowly stirred for 30 seconds to obtain material 2; material 1 and material 2 are poured into the mixer together, and slowly stirred for 60 seconds to obtain a precursor mixture; 32 parts of water and 9 parts of activator are mixed evenly to obtain material 3; the precursor mixture and material 3 are mixed and slowly stirred for 60 seconds, then 0.24 parts of retarder are added, and quickly stirred for 30 seconds to obtain alkali-activated crack-resistant mortar. The slag powder is S95 grade slag powder; the fly ash is Class C II fly ash; the fiber is polypropylene synthetic monofilament fiber with a fiber length of 6 mm; the redispersible latex powder is VAE latex powder; the water-reducing agent is naphthalene-based water-reducing agent; the activator is liquid sodium hydroxide solution with a solution concentration of 32%; the retarder is boric acid; then, alkali-activated crack-resistant mortar is coated on the surface of the ductile iron pipe body and cured under natural curing conditions for 28 days to obtain alkali-activated crack-resistant mortar coated ductile iron pipe.

[0035] Example 2

[0036] In this embodiment, the alkali-activated crack-resistant mortar coating comprises the following raw materials by weight: 80 parts slag powder, 15 parts fly ash, 15 parts steel slag powder, 9 parts polypropylene fiber, 3 parts redispersible latex powder, 0.14 parts water-reducing agent, 150 parts sand, 34 parts water, 17 parts activator, and 0.2 parts retarder. The activator is water glass, and sodium hydroxide is used to adjust the water glass modulus to 1.0. The other raw materials and preparation methods for the alkali-activated crack-resistant mortar coating, as well as the preparation method and curing conditions for the ductile iron pipe, are the same as in Example 1.

[0037] Comparative Example 1

[0038] In this comparative example, the crack-resistant mortar comprises the following raw materials by weight: 100 parts cement, 10 parts polypropylene fiber, 3 parts redispersible latex powder, 0.14 parts water-reducing agent, 150 parts sand, 34 parts water, and 0.2 parts retarder. The cement used is 52.5 ordinary Portland cement. Except for the cement, the raw materials and preparation methods of the crack-resistant mortar coating, as well as the preparation method and curing conditions of the ductile iron pipe, are the same as in Example 1. This comparative example is mainly set up to compare the performance differences between the crack-resistant mortar under the ordinary Portland system and the alkali-activated crack-resistant mortar of this invention.

[0039] Comparative Example 2

[0040] In this comparative example, the alkali-activated crack-resistant mortar comprises the following raw materials in parts by weight: 90 parts slag powder, 10 parts polypropylene fiber, 0.1 parts water-reducing agent, 150 parts sand, 36 parts water, 8 parts activator, and 0.2 parts retarder to obtain the alkali-activated crack-resistant mortar coating. The raw materials and preparation method of the above-mentioned alkali-activated crack-resistant mortar coating, the preparation method of the ductile iron pipe, and the curing conditions are the same as in Example 1.

[0041] Comparative Example 3

[0042] In this comparative example, the alkali-activated crack-resistant mortar comprises the following raw materials in parts by weight: 120 parts slag powder, 10 parts polypropylene fiber, 0.1 parts water-reducing agent, 150 parts sand, 36 parts water, and 20 parts activator to obtain the alkali-activated crack-resistant mortar coating. The raw materials and preparation method of the above-mentioned alkali-activated crack-resistant mortar coating, as well as the preparation method and curing conditions of the ductile iron pipe, are the same as in Example 1.

[0043] Comparative Example 4

[0044] In this comparative example, the alkali-activated crack-resistant mortar comprises the following raw materials by mass: 100 parts slag powder, 3 parts redispersible latex powder, 0.1 parts water-reducing agent, 150 parts sand, 36 parts water, and 20 parts activator to obtain the alkali-activated crack-resistant mortar coating. The raw materials and preparation method of the above-mentioned alkali-activated crack-resistant mortar coating, as well as the preparation method and curing conditions of the ductile iron pipe, are the same as in Example 1.

[0045] Performance testing

[0046] (1) The initial setting time and crack conditions of the crack-resistant mortars in Examples 1-2 and Comparative Examples 1-3 are as follows:

[0047] Table 1. Initial setting time and crack condition of mortars in Examples 1-2 and Comparative Examples 1-3

[0048] Example 1 40 No cracks visible to the naked eye Example 2 30 No cracks visible to the naked eye Comparative Example 1 45 There are visible cracks Comparative Example 2 60 No cracks visible to the naked eye Comparative Example 3 15 There are visible cracks Comparative Example 4 32 Severe cracking

[0049] As shown in Table 1 above, the setting time of Examples 1-2 after adding retarders was significantly improved compared to Comparative Example 3 without retarders, and was close to the setting time of ordinary Portland cement in Comparative Example 1, effectively increasing its workability. At the same time, the addition of fibers also effectively improved its crack resistance compared to Comparative Example 4. The results in the table above clearly show that the addition of retarders and fibers effectively improved the workability and crack resistance of alkali slag crack-resistant mortar, making it more suitable for application in the field of ductile iron pipes.

[0050] (2) The performance and properties of the ductile iron pipes prepared by applying crack-resistant mortar in Examples 1-2 and Comparative Examples 1-3 are as follows: Figure 1 and Figure 2 As shown, the bonding effect of Comparative Example 2 and Comparative Example 3 was not ideal. After applying the alkali-activated anti-cracking mortar, the bonding effect was poor, resulting in some of the alkali-activated anti-cracking mortar wrinkling or even falling off. Therefore, it could not be used to prepare alkali-activated anti-cracking mortar for ductile iron pipes.

[0051] For the ductile iron pipes prepared in Examples 1-2 and Comparative Example 1, the pull-out strength was tested according to the test method of GB / T 5210, and the impact test was tested according to the test method described in EN15542. The results are shown in the table below:

[0052] Table 2 shows the results of tensile strength, impact test, and compressive strength tests for Examples 1-2 and Comparative Example 1.

[0053]

[0054] As shown in Table 2, products tested according to EN 15542 should meet a pull-out strength requirement of at least 0.5 MPa. As shown in the table, Examples 1-2 and Comparative Example 1 significantly exceed the standard requirements. Products tested according to EN 15542 should not break after being subjected to an impact energy of at least 15 joules. Figures 3-5 The images show the state of the ductile iron pipes obtained in Examples 1-2 and Comparative Example 1 after impact testing. It can be seen that Examples 1-2 are significantly superior to the standard requirements. Although Comparative Example 1 did not show any fragmentation, it exhibited obvious cracks. Furthermore, observation of early strength clearly shows that Examples 1-2 have higher early strength, which allows for earlier production and faster production. Comparative Example 1, on the other hand, has lower early strength, which is detrimental to improving production efficiency.

[0055] (3) Mechanical properties of the products from Examples 1-2 used in the manufacture of ductile iron pipes

[0056] As shown in item (1) of the above-mentioned effect test data, the pull-out test and impact test proved that the ductile iron pipe made by applying the product of Examples 1-2 has pull-out resistance and impact resistance that are significantly better than the standard requirements. This indicates that the outer coating of the ductile iron pipe made by Examples 1-2 has greater strength. It can be seen that the mechanical strength of the crack-resistant mortar is obviously able to cope with wear and scratches that occur during long-distance transportation and engineering installation. At the same time, compared with the coating in the prior art, the alkali-activated crack-resistant mortar coating is thicker and has a denser structure, thus having a better anti-corrosion effect.

[0057] The examples and comparative examples described above are merely illustrative of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements to the technical solutions of the present invention made by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. An alkali-activated crack-resistant mortar coating for ductile iron pipes, characterized in that: The alkali-activated crack-resistant mortar coating for ductile iron pipes is made of a precursor, an activator, sand, water, fiber, and additives. The precursor is one or a mixture of three materials: blast furnace slag powder, steel slag powder, and fly ash. The weight proportions of the alkali-activated crack-resistant mortar coating are as follows: 90-110 parts of precursor, 9-17 parts of activator, 120-150 parts of sand, 5-15 parts of fiber, and the mass ratio of water to precursor is 0.25-0.

50. The thickness of the alkali-activated crack-resistant mortar coating used for the ductile iron pipe is 3-5 mm. The coating has a pull-out strength ≥0.64MPa with the ductile iron pipe metal substrate, no fragments or cracks after 15 Joule impact, an early (6h) compressive strength ≥6.25MPa, an initial setting time of 30-40min and no visible cracks.

2. The alkali-activated crack-resistant mortar coating for ductile iron pipes according to claim 1, characterized in that, The activator is one or a mixture of several of the following three activators: alkali metal hydroxide, water glass, and alkali metal carbonate.

3. The alkali-activated crack-resistant mortar coating for ductile iron pipes according to claim 1, characterized in that, The fiber is a synthetic fiber or a natural fiber, with a length of 3-20mm.

4. The alkali-activated crack-resistant mortar coating for ductile iron pipes according to claim 1, characterized in that, The additives include 0.5%-5% by weight of redispersible latex powder as precursors.

5. The alkali-activated crack-resistant mortar coating for ductile iron pipes according to claim 1, characterized in that, The admixture also includes a water-reducing agent at a rate of 0.05%-3% of the precursor mass.

6. The alkali-activated crack-resistant mortar coating for ductile iron pipes according to claim 1, characterized in that, The admixture also includes 0.01-0.5% of a retarder by mass of the precursor.

7. The method for preparing an alkali-activated crack-resistant mortar coating for ductile iron pipes as described in claim 1, characterized in that, Includes the following steps: A. Material 1 and Material 2 are uniformly mixed to obtain a precursor mixture, wherein Material 1 is a uniform mixture of one or more of the following three materials: blast furnace slag powder, steel slag powder and fly ash, and fiber; Material 2 is a uniform mixture of redispersible latex powder, water-retaining agent, water-reducing agent and sand. B. After uniformly mixing the precursor mixture with material 3, an alkali-activated crack-resistant mortar is obtained. Material 3 is a mixture of activator, water and retarder. The order of addition is to first mix the activator and water with the precursor mixture, and then add the retarder. C. Apply alkali-activated crack-resistant mortar to the outer surface of the ductile iron pipe; D. Perform maintenance.

8. The preparation method according to claim 7, characterized in that, In step C, the coating is one of extrusion coating, spraying, and mold grouting; wherein, extrusion coating involves placing alkali-activated crack-resistant mortar in the hopper of an extrusion pump, pumping the alkali-activated crack-resistant mortar to an extrusion device, and using pressure to extrude the alkali-activated crack-resistant mortar onto the outer surface of the ductile iron pipe to form a coating; spraying involves placing alkali-activated crack-resistant mortar in the hopper of a spraying pump, and using compressed air assisted by a spraying pump to uniformly spray the alkali-activated crack-resistant mortar onto the outer surface of the ductile iron pipe to form a coating; mold grouting involves placing the ductile iron pipe body in a pre-processed mold and pouring the alkali-activated crack-resistant mortar into the mold to form a coating; in step D, the curing method is steam curing or natural curing, the steam curing conditions are relative humidity above 95%, temperature 40-80℃, curing for 1-4 hours, and curing with a film and watering for 1-7 days.

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