A sprayable mortar for repairing concrete structures and its preparation method

Abstract

This invention relates to a sprayable mortar for repairing concrete structures and its preparation method, comprising the following components in parts by weight: 100 parts phosphate cement, 20-150 parts fine aggregate, 10-50 parts admixture, 0.1-5 parts modifier, 0.02-0.5 parts additive, and 10-40 parts water. The sprayable mortar provided by this invention has the following advantages and effects: high mortar consistency, easy spraying application, good anti-sagging and anti-cracking properties, and good bonding strength, mechanical properties, and resistance to salt-freezing erosion. It is highly suitable for the rapid repair of concrete structure facades / roofs with extensive salt-freezing erosion damage.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a sprayable mortar for repairing concrete structures and its preparation method, especially for repairing facades / roofs. Background Technology

[0002] Traditional cement-based materials possess good plasticity. By incorporating raw materials such as cellulose ethers and starch ethers, they can achieve excellent anti-sagging properties, maintaining a uniform distribution on vertical or inclined surfaces without flowing or sag. Phosphate cement mortar not only boasts excellent bond strength, high mechanical properties, and good resistance to (salt) freezing and steel corrosion, but also exhibits extremely low shrinkage and good volume stability, making it highly suitable for rapid repair of cement concrete structures. However, conventional phosphate cement mortar has high viscosity and good fluidity, which cannot meet the requirements for vertical / ceiling surface repairs.

[0003] Patent CN 106966687 B discloses a non-flowing, fast-setting, strong-adhesion phosphate cement repair material and its preparation method. It is composed of adhesive powder, sand, magnesium oxide, ammonium dihydrogen phosphate, fly ash, sodium silicate, polypropylene fiber, retarder, polycarboxylate superplasticizer, and water. Its gel material is mainly adhesive powder and supplemented with phosphate cement. It is mainly used for repairing defects in special locations on bridge slabs or building facades. However, this solution is only suitable for manual plastering and not for spraying. Patent CN 109592959 B describes an easy-to-apply, high-adhesion facade repair material and its preparation method, comprising quartz sand, metal oxides, brucite powder, ammonium dihydrogen phosphate, talc powder, silica fume, xanthan gum, air-entraining agent, retarder, and water. It exhibits good anti-sagging properties and bonding strength, making it suitable for repairing the top or facade surfaces of structures. However, while this technical solution performs well on walls and does not sag when applied manually with a thin layer, its anti-sagging properties significantly decrease when sprayed, failing to meet the requirements for facade or top surface repair. Summary of the Invention

[0004] In view of the shortcomings of the current technical solutions, the purpose of this invention is to provide a sprayable mortar for repairing concrete structures, which can be applied by spraying, does not clog pipes, has high construction efficiency, has good anti-sagging and cohesive properties, and also has excellent comprehensive durability.

[0005] A second objective of this invention is to provide a method for preparing the sprayed mortar.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] This invention provides a sprayable mortar for repairing concrete structures, the sprayable mortar comprising the following raw materials in parts by weight:

[0008] 100 parts phosphate cement, 20-150 parts fine aggregate, 10-50 parts admixture, 0.1-5 parts modifier, 0.02-0.5 parts additive, and 10-40 parts water.

[0009] The phosphate cement is composed of ammonium dihydrogen phosphate, potassium dihydrogen phosphate, metal oxides, and borax. Specifically, the phosphates include ammonium dihydrogen phosphate and potassium dihydrogen phosphate, with a molar ratio of ammonium dihydrogen phosphate to potassium dihydrogen phosphate of 1:(0-1). The metal oxide is magnesium oxide. The phosphate cement has an initial setting time of more than 20 minutes, flexural and compressive strengths of more than 3.5 MPa and 20.0 MPa at 1 hour, and flexural and compressive strengths of more than 8.0 MPa and 50.0 MPa at 28 days, respectively.

[0010] The fine aggregate is quartz sand, including any one of manufactured sand, washed sand and river sand; the quartz sand has a silica content greater than 96%, a mud content less than 0.2%, and a maximum particle size of 0.6 mm.

[0011] The admixture includes one or more of fly ash, silica fume, ultrafine fly ash, metakaolin, and bentonite. The fly ash is grade I or grade II low-calcium ash, and the silica fume contains more than 92% silica.

[0012] The modifier is one or more of polyacrylate resin, polysaccharide polymer, and nano-silica.

[0013] The additive is one or more of melamine water-reducing agent, naphthalene-based water-reducing agent, sodium lignosulfonate water-reducing agent, and calcium lignosulfonate water-reducing agent.

[0014] The water mentioned is tap water.

[0015] To achieve the above objectives, the present invention also proposes a method for preparing and constructing spray mortar: first, the modifier and additives are mixed evenly, and then a small amount of water is used to prepare an aqueous solution for later use. Then, phosphate cement, fine aggregate and admixture are dry-mixed evenly, and the remaining water is poured in and stirred for 2-3 minutes. Finally, the aqueous solution is added and stirred for 1 minute to obtain the spray mortar.

[0016] Before construction, the concrete structure surface or wall surface should be cleaned. You can use a high-pressure water gun to wash off the surface dust, moss, oil and other impurities and let it dry. If the exposed steel bars are rusted, they should be derusted first, and then the mortar should be evenly sprayed onto the structure surface using a mortar spraying machine.

[0017] Preferably, the molar ratio of ammonium dihydrogen phosphate to potassium dihydrogen phosphate in the phosphate cement is 1:(0.1-0.8); the fine aggregate is machine-made quartz sand; the bentonite is organic bentonite; the modifier is a mixture of polysaccharide polymer (or polyacrylate resin) and nano-silica; and the additive is a mixture of melamine water-reducing agent and lignocal / lignosodium water-reducing agent or naphthalene-based water-reducing agent. Specifically, the phosphate cement uses a combination of ammonium dihydrogen phosphate and potassium dihydrogen phosphate, which reduces the cement's fluidity while ensuring material strength; the addition of organic bentonite to the admixture exhibits good thixotropy in the system; the modifier, a combination of polysaccharide polymer (or polyacrylate resin) and nano-silica, increases the slurry's consistency and water retention, further improving its thixotropy; and the additive, a mixture of melamine and lignocal / lignosodium / naphthalene-based water-reducing agent, not only reduces the slurry's viscosity but also improves its plasticity. However, when using only a modifier or only an additive, the anti-sagging performance of the slurry cannot achieve the best effect. When the water consumption is high or the repair thickness is large, the slurry still sags during vertical construction. When the modifier and the additive are combined, the anti-sagging performance of the slurry is significantly improved, and the slurry is soft, has low internal shear force, and is easy to mix and apply.

[0018] Preferably, the spray mortar for repairing concrete structures comprises the following raw materials in parts by weight: 100 parts phosphate cement, 30-110 parts fine aggregate, 15-40 parts admixture, 0.5-3 parts modifier, 0.04-0.4 parts additive, and 10-30 parts water.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. The slurry has good plasticity and anti-sagging properties, and will not produce defects such as teardrop, flow or sagging. The slurry consistency can reach more than 80mm, and the internal frictional resistance is small, making it very suitable for spraying.

[0021] 2. It has high bonding strength, and its flexural strength bonded to concrete structures can reach over 8.0 MPa. Moreover, the damaged surface is on the original concrete specimen and can be integrated with the repaired surface.

[0022] 3. Rapid strength development and high comprehensive mechanical properties; the flexural / compressive strength can reach over 4.5MPa / 25.0MPa in 1 hour, allowing for rapid recovery and use; the flexural / compressive strength is greater than 10.0MPa / 50.0MPa in 7 days, meeting the requirements for structural repair.

[0023] 4. Good durability: This sprayed mortar has good crack resistance, (salt) frost resistance and steel corrosion resistance, making it very suitable for the rapid repair of damaged areas on the facade / roof of concrete structures such as exposed rebar and salt frost erosion.

[0024] 5. Mechanical spraying is used for construction, which is simple, efficient, and has controllable quality. It requires less labor and has lower construction costs. Detailed Implementation

[0025] The present invention will now be described in detail with reference to specific embodiments.

[0026] The consistency of the sprayed mortar was tested using the consistency test in JGJ / T 70-2009 "Standard for Test Methods of Basic Performance of Building Mortar". The arithmetic mean of the two test results was taken as the measured value, accurate to 1 mm.

[0027] The anti-sagging performance was determined according to GB / T 9264-2012 "Evaluation of Anti-Sagging Properties of Paints and Varnishes". The specific method is as follows: A test board with a side length of 50cm was prepared using ordinary cement concrete and cured for 28 days before use. Surface dust was removed before the test. The test board was placed vertically, and the repair mortar was sprayed evenly onto the test board. The spraying thickness was controlled by the number of spraying passes. After reading the spraying thickness with vernier calipers, a horizontal thin line was immediately drawn across the test board, approximately 250mm from the top. Sagging marks on the test board were checked immediately after drawing the horizontal line (depending on the rheological properties of the repair mortar, sagging can be observed almost immediately after application or may take several minutes to be observed). If the horizontal line moved, sagging had occurred. Defects such as teardrop-shaped, flowing, and sagging were evaluated on the entire test board area, including the area marked by the horizontal line.

[0028] Interfacial flexural strength is an effective way to characterize the bond strength of repair mortar. It was determined according to the method in JC / T 2537-2019 "Magnesium Phosphate Repair Mortar". The reference cement mortar block was made with grade 42.5 cement as specified in GB 175. Before use, the reference cement mortar block should be sanded with 200-grit sandpaper to remove residual debris at the contact interface. The repair mortar mixture was poured into a three-piece mold containing the cement mortar block, tamped evenly 15 times with a trowel, and then manually compacted 5 times. The mortar surface was then smoothed with a scraper to form a test bonding specimen. The formed test bonding specimens were cured in the test environment for 1 hour and 7 days, and their flexural strength was determined according to the mortar flexural strength test method. The interfacial flexural strength was expressed as flexural strength, accurate to 0.1 MPa.

[0029] The flexural and compressive strengths were tested in accordance with GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)".

[0030] Crack resistance was tested by simulating cracking under strong winds and dry conditions, with a test sprayed area of ​​no less than 1m². 2 With a wind speed of 5 m / s and humidity below 10%, the mortar was immediately placed in a test environment after spraying and the cracking condition before the repair mortar was fully hardened was recorded.

[0031] The salt freeze-thaw resistance performance was tested according to Appendix B of MH 5006-2015 "Technical Specification for Construction of Cement Concrete Surface Layer in Civil Airports"—the test method for freeze-thaw damage of cement concrete against de-icing liquid. The test corrosion solution was prepared with 96% distilled water and 4% potassium formate by mass. The mortar specimens were 150 mm in diameter and 100 mm in height, with the molded surface as the test surface. After 7 days of natural curing followed by 4 days of water immersion curing, the salt freeze-thaw resistance performance test was conducted. The amount of spalling per unit surface area of ​​the specimen after 30 freeze-thaw cycles was measured, accurate to 0.01 kg / m². 2 .

[0032] Example 1

[0033] A sprayable mortar for repairing concrete structures comprises the following components in parts by weight:

[0034] 100 parts phosphate cement, 80 parts fine aggregate, 30 parts admixture, 1.2 parts modifier, 0.13 parts additive, and 22 parts water.

[0035] The phosphate cement has a molar ratio of ammonium dihydrogen phosphate to potassium dihydrogen phosphate of 1:0.2. The initial setting time of the phosphate cement is greater than 20 minutes, and the flexural and compressive strengths at 1 hour are greater than 3.5 MPa and 20.0 MPa, respectively. The flexural and compressive strengths at 28 days are greater than 8.0 MPa and 50.0 MPa, respectively. The fine aggregate is machine-made quartz sand. The admixture is a mixture of fly ash, ultrafine fly ash, and silica fume in a mass ratio of 1:1:1. The modifier is a mixture of polyacrylate resin and nano-silica in a mass ratio of 2:1. The additive is a mixture of commercially available melamine water-reducing agent and calcium lignosulfonate water-reducing agent in a mass ratio of 2:3. The water is tap water.

[0036] The preparation method of the spray mortar is as follows: First, mix the modifier and additive evenly, and prepare an aqueous solution with a small amount of water for later use. Then, dry mix the phosphate cement, fine aggregate and admixture evenly, pour in the remaining water and stir for 2-3 minutes. Finally, add the aqueous solution and continue stirring for 1 minute to obtain the spray mortar mixture.

[0037] Before spraying, the concrete structure surface or wall surface should be thoroughly cleaned. This can be done by pre-washing the surface with a high-pressure water gun to remove dust, moss, oil, and other impurities, and then allowing it to dry. If exposed reinforcing bars are rusted, they should be removed first. Then, use a mortar spraying machine to evenly spray mortar onto the concrete structure surface to be repaired. Performance test results are shown in Table 1.

[0038] Example 2

[0039] A sprayable mortar for repairing concrete structures comprises the following components in parts by weight:

[0040] 100 parts phosphate cement, 100 parts fine aggregate, 36 parts admixture, 1.5 parts modifier, 0.16 parts additive, and 23 parts water.

[0041] The phosphate cement has a molar ratio of ammonium dihydrogen phosphate to potassium dihydrogen phosphate of 1:0.5. The initial setting time of the phosphate cement is greater than 20 minutes, and the flexural and compressive strengths at 1 hour are greater than 3.5 MPa and 20.0 MPa, respectively. The flexural and compressive strengths at 28 days are greater than 8.0 MPa and 50.0 MPa, respectively. The fine aggregate is washed silica sand. The admixture is a mixture of fly ash, ultrafine fly ash, silica fume, and bentonite in a mass ratio of 1:1:1:0.5, and the bentonite is organic bentonite. The modifier is a mixture of polysaccharide polymer and nano-silica in a mass ratio of 2:1. The additive is a mixture of commercially available melamine water-reducing agent and naphthalene-based water-reducing agent in a mass ratio of 1:1. The water is tap water.

[0042] The preparation and construction methods of the sprayed mortar are the same as in Implementation Case 1, and the performance test results are shown in Table 1.

[0043] Example 3

[0044] A sprayable mortar for repairing concrete structures comprises the following components in parts by weight:

[0045] 100 parts phosphate cement, 40 parts fine aggregate, 27 parts admixture, 1.3 parts modifier, 0.15 parts additive, and 20.5 parts water.

[0046] The phosphate cement has a molar ratio of ammonium dihydrogen phosphate to potassium dihydrogen phosphate of 1:0.7, an initial setting time of more than 20 minutes, flexural and compressive strengths of more than 3.5 MPa and 20.0 MPa at 1 hour, and flexural and compressive strengths of more than 8.0 MPa and 50.0 MPa at 28 days, respectively. The fine aggregate is washed quartz sand. The admixture is a mixture of fly ash, ultrafine fly ash, silica fume, and metakaolin in a mass ratio of 1:1:1:0.5. The modifier is a mixture of polysaccharide polymer and nano-silica in a mass ratio of 2:1. The additive is a mixture of commercially available melamine water-reducing agent and sodium lignosulfonate water-reducing agent in a mass ratio of 2:3. The water is tap water.

[0047] The preparation and construction methods of the sprayed mortar are the same as in Implementation Case 1, and the performance test results are shown in Table 1.

[0048] Comparative Example 1

[0049] A sprayable mortar for repairing concrete structures comprises the following components in parts by weight:

[0050] 100 parts phosphate cement, 80 parts fine aggregate, 35 parts admixture, 2 parts modifier, and 21 parts water.

[0051] This comparative example does not contain any additives. The molar ratio of ammonium dihydrogen phosphate to potassium dihydrogen phosphate in the phosphate cement is 1:0.2. The initial setting time of the phosphate cement is greater than 20 minutes. The flexural and compressive strengths at 1 hour are greater than 3.5 MPa and 20.0 MPa, respectively. The flexural and compressive strengths at 28 days are greater than 8.0 MPa and 50.0 MPa, respectively. The fine aggregate is washed silica sand. The admixture is a mixture of fly ash, ultrafine fly ash, and silica fume in a mass ratio of 1:1:1. The modifier is a mixture of polysaccharide polymer and nano-silica in a mass ratio of 2:1. The water is tap water.

[0052] The preparation and construction methods of the sprayed mortar are the same as in Implementation Case 1, and the performance test results are shown in Table 1.

[0053] Comparative Example 2

[0054] A sprayable mortar for repairing concrete structures comprises the following components in parts by weight:

[0055] 100 parts phosphate cement, 50 parts fine aggregate, 28 parts admixture, 0.3 parts additive, and 21 parts water.

[0056] This comparative example does not contain any modifiers. The molar ratio of ammonium dihydrogen phosphate to potassium dihydrogen phosphate in the phosphate cement is 1:0.5. The initial setting time of the phosphate cement is greater than 20 minutes, and the flexural and compressive strengths at 1 hour are greater than 3.5 MPa and 20.0 MPa, respectively. The flexural and compressive strengths at 28 days are greater than 8.0 MPa and 50.0 MPa, respectively. The fine aggregate is washed silica sand. The admixture is a mixture of fly ash, ultrafine fly ash, silica fume, and bentonite in a mass ratio of 1:1:1:0.5, and the bentonite is organic bentonite. The additive is a mixture of commercially available melamine water-reducing agent and sodium lignosulfonate water-reducing agent in a mass ratio of 2:3. The water is tap water.

[0057] The preparation and construction methods of the sprayed mortar are the same as in Implementation Case 1, and the performance test results are shown in Table 1.

[0058] Comparative Example 3

[0059] According to Example 1 of the patent CN 106966687 B, a non-flowing, fast-setting, strong-adhesion phosphate cement repair material and its preparation method, a phosphate cement-based rapid repair material was prepared. Although the mortar mixture was non-flowing, it was relatively loose, resulting in high resistance on the construction surface. When the water content was increased by 2 times, the slurry had a certain degree of cohesion, but it still could not meet the requirements for spraying construction. Specific test data are shown in Table 1.

[0060] Comparative Example 4

[0061] Referring to Example 4 of Patent CN 109592959 B, "An Easy-to-Construct High-Adhesion Facade Repair Material and Its Preparation Method," the facade repair material was prepared. When applied by troweling, the mixture was relatively soft and easy to apply, with good anti-sagging properties and no obvious sagging was observed. However, when applied by spraying, the slurry showed obvious sagging defects. For specific test results, please refer to Table 1.

[0062] Comparative Example 5 was based on Example 1 without the addition of additives, and Comparative Example 6 was based on Example 1 without the addition of modifiers. All other preparation and construction methods were exactly the same as those in Example 1. The performance test results are shown in Table 1.

[0063] As shown in Table 1, the repair mortars of Examples 1-3 have significantly higher consistency, are softer, and exhibit good anti-sagging properties. No sagging marks appeared even after three coats, indicating that even with a larger repair thickness, the repair mortar prepared using this method still has high anti-sagging performance and will not exhibit teardrop, flowing, or sagging defects, meeting the requirements for conventional facade or ceiling repairs. Comparative Examples 1, 2, and 4, although having lower consistency and being drier, still showed defects such as sagging marks, indicating that they cannot meet the requirements for facade repair under spraying conditions. Comparative Example 3 has excellent anti-sagging properties, but the mortar is too dry. Even with a significant increase in water content, it cannot meet the requirements for spraying, and its overall mechanical properties are too low after a significant increase in water content, failing to meet repair requirements. Based on Examples 1, 1, 2, 5, and 6, it can be seen that adding a single modifier does not significantly improve the anti-sagging performance of the repair mortar. Adding a single additive improves the anti-sagging performance, but some sagging traces still remain. Through the synergistic effect of multiple factors such as phosphate compounding, optimal design of admixtures, modifiers, and additives, the anti-sagging performance of the repair mortar is significantly improved. Moreover, its slurry consistency is larger, frictional resistance is smaller, and it is easier to spray and apply, achieving excellent results. At the same time, the repair material prepared using this technical solution has high interfacial flexural strength and self-flexural and compressive strength, excellent crack resistance and salt freeze-thaw resistance, which can meet the repair requirements of conventional concrete structure facades / top surfaces. It is particularly suitable for the rapid repair of facades / top surfaces of bridge guardrails, piers, etc., in northern regions where de-icing salt / salt spray erosion damage has occurred.

[0064] Table 1

[0065]

[0066] Note: ① The test environment temperature was 10℃, and the initial setting time of the repair mortar in all examples and comparative examples was greater than 20 minutes; ② All repair mortars in all examples and comparative examples passed the crack resistance test, and no cracks appeared on the surface; ③ In the anti-sagging performance test, the test boards of Examples 1 to 3 were sprayed with 3 coats of repair mortar; the repair mortar of Comparative Example 3 was applied to the test board by manual wiping, and the test boards of the other comparative examples were sprayed with 1 coat of repair mortar; ④ The water consumption of Comparative Example 3 was greatly increased, resulting in very low strength of the test specimen. The specimen could be broken by hand. Therefore, its interfacial flexural strength, flexural compressive strength and salt freeze-thaw resistance were not tested.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sprayable mortar for repairing concrete structures, characterized in that, The composition comprises the following components in parts by weight: 100 parts phosphate cement, 20-150 parts fine aggregate, 10-50 parts admixture, 0.1-5 parts modifier, 0.02-0.5 parts additive, and 10-40 parts water; wherein the phosphate cement comprises ammonium dihydrogen phosphate and potassium dihydrogen phosphate, wherein the molar ratio of ammonium dihydrogen phosphate to potassium dihydrogen phosphate is 1:(0.1-0.8); the modifier is a mixture of polysaccharide polymer and nano-silica in a mass ratio of 2:1, or a mixture of polyacrylate resin and nano-silica in a mass ratio of 2:1; the additive is a mixture of melamine water-reducing agent and one or more other water-reducing agents, wherein the other water-reducing agents are naphthalene-based water-reducing agents, sodium lignosulfonate water-reducing agents, and calcium lignosulfonate water-reducing agents.

2. The spray mortar for repairing concrete structures according to claim 1, characterized in that, The phosphate cement has an initial setting time of more than 20 minutes, a flexural strength and compressive strength of more than 3.5 MPa and 20.0 MPa at 1 hour, and a flexural strength and compressive strength of more than 8.0 MPa and 50.0 MPa at 28 days, respectively.

3. The spray mortar for repairing concrete structures according to claim 1, characterized in that, The sprayed mortar comprises the following components in parts by weight: 100 parts phosphate cement, 30-110 parts fine aggregate, 15-40 parts admixture, 0.5-3 parts modifier, 0.04-0.4 parts additive, and 10-30 parts water.

4. The spray mortar for repairing concrete structures according to claim 1, characterized in that, The fine aggregate is quartz sand, which can be any one of manufactured sand, washed sand, and river sand; the quartz sand has a silica content greater than 96%, a mud content less than 0.2%, and a maximum particle size of 0.6 mm.

5. The spray mortar for repairing concrete structures according to claim 1, characterized in that, The admixture includes one or more of fly ash, silica fume, ultrafine fly ash, metakaolin, and bentonite. The fly ash is grade I or grade II low-calcium ash, the silica fume has a silica content greater than 92%, and the bentonite is organic bentonite.

6. A method for preparing sprayable mortar for repairing concrete structures according to any one of claims 1-5, characterized in that, The process includes the following steps: First, mix the modifier and additives evenly and prepare an aqueous solution with a small amount of water for later use. Then, dry mix the phosphate cement, fine aggregate and admixture evenly, pour in the remaining water and stir for 2-3 minutes. Finally, add the aqueous solution and continue stirring to obtain the spray mortar.

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