Mortar with self-repairing function and preparation method thereof

Abstract

The application belongs to the technical field of building materials, and particularly relates to a mortar with self-repairing function, which is composed of the following components: 25 parts of water, 100 parts of cement, 180 parts of sand, 0.3 parts of water reducing agent, 1.3 parts of PVA fiber, 1.5 parts of crystallization additive, and 10 parts of calcium sulphoaluminate-based expansion additive. The crystallization additive and the calcium sulphoaluminate-based expansion additive can make the cement hydration process produce a large amount of calcium hydroxide crystals and C-S-H gel, greatly improve the mechanical properties and self-repairing function of the mortar structure, and can control the generation of large cracks in the mortar matrix, and has a certain deformation capacity. In the initial stage of the generation of the mortar cracks, the mortar can be effectively repaired by itself, the cost of repairing the mortar cracks in the project is reduced, and further guarantee is provided for the safety, economy and durability of the mortar structure.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a mortar with self-healing function and its preparation method. Background Technology

[0002] Self-healing mortar is a special type of mortar that can self-repair cracks in concrete structures. This mortar is typically composed of polymer materials that form a network structure within the concrete, allowing it to self-repair cracks. Due to its self-healing properties, it can effectively extend the lifespan of buildings and reduce maintenance and replacement costs. Currently, the self-healing mechanism of common self-healing mortars is mainly based on the further hydration and expansion of unreacted particles in the mortar's internal binder material. These unreacted particles include common silicate materials or other types of bonding materials.

[0003] However, existing self-healing mortars containing polymers such as cementitious materials are not very effective in repairing major cracks in concrete because their effective components have limited remaining hydration and expansion potential. The volume of the cementitious material hydration products is insufficient to repair large cracks in concrete, and the availability of existing self-healing mortars is limited, failing to enable concrete materials to achieve robust self-healing behavior. Summary of the Invention

[0004] The present invention addresses the problem that existing self-healing mortars are insufficient to repair large cracks in concrete and have limited usability, failing to enable concrete materials to achieve robust self-healing behavior. It provides a mortar with self-healing function and its preparation method.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: by mass parts, it consists of the following components: 25 parts water, 100 parts cement, 180 parts sand, 0.3 parts water-reducing agent, 1.3 parts PVA fiber, 1.5 parts crystallizing additive, and 10 parts calcium sulfoaluminate-based expansion additive.

[0006] Preferably, the crystallizing additive is composed of the following components by weight percentage: 73.4% calcium oxide, 13.72% silicon dioxide, 3.66% aluminum oxide, 2.28% iron oxide, 1.24% sodium oxide, 0.4% potassium oxide, 3.91% solid sulfur trioxide, 0.7% magnesium oxide, and 0.69% titanium dioxide, with the sum of the above components being 100%.

[0007] Preferably, the calcium sulfoaluminate-based expanding additive is composed of the following components by weight percentage: calcium oxide 48.09%, silicon dioxide 1.71%, aluminum oxide 12.66%, iron oxide 0.45%, sodium oxide 0.05%, potassium oxide 0.06%, solid sulfur trioxide 35.48%, magnesium oxide 0.92%, titanium dioxide 0.31%, phosphorus pentoxide 0.17%, and manganese trioxide 0.1%, with the sum of the above components being 100%.

[0008] Preferably, the PVA fiber has a density of 1.27 g / cm3, a length of 6-8 mm, a diameter of 20-30 µm, and an ultimate tensile strength of not less than 1200 MPa.

[0009] Preferably, the cement is PO 42.5 grade with a density of 3100-3200 kg / m³. 3 The apparent density of the sand is 2650-2750 kg / m³. 3 The water absorption rate is 0.8%-1.02%, and the fineness modulus is 2.0-2.2; the water-reducing agent is a polycarboxylate high-efficiency water-reducing agent with a water reduction rate of 15%-25% and a dosage of 0.5%-1.5%.

[0010] A method for preparing a self-healing mortar, the specific steps of which are as follows: Step 1: Prepare the crystallization additive. Mix the following chemical powders in proportion: 73.4% calcium oxide, 13.72% silicon dioxide, 3.66% aluminum oxide, 2.28% iron oxide, 1.24% sodium oxide, 0.4% potassium oxide, 3.91% solid sulfur trioxide, 0.7% magnesium oxide, and 0.69% titanium dioxide. Then, use a powder mixer to stir at high speed for 30 minutes, let it stand for 10 minutes, and then take it out. Step 2: Prepare calcium sulfoaluminate-based expansion additive. Mix the following chemical powders in proportion: 48.09% calcium oxide, 1.71% silicon dioxide, 12.66% aluminum oxide, 0.45% iron oxide, 0.05% sodium oxide, 0.06% potassium oxide, 35.48% solid sulfur trioxide, 0.92% magnesium oxide, 0.31% titanium dioxide, 0.17% phosphorus pentoxide, and 0.1% manganese trioxide. Then, stir the mixture for 30 minutes using a powder mixer, let it stand for 10 minutes, and then remove it. Step 3: Mix cement and sand in a ratio of 100:180 by weight, then add 1.3 parts PVA fiber, 0.3 parts water-reducing agent, 1.5 parts crystallizing additive, 10 parts calcium sulfoaluminate-based expansion additive and 25 parts water in sequence, and stir evenly.

[0011] Compared with the prior art, the advantages and positive effects of the present invention are as follows: Compared to existing technologies, the mortar of this invention has a self-healing function. (1) The use of crystallizing additive CA and calcium sulfoaluminate-based expansive additive CSA during cement hydration produces a large amount of calcium hydroxide crystals and CSH gel. The active chemical substances enter the concrete with water, reacting with ionized calcium ions in the calcium hydroxide solution to form water-soluble and unstable complexes, which continue to diffuse in the pore solution of the concrete. The calcium ion complexing agent can reduce the activation energy of the hydration products reacting with calcium ions. When reaching areas rich in cement gel, due to differences in solubility and stability of the products, the anions in the complexing agent are replaced by silicate and aluminate ions, and the resulting hydrated calcium silicate fills the cracks inside the mortar, effectively repairing the cracks.

[0012] (2) It is simple to prepare, uses readily available raw materials, and significantly improves the mechanical properties and self-healing function of mortar structures. It can control the generation of large cracks in the mortar matrix and has a certain deformation capacity. In the early stage of mortar crack formation, it can effectively repair itself, reducing the cost of repairing mortar cracks in engineering projects and providing further assurance for the safety, economy and durability of mortar structures. Detailed Implementation

[0013] To better understand the above-described objects, features, and advantages of the present invention, the present invention will be further described below with reference to embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; however, the present invention may be practiced in other ways than those described herein, and therefore, the present invention is not limited to the specific embodiments disclosed in the following specification.

[0014] Example 1 1. Preparation of mortar: (1) Preparation of crystallization additive: 73.4% calcium oxide, 13.72% silicon dioxide, 3.66% aluminum oxide, 2.28% iron oxide, 1.24% sodium oxide, 0.4% potassium oxide, 3.91% solid sulfur trioxide, 0.7% magnesium oxide and 0.69% titanium dioxide were mixed in proportion, and then stirred at high speed for 30 min using a powder mixer. After standing for 10 min, it was taken out and set aside. (2) Preparation of calcium sulfoaluminate-based expansion additive: 48.09% calcium oxide, 1.71% silicon dioxide, 12.66% aluminum oxide, 0.45% iron oxide, 0.05% sodium oxide, 0.06% potassium oxide, 35.48% solid sulfur trioxide, 0.92% magnesium oxide, 0.31% titanium dioxide, 0.17% phosphorus pentoxide, and 0.1% manganese trioxide were mixed in proportion, then stirred for 30 min with a powder mixer, and left to stand for 10 min before being taken out for later use. (3) Determine the water-cement ratio to be 0.25 according to the mortar strength grade requirements. Mix cement and sand in a ratio of 100:180 by weight, and then put them into a horizontal forced mixer. Add 1.5 parts of crystallizing additive and 10 parts of calcium sulfoaluminate-based expansion additive and stir at 60 r / min for 60 s.

[0015] (4) Mix 25 parts water and 0.3 parts water-reducing agent to make a mixture, and divide it into two parts: mixture one and mixture two. Add mixture one and 1.3 parts PVA fiber to a horizontal forced mixer and stir at 60 r / min for 120 s. Then add mixture two and stir at 60 r / min for 120 s.

[0016] 2. Molding: Pour the mixed mortar into the molding mold, place it on a cement mortar vibrating table, and vibrate it at a frequency of 2860 times / minute. Write a label, seal it with plastic film, and after 20 hours, spray a small amount of water on the surface of the cured mortar to slightly moisten it.

[0017] 3. Demolding: Remove the cured mortar from the mold after 24 hours.

[0018] 4. Hydration and water protection: Place the removed mortar sample in water for water protection, with the water level 2 cm above the mortar sample.

[0019] 5. Crack pre-creation: After the sample has been cured for 7 days, mechanical testing was used to pre-crease the cracks. The pre-creased cracks were all 15cm in length and 0.1mm in width.

[0020] 6. Curing: The pre-cracked mortar specimens were placed in a prepared artificial seawater solution for curing, and the crack repair effect was observed after 28 days.

[0021] Comparative Example 1 Compared with Example 1, Comparative Example 1 did not contain calcium sulfoaluminate-based expansion additives and crystallization additives, but the other components and preparation methods were the same.

[0022] Comparative Example 2 Compared with Example 1, Comparative Example 2 did not have the calcium thioaluminate-based expansion additive, but the other components and preparation methods were the same.

[0023] Comparative Example 3 Compared with Example 1, Comparative Example 3 did not have a crystallizing additive, but the other components and preparation methods were the same.

[0024] The repair performance of Examples 1 and Comparative Examples 1-3 was measured using a crack observation instrument and an electron scanning microscope, and the relevant data in Table 1 were obtained.

[0025] Table 1 During crack self-healing, the crystallizing additive CA and the calcium sulfoaluminate-based expansive additive CSA induce the production of abundant calcium hydroxide crystals and CSH gel during cement hydration. The active chemicals enter the concrete with water, reacting with ionized calcium ions in the calcium hydroxide solution to form water-soluble and unstable complexes, which continue to diffuse in the pore solution of the concrete. The calcium ion complexing agent reduces the activation energy of the hydration products reacting with calcium ions. When reaching areas rich in cement gel, due to differences in solubility and stability of the products, the anions in the complexing agent are replaced by silicate and aluminate ions. Therefore, the generated hydrated calcium silicate fills the cracks within the mortar, effectively repairing them. Comparative testing of Example 1 and Comparative Example 1 showed that Comparative Example 1 had virtually no repair effect on the cracks, while Example 1, with the addition of crystallizing additive CA and calcium sulfoaluminate-based expansive additive CSA, exhibited a significant crack repair effect.

[0026] The active chemicals in the crystallizing additive CA can penetrate or disperse into the structure with the help of water. Some of these active chemicals react with the hydration products of cement to form insoluble crystals, while others catalyze the hydration of cement particles. The crystallizing additive particles have a similar morphology to cement particles, being irregular and ranging in size from 1 to 20 μm. Adding crystallizing additive CA to mortar can repair concrete cracks and refine pores, thereby improving the strength and durability of concrete. Comparative tests between Example 1 and Comparative Example 3 showed that mortar without crystallizing additive CA exhibited decreased compressive and flexural strength, longer healed crack lengths, and reduced crack healing effectiveness.

[0027] Calcium sulfoaluminate-based expandable additive (CSA) exhibits strong hydration activity, enabling it to rapidly absorb moisture from the air and expand, thus plugging and filling microcracks and achieving a good self-healing effect. Comparative testing of Example 1 and Comparative Example 2 revealed that the crack length after healing was the longest, indicating a significant decrease in crack healing effectiveness.

[0028] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a mortar with self-healing function, characterized in that, By weight, the self-healing mortar consists of the following components: 25 parts water, 100 parts cement, 180 parts sand, 0.3 parts water-reducing agent, 1.3 parts PVA fiber, 1.5 parts crystallizing additive, and 10 parts calcium sulfoaluminate-based expansive additive. The crystallizing additive, by weight percentage, comprises the following components: calcium oxide 73.4%, silicon dioxide 13.72%, aluminum oxide 3.66%, iron oxide 2.28%, sodium oxide 1.24%, potassium oxide 0.4%, solid sulfur trioxide 3.91%, magnesium oxide 0.7%, and titanium dioxide 0.69%, with the sum of the above components being 100%. The calcium sulfoaluminate-based expanding additive comprises, by weight percentage: 48.09% calcium oxide, 1.71% silicon dioxide, 12.66% aluminum oxide, 0.45% iron oxide, 0.05% sodium oxide, 0.06% potassium oxide, 35.48% solid sulfur trioxide, 0.92% magnesium oxide, 0.31% titanium dioxide, 0.17% phosphorus pentoxide, and 0.1% manganese trioxide, with the sum of the above components being 100%. The specific steps in the preparation method are as follows: Step 1: Prepare the crystallization additive. Mix the components of the chemical powder crystallization additive in proportion, then use a powder mixer to stir at high speed for 30 minutes, let stand for 10 minutes, and then take it out. Step 2: Prepare calcium sulfoaluminate-based expansion additive. Mix the components of the calcium sulfoaluminate-based expansion additive in chemical powder form according to the proportion, then stir with a powder mixer for 30 minutes, let stand for 10 minutes and then take it out. Step 3: Mix cement and sand according to the weight ratio, and then add PVA fiber, water-reducing agent, crystallizing additive, calcium sulfoaluminate-based expansion additive and water in the same weight ratio, and stir evenly. Step 4: Crack repair testing of mortar samples; Molding: Pour the mortar mixed in step three into the molding mold, place it on the cement mortar vibrating table and vibrate to shape; write a label, seal it with plastic film, and after 20 hours, spray water on the surface of the cured mortar to moisten the mortar surface; Demolding: Remove the cured mortar from the mold after 24 hours; Hydration and water protection: Place the removed mortar sample in water for water protection, with the water level 2 cm above the mortar sample; Crack pre-casting: After the mortar samples were cured for 7 days, mechanical tests were used to pre-cast cracks on them. The pre-cast cracks were all 15cm in length and 0.1mm in width. Curing: The pre-cracked mortar specimens were placed in a prepared artificial seawater solution for curing, and the crack repair effect was observed after 28 days.

2. The method for preparing self-healing mortar according to claim 1, characterized in that, The PVA fiber density is 1.27 g / cm³. 3 It has a length of 6-8 mm, a diameter of 20-30 µm, and an ultimate tensile strength of not less than 1200 MPa.

3. The method for preparing mortar with self-healing function according to claim 1 or 2, characterized in that, The cement mentioned is PO42.5 grade, with a density of 3100-3200 kg / m³. 3 The apparent density of the sand is 2650-2750 kg / m³. 3 The water absorption rate is 0.8%-1.02%, and the fineness modulus is 2.0-2.2; the water-reducing agent is a polycarboxylate high-efficiency water-reducing agent with a water reduction rate of 15%-25% and a dosage of 0.5%-1.5%.

Images