Abstract: Cement based materials such as cement mortar and concrete are the most important matrix materials for building structures, exterior wall enclosures, and underground engineering. However, their inherent porous microstructure makes them highly susceptible to external moisture, chloride ions, and sulfate corrosion. Long term service can easily lead to microcracks, surface carbonization, and mortar loosening and peeling, greatly reducing structural durability and waterproof protection performance. Although traditional acrylic protective coatings have good film-forming properties, adhesion, and weather resistance, they belong to passive protection systems. After the coating is subjected to external forces, substrate deformation, and temperature induced stress, microcracks cannot be repaired independently, and defects continue to propagate, ultimately leading to water seepage, corrosion, and delamination failure. To solve the industry pain points of difficult self-healing and poor long-term protection of micro cracks in cement-based coatings, this paper uses functional monomer modification technology to prepare intelligent acrylic protective coatings with dynamic self-healing ability. Based on the dual mechanism of hydrogen bonding reversible association and dynamic molecular reconstruction, the self closing and performance recovery of micro cracks on mortar surface are achieved. The system explores the influence of functional monomer ratio, polymerization process, and curing conditions on the microstructure, interfacial adhesion, waterproofing and impermeability, chloride ion barrier, and self-healing efficiency of coatings. Through microscopic characterization, the self-healing mechanism and protective mechanism are revealed. The experimental results show that the modified acrylic coating can achieve self repair of microcracks in a room temperature and humid environment. After repair, the coating has excellent density, impermeability, and interface bonding strength recovery rate, which can effectively block the penetration of harmful media into the mortar and significantly improve the long-term durability of cement-based structures. This self-healing acrylic coating provides a new green intelligent material solution for long-term waterproof and anti-corrosion protection of building mortar and concrete structures.
1 Introduction
Cement based mortar and concrete materials are widely used in civil construction, municipal engineering, underground pipe galleries, hydraulic structures, and other fields due to their advantages of high strength, high stability, low cost, and convenient construction. However, cement-based materials belong to porous and brittle materials, with a large number of capillary pores and micro defects inside. Under the coupling effects of dry wet cycles, freeze-thaw cycles, ultraviolet aging, load stress, and micro deformation of the base layer, micro scale cracks are easily generated on the surface. Once microcracks are generated, they will become a rapid permeation channel for moisture, salt, and acidic media, accelerating mortar carbonization, steel corrosion, surface powdering and peeling, causing waterproof failure and durability degradation of building structures, significantly increasing later operation and renovation costs.
Surface polymer coating protection is the most economical and efficient technical means to improve the durability of cement-based materials. Among them, acrylic polymer coating has become the mainstream protective material for building exterior walls, structures, and underground structures due to its water-based environmental protection, excellent film-forming properties, good flexibility, outstanding weather resistance, and strong compatibility with mortar interfaces. However, traditional ordinary acrylic coatings do not have the ability to repair damage. The microcracks generated by the coating under base deformation, temperature stress, and external friction are permanent defects. Conventional coating systems can only achieve “passive barrier protection” and cannot cope with the continuous crack propagation problem caused by structural micro deformation. After long-term service, the protective system gradually fails.
Self repairing intelligent coatings have been a research hotspot in building protective materials in recent years, mainly divided into three technical systems: microcapsule assisted, dynamic chemical bonding, and supramolecular hydrogen bonding. The acrylic acid modification system based on supramolecular dynamic hydrogen bonding does not require external triggering reagents or complex packaging processes. It can independently achieve crack closure and membrane reconstruction in room temperature and humid environments, and is suitable for outdoor, humid, and complex temperature changing working conditions in buildings. It has the advantages of strong engineering practicality, long service life, and controllable cost. Based on this, this article prepares urea based functionalized self-healing acrylic coatings, which rely on reversible hydrogen bonding between molecular chains to achieve dynamic self-healing. The film forming performance, interface bonding, waterproof and anti-seepage properties, chloride ion penetration resistance, and self-healing performance on the surface of mortar substrates are systematically studied, and the self-healing mechanism and durability protection mechanism are elucidated. This provides theoretical support for the research and engineering application of long-term intelligent protective coatings for cement-based structures.
2 Experimental section
2.1 Experimental raw materials and reagents
The main raw materials for the experiment include acrylic hard monomer, acrylic soft monomer, urea based functional modified monomer, ammonium persulfate thermal initiator, butyl acetate cosolvent, ammonia pH regulator, and deionized water; The supporting water-based additives include wetting and dispersing agents, defoamers, film-forming agents, and thickeners. The substrate is made of standard cement mortar specimens with dimensions of 40mm × 40mm × 40mm. After standard curing, the strength is stable, the surface is flat, without floating ash, sanding, or obvious defects, simulating the actual working conditions of the mortar base layer in engineering. All raw materials meet the low VOC and green environmental standards of water-based building coatings, and are suitable for outdoor and underground humid service environments.
2.2 Self healing acrylic lotion and coating preparation process
The modified self-healing acrylic lotion was prepared by pre emulsification semi continuous polymerization process. Firstly, mix acrylic soft and hard monomers, functional modified monomers, and some emulsifiers with deionized water for high-speed pre emulsification to prepare a uniform and stable pre emulsion; Add the remaining emulsifier and bottom water into the reaction kettle to raise the temperature, and add a portion of the initiator solution dropwise to initiate the polymerization reaction; Subsequently, the pre emulsified monomer solution is added dropwise at a constant speed, and the reaction is carried out in stages at a constant temperature to ensure uniform polymerization and stable molecular chain structure; Add the remaining initiator system in the later stage of the reaction, eliminate residual monomers, and continue the constant temperature insulation reaction to ensure complete polymerization; After the reaction, it is naturally cooled, the pH of the system is adjusted to neutral, and the discharge is filtered to obtain a yellowish transparent modified acrylic lotion.
The prepared self-healing acrylic lotion is evenly mixed with functional additives, and the protective coating is prepared by low-speed dispersion mixing. The coating method is used to evenly form a film on the surface of standard cement mortar specimens. The coating is applied in two layers to ensure that the coating is continuous, compact, free of pinholes and holidays. After the surface is dry at room temperature, it is transferred to the standard curing environment for curing for 7 days. After the coating film is completely cross-linked and stable, various performance tests are carried out.
2.3 Test characterization methods
Microscopic morphology analysis: Scanning electron microscopy (SEM) was used to observe the changes in microscopic morphology before and after coating crack repair, and to observe the effect of crack closure and film reconstruction;
Interface bonding performance testing: testing the interfacial tensile bonding strength between the coating and the mortar substrate, evaluating the coating interface adaptation and anti detachment ability;
Anti permeability and waterproof performance test: Evaluate the anti permeability ability of intact coatings and repaired coatings through water pressure penetration test;
Anti chloride ion penetration performance: Test the chloride ion diffusion coefficient and evaluate the coating’s ability to block harmful ions;
Self repair performance evaluation: Manually prefabricated standard microcracks are cured in a room temperature and humid environment, and the crack closure is observed at different curing times. The mechanical and anti-seepage performance recovery rate after repair is tested.
3 Experimental results and performance analysis
3.1 Effect of functional monomer on film formation and interfacial properties of lotion
The introduction of urea based functional monomers is the core of achieving self-healing and interface enhancement of coatings. Ordinary acrylic lotion has strong molecular chain inertia, weak intermolecular force, limited flexibility after film formation, physical adsorption only on the porous interface with mortar, and low bond strength. After introducing urea based functional groups, acrylic acid molecular segments can form a large number of reversible hydrogen bonds, which not only enhances the flexibility and elastic deformation ability of the coating itself, but also adapts to the micro deformation of mortar base layer; On the other hand, polar groups such as urea and carboxyl can form interfacial hydrogen bonds with hydroxyl groups and hydration products on the surface of mortar, greatly improving the interfacial bonding strength between the coating and cement mortar, effectively improving coating peeling, debonding, and hollowing defects, and ensuring the integrity of the protective system.
3.2 Micro mechanism analysis of self-healing
The self-healing acrylic coating relies on the supramolecular dynamic hydrogen bonding reversible binding mechanism to achieve intelligent repair. When the coating is subjected to stress and micro scale cracks occur, the hydrogen bond network of the molecular chain segments on both sides of the crack breaks; At room temperature and humidity, water molecules can act as hydrogen bond mediators, promoting the re stretching, diffusion, and arrangement of broken molecular segments. The broken urea hydrogen bond sites recombine, achieving autonomous crack closure and molecular network reconstruction. This repair mechanism does not require external stimuli such as high temperature, light, catalysts, etc., and is suitable for the natural service environment of buildings. It can repeatedly repair microcrack damage, continuously maintain the dense structure of the coating, and solve the problem of cumulative propagation of microcracks in traditional acrylic coatings from the root. Microscopic morphology observations indicate that prefabricated microcracks gradually shrink and close under humid curing conditions, and ultimately the film layer returns to a continuous and flat structure without obvious crack residue.
3.3 Changes in waterproof and anti-seepage performance before and after self repair
After the ordinary acrylic coating produces microcracks, the waterproof channel is completely penetrated, and the water pressure resistance is greatly reduced. Moisture is easily infiltrated into the interior of the mortar along the cracks, causing the mortar to become loose, carbonized, and leak. After the formation of microcracks, self-healing modified acrylic coatings can quickly close the cracks, repair membrane defects, and restore the dense water barrier of the coating through dynamic molecular reconstruction. The test results show that the repaired coating still has excellent water resistance and high recovery of waterproof performance. It can effectively block the penetration of liquid water and water vapor, maintain the dryness and stability of the mortar surface, and greatly improve the waterproof durability of the mortar structure.
3.4 Chloride ion barrier and corrosion resistance performance
In coastal, saline alkali, and snow melting environments, the invasion of chloride ions is the core cause of corrosion and damage to reinforced concrete structures. Once the ordinary acrylic coating cracks, chloride ions quickly infiltrate and accumulate along the crack channel, posing a serious threat to structural safety. The self-healing acrylic coating can self repair through microcracks, continuously maintain a dense barrier system, effectively block harmful media such as chloride ions and sulfates from migrating into the matrix, significantly reduce the ion diffusion coefficient of the mortar matrix, improve the corrosion and carbonation resistance of cement-based structures, and meet the protection needs of underground and coastal high corrosion conditions.
3.5 Coating Mechanics and Durability Stability
The modified self-healing acrylic coating retains the advantages of high elasticity and good weather resistance of traditional acrylic materials, while enhancing the toughness and deformation resistance of the coating through dynamic cross-linking networks. Faced with dry and wet deformation, thermal expansion and slight settlement displacement of the base layer, the coating can adaptively stretch and shrink with the deformation of the base layer, and is not prone to hard cracking; Even if minor damage occurs, it can be self repaired, achieving a long-term cyclic protection system of “damage repair re protection”, effectively extending the protective life of mortar structures, and reducing the frequency of later maintenance and renovation of buildings.
4 Advantages and Applicable Scenarios of Engineering Applications
Compared with traditional ordinary acrylic protective coatings, epoxy resin rigid coatings, and polyurethane elastic coatings, self-healing acrylic intelligent protective coatings have multiple engineering advantages: firstly, they can self heal at room temperature, adapt to the outdoor natural environment of buildings, and repair micro crack defects without manual repair, solving the problem of hidden damage accumulation in coatings; Secondly, it has strong interface adaptability, firmly adheres to cement mortar and concrete substrate, and is not easily prone to hollowing and delamination; The third is the integration of waterproofing and anti-corrosion, while achieving multiple protective functions such as waterproofing, salt resistance, and carbonation resistance; The fourth is good green construction performance, with a water-based system that has low VOC, no odor, convenient construction, and good compatibility between new and old base layers.
This coating can be widely used in scenarios such as exterior wall mortar protection, roof mortar protection layer, underground garage roof, water tank hydraulic structure, bridge pier column, coastal building concrete protection, and renovation and repair of old mortar structures. It is particularly suitable for key protection projects where the base layer is prone to slight deformation, the environment is complex, the later maintenance is difficult, and durability requirements are high.
5 Existing Problems and Development Prospects
There are still certain technological shortcomings in the current self-healing acrylic coating: at present, it mainly has excellent repair effects on micro scale fine cracks, but has limited ability to repair wide macroscopic cracks; The stability of dynamic hydrogen bond networks decreases under strong alkaline and high salt long-term immersion environments; Compared to ordinary acrylic coatings, the cost of functional modified raw materials has slightly increased. In the future, self-healing protective coatings will develop towards the direction of multiple dynamic mechanism composites, strong environmental stability, low-cost mass production, and multifunctional integration. Through chemical bonding and supramolecular hydrogen bonding composite modification, the ability to repair wide cracks and improve medium stability will be enhanced; Introducing nano inorganic fillers to synergistically enhance density and weather resistance; Develop multi-functional intelligent protective coatings with self-healing, self-cleaning, heat insulation and anti-aging functions to achieve ultra long-term protection of cement based building structures.
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Post time: Sep-14-2026