# Bonding and Repairing Properties of Fiber-Polymer Mortar for Concrete Repair

Authors: Wei Li; Zhongbin Li
Journal: Advances in Materials Science and Engineering
 (2022)

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## Abstract

This article mainly introduced the effect of polymers on the bonding and repairing properties of mortar, explained the reason why concrete is easily damaged in actual operation, and introduced the improvement method. Through the influencing factors of mortar cohesiveness, the corresponding improvement measures were put forward and the factors affecting the bonding strength were explained. Through the comparison of the influencing factors of mortar cohesiveness, the experimental analysis was carried out. The polymer was added to the common mortar and compared in terms of flexural and compressive strength, water absorption, shrinkage rate, and frost resistance. After analyzing the experimental data, the principle of adding polymer performance enhancement was explained. The experimental results showed that the compressive and flexural strength of the mortar added with the polymer was effectively improved, the toughness was also enhanced, and the shrinkage rate was reduced by 49.7%. In the antifreeze test, the quality of ordinary mortar decreased by 1.35%, the quality of mortar added with polymer decreased by 0.33%, and the strength of the polymer was also strengthened. The water absorption decreased by 10%, and the tensile strength increased exponentially at the same time. At 7 d, it was 3.8 times that of ordinary mortar, at 28 d, it was 5.2 times, and the tensile strength was greatly improved. In construction regulations, polymer mortar has more practical application value and can meet various needs of engineering.


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## Body

## 1. Introduction

Ordinary mortar in construction projects, because of the different needs of the project, requires good quality, high viscosity, long service life, low water absorption, and other requirements, and the mortar is also improved accordingly. The various properties of ordinary mortar cannot meet many requirements in construction, and its water absorption, strength, toughness, and other aspects are relatively poor, and it is easy to cause subsequent construction problems. In actual construction, it is easy to cause the wall to fall off, which is also a potential danger. The adaptability of the mortar to the outside weather is relatively low, resulting in a short use time, and it is easy to cause the wall to be hollowed out after shrinking, which affects the appearance and quality.The polymer-added mortar can solve this problem very well. By adding organic matter to improve the performance of mortar, it can well deal with the problems of ordinary mortar, improve the performance of ordinary mortar, and greatly improve it, which has great value for actual engineering construction.Through a series of experiments, it can be known that adding polymer to ordinary mortar can greatly improve the performance of mortar. Before adding the polymer, the performance of the mortar is relatively low, and it is easy to cause many problems, resulting in a relatively short use time of the building wall, and the wall is easy to fall off, which affects the appearance and has potential risks. After adding the polymer, the water absorption of the mortar was reduced by 10%, and the shrinkage of the mortar was also reduced by 49.7%. Buildings made of concrete are also more resistant to freezing, bending, and compression. In terms of tensile strength, after being placed for a period of time, the tensile strength of polymer-added mortar is several times that of ordinary mortar, the polymer-added mortar was 3.8 times that of the ordinary mortar after standing for 7 days, and 5.2 times that after standing for 28 days. After construction, the amount of building wall mass reduction is also improved, and the overall strength of the building is enhanced. In contrast, the mortar added with polymers is more in line with the needs of construction, and its performance has been improved.


## 2. Related Work

The cohesiveness of mortar has always been a headache in construction, and many scholars have carried out research on this issue. The failure of the combination of cement mortar and cement gaps often leads to the deterioration of reinforced concrete structures. Although there have been several different approaches to improve their integration, no system has yet been able to evaluate their effectiveness from the perspective of durability. To this end, Zhang proposed a method for evaluating the durability of paint and cement bonding systems at the laboratory level. In this process, circulating heat is applied to the surface of the locally plastered mortar, accelerating its aging rate; this area represents the façade exposed to the sun. On this basis, the corresponding constraints of the cement mortar were made to reproduce its actual failure mechanism. The simulation and experimental results showed that the method is effective [1]. The special technology of dry construction mortar for construction concrete printing is one of the related fields of innovative construction development. The study covered dry construction mortar technology with redispersible polymer powders. Poluektova proposed an optimal solution for mixing the components using a high-speed paddle wheel mixer. The results showed that a certain level of compositional stability and performance optimization can only be provided in the production automation of building materials for 3D printing. Based on the results obtained, a specially designed mortar composition was identified, with reduced hardening time and good bonding properties [2]. Once the mortar is applied to the substrate as a thin layer, the surface of the mortar is exposed to the environment and changes its properties over time, reducing the bond strength. Zurbriggen proposed a new rheological in situ method to measure the crust buildup within the first 30 minutes. With a spatial resolution of 1 micron, the shell formed by the mortar can be made thicker, thereby increasing the time that the surface of the mortar is not affected by the outside world, and increasing the internal characteristics of the mortar. This method can be applied to any soft material with a viscosity gradient perpendicular to its surface [3]. In order to test the compatibility of construction and demolition waste and self-compacting mortar (SCM) mixtures with parent concrete, at different temperatures, Benyahia prepared four SCM mixtures with substitution rates of 0%, 10%, 20%, and 30% RP according to EFNARC specifications. Compatibility was measured at various elevated temperature levels by conducting skew shear tests on composite cylindrical samples (half SCM/half concrete) cured in a water curing tank at a 28-day curing age. The results showed that partial replacement of cement with RP reduced dry weight and compressive strength, and increased water absorption of SCM [4]. Although the above-mentioned related scholars have carried out research and discussion on the bond repairability of mortar, the practical application still fails to meet the expectations of buildings. Therefore, relevant scholars began to analyze the fiber polymer and study its repairability in mortar bonding.Fiber polymers are being used in a wide variety of industries, and the construction industry is revolutionizing in two main ways. One approach is to develop construction techniques, such as the use of automated tools in construction. Another is the advancement of high-performance building materials, such as the introduction of high-strength composite materials such as glass fibers, carbon fibers, boron fibers, aramid fibers, silicon carbide fibers, asbestos fibers, whiskers, and metals. Natural fibers have replaced synthetic fibers with their superior properties such as high specific strength, lightweight, low cost, moderate mechanical properties, non-abrasive recyclability, and biodegradation. In this regard, Kumre mixed natural fiber-polymer composites with glass fibers to verify the mechanical properties of the composites. The results showed that glass fiber-reinforced polymer blended with sisal with various sisal fiber lengths (5, 10, 15, and 20 mm) can increase its properties and can be used in engineering [5]. Microstructural characterization is critical to understanding and predicting the behavior of concrete-reinforced glass fiber-reinforced polymer (GFRP) rebars. Considering the lack of extensive knowledge of GFRP microstructure, Gooranorimi provided documentation of GFRP microstructure and demonstrated its contribution to the durability of GFRP reinforcement. Due to the different pultrusion production methods, each raw bar exhibits a unique microstructural pattern, including voids, defects, and fiber distribution. And through the horizontal shear test, it was found that the difference in the microstructural mode is helpful to judge the durability of GFRP [6]. In order to measure the shear interface strength of fiber-reinforced polymers, Naya proposed a new method. The method was based on fiber push-in testing of central fibers with high-density fiber clusters with hexagonal symmetry, and was supported by a detailed and finite analysis of push-in tests to account for the effects of damp heat residual stress, fiber confinement, and fiber anisotropy on interfacial strength. Thermosets or thermoplastics were applied to determine the shear interfacial strength of matrix-reinforced carbon fiber and glass fiber composites [7]. Related scholars have carried out a series of researches on fibrous polymers, but they have not been used in mortar, and the application of fibrous polymers was not perfect.


## 3. Causes of Concrete Damage and Repair Methods

### 3.1. Reasons for Concrete Damage

Carbonization reaction: the hydration of cement and water makes the concrete finally show alkaline, and the long-term contact with the atmosphere produces carbonation. As a result, the concrete structure becomes loose and the porosity changes, resulting in a decrease in the bearing capacity of the structure. Concrete structures are often exposed to more than one corrosion factor, and may also cause chemical corrosion due to weather, temperature, and daily wear and tear. Many scholars have done a lot of research on its destruction in complex environments, and have carried out the mixing of chloride salts and carbides, and different carbonization treatments [8].Sulfate attack: corrosion of cement components by sulfate solutions is also another major factor in nonmechanical effects. Scholars started from the principle and comprehensively studied the influence of sulfate solution on the substances produced by concrete hydration and the change of cement void ratio. And pointed out that in order to weaken the anti-sulfate solution corrosion effect, cement can be mainly from two aspects of adding mineral fillers such as fly ash cement and improving the density of cement [9].Corrosive in acidic environment: concrete and cement undergo a strong hydration reaction, producing alkaline calcium hydroxide, C-S-H gel materials, and other chemicals. If the cement is in an acidic environment for a long time, it will slowly corrode the cement components. Since concrete is a porous structure, hydrogen ions will not only adversely affect the surface cement structure, but also enter the structure, causing the internal structure of the wall to be loose and corroded, reducing the quality of aggregates, and shortening the service life. There are also many effects of strong acid environment on cement erosion, mainly including concrete properties, aggregate quality, mix ratio, and other factors [10]. From a mechanical point of view, the acid corrosion resistance of concrete can reduce the content of C-S-H gel and alumina by reducing the water-cement ratio of concrete, thereby increasing the density of concrete.Chloride corrosion: chloride corrosion mainly occurs in concrete buildings, and the snow-melting agent used in winter is mainly chloride [11]. When studying chloride corrosion, it is necessary to consider not only the damage mechanism of chloride to concrete, but also to combine it with the freezing and heat cycle of concrete [12]. Relevant scholars have established a multifactor coupling model of chloride corrosion based on the multifactor coupled chloride corrosion model. The service life of the mixture was significantly improved [13]. While improving the resistance to chloride corrosion of concrete, carbon fiber-reinforced material can also be used to enhance the performance of the material [14].Cement cracks: there are many reasons for concrete cracks, and their types and causes are also different [15]. There are mainly load cracks, shrinkage cracks, temperature cracks, shrinkage cracks, subsidence cracks, steel corrosion cracks, etc. These defects not only affect the appearance, but also show obvious structural problems or lack of staying power. Cracks can indicate the extent of the entire failure, as well as the severity of the problem. The extent of its damage is related to the type of structure and the characteristics of the fractures. For example, in a structure that retains moisture, cracks that the building can withstand are not allowed. Correctly repairing cracks depends on understanding the cause and choosing the appropriate repair method; otherwise, repairs can become repetitive. A successful maintenance program must understand the causes of cracks and how they can be repaired.


### 3.2. Repair Methods for Concrete Damage

Epoxy substances: some scholars have carried out experimental research on epoxy resin repairing concrete cracking [16]. The wedge-splitting experiment was carried out first, then the epoxy resin grouting technique was used to repair it, and then the wedge-splitting experiment was carried out. It was found that the repaired sample will not appear in the bonding place; repair with glue injection method can delay the recurrence of cracks and improve the fracture capacity of concrete. The fracture index of the repair effect by glue injection is proposed, and the application of glue injection method in engineering is supplemented, which has certain reference value. After repairing with epoxy adhesive, the failure interface is initiated from the initial interface, rather than the initial failure interface. When repairing cracks, the method of water injection or self-weight pouring is used to repair the cracks and make the structure complete. Before applying epoxy resin, due to its versatility and wide range of physical and chemical energies, it is necessary to fully understand the environment before entering epoxy resin samples. In addition to repairing cracks, epoxy resin is also widely used in the concrete industry.Self-healing concrete: concrete cracks can repair themselves in wet conditions, but only in small cracks. In fact, cracks can cause leakage and damage to the structure. The research on the self-healing properties of concrete has always been in its infancy, and many engineering technologies have improved the self-healing properties of concrete to a great extent. For example, fiber-reinforced cement has a higher self-healing potential than general concrete; the method of mineral precipitation can also be used; and a variety of mineral additives have good results in practical applications. On this basis, combined with the design idea of smart materials, the researchers proposed a new type of self-repairing concrete. Self-repairing concrete is the main function of three smart materials: first induction, second processing, and third transmission [17].


### 3.3. Main Factors and Improvement Measures That Affect the Cohesiveness of Mortar

Moisture pressure: the main reason is that the temperature difference between the inside and outside affects the direct stress of the board, and after passing through the natural environment, the adhesion between the board and the polymer is reduced. It refers to the high density and high hardness of the extruded sheet (surface), which means that the extruded sheet will change greatly due to the change in the surrounding temperature due to the properties of the material itself. The thin powder coating structure of the point-and-frame adhesive extruded sheet, because the thermal conductivity ratio of the polymer is 31 times that of the extruded sheet, the linear expansion coefficient of the plastering layer and the plastic polystyrene foam sheet is very different. In addition, the temperature of the outer wall and the inner wall fluctuates greatly in summer. After long-term exposure to the sun, rapid storms will cause thermal stress decomposition inside the board, resulting in an uneven temperature change rate of the two adjacent materials. The thermal expansion and contraction of the material, and the long-term maintenance of an unbalanced thermal expansion and contraction, cause the thermal shear force between the polymer and the extruded sheet, which in turn affects the bonding strength of the two [18].Foam properties of plastic sheets: point frame viscose plastic polystyrene foam board, because of its poor permeability with thin cement mortar after plastering, and smooth surface, extremely low water absorption, no OH group at the end of the molecular chain, and is a hydrophobic group, so it is not easy to bond with inorganic cement-based substances. When using bonding mortar or coating cement, it is more likely to form false bonding and debonding. The process of molting and brushing on the formed sheet helps to improve its surface roughness and increase its internal friction, thereby reducing the internal stress of the structure, making the bonding between the board and the cement stronger, and not easy to absorb water, while the bond strength is mainly based on mechanical meshing. According to these circumstances, the following ways can be used to improve.To improve the plasticity of cement mortar is to ensure sufficient filling of cement mortar and improve the bonding strength of cement. The selection of raw materials for cement mortar is very critical, which can ensure that the cement of the building reaches a certain age, and can make the quality of the mortar better and the viscosity better. Sand and gravel cement should be used within the shelf life. The addition of thickener cellulose ether and redispersible latex powder can increase the viscosity of the mortar. For the renovation of brickwork, it is not suitable to use the method of laying grout or laying bricks, but the “three-one brick” method [19], that is, the masonry method of large shovel, one shovel of ash, and one shovel and one kneading. When using the grouting method for masonry, the length of grouting should be strictly controlled, usually the spacing should not be greater than 750 mm, and when the temperature is higher than 30°C during the construction process, it should not exceed 500 mm, and it is forbidden to use it on brick walls. 1∼2 days before masonry, the bricks must be poured first to ensure that the moisture content of sintered ordinary bricks and porous bricks is between 10% and 15% during the masonry process; among them, the moisture content of lime-sand bricks and fly ash bricks is 8%–12% [20].


### 3.4. Calculation of Bond Mortar Strength

There are many factors that affect the adhesion, such as the quality of sand, fineness, the amount of water, and the quality of cement. It is difficult to quantitatively control these factors in the previous manual analysis. Multivariate analysis by computer can not only quantitatively control various factors of early bond strength and long-term bond strength, but also estimate the bond strength within the experimental error range by predicting various input variables. Multivariate analysis was performed using a computer, according to Quantitative Class I. Analysis methods for the same purpose are also experimental design methods, while multivariate analysis methods have the following advantages:Multivariate analysis will not go beyond the scope of experimental data, and careful experimental planning can analyze field operation data that is difficult to organize. The more field operation data is accumulated, the higher the accuracy of multivariate analysis [21].Qualitative factors can be quantified. When the multivariate analysis is carried out according to the quantitative chemical class I, the estimated valuey0 of the bond strength can be obtained from the reckoning y1 composed of qualitative factors and the reckoning y2 composed of nonquantitative factors, which is(1)y0=y1+y2.Among them, qualitative factors refer to the material of the polymer, and factors that cannot be quantified are the shape of concrete and the type of sand. Ifxij is used to represent the factor, i represents the item and j represents the category. Then, the relationship between the factor and the estimated value can be expressed by(2)y1=a11x11+a12x12++a1nx1n+a21x21+a22x22+a2mx2m.The quantitative factor is the latex polymer-cement ratio (P/C), and the variable factor is the open time (T). When the polymer-cement ratio is the parameter, the functional relationship between the open time and the bond strength is a quadratic function, which is(3)y2=a1PC2+a2PC+a3PC×T.According to Formulas (2) and (3), it is determined by the least squares method. When y0−y22 takes the minimum value, the mortar strength can be calculated through the strength contour line of the functional relationship between the polymer-cement ratio and Formulas (2) and (3). By inferring and calculating the ratio of the correlation coefficient of the values, if the ratio of the two values is 0.9, it means that the correlation is better [22].The main factors affecting the early bond strength are the construction environment and maintenance conditions of the mortar. The influencing factors of construction mainly refer to climate, temperature, humidity, wind speed, and the type of base. The influencing factors of mortar mainly refer to the type of sand, the ratio of lime to sand, the ratio of binder and cement, the thickness and method of application, the mixing time, and the drying time. The maintenance conditions mainly refer to the maintenance age, which is generally more than one week. Among them, the factors affecting the fixation are the compaction method, the ratio of binder to cement, the thickness of application, the stirring time, and the curing age [23]. The rest are variable influencing factors, and the variable factors are divided into quantitative factors and qualitative factors.


## 3.1. Reasons for Concrete Damage

Carbonization reaction: the hydration of cement and water makes the concrete finally show alkaline, and the long-term contact with the atmosphere produces carbonation. As a result, the concrete structure becomes loose and the porosity changes, resulting in a decrease in the bearing capacity of the structure. Concrete structures are often exposed to more than one corrosion factor, and may also cause chemical corrosion due to weather, temperature, and daily wear and tear. Many scholars have done a lot of research on its destruction in complex environments, and have carried out the mixing of chloride salts and carbides, and different carbonization treatments [8].Sulfate attack: corrosion of cement components by sulfate solutions is also another major factor in nonmechanical effects. Scholars started from the principle and comprehensively studied the influence of sulfate solution on the substances produced by concrete hydration and the change of cement void ratio. And pointed out that in order to weaken the anti-sulfate solution corrosion effect, cement can be mainly from two aspects of adding mineral fillers such as fly ash cement and improving the density of cement [9].Corrosive in acidic environment: concrete and cement undergo a strong hydration reaction, producing alkaline calcium hydroxide, C-S-H gel materials, and other chemicals. If the cement is in an acidic environment for a long time, it will slowly corrode the cement components. Since concrete is a porous structure, hydrogen ions will not only adversely affect the surface cement structure, but also enter the structure, causing the internal structure of the wall to be loose and corroded, reducing the quality of aggregates, and shortening the service life. There are also many effects of strong acid environment on cement erosion, mainly including concrete properties, aggregate quality, mix ratio, and other factors [10]. From a mechanical point of view, the acid corrosion resistance of concrete can reduce the content of C-S-H gel and alumina by reducing the water-cement ratio of concrete, thereby increasing the density of concrete.Chloride corrosion: chloride corrosion mainly occurs in concrete buildings, and the snow-melting agent used in winter is mainly chloride [11]. When studying chloride corrosion, it is necessary to consider not only the damage mechanism of chloride to concrete, but also to combine it with the freezing and heat cycle of concrete [12]. Relevant scholars have established a multifactor coupling model of chloride corrosion based on the multifactor coupled chloride corrosion model. The service life of the mixture was significantly improved [13]. While improving the resistance to chloride corrosion of concrete, carbon fiber-reinforced material can also be used to enhance the performance of the material [14].Cement cracks: there are many reasons for concrete cracks, and their types and causes are also different [15]. There are mainly load cracks, shrinkage cracks, temperature cracks, shrinkage cracks, subsidence cracks, steel corrosion cracks, etc. These defects not only affect the appearance, but also show obvious structural problems or lack of staying power. Cracks can indicate the extent of the entire failure, as well as the severity of the problem. The extent of its damage is related to the type of structure and the characteristics of the fractures. For example, in a structure that retains moisture, cracks that the building can withstand are not allowed. Correctly repairing cracks depends on understanding the cause and choosing the appropriate repair method; otherwise, repairs can become repetitive. A successful maintenance program must understand the causes of cracks and how they can be repaired.


## 3.2. Repair Methods for Concrete Damage

Epoxy substances: some scholars have carried out experimental research on epoxy resin repairing concrete cracking [16]. The wedge-splitting experiment was carried out first, then the epoxy resin grouting technique was used to repair it, and then the wedge-splitting experiment was carried out. It was found that the repaired sample will not appear in the bonding place; repair with glue injection method can delay the recurrence of cracks and improve the fracture capacity of concrete. The fracture index of the repair effect by glue injection is proposed, and the application of glue injection method in engineering is supplemented, which has certain reference value. After repairing with epoxy adhesive, the failure interface is initiated from the initial interface, rather than the initial failure interface. When repairing cracks, the method of water injection or self-weight pouring is used to repair the cracks and make the structure complete. Before applying epoxy resin, due to its versatility and wide range of physical and chemical energies, it is necessary to fully understand the environment before entering epoxy resin samples. In addition to repairing cracks, epoxy resin is also widely used in the concrete industry.Self-healing concrete: concrete cracks can repair themselves in wet conditions, but only in small cracks. In fact, cracks can cause leakage and damage to the structure. The research on the self-healing properties of concrete has always been in its infancy, and many engineering technologies have improved the self-healing properties of concrete to a great extent. For example, fiber-reinforced cement has a higher self-healing potential than general concrete; the method of mineral precipitation can also be used; and a variety of mineral additives have good results in practical applications. On this basis, combined with the design idea of smart materials, the researchers proposed a new type of self-repairing concrete. Self-repairing concrete is the main function of three smart materials: first induction, second processing, and third transmission [17].


## 3.3. Main Factors and Improvement Measures That Affect the Cohesiveness of Mortar

Moisture pressure: the main reason is that the temperature difference between the inside and outside affects the direct stress of the board, and after passing through the natural environment, the adhesion between the board and the polymer is reduced. It refers to the high density and high hardness of the extruded sheet (surface), which means that the extruded sheet will change greatly due to the change in the surrounding temperature due to the properties of the material itself. The thin powder coating structure of the point-and-frame adhesive extruded sheet, because the thermal conductivity ratio of the polymer is 31 times that of the extruded sheet, the linear expansion coefficient of the plastering layer and the plastic polystyrene foam sheet is very different. In addition, the temperature of the outer wall and the inner wall fluctuates greatly in summer. After long-term exposure to the sun, rapid storms will cause thermal stress decomposition inside the board, resulting in an uneven temperature change rate of the two adjacent materials. The thermal expansion and contraction of the material, and the long-term maintenance of an unbalanced thermal expansion and contraction, cause the thermal shear force between the polymer and the extruded sheet, which in turn affects the bonding strength of the two [18].Foam properties of plastic sheets: point frame viscose plastic polystyrene foam board, because of its poor permeability with thin cement mortar after plastering, and smooth surface, extremely low water absorption, no OH group at the end of the molecular chain, and is a hydrophobic group, so it is not easy to bond with inorganic cement-based substances. When using bonding mortar or coating cement, it is more likely to form false bonding and debonding. The process of molting and brushing on the formed sheet helps to improve its surface roughness and increase its internal friction, thereby reducing the internal stress of the structure, making the bonding between the board and the cement stronger, and not easy to absorb water, while the bond strength is mainly based on mechanical meshing. According to these circumstances, the following ways can be used to improve.To improve the plasticity of cement mortar is to ensure sufficient filling of cement mortar and improve the bonding strength of cement. The selection of raw materials for cement mortar is very critical, which can ensure that the cement of the building reaches a certain age, and can make the quality of the mortar better and the viscosity better. Sand and gravel cement should be used within the shelf life. The addition of thickener cellulose ether and redispersible latex powder can increase the viscosity of the mortar. For the renovation of brickwork, it is not suitable to use the method of laying grout or laying bricks, but the “three-one brick” method [19], that is, the masonry method of large shovel, one shovel of ash, and one shovel and one kneading. When using the grouting method for masonry, the length of grouting should be strictly controlled, usually the spacing should not be greater than 750 mm, and when the temperature is higher than 30°C during the construction process, it should not exceed 500 mm, and it is forbidden to use it on brick walls. 1∼2 days before masonry, the bricks must be poured first to ensure that the moisture content of sintered ordinary bricks and porous bricks is between 10% and 15% during the masonry process; among them, the moisture content of lime-sand bricks and fly ash bricks is 8%–12% [20].


## 3.4. Calculation of Bond Mortar Strength

There are many factors that affect the adhesion, such as the quality of sand, fineness, the amount of water, and the quality of cement. It is difficult to quantitatively control these factors in the previous manual analysis. Multivariate analysis by computer can not only quantitatively control various factors of early bond strength and long-term bond strength, but also estimate the bond strength within the experimental error range by predicting various input variables. Multivariate analysis was performed using a computer, according to Quantitative Class I. Analysis methods for the same purpose are also experimental design methods, while multivariate analysis methods have the following advantages:Multivariate analysis will not go beyond the scope of experimental data, and careful experimental planning can analyze field operation data that is difficult to organize. The more field operation data is accumulated, the higher the accuracy of multivariate analysis [21].Qualitative factors can be quantified. When the multivariate analysis is carried out according to the quantitative chemical class I, the estimated valuey0 of the bond strength can be obtained from the reckoning y1 composed of qualitative factors and the reckoning y2 composed of nonquantitative factors, which is(1)y0=y1+y2.Among them, qualitative factors refer to the material of the polymer, and factors that cannot be quantified are the shape of concrete and the type of sand. Ifxij is used to represent the factor, i represents the item and j represents the category. Then, the relationship between the factor and the estimated value can be expressed by(2)y1=a11x11+a12x12++a1nx1n+a21x21+a22x22+a2mx2m.The quantitative factor is the latex polymer-cement ratio (P/C), and the variable factor is the open time (T). When the polymer-cement ratio is the parameter, the functional relationship between the open time and the bond strength is a quadratic function, which is(3)y2=a1PC2+a2PC+a3PC×T.According to Formulas (2) and (3), it is determined by the least squares method. When y0−y22 takes the minimum value, the mortar strength can be calculated through the strength contour line of the functional relationship between the polymer-cement ratio and Formulas (2) and (3). By inferring and calculating the ratio of the correlation coefficient of the values, if the ratio of the two values is 0.9, it means that the correlation is better [22].The main factors affecting the early bond strength are the construction environment and maintenance conditions of the mortar. The influencing factors of construction mainly refer to climate, temperature, humidity, wind speed, and the type of base. The influencing factors of mortar mainly refer to the type of sand, the ratio of lime to sand, the ratio of binder and cement, the thickness and method of application, the mixing time, and the drying time. The maintenance conditions mainly refer to the maintenance age, which is generally more than one week. Among them, the factors affecting the fixation are the compaction method, the ratio of binder to cement, the thickness of application, the stirring time, and the curing age [23]. The rest are variable influencing factors, and the variable factors are divided into quantitative factors and qualitative factors.


## 4. Performance Results of Polymer Mortar and Ordinary Mortar

Mainly taking fiber polymer as the improvement object, the effect of fiber polymer on bonding mortar was studied. By testing the performance in the mortar, comparing the waterproof and frost resistance, shrinkage rate, flexural and compressive strength, and tensile strength, to judge the difference with ordinary bonded mortar. Material: cement Jidong 42.5 ordinary Portland cement, sand: fineness modulus 2.1, mud content less than 1.5%, in line with the regulations in JGJ-52, and water: tap water. The mass ratio of cement and sand is 1:2.5, and the content of polymer is 2% cement and 0.5 water-cement ratio. A sample of 40 mm × 40 mm × 160 mm was made, and cured and tested in the same environment [24, 25].The bending, compression, adhesive tensile, water absorption, and shrinkage properties of different periods were compared. Contrast the antifreeze environment: freeze for 24 hours, control the temperature at −19°C, and then heat for 24 hours, and control the temperature at 27°C. This was used as a freeze-heat cycle, and it was performed five times. The microscopic properties of polymer-bonded mortar were observed by scientific instrument SEM (S-3400 N, Hitachi, Japan), the bonding tensile test was carried out with XLW (EC) intelligent electronic tensile testing machine, and the effect of polymer on mortar was studied with EDS. The test fixture mold is shown in Figure1. The forming mold is shown in Figure 2.Figure 1
Test fixture die.Figure 2
Forming die.Figure3 shows the effect of different polymer contents on the flexural and compressive strength of the bonded mortar.Figure 3
Effect of polymer content on flexural and compressive strength of bonded mortar.As shown in Figure3, adding different polymer materials to the mortar will affect the flexural and compressive strength of the mortar. At the same time, the flexural and compressive strength of the mortar decreased when polymers were added to the mortar. When adding polymer to the mortar, the flexural strength will also be improved, but the compressive capacity was still reduced. In this case, the polymer was mainly in the mortar, and the polymer formed a network film in the concrete, which can disperse the stress in the concrete and control the generation and diffusion of cracks [25, 26].In ordinary cement mortar, the ratio of compressive strength to flexural strength will not fluctuate too much, usually the compression-folding ratio is 3. However, after adding fiber-polymer material, the ratio of compressive strength to bending strength is shown in Figure4.Figure 4
Indentation ratio.As can be seen from Figure4, when the polymer was added to the ordinary mortar, the compression-folding ratio fluctuated around 4.2. When polymer was added to the viscous mortar, the indentation ratio gradually decreased, and the decrease was relatively fast. With the addition of more polymer content, the increase followed. It also showed that the viscous mortar has strong toughness.Through six experiments, it can be known that shrinkage rate = (mold size − plastic size)/mold size × 100%. The shrinkage rate of ordinary mortar is 0.068%, and the shrinkage rate of viscous mortar added with polymer is 0.035%, and the shrinkage rate was reduced by 49.7%. The comparison chart of shrinkage rate is shown in Figure5 and the shrinkage rate of ordinary mortar increased with the increase in curing time. On 28 d, the maximum value was reached. After adding the polymer to the mortar, the shrinkage rate decreased significantly, and in some cases, the shrinkage rate may also increase. After adding the polymer, the gap ratio in the mortar was reduced due to the polymer, and the density was increased. At the same time, the polymer formed an adsorption film, which reduces the loss of water and prevents carbonization and drying in the mortar, thereby reducing the shrinkage of the mortar.Figure 5
Shrinkage comparison.Comparing the performance of the viscous mortar after adding the polymer, the shrinkage rate and the compression ratio are not enough. The experiment was also compared in terms of frost resistance, water absorption, and bond tensile strength. It is more explanatory through the comparison and verification of various properties of the mortar. In terms of frost resistance, through the above freezing and heating cycles, the two microscopic characteristics observed by the instrument are shown in Table1.Table 1
Freeze resistance of mortar.
The specimen namesFreezing heat testCompressive strengthStrength reduction/%Mass loss/%Cycle temperatureTime (h)BeforeAfterOrdinary mortar−19°C 24 h/27°C634.7533.216.51.35Mortar with polymer-added−19°C 24 h/27°C629.4535.24−17.50.33It can be seen from Table1 that after adding the polymer, the frost resistance of the mortar was improved, and the mass loss of the mortar and the strength of the mortar were effectively reduced. The quality of ordinary mortar decreased by 1.35%, the quality of mortar with polymer decreased by 0.33%, the strength of ordinary mortar decreased by 6.5%, and the strength of mortar with polymer also increased by 17.5%. The resistance of the polymer-added mortar was enhanced by the cycle of freezing and heating. This is mainly because of the chemical properties involved, the polymer was in the mixture, hydrated in the concrete to form a film, and the film was tightly wrapped by the hydration particles. When the sample was at low temperature, the free water in the film and concrete formed ice cubes, caused internal damage and release of hydrated particles. During the heating process of the sample, the hydrated particles continued to react with water, and the cycle continued until the end of the experiment. Because the polymer film can act as a moisture barrier, the hydration progress of the polymer-added mortar was also relatively slow. The calcium ion concentration in the concrete decreased, the crystallization progress of the silicate ion in the concrete will be slower, and it was easy to form large crystals. And there may be a small amount of grain boundaries, so it will not be weaker than ordinary mortar in terms of strength. From another point of view, when the progress was relatively slow, the formed crystallization was also likely to cause the structure to be relatively loose, and the strength of the sample will also decrease.The water absorption of mortar is also an important factor in the performance of mortar. Water absorption affects the compressive strength, tensile bond strength, consistency, and delamination of cubes. The greater the water content in the mortar, that is, the ratio of water to ash, the less strength of the resulting concrete and the less the tensile bond strength. If the moisture content is less, the compressive strength of the concrete will also increase, and the tensile bond strength will also increase, but this is only a theory, and many factors need to be considered, such as the density of the concrete, the storage time, and the water retention. The water absorption of both is shown in Figure6.Figure 6
Water absorption comparison.As can be seen in Figure6, the water absorption of ordinary mortar was higher than that of polymer viscous mortar. The compressive strength of such concrete will also be greatly reduced. With the change in the amount of added polymer, the water absorption decreased somewhat, but the water absorption of the viscous mortar decreased more rapidly. Compared with ordinary mortar, the water absorption rate of polymer viscous mortar was reduced by 10%, mainly because the pores in the viscous mortar were blocked when the amount of polymer increased, which affected the water absorption of the mortar, resulting in a relatively large decrease in water absorption. The gap in ordinary mortar is relatively large, and although the polymer has some effects, it was not obvious. The polymer can reduce the pore size in the mortar, and for the water absorption of the mortar, the more polymer added, the lower the water absorption will be. But do not exceed the cement mixing ratio specified in the concrete.Bond tensile strength refers to the maximum stress a material can withstand before being stretched. By clamping the sample, the longitudinal axis of the sample and the center of the clamp were coincident, and the tightness of the clamp was suitable. Tensile strength = Tensile force/sample thickness and width. By testing the tensile strength of the two, the test results are shown in Figure7.Figure 7
Tensile strength comparison.It can be seen from the comparison chart that after adding polymer materials, the tensile strength of mortar was higher than that of ordinary cement. With the increase of placement time, the polymer in the mortar was directly penetrated into the mortar because the polymer diffused in the concrete, and became the connection structure of cement and ash, which enhanced the tensile strength. And the polymer achieved a global connection during the hydration process, which increased its strength. At 7 d, after adding polymer material, its tensile strength was 3.8 times higher than that of ordinary mortar, and at 28 d, it was 5.2 times.Through experimental comparison, it was found that the polymer can enhance the properties of the mortar and make the concrete have a strong bonding effect. When the polymer was added to the viscous mortar, the cement gradually hydrated and absorbed the polymer. The polymer was dehydrated in the concrete to form polymer particles, which gradually combined with the particles in the concrete to form a network film, which is attached to the cement hydration product; or a cross-wound structure was formed in the cement, which strengthened the connection between the cements. During the cement mixing process, the viscosity between the material and the cement was also improved, thereby having enhanced the tensile strength of the mortar. In the process of cement hydration, the polymer was mainly distributed in the gaps in the mud. In the process of cement hydration, the cement absorbed polymer particles and combined them, so that the particles were closely connected, and a polymer layer was gradually formed inside the concrete. The network structure of the polymer can fill the gaps between the cements and greatly enhance the resistance to damage. The stress in the cement can be dispersed, and the mesh structure can reduce the gap ratio in the mud, improve the permeability and frost resistance of the mortar, and reduce water penetration and water absorption.


## 5. Conclusion

In this article, by analyzing the properties of mortar using polymers, the flexural and compressive strength, tensile strength, water absorption, shrinkage, and frost resistance of mortar were compared. Through the introduction of the reasons for the easy damage of ordinary concrete and the method of repair, the improvement plan for the mortar was drawn. Through experiments, the performance of ordinary mortar and adhesive mortar added with polymer were compared. The results showed that the strength in compression and bending has been greatly improved. Through the comparison of the compression ratio of the two, it was known that the bonded mortar with the addition of polymer had more toughness, the shrinkage rate and water absorption were greatly reduced, and the frost resistance performance and the adaptability to temperature were also enhanced. The overall tensile strength of concrete was also multiplied. The article also put forward the influencing factors that affected the mortar and the corresponding improvement methods. However, the disadvantage is that when the samples were subjected to freezing and heating cycles, when the amount of polymer had been increasing, the comparison results need to be further verified. In this article, it was mainly concluded that by adding polymer, the performance of bonding mortar can be greatly improved, which has practical reference significance for construction engineering.



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*Source: 7663729-2022-09-02.xml*