The chapter delves into the improvement of thermal shock resistance in epoxy resin coatings for industrial floors, which are often damaged by thermal loads. Numerical simulations using Abaqus software are employed to analyze heat flow and stress generation in floor structures composed of epoxy resin coating and concrete substrate. The simulations reveal that the use of recycled fine aggregate can significantly reduce thermal expansion and stress in the interphase zone between the coating and substrate. The chapter compares different coating types, including pure epoxy resin, specially homogenous, and functionally graded materials, highlighting the advantages and disadvantages of each. The results show that functionally graded materials (FGM) can effectively reduce thermal gradients and enhance durability, while specially homogenous coatings can improve abrasion resistance. The chapter concludes by emphasizing the importance of proper aggregate design to achieve optimal thermal shock resistance.
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Abstract
The floors made of epoxy resin coating that are exposed to the thermal loads are usually not durable enough to be used in industrial facilities. To enhance thermal properties of the coating recycled fine aggregate was used to reduce thermal expansions in the interphase zone in between the coating and substrate. Three different types of coating were analyzed: pure epoxy, specially homogenous, and functionally graded material. The top floor was loaded with temperature to obtain heat flux and strain results. Finite element method was used to simulate the heat transfer and heat load. Simulations show that sedimentation of the aggregate reduces heat flow to the substrate during loading. It means that properly designed aggregate can improve durability of the industrial floor which can be more resistance to thermal gradient.
1 Introduction
The industrial floors are often exposed to the forklifts loads. The damage of the floor is usually caused by mechanical and dynamic loads [1]. However, thermal load can also damage floor structure [2]. All kind of floors can be damaged by temperature gradient [3], but the polymer coatings are one of the most sensitive [4]. The thermal durability of polymer coatings depends on thermal expansion and conductivity. Therefore, in this work authors present numerical simulation of heat flow in floor structure made of epoxy resin coating and concrete substrate. The simulation helps to analyze impact of the temperature growth on the interphase zone where the crack can be occurred during thermal loading [5]. The thermal load is simulated as a temperature growth in the place of spinning wheel of the forklift [6]. To change thermal expansion properties of the coating the epoxy resin is modified with recycled fine aggregate sourced from old concrete [7]. Various size of the filler is used to obtain different structure of the polymer composite: specially homogenous, and functionally graded material. The numerical simulations are carried out in Abaqus software. The results show that the aggregate reduces thermal expansion in the interphase zone in between the coating and substrate.
2 Materials and Methods
2.1 Materials
The composite structure is designed with a 3 mm coating layer and a 97 mm concrete substrate, 100 mm in total. Three coating types were selected for the simulation. First coating type is pure epoxy resin (ER) Sto IHS BV made of component (A) bisphenol and component (B) hardener, where A:B is 100:33. Second coating type contains IHS BV epoxy resin and recycled fine aggregate which does not sediment in liquid epoxy resin matrix. The hardened composite creates specially homogenous (SH) coating. Third and last coating type is made of recycled fine aggregate which sediments in epoxy resin matrix during curing time. The sedimentation of the aggregate depends on curing temperature, curing time, viscosity and density of the epoxy resin, A:B ratio, density, roughness and diameter of the aggregate. In this particular case authors change aggrege size to create different type of the coatings. Sedimentation of the aggregate in third type of the coating creates pure layer of the epoxy resin in upper part of the coating. The structure of the middle coating contains light and small particles (graded material – 1). The lower part of the coating is made of the aggregate with the greatest size (graded material – 2). Above described layers create functionally graded material (FGM) coating that is presented in Fig. 1c.
Fig. 1.
The materials used in FEM simulations: a) pure epoxy resin (ER) coating; b) specially homogenous (SH) coating; c) functionally graded material (FGM) coating.
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The substrate is designed of concrete C25/30. The properties of materials are summarized in Table 1. Material properties.. In simulation temperature depended properties are used. Because of lack of space in Table 1. Material properties. Are presented only properties in room temperature 20℃. In FEM model all properties are in range between 20 and 120℃.
Table 1.
Material properties.
Property
Concrete
ER
SH
FGM
Graded mat. 1
Graded mat. 2
Density [kg/m3]
2100
1080
1437
1488
1947
Thermal conductivity [W/(mK)]
1.333
0.188
0.467
0.585
0.704
Thermal expansion [10–6 1/K]
11.00
26.49
21.07
20.29
13.32
Heat capacity [J/(kgk)]
900
1270
1141
1122
956
Young's modulus [MPa]
31000
1500
2000
2100
2500
Poisson's ratio [-]
0.20
0.32
0.27
0.28
0.22
2.2 FEM Simulation
The FEM simulation is carried out in Abaqus 2017. The composite size is 100x100 mm. The coating is divided into 3 equal horizontal stripes with 1 mm thickness. The displacement in y and x direction is fixed at the bottom and right edge, respectively (Fig. 2a). The initial temperature 20℃ is applied to the whole model. The temperature load is applied to the 25 mm long top-left edge. The radiation of the top-right edge is designed with emissivity of 0.7.
Fig. 2.
The FEM model: a) highlighted load and boundary conditions; b) mesh size.
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To obtain heat flux and displacement results two simulations are necessary to be created. The first simulation is heat transfer which gives heat flux results. Second model is created in static mode with thermal load imported from the results of the first model. All models are created as axisymmetric. As a result the model can be presented as a cylinder using symmetry axis on the vertical right edge.
2.3 Temperature Load
The electrical heater SKU: HA502AC (2000W) is used to obtain thermal load amplitude. The heater is installed 10 cm above the floor surface with heating temperature T = 200℃, and fan speed 2/5. The temperature data is collected with temperature recorder TERMIO 31 (±0,6 ℃) and 30 cm STK probe (with range up to 800℃). The end of the probe is installed in the center of heating area 3 mm above the floor surface. The collected data is presented in Fig. 3.
Fig. 3.
The temperature load over time applied to the top surface of the composite.
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3 Results and Discussion
First simulation contains heat flux for whole composite. The results are presented in Fig. 4. It can be seen that the ER coating with low thermal conductivity is slowing down heat flux. As a result, the temperature of the concrete does not increase a lot. It means that high temperature difference occurs in this model. Great temperature difference can affect thermal expansion and generates stress. Nevertheless, the other models present dipper heat propagation, except for the right side of the model where that the surface lose heat by radiation.
Fig. 4.
The results of heat flux after 60 s of heating: a) pure epoxy resin (ER) coating; b) specially homogenous (SH) coating; c) functionally graded material (FGM) coating; d) 3D view of composite with ER coating.
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From Fig. 4 it can be seen that there are two areas where the results differ. Close to the symmetry and to the edge of load. In these areas two paths (Fig. 5) are created: center path (black line), and load edge path (magenta line).
Fig. 5.
The description of paths used during results generation – path no. 1 - center (black line); path no. 2 - load edge (magenta).
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Figure 6 presents nodes temperature over the height of the model. The radiation influence on heat loss at the load edge is highly visible. The temperature at the load edge is lower than in the center up to 30℃, depending on the coating. The grates temperature difference between top coating surface and concrete boundary has composite with ER coating (around 50℃). The coating with SH seems to have the lowest temperature difference between those surfaces. However, the important areas are between 3rd layer and concrete where thermal expansion of different material can generate the stress. For this particular case FGM has the lowest thermal gradient.
Fig. 6.
The heat flux results for two paths (center and load edge) and different coatings (ER, SH, and FGM). The vertical blue lines represent boundaries between the layers.
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Figure 7 shows magnitude displacement of all models. Great thermal expansion of epoxy resin cab be observed in Fig. 7a. Two other models have similar total displacement. It is because these two coatings were designed to contain the same volume value of aggregate. By having the same amount of epoxy resin matrix the behave of these two coatings should be similar in some cases.
To understand how the displacement affects models it is important to calculate the average strain between the layers ∆εi using Eq. 1. Where εavg is average strain in upper (j) and lower (k) layer.
The magnitude displacement of: a) pure epoxy resin (ER) coating; b) specially homogenous (SH) coating; c) functionally graded material (FGM) coating.
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Figure 8 presents the strain difference between the layers in the load edge area where strain value is high in x direction. Each great value in the chart means that there is a high chance of stress generation. However, the difference between coating layers is not the most important. Because those layers have similar properties. Moreover, the temperature of the top layer can exceed glass transition temperature. It can make the material softer and more vulnerable. The most important in the case of durability should be analyzed the strain difference between 3rd layer and concrete substrate. It is visible that FGM coating obtains the lowest value of ∆εi.
Fig. 8.
The strain difference ∆ε between the layers along load edge path.
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4 Conclusions
This work is focused on improvement of the thermal shock resistance of epoxy resin coating using sedimented recycled fine aggregate. Based on the performed analysis and simulations it can be stated that modification of the epoxy resin coating with recycled fine aggregate can improve the thermal shock by reducing thermal expansion in near-substrate area. However, to obtain such an improvement it is important to properly designed size of the aggregate to obtain pure epoxy resin layer at the top of the coating. This pure layer slows down heat flux into the composite and aggregates at the bottom reduce the thermal expansion. Nonetheless, FGM has almost the same abrasion resistance comparing to ER. Pure epoxy resin occurs in the top layer in both types of coating. The only composite that can enhance its abrasion resistance is SH because of filler particles that are allocated in near-surface area. Each coating type has different assets which should be taken into account during design process.
Acknowledgements
The authors received funding from the project supported by the National Centre of Science, Poland [Grant No. 2019/35/O/ST8/01546].
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