Developing a Novel Structural Brick by Combining Polyurethane and Composite Fibers

doi:10.21203/rs.3.rs-5023177/v1

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Developing a Novel Structural Brick by Combining Polyurethane and Composite Fibers

https://doi.org/10.21203/rs.3.rs-5023177/v1

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Composite materials, with their remarkable performance attributes, have emerged as pivotal components to increase energy efficiency. This work explores the utilization of polyurethane (PU) matrix composite materials as structural elements, with a focus on enhancing mechanical properties through fiber reinforcement. This research aims to investigate and develop lightweight structural materials designed to bear less load during earthquakes instead of conventional brick and reinforced concrete building systems. This study employs a systematic experimental approach, including the Taguchi experimental design methodology, to investigate the effects of glass, carbon, and basalt fibers on PU strength.

The results provide insights into the mechanical behavior of fiber-reinforced PU composites, highlighting the factors influencing their compressive and bending strengths. In the compression tests, the glass fiber-reinforced PU samples presented the highest compressive strength of 2460.15 ± 326.2 N, closely followed by the basalt fiber-reinforced samples at 2490.21 ± 210.2 N. In contrast, the carbon fiber-reinforced samples presented a lower strength of 2055.05 ± 74.6 N. Similarly, in the bending tests, the glass fiber-reinforced samples presented superior performance, with a peak force of 108.25 ± 16.9 N, compared to that of the carbon fiber-reinforced samples at 62.45 ± 4.1 N.

Further analyses utilizing ANOVA and S/N ratio assessments elucidate the impact of varying parameters on material properties, emphasizing the role of the fiber dimension and material type. This study highlights the potential of glass fiber reinforcement for optimizing mechanical performance, whereas carbon fibers present challenges in maintaining structural integrity during casting. Analytical investigations through finite element modeling (FEM) provide additional insights into the behavior of glass fiber composites under compression and bending loads. The simulation results demonstrate the potential of glass fiber clusters to increase rigidity and reduce displacement in PU matrices.

Overall, this study contributes to advancing the understanding of the mechanical properties of fiber-reinforced PU composites, offering valuable insights for optimizing material selection and fabrication processes in pursuit of energy-efficient structural solutions.

Civil Engineering

Polyurethane

composite

fiber

structural earthquake performance

retrofitting

Composite materials are preferred in systems that achieve energy efficiency because of their superior performance characteristics. They allow for the design and production of products or systems much lighter than conventional materials while providing the same level of strength. Composites, which have been chosen to increase energy efficiency in systems such as aircraft, spacecraft, marine vehicles, and automobiles, have also begun to be used in construction.

A composite structure consists of two main materials: a matrix material that holds the structure together and a fiber material that primarily carries the load in the composite structure. In fact, in construction, both concrete and load-bearing columns can be considered separate composite structures. While concrete forms the matrix material, gravel stones, although not precisely fiber materials, are particle-shaped and resemble the role of fibers. Conversely, columns are a direct example of a composite structure, where concrete serves as the matrix material, and steel rods act as the fibers.

In particular, on floors, steel bars and concrete materials impose a significant load on the structure. Although they do not have load-bearing duties as significant as columns do, their mass results in a high weight. Applying a material with a lower mass density instead of concrete, which serves as the matrix material here, significantly reduces the weight. Additionally, the low thermal permeability of this material provides energy efficiency without additional insulation. The relatively soft nature of the material will also improve comfort in ground movements.

In recent years, research on the use of nanostructures within PU matrices has become a commonly studied topic [1], [2], [3]. Studies have shown that improvements in mechanical properties can be achieved in fiber-reinforced composite structures created from a polyurethane matrix material. In comparative studies between PU composites using bamboo fiber fillers and oriented strand boards (OSBs), PU composites with bamboo fibers have been shown to exhibit improvements in their mechanical properties, impact resistance, and bending strength compared with OSB-type boards [4].

In addition, studies related to recycling have shown that PU-based materials, which are in a residual state after processing, can be transformed into a usable form. For this purpose, the two fundamental methods used are glycolysis and regrinding systems. PU recycling through these methods offers significant benefits in terms of energy and cost, and the products obtained after recycling can provide the desired mechanical performance at desired intervals [5].

In the context of this project, similar research has been conducted on PU matrix composite materials. Studies in this field have explored the effects of chemical differences in PU-based materials on mechanical properties, surface silanization effects in carbon fiber-reinforced PU composites, and the production of PU composites with low thermal permeability and high compressive strength, among other topics. These studies can be found in the literature, and scientific research in this area is ongoing [6], [7], [8].

Cakir reported that polymer mortar produced with chopped glass and basalt fibers significantly altered the mechanical properties and failure modes of the material [9]. Manalo examined the structural behavior of a prefabricated wall system made from glass fiber-reinforced polyurethane foam and magnesium oxide plates. After preparing the full-scale wall samples, they underwent bending, compression, and shear tests [10]. Öteyaka et al. used a polyurethane nanofiber mat produced via the electrospinning method as an additional filler material in glass fiber and carbon fiber polymer composites. The experimental results revealed that the composite with additives had at least 30% greater tensile strength than those without additives [11].

Kosari et al. reported that the tensile strength increased significantly when polyurethane nanocomposites were reinforced with carbon and glass fibers [12]. Cheng et al. experimentally investigated the behavior and fundamental characteristics of shape memory polyurethane composites reinforced with carbon fibers and reported an improvement in the mechanical properties of carbon fibers [13]. Hülsbusch et al. developed a methodology for in situ computed tomography and applied it to glass fiber-reinforced polyurethane [14]. Zhao et al. examined the mechanical properties of glass fibers, nylon 66 fibers, and carbon fiber-reinforced polyurethane foam. According to previous studies, the tensile strength reached its optimal level when the SiO2 and glass fiber contents were 20% and 7.8%, respectively [15].

Our study aims to use composite materials produced with a PU matrix as a structural material. PU-based materials may have a wide range of applications. Owing to their chemical structures, PU-based materials can be used to produce structures with different physical properties. They can provide properties ranging from the hardness and rigidity of metallic materials to the elasticity of rubber-like structures. A wide range of structural properties can be achieved by altering the characteristics of PU materials, making them suitable for various applications. They serve as driving forces in various fields, such as adhesives, coatings, sealing products, elastomers, foam products, textile products, and the automotive and maritime industries. In recent years, they have also found applications in biomedical products. PU materials can produce different types of products with diverse material properties via a wide range of polyol and isocyanate combinations.

Polyurethanes are polymers that hold a significant place in polymer chemistry and have many applications. They exhibit diverse production methods, properties, and areas of use. Polyurethanes are a polymer group formed by the reaction of isocyanate groups with polyols (compounds containing alcohol groups). This reaction results in the formation of long-chain polymer structures. Polyurethanes produce a wide range of products, including rigid and elastic materials, foams, adhesives, coatings, and various industrial applications. Polyurethanes are typically produced by reacting two main components (isocyanate and polyol) in specific ratios and under specific conditions. This reaction can be modified to obtain various types of products. Production processes include casting, injection molding, mold foaming, continuous panel production, and reactive extrusion, among others.

The properties of polyurethanes can vary significantly depending on the type of polyols and isocyanates used. In general, polyurethanes can exhibit good mechanical strength, chemical resistance, elasticity, high load-bearing capacity, and surface hardness. These properties determine how the material will be used in specific applications. Owing to their wide range of applications and customizable characteristics, polyurethanes are important polymers commonly used in industrial and commercial fields.

This study aimed to investigate the effect of fiber reinforcement materials on the strength of polyurethane. Glass fibers, carbon fibers, and basalt were selected as the fiber reinforcement materials. Fiber materials were mixed in different ratios by weight and were of different sizes. The determined weight ratios, fiber sizes, and material types are given in Table 1.

Table 1

The parameters and level values employed in the experimental design
	Level
Factor	Code	1	2	3	Unit
Material	P1	Glass	Carbon	Bazalt
Weight Percentage	P2	1	3	5	%
Fiber Dimension	P3	3	6	12	mm

The three parameters to be investigated are tested for three different levels. To reduce the number of experiments, the L9 TAGUCHI experimental design method was applied (Table 2). Each experiment was repeated three times to measure the repeatability and reveal random errors.

Table 2

Design of the experiment with the L9 Taguchi orthogonal array for the compression and 3-point bending tests.
Run number	Material	Level Number	Weight % (gr)	Level Number	Fiber Dimension (mm)	Level Number
1	Glass	1	3	1	3	1
2	Glass	1	5	2	6	2
3	Glass	1	1	3	12	3
4	Carbon	2	3	1	6	1
5	Carbon	2	5	2	12	2
6	Carbon	2	1	3	3	3
7	Bazalt	3	3	1	12	3
8	Bazalt	3	5	2	3	1
9	Bazalt	3	1	3	6	2

Steel molds with dimensions of 60*15*15 cm were used to produce fiber-reinforced polyurethane samples. Before the process, a release agent was applied to the mold walls to prevent adhesion. After the prepared polyurethane material and fiber were poured into the mold, they were mixed for 30 seconds to obtain a homogeneous structure. When the polyurethane expansion reached half the volume of the mold, the mold was closed and supported with a hydraulic press. The mold was left for one day for solidification. This process was repeated for all the scenarios in the experimental design.

The demolded block was saw-cut to obtain samples for compression and flexure tests. Some parts of the blocks produced were damaged during expansion. Sample cuttings were made from relatively medium and undamaged sections of the blocks. The dimensions of the samples used in the compression and 3-point bending tests are given in Fig. 1. The ASTM 1 (ASTM D 1621-10) standard was applied for the compression test, and the ASTM 2 (ASTM D 790-03) standard was applied for the flexure test. The compression test speed was determined to be 5 mm/min. The test was continued until there was a 10% change in the original size of the material. In the 3-point bending test, the crosshead speed was determined to be 2.5 mm/min. The tests were continued until the samples were broken or 3 mm of damage occurred.

There are nine species shown in Fig. 2. Polyurethane was combined with carbon, glass, and basalt fibers in specific amounts to make these samples.

After the test samples were prepared, ASTM standards were used to carry out compression and bending tests. Figure 3 shows the test setup and results.

To reveal the mechanical properties of the samples manufactured according to the test matrix, compression and three-point bending tests were carried out with a tensile testing machine equipped with a 30 kN load cell. For the strength forces used in the statistical analysis of the test results, the values at the moment when 5 mm deformation is reached in the compression tests and at the moment when 3 mm deformation is reached in the bending tests are taken as the basis. The results of these tests allowed us to gain a deeper understanding of the mechanical properties and durability of the material. Each test was repeated at least 3 times to minimize the effect of random error. The results were analyzed via the average of the test results. According to the results obtained, the highest compressive strength was 0.996 ± 0.084 MPa for specimen number 7. The second highest value was 0.984 ± 0.013 MPa for specimen number 3. When analyzed according to the standard deviation values, it can be said that both samples have very similar compressive strengths. According to the experimental design parameters, the common parameter of the two tests is a fiber length of 12 mm. Although specimen 5 also has a fiber length of 12 mm, its strength is 35% lower than that of specimens 3 and 7. This suggests that other fiber parameters in addition to fiber length are also effective.

Table 3

Results of the compression and 3-point bending tests.
Run number	Material	Weight %	Fiber Dimension	Compression	3-point
Run number	Material	Weight %	Fiber Dimension	F @5 mm, N (± SDV)	F @3 mm, N (± SDV)
1	Glass	3	3	1803.01 ± 20.5	80.85 ± 4.6
2	Glass	5	6	2089.25 ± 13.6	104.95 ± 3.4
3	Glass	1	12	2460.15 ± 326.2	108.25 ± 16.9
4	Carbon	3	6	858.95 ± 42.1	62.45 ± 4.1
5	Carbon	5	12	1589.35 ± 18.5	102.71 ± 14.2
6	Carbon	1	3	2055.05 ± 74.6	62.45 ± 4.1
7	Bazalt	3	12	2490.21 ± 210.2	120.62 ± 0.3
8	Bazalt	5	3	1218.85 ± 54.4	67.75 ± 7.8
9	Bazalt	1	6	1558.85 ± 18.9	80.03 ± 8.9

As the length of the fiber reinforcement increases, the strength of the sample is expected to increase. However, this was not the case for the carbon fiber samples. Basalt and glass fibers are structurally harder. The glass fibers and basalt used in the experiments retained their flat shape and formed a mixture. At the same time, the threads did not separate. However, when carbon fibers were used, the reinforcement material dispersed during mixing and formed a complex shape. The situation is shown in the right-hand picture in Fig. 2. This deformation and disorganization may be the reason for the lower compressive strength than that of the basalt and glass fiber samples. Statistical analysis methods are used in the next section to reveal the relevant situation.

3.1. Design of experiment (DOE) analysis

The S/N ratio is a measure that reflects how much irregularity or random variation (noise) the output of a process or system has relative to the desired signal (signal). S/N ratios for the mechanical properties of the samples were generated via Minitab software. Three S/N ratios are considered: smaller is better, larger is better, and nominal is better. In accordance with the study's objective to increase the compressive strength, the characteristic of "larger is better" was chosen, employing Eq. (1).

S/N = -10 * log10(1 / n * Σ(1/Yi^2)) (1)

where:

n is the number of samples.

Yi represents the output value for each sample.

Under the assumption that "bigger is better," this formula is used to determine how close or far the output is from the desired goal. If the S/N ratio is higher, the output is closer to the target, which means that the performance is better.

To achieve the highest strength of the material in both compression and flexure tests, the parameter levels with the highest signal-to-noise ratios were selected from the S/N graphs. According to the results, glass fibers, 1% material weight, and the 12 mm fiber length yield the highest values. As shown in Fig. 4, the parameters with the greatest difference from the average value are the fiber size and material type. When the weight percentage of the reinforcing material is examined, the highest effect is 1%. Increasing the amount of material has no relative improvement effect. In terms of material type, carbon fibers have the worst performance, whereas basalt affects the average value. In terms of fiber size, 3 mm and 6 mm resulted in values that were below the average values. However, increasing the fiber size above these values considerably increased the strength.

The factorial plot for the standard deviations of the compression test results is given in Fig. 5. The highest signal difference was observed for the fiber dimension parameter. The average standard deviation is approximately 23 units for a 12 mm fiber size. The average standard deviations for 3 mm and 6 mm are 12 and 7 units, respectively. To control the fiber size to obtain the highest value of compressive strength, it is necessary to set the fiber size to 6 mm. However, since the fiber dimension is also the most influential parameter in the mean factorial plot (Fig. 4), the two cases should be considered together. The fiber size should be between 6 and 12 mm in this case. The material type has almost no effect on the standard deviation. Although the best value of the weight percentage parameter is 5%, its effect on the standard deviation is negligible and can be determined according to the mean plot. Thus, the result would be more consistent and optimized.

The main effects of the factorial plots for the 3-point bending test results are given in Fig. 6. All the variables have significant effects on the response. The most influential variable is the fiber dimension. The other two variables have nearly the same effect. As in the compression test, glass fibers showed the best performance as the material type. The increase in the percentage of reinforcing material contributes linearly to the increase in flexural resistance. Accordingly, increasing the amount of supporting material increases the resistance to bending. A similar situation is also observed for the fiber size. As the fiber length increases, the strength of the sample increases. When the compression and flexure tests are compared, the amount of reinforcing material varies. Although it shows a relatively low performance in the compression test, the increase in the material in the flexure test has a positive effect on the strength. The material type had the same effect in both tests. The glass fibers had the best performance, whereas the strength of the carbon fibers was the lowest. This is thought to be due to the dispersion and bending of the carbon fibers during the casting process.

An analysis of variance (ANOVA) was conducted via Minitab software to examine the relationships between the parameters and their contributions to the outputs. As shown in Table 4, the contributions of the variables are observed in the same order in both test results. The highest contributions for the compression and flexure tests were 52.7% and 54.46%, respectively, for the fiber dimensions. The lowest contribution for both tests was the weight ratio of the reinforcing material. A p value less than 0.05 (statistically significant) was not found. However, the fiber dimension, which is the most influential factor in both tests, is the parameter closest to statistical significance.

Table 4

ANOVA results for the compression and flexural tests.
Test Type	Source	DF	Seq SS	Contribution	Adj SS	Adj MS	F Value	P Value
Compression	Material	2	896225	33.00%	896225	448113	2.92	0.255
	% Weight	2	81530	3.00%	81530	40765	0.27	0.79
	Fiber Dimension	2	1431337	52.7%	1431337	715668	4.67	0.176
	Error	2	306688	11.29%	306688	153344
	Total	8	2715780	100.00%
Flexural	Material	2	435.2	15.72%	435.2	217.6	0.86	0.539
	% Weight	2	316.8	11.44%	316.8	158.4	0.62	0.616
	Fiber Dimension	2	1507.9	54.46%	1507.9	754	2.96	0.252
	Error	2	508.8	18.38%	508.8	254.4
	Total	8	2768.7	100.00%

Table 5
Test Type	S	R-sq	R-sq(adj)	PRESS	R-sq(pred)	AICc	BIC
Compresison	391.592	88.71%	54.83%	6210432	0	*	137.05
Flexural	15.9497	81.62%	26.50%	10302.9	0	*	79.43

3.2. Finite Element Analysis

Analytical studies were carried out by preparing finite element models of the test samples via Ansys software to examine the effects of additive materials. The test samples were modeled as clustered fiber prisms inside polyurethane matrices. The material properties of the matrix and the fibers are given in Table 6.

Table 6

The parameters and level values employed in the experimental design
Material Type	Young’s Modulus (GPa)	Poisson’s Ratio	Density (kg/m³)
Polyurethane	0.01	0.4	120
Glass Fiber	95	0.22	1857
Carbon Fiber	240	0.26	1750
Basalt Fiber	90	0.3	2800

Figure 7 shows the assembly of the composite models. Ansys software allows the user to model the differential composite elements with the appropriate weight and volume fraction values for the additive materials.

In the mesh models, the nodes of the small cubic elements and the matrix material are bonded together. New anisotropic material properties for the composite samples are determined after generating the mesh models, and new material data are assigned to the geometry for static structural finite element tests.

A compression test was performed on a cubic sample. Figures 8, 9, and 10 show the results of the displacement values after the material is compressed with a load of 2500 N from the top. The results show that the displacement values decrease with increasing weight fraction of the additive materials. With increasing weight percentage of the additive materials, it is possible to detect a decrease in the deformation values of the samples.

Figure 11 shows a comparison of the maximum deformation values of the additive material types. The weight percentage is an important factor, but the effect of increasing the Young’s modulus cannot be observed because of the low percentage of additives.

Bending tests were also performed on unadulterated polyurethane and basalt fiber composite samples.

Figure 12 shows the total deformation values of the samples. The displacement values decrease for the basalt fiber composite sample. The weight factor for the basalt fiber composite was determined to be 5%. This result is caused by the increasing rigidity of the models with increasing mass of the additive materials. The bending strength is increased by the addition of the composite additives, similar to the experimental tests.

The material weight consistently yields the best results, whereas increasing the amount does not substantially improve the results. Carbon fibers perform the worst, basalt moderately, and longer fibers (beyond 6 mm) greatly enhance the strength. Standard deviation analysis indicates that the fiber dimension has the greatest impact, with the optimal compressive strength ranging between 6 mm and 12 mm. The material type minimally affects the standard deviation, and the best reinforcing material weight percentage (5%) has a negligible effect on it.

In 3-point bending tests, the fiber dimension is most influential, with all the variables significantly affecting the response. Glass fibers perform best, and increasing the reinforcing material percentage linearly improves the flexural resistance. Longer fibers also correlate with stronger samples. Compared with the tests, the variation in the amount of reinforcing material used is notable: it has a minimal impact on the compression strength but a significant effect on the flexural strength. Glass fibers consistently perform best, and carbon fibers perform the worst, which is likely due to dispersion and bending issues during casting.

ANOVA confirmed that fiber dimensions contributed the most to both compression (52.7%) and flexure (54.46%) outcomes, with the reinforcing material weight ratio contributing the least. Although the p values are not statistically significant, the fiber dimension remains the most critical factor in optimizing the material strength. According to the finite element analysis, the mean value of the decrease in the maximum deformation is nearly 0.86% for the compression tests when the additive material weight percentage is increased from 1–5% and 7.69% for the bending tests between samples with no additive material and those with basalt fiber additives with 5% weight fractions.

Research and tests have revealed that newly discovered structural materials can be used in civil engineering. In addition to insulation, this material can also be used as a load-bearing element in the design of buildings. Advanced building materials with different combinations of density and fiber additives can be explored.

Compliance with ethical standards

This study was prepared in accordance with ethical standards.

Conflict of interest

All the authors declare that they have no conflicts of interest.

Funding

This work was funded by the Doğuş University Scientific Research Projects Coordination Unit under grant number 2021–22-D1-B04.

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The authors declare no competing interests.

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Developing a Novel Structural Brick by Combining Polyurethane and Composite Fibers

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Abstract

Figures

1. Introduction

2. Materials and Methods

3. Results

3.1. Design of experiment (DOE) analysis

3.2. Finite Element Analysis

4. Conclusions

Declarations

References

Additional Declarations

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