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Glass Fiber Concrete Additive: Alkali-Resistant Glass Fiber-Reinforced Concrete

By nature, concrete exhibits low tensile strength, brittleness, unstable crack propagation, low breaking strength, and inadequate ductility. These shortcomings are generally eliminated through conventional reinforcement or pre-strain applications in reinforced concrete structures without having improvement in the properties specific to concrete. Alternatively, it was found that strength and ductility of concrete are increased by including strong hard fibers in the concrete. Fibers are reasonably effective in reducing early plastic shrinkage cracks. Because addition of fibers increases material’s ductility after cracking. Thus, high strength and hardness of alkali-resistant glass fibers mean high potential for strengthening cement-based composites. In this article, we will talk about how to obtain suitable and durable concrete by using alkali-resistant glass fibers along with the desired changes in concrete properties.

Experimental Study

The current study analyzed the impact of alkali-resistant glass fibers  on the properties of wet concrete and the obtained results were presented as experimental results. Alkali-resistant glass fiber, which has physical and mechanic material properties as shown in Table 1 was used in this study together with Portland cement, fine and coarse aggregates.

  Table 1. Physical and Mechanic Properties of Alkali-Resistant Glass Fiber

Experiment Conditions

Cement, fine aggregate, coarse aggregate at ratios of 1: 1.59: 3.70 and water/cement at a ratio of 0.51 were used throughout the experiments. And fibers were added to the wet concrete and the mortar was thoroughly mixed again. 150 mm cubes for compressive and adhesive strength, cylinders with 300 mm length and 150 mm diameter for splitting tensile strength, 100 x 100 x 500 mm beams for flexural strength were joined using a range of 0 – 4.50% alkali resistant glass fiber and 0.5% cement in weight, and three samples were casted with fiber and three samples were casted without fiber for each test. A table vibrator was used to compress all samples in order to prevent fiber clustering. All samples were cured with water for 28 days at room temperature and tested on 1000 kN Universal Test Machine with a dry surface. In addition, a total of 150 samples were cast and tested in order to evaluate strength performance. Each value of the results presented in this study was given as the average of three test samples.

What Is Hardened Glass Fiber-Reinforced Concrete and What Are the Conducted Tests?

Hardened glass fiber-reinforced concrete is a concrete type with fiber reinforcement. It is also known as precast. Glass fiber-reinforced concretes consist of high strength and alkali-resistant glass fibers embedded in the concrete matrix. Alkali-resistant glass fiber-reinforced concrete’s workability is determined through slump cone test. A wet cylinder’s weight and volume are measured, and its pressed density is obtained with the help of standard cylinders. The results of these properties are presented in Table 2. Compressive, flexural, adhesive, and splitting tensile strengths are among the tests conducted on hardened glass fiber-reinforced concrete. A standard test procedure was followed according to the relevant standards for each test and strength performance of hardened glass fiber-reinforced concrete was examined. Workability is measured with a slump test.  

Table 2. Workability and Pressed Density of Normal Fresh Concrete and Hardened Glass Fiber-Reinforced Concrete

  • According to Table 2, workability is lower in hardened glass fiber-reinforced concrete compared to normal concrete with the increase in fiber content. Maximum reduction in slump is observed to be 44.44% with 4.5% fiber content. Wet unit density of hardened glass fiber-reinforced concrete increases with the increase in fiber content, however the increase is marginal.

Strengths Calculated in the Study

Various strengths were calculated during this study after damaged examination of normal and hardened glass fiber-reinforced concrete samples. Each test was conducted as three copies and the average of the results were recorded. Each strength value is the average of three test samples.

  • Compressive Strength: This was obtained by applying pressure on cubes of 150 mm using UTM. The results of compressive strength and the increase in the compressive strength of hardened glass fiber-reinforced concrete compared to normal concrete are presented in Tablo 3.

Table 3. Compressive Strength (MPa) of Normal Concrete and Hardened Glass Fiber-Reinforced Concrete

  • Compressive strength continuously increases with the increase in fiber content. Maximum increase in compressive strength was obtained as 28.46% with 4.5% fiber ratio. Increase in strength is in direct proportion to fiber content.
  • Flexural Strength: To determine this strength, each sample of 100 x 100 x 500 mm was supported on a 400 mm gap and a two-point load was applied on the middle one third of the gap. Central slumps were recorded until the first crack. All beams were loaded until they slumped.
  • Flexural strength increases up to 4% fiber content. Maximum increase in strength compared to normal concrete was obtained as 50.08% with 4% fiber content. Flexural strength decreases to 42% in the case of 4.5% fiber content.
  • Flexural Shear Strength: Shear strengths of flexural components were calculated using materials’ strength theory. The maximum shear strength equation is proposed based on; volume ratio of fiber, elastic module of matrix (concrete), elastic module of fiber and flexural strength obtained through four-point bend test. Proportional increases in strength and results of flexural strength and load-slump are given in Table 4.
  • Flexural Shear strength is found to change in direct proportion to flexural strength.

Table 4. Load-Slump, Flexural and Shear Strengths of Normal Concrete and Hardened Glass Fiber-Reinforced Concrete (MPa)

  • Splitting Tensile Strength: Cylinder splitting test was used to determine tensile strength of the concrete. Pressure line loads were applied in this test throughout a vertical symmetrical plane which causes the sample to split up and sets tensile plane to a normal level. During the study, formula derived using elasticity theory was used to calculate splitting tensile strength. The results obtained for splitting tensile strength are presented in Table 5.
  • Cylinder splitting tensile strength of the concrete increases with the increase in fiber content. Splitting tensile strength increases up to a maximum of 48.68% with 4.5% fiber content compared to normal concrete. Splitting tensile strength is found to change with the natural algorithm of hardened glass fiber-reinforced concrete’s compressive strength.

Table 5. Splitting Tensile and Bond Strengths of Normal Concrete and Hardened Glass Fiber-Reinforced Concrete (MPa)

  • Bond strength increased with the addition of glass fiber into the concrete and a maximum increase of 35% was observed compared to normal concrete up to 3.0% fiber content. However, it was found to rapidly decrease with higher fiber content, and it decreased down to 9.60% at 4.5% fiber content. This decrease in bond strength with the increase in fiber content may be due to clustering of fibers. This strength is found as a function of the natural logarithm of compressive strength.

What Is Poisson’s Ratio?

Poisson’s ratio is defined for a uniaxial state of stress as the lateral stress and axial stress ratio with a negative sign. If a stress load is applied on a material, material would stretch as shown in the left image found in Figure 1 in the direction of the applied load, i.e., perpendicular to the stress plane. And under compression force, the axial dimension would decrease as shown in the right image found in Figure 1. If the volume is constant, there should be a lateral contraction or expansion corresponding to the deformation. This lateral change shows a constant relation with the axial change. The relation of this axial-lateral deformation is referred to as Poisson’s ratio.

Figure 1. Axial-Lateral Deformation of the Material with Stress Load and Compression Force Applied

According to Neville, Poisson’s ratio (μ) is calculated as follows.

possions's-ratio

However, differences were obtained between the Poisson’s ratio calculated in this study and the values calculated using formula defined by Neville. Thus, a new Poisson’s ratio equation was created and used in the study to reach the correct results. It was found that Poisson’s ratio of hardened glass fiber-reinforced concrete ranges between 0.11 and 0.16 and it usually varies between the limits of 0.11 and 0.21.

Optimum Fiber Content

Optimum fiber content is the fiber content amount at which hardened glass fiber-reinforced concrete reaches maximum strength. Optimum fiber contents for various strengths are shown in Table 7.

  Table 7. Optimum Fiber Content and Maximum Increase Rates at Various Strengths

Test Results

  • The workability of wet glass fiber-reinforced concrete (GFRC) decreases with the increase in fiber content. The concrete’s pressed density increases with the increase in fiber content; however, the increase is marginal.
  • In 28 days, the increase in the percentages of cube compressive strength, flexural strength, splitting tensile strength and bond strength are 4.5%, 4.0%, 4.5% and 3% compared to normal concrete for fiber contents of 28.46, 50.08, 48.68 and 35.20, respectively.
  • Load-deflection behavior shows that glass fiber addition in concrete flexural member increases its load bearing capacity compared to normal concrete. This shows the increase in the concrete’s flexural strength and ductility with the addition of glass fiber.
  • Experimental statements were created based on cube compressive strength in order to find flexural strength, cylinder splitting tensile strength and bond strength of GFRC, and an empirical statement was proposed for flexural shear strength over flexural strength. Estimated results obtained from these statements perfectly match the theoretical and experimental results obtained in the study.
  • Elastic constants of GFRC are obtained through various methods. An empirical statement was developed for elasticity module over fiber volume ratio and GFRC’s cube compressive strength and Poisson’s ratio statement was created based on fiber volume ratio and fiber’s aspect ratio. The estimated values of Poisson’s ratio perfectly match with the method of Neville.
  • Generally, significant improvements were observed at various strengths with the addition of glass fibers into plain concrete. Also, the maximum gain in concrete strength (GFRC) was found to be dependent on fiber content’s amount. The optimum fiber content amount to be used to obtain maximum gain in strength depends on the strength type.

Result: What Is the Function of Glass Fiber Concrete Additive?

Alkali-resistant glass fiber-reinforced concrete is a material that contributes to economy, technology, and construction aesthetics across the world today. Because by nature, concrete exhibits low tensile strength, brittleness, unstable crack propagation, low breaking strength, and inadequate ductility. Thus, eliminating these properties enables us to have stronger structures. In this article, we talked about whether it is possible to obtain suitable and durable concrete by using alkali-resistant glass fibers. Adding hard fibers into the concrete has a positive impact on the concrete strength and ductility is among the key results of this study. The findings of this study showed that high strength and hardness of alkali-resistant glass fibers have high potential for strengthening cement-based composites.

References:

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