Investigating the effect of pozzolanic fibers and materials on the mechanical properties of concrete reinforced with glass fibers

The effect of fiber and pozzolanic materials on the mechanical properties of glass fiber reinforced concrete. With increasing loading, microcracks are connected and form cracks. In order to solve this problem and also to create homogeneous conditions, in the last few decades, a series of thin strands that are spread throughout the volume of concrete are used; which are called fibers. One of the most widely used fibers used in concrete is glass fiber. Concrete reinforced with glass fibers, composite materials include a mortar of hydraulic cement and fine aggregates that are reinforced with glass fibers. The use of glass fibers in concrete improves the properties of concrete, which include increasing tensile strength, increasing bending strength, improving impact resistance, increasing the amount of energy absorption, improving the behavior of concrete in a non-linear area and high ductility. Since the properties of concrete reinforced with glass fibers are directly related to the conditions of glass fibers used on the concrete surface, issues related to the performance of glass fibers over time have always been of interest to researchers. Factors such as the alkaline environment of concrete and the products produced due to the cement hydration process cause changes in the mechanical properties of concrete reinforced with glass fibers over time with the destruction of glass fibers. In this research, in order to reduce the effects caused by the alkaline environment of concrete, glass fibers resistant to alkaline environment and to prevent the destructive effect of the cement hydration process, pozzolanic materials with different percentages have been used. In order to investigate the compressive strength, flexural strength and strength indices of concrete produced by premix and spray methods, 15 mixing designs containing different percentages of glass fibers and pozzolanic materials (microsilica, metakaolin and nanosilica) in premix method and 14 mixing designs in spray method have been tested. From the obtained results, it can be concluded that the compressive strength of concrete reinforced with glass fibers largely depends on the quality of the mortar. Based on this, it can be seen that adding glass fibers reduces the compressive strength of concrete. According to these results, the decrease in compressive strength of glass fiber reinforced samples is minimized in the presence of pozzolanic materials. In this condition, the compressive strength of some samples armed with glass fibers and containing pozzolanic materials has increased compared to the control samples. According to the obtained results, reinforcing concrete with glass fibers significantly increases the modulus of rupture. The modulus of rupture first goes up and then goes down with the increase in the amount of glass fibers. The use of pozzolanic materials in samples reinforced with glass fibers improves the modulus of rupture. Also, the reduction of modulus of rupture over time and with the presence of pozzolanic materials is minimized. In this research, in order to check the strength of samples reinforced with glass fibers, the surface under the load-displacement diagram has been used. In general, the use of glass fibers in concrete increases the strength of concrete. According to the obtained results, it can be seen that with the increase of glass fibers, all three strength indices increase; Although in the I5 index, this increase is insignificant. In fact, this shows that in larger displacement, more energy is absorbed by glass fibers. Among the samples reinforced with glass fibers, the highest characteristic values ??of mechanical properties are related to designs containing 10% and 15% metakaolin. The use of nanosilica in mixing designs causes a sharp reduction in compressive strength, flexural strength and strength in glass fiber reinforced concrete. Keywords: glass fiber reinforced concrete, microsilica, metakaolin, nanosilica, compressive strength, flexural strength, strength index. Chapter 1 overview and research objectives. 1-1- Introduction. Serviceability and increase. The bearing capacity of construction materials has long been considered as an important economic issue.

Concrete as a widely used construction material is widely used today. From 1992 to 1993, 63 million tons of Portland cement were used to produce 500 million tons of concrete in the United States alone; This is five times the production of steel, by weight, in the same period. In most countries of the world, the ratio of concrete to steel consumption has exceeded 10 to 1 [1].So far, there have been many definitions of concrete. According to these definitions, concrete consists of three main materials. These materials include: cement materials, water with which cement materials react and become sticky; and filler materials that make up a significant volume of concrete. Despite the remarkable features of this material, including high ductility, strength and long life, being available and cheap, concrete is a brittle material and performs extremely poorly under bending and tensile loads. Steel reinforcements reinforce concrete under tension; But they have almost no effect on the Turkish development process. In other words, when the end of the crack reaches the position of tensile reinforcements, the rate of crack opening and crack propagation decreases, and then when the crack passes through the reinforcement, the crack development increases at a higher rate. In addition, the presence of reinforcement in certain tensile areas makes the concrete out of homogenous and uniform state and the assumption of homogeneity of concrete in analysis methods is problematic [1]. With increasing loading, microcracks are connected and form cracks [2]. In order to solve this problem and also to create homogeneous conditions, in the last few decades, a series of thin strands are used that are spread throughout the entire volume of concrete; which are called fibers.

1-2- Fiber concrete

According to the definition of ACI 544.2R-89 [3], fiber concrete is concrete that is made with hydraulic cement, fine and coarse stone materials and is reinforced by fibers. Furnaces, etc., started [4]. The most important feature of fiber concrete is its energy absorption and flexibility. For this reason, today this concrete plays a very serious role in the advancement of concrete technology.

In general, fiber concrete can be expected to improve the parameters related to load coefficients such as compressive, tensile, bending, shear resistance and resistance to creep, wear and erosion.

1-3- Fibers used in concrete

As mentioned, when the stresses reach the maximum strength of the mortar, cracks are formed. Finally, the accumulation of these cracks in one area causes the destruction of concrete. In this situation, the use of fibers prevents the spread of cracks and their connection to each other.

The use of fibers in concrete started about 50 years ago and the use of this material in concrete mixing plans is increasing day by day. The various advantages of using fibers in concrete, such as increased bending strength, increased shear strength, increased tensile strength, increased resistance to impact loads, increased energy absorption, and increased cross-sectional resistance against cracking, have led to the use of fibers in strengthening and repairing all kinds of concrete structures [5].

Choosing the type of fibers determines the properties of composites. Today, in order to strengthen concrete, various fibers are used, including steel fibers, polypropylene fibers, aramid fibers (Kevlar), carbon fibers, and glass fibers (Figure 1-1).

Fibers used in concrete can be divided into the following 4 groups in terms of type [6]:

Organic synthetic materials such as polypropylene and carbon

Inorganic synthetic materials such as steel and glass

Natural organic materials such as cellulose

Materials Natural inorganic such as asbestos

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1-3-1- Natural fibers

Natural fibers such as coconut, sisal, sugarcane bagasse, bamboo, hemp, flax, wood and plant fibers were tested in 40 countries to determine their engineering properties and the possibility of using them in construction. Although the results were encouraging, due to the interaction between cement mortar and fibers, weaknesses in their durability were observed. Plant fibers do not have high strength, and as a result of increased loads by tearing the fibers or by pulling them out of the concrete mortar, failure occurs in the concrete structure [9]. Concrete reinforced with steel fibers can be locally or completely replaced concrete reinforced with steel bars.