Master's thesis in the field of civil engineering with structural orientation
October 1390
Chapter one
Overview
1-1 Introduction
In recent years, there have been many advances in the field of earthquake engineering and design. The structures have been made in such a way that today it is possible to design earthquake-resistant structures with more confidence. Many concrete structures are damaged due to the reasons 1- Calculation errors 2- Mistakes in construction and implementation 3- Weakness of old regulations 4- Change of use of the structure and operating loads on the structure 5- Corrosion and rusting of reinforcements and . . . does not satisfy the requirements of the new regulations, therefore strengthening Structures with fiber-reinforced polymers [1] (FRP) in the form of plates or sheets create significant economic benefits in the construction industry. The recent advances in FRP indicate that in the future these materials will play a big role in construction applications and restoration of structures.
In the last decade, FRP has found many applications in civil engineering. The growing demand for the use of FRP in strengthening beams, columns, walls, slabs and concrete pipes has created a great need to understand the short-term and long-term behavior of the composite system under different loading conditions and environmental conditions. Composite materials may withstand a variety of operating conditions, which may include some truly aggressive conditions. For example, hot and humid weather, prolonged high temperature, sudden changes in degree Ambient temperature and chemical corrosion can affect the durability of FRP. Adhesion and cohesion of composite materials may undergo environmental erosion and affect the bond between concrete and these materials. This may alter the performance and durability of the composite system. Another reason for this lack of connection between the composite and concrete is the temperature mismatch between the fibers and the matrix, which can create compressive stresses in the fibers. Another reason is the ability of composite materials to absorb moisture, which may affect the integrity between the fibers and the matrix. Currently, the use of FRP in strengthening structures has increased dramatically, while there is not enough information about the durability of FRP, one of which is the alkaline reaction of aggregates. In this research, the polymer reinforced with glass fibers [2] (GFRP) of E-glass [3] type, which is good electrical insulator and has relatively high mechanical resistance, and has a cheap and reasonable price compared to other fibers, has been used.
Structural failure Concrete damage can occur as a result of the reaction between alkaline liquids in the voids (mostly originating from Portland cement) and reactive minerals that are present in some aggregates. This failure mechanism is known as aggregate alkali reaction and occurs in different forms, the most common of which is alkali-silicate reaction. This reaction was first reported in 1940 (1319 solar years) in the United States[1]. Although damage due to this reaction has rarely been reported in our country, probably a large number of concrete structures in our country, including the Shahryar Dam located in East Azerbaijan province, where the aggregates were obtained from, are also affected by this reaction. This is when using cement with high alkalinity is more likely to cause this reaction. Therefore, it will be important to pay attention to this reaction.
The general alkaline-silica reaction is the most alkaline reaction of aggregates in the world and occurs when the reaction between the alkaline solution inside the cavities and the silica minerals in some aggregates occurs and forms an alkaline calcium silicate gel. The aforementioned gel absorbs water and increases in volume, which results in concrete cracking. Another alkaline reaction of aggregates is the alkaline-carbonate reaction. This reaction occurs when cement alkalis react with dolomite limestone aggregates.. Alkaline reaction of active aggregates takes place after concrete curing and causes internal expansion and destruction of concrete. Therefore, the resistance of FRP and concrete over time and under adverse environmental conditions requires investigation and understanding of the factors affecting FRP when it is exposed to different environmental conditions. 1-2 The necessity of doing Research
During the recent years, the issue of strengthening and strengthening structures has been widely discussed in the scientific and engineering communities. In this connection, depending on the type of structure and the purpose of strengthening, various methods have been proposed by researchers. On the other hand, the alkaline reaction of active aggregates, which takes place after concrete curing and causes the internal expansion and destruction of concrete, can cause a lot of damage and damage to concrete structures. One of the methods that has been widely used in the repair and strengthening of concrete members and is increasing, is the use of FRP sheets. Therefore, it is absolutely necessary to understand the short-term and long-term behavior of the composite system under various loading conditions and environmental conditions, and to recognize and recognize the alkaline reaction in reinforced concrete structural members. Examining the durability of reinforced concrete beams reinforced with glass fiber reinforced polymers (GFRP) under the alkaline reaction of aggregates.
After performing alkaline reaction in the beams and strengthening them with GFRP, these beams are compared with beams in which alkali reaction did not take place in terms of bending load.
· Investigating the durability of reinforced concrete beams reinforced with GFRP sheet in alkaline solution.
The effect of a normal sodium hydroxide solution in carrying out the alkaline reaction and the role of GFRP in improving the bending strength of the beams are investigated.
· Investigating the effect of GFRP sheet on increasing the bending strength of reinforced concrete beams reinforced with these sheets.
The effect of GFRP sheet on improving the bending strength of reinforced concrete beams reinforced with these sheets is expressed in comparison to unreinforced beams. Therefore, after collecting information about the strengthening of reinforced concrete beams with FRP and the durability of composite materials in different environments, as well as the effect of alkali additives on concrete and the description of the alkaline reaction of aggregates, the materials and materials used in this research are described, which are presented in the second and third chapters. Then, two series of reinforced concrete beams, one containing active sand and the other with inactive sand, were designed and built. Therefore, 16 reinforced concrete beams of 400 x 80 x 80 mm were molded and concreted and after 28 days of processing, they were divided into eight groups and in two environmental conditions. were placed These beams were kept in these environments for eight months and then tested under single-point bending test. In the fourth chapter, the details of the construction and design of the samples and the test procedure are fully presented. After carrying out the test, the breaking load of the beams and the displacement corresponding to them were obtained, and the results were compared and subjected to further investigation. Also, to measure the expansion of the samples, 6 unarmored beams were also considered, and in the fifth chapter, the test results are presented. Examples and discussions on the results were done and at the end of the results The result of this research is stated.
Chapter Two
Overview of the conducted research
2-1 Introduction
Following the deterioration of structures and the need to strengthen them to meet Due to the stringent design conditions, during the last two decades, there has been a lot of emphasis on the repair and strengthening of structures all over the world. On the other hand, seismic improvement of structures has become very important, especially in earthquake-prone areas. In the meantime, the technique of using FRP composite materials as external reinforcement has gained special interest due to its rapid implementation in strengthening and revitalizing structures. The technology of using FRP materials on structural members was first introduced in (Swiss Central Research and Laboratory) [2].