Investigating the effect of nanosilica on the mechanical properties and durability of concrete containing polypropylene fibers

Education: Master's Degree: Civil Engineering, Major: Structures

Abstract:

In this thesis, the effect of nanosilica on the mechanical properties and durability of concrete containing polypropylene fibers was investigated. Polypropylene fibers with a length of 18 mm and a ratio of length to diameter of 0.9 mµ were used. The effect of fibers and nanosilica in three different percentages for each in the proportions of 0.1, 0.2 and 0.3% for fibers and 2, 4 and 6% for nanosilica on concrete with a water to cement ratio of 0.38 was compared and investigated. In total, more than 192 cubic and cylindrical samples were made based on ASTM standards, and tests of compressive strength, indirect tensile strength, ultrasonic testing, and electrical resistance were performed on the samples. The results of the tests showed a significant increase in the mechanical characteristics and durability of concrete. Compressive strength increased by 55% and tensile strength by 25%. The significant increase in electrical resistance also showed the high durability of this type of concrete. Chapter 1 Introduction and generalities Chapter 1 Introduction and generalities 1-1. Introduction

Today, concrete is known as one of the most widely used materials in the world and as the building material of the 21st century. The construction of this composite material by using the cheapest and most available simple materials on the one hand, its flexibility, resistance properties and durability on the other hand, as well as the use of materials in its construction that help to clean and reduce environmental pollution has made concrete stand out as a premium material [1]. Concrete is a material that has high resistance to pressure, and therefore it is very suitable for parts under pressure such as columns and arches. But despite the significant compressive strength, the low tensile strength and relatively high fragility of concrete limit its use for parts that are fully or locally under tension [2]. This basic defect of concrete is solved in practice by arming it with the deployment of steel reinforcements in the direction of tensile forces. It is worth mentioning that in many cases the direction of these tensile forces is not known precisely. Also, considering that the reinforcement forms a small part of the cross-section, it is not correct to think that the concrete cross-section is a homogeneous and isotropic cross-section. In order to create isotropy conditions and reduce the brittleness and brittleness of concrete as much as possible, in the last few decades, it has become common to use thin and relatively long fibers that are dispersed throughout the volume of concrete [3]. Another issue that has recently attracted the attention of concrete scientists is the use of nanomaterials in concrete. Through various experiments, the researchers came to the conclusion that the characteristics of concrete containing nanomaterials compared to normal concrete are influenced by the chemical reactions of nanomaterials with cement particles and calcium hydroxide crystals in cement, which strongly affects the performance of the concrete composite material] 4. [

1-2. Introduction of fiber concrete

1-2-1. Definition: According to the definition of ACI 544.1R-82, concrete made of hydraulic cement, water, sand, sand and fibers is called fiber reinforced concrete or fiber concrete. Pozzolans and other additional materials can be used in fiber concrete like ordinary concrete. Fibers are used in different shapes and sizes, made of steel, polymer materials, glass and natural materials [5].

1-2-2. Valid regulations of fiber concrete

In addition to studies and researches that have been presented as valid articles in magazines or conferences. Concrete regulations have also dedicated some of their parts to fiber concrete. Among these regulations is the regulation of ACI (American Concrete Association) which has investigated fiber concrete issues by introducing separate committees called ACI-544. This committee presented the first report in 1973 and so far this committee has increased its work with four general reports. The reports of this committee are called 3R, 2R, 1R, and 4R. In the report of ACI, 544-1R, which was presented in 1996 and revised in 1999, there is complete information about the types of fibers and their properties and their effect on the mechanical properties of concrete, in addition to testing the strength of fiber concrete. Basically, this report has identified the types of fibers that can be used in concrete and compared them] 6.[

In the ACI report, 544-2R, which was presented in 1989, the method of conducting the necessary tests and standards is given, and in cases such as the impact test and Even the method of making the test device is also explained [7].

In the ACI report, 544-3R, which was presented in 1998, it is explained about the mixing plan and suitable materials for fiber concrete. In this report, there is no method for the mixing plan, but two examples of mixing plans are given and suggestions are given to improve the properties of fiber concrete. For example, the smaller the aggregates in fiber concrete, the more effective the role of fibers in concrete will be, or it is suggested that more cement be used in fiber concrete if possible [8]. Design methods with steel fibers have been discussed. Of course, the results of these designs have not yet been included in ACI-318 [9].

Among other regulations, there is the JSCE regulation [1] of Japan, the method of measuring the strength of fiber concrete provided by this regulation is of great importance to researchers. In addition, RILEM regulation in Europe has also published reports about fiber concrete. 10. 3. Applications of fiber concrete Fiber reinforced concrete can be used alone or together with normal reinforced concrete. In cases where fiber concrete can be used alone, they include: floors of factories, bus stops, gas stations and industrial halls concrete paving of highways, roads and airports explosion-proof and fire-proof structures walls and floors of canals prefabricated parts in other cases where normal reinforced concrete or precast concrete can be used Built and used:

Scaffolding for engines and large machines, large presses, diesel generators

Parts related to tunneling and mining excavations

Protective walls, shelters

Prestressed concrete beams, impact piles

Uses of cement products reinforced with various fibers are given in Table 1-1.

The important applications of fiber concrete are [11]:

1-3-1. Shotcrete [2]

One of the important applications of fibers is in concrete spraying, concrete spraying is usually suitable for the implementation of thin layers. In general, concrete spraying can be done in two ways: wet and dry. In the dry method, after mixing the dry materials, the required water is added during the passage of the sprinkler. In the new method, the mixture is made completely and then it is placed in the pump chamber of the concrete sprayer and transferred to the sprayer through the pipe. The dry method is used in most fiber concrete shotcretes. It is also possible to use more methods, however, more attention should be paid to the distribution of fibers. The most use of concrete spraying with fibers is in the maintenance of basements, especially the walls of tunnels and mines, shell structures and repairs of marine structures and water channels [12 and 13]. 1-3-2. Slabs on the bed

Slabs on the bed containing fibers to prevent fractures caused by dynamic and concentrated loads and cracks caused by loads and others (such as heat and shrinkage) are used in the floors of industrial halls and replace reinforced slabs in most cases. These slabs are used in paving roads, sidewalks, airports and especially industrial halls. By using this type of concrete (fiber concrete), airport pavements can be made 25 to 40% thinner than unreinforced concrete and with more joint spacing.

Bending fatigue is an important factor that affects pavement performance. Available information shows that fibers significantly increase the resistance of concrete locally and overall against fatigue [12].

3-3. Military industries Fiber reinforced concrete is widely used in military industries in some countries. Its structural applications are the use of fibers with or without reinforcement by ordinary reinforcements, which are used in parts of slabs, walls, floors, beams and columns. The results of the tests have shown that such parts cause much less spread and dispersion in front of the explosion compared to unreinforced slabs to normal reinforcement [12].

1-3-4.