What is Concrete?
Concrete is broadly defined as any material or compound made of a cementitious adhesive. Concrete may be made from different types of cement, additives, sulfur, admixtures, polymers, fibers, etc.
But in fact, concrete is composed of sand, gravel, and cement which acts as the boding grain in the concrete and has a direct relationship to the strength of concrete. The role of water is plasticizing the concrete for better workability and hydration.
Heat, autoclave water vapor, vacuum, hydraulic pressures, and various condensers may be used in the production of concrete.
Concrete is one of the most used construction materials and its main feature is that its raw materials are inexpensive. In general, it is a product that is obtained by mixing water with hydraulic cement and various aggregates due to the reaction of water with cement in certain ambient conditions and has special characteristics.
The availability of its materials, relatively high durability, and the need for abundant construction of concrete structures such as buildings, dams, bridges, tunnels, roads, etc. have made concrete is widely used.
Due to the chemical reaction of cement and water, the hardening process continues and as a result, the grains (sand and gravel) stick together like a rock mass.
* Gravel: coarse-grained aggregates from 0.5 to 2.5 cm
* Sand: grains smaller than 0.5 cm
This size depends on the largest grain.
This mix is plasticized with water. Cement paste generally makes up about 25 to 40 percent of the concrete. The absolute amount of cement is between 7 and 15 percent and the amount of water is 14 to 21 percent. Concrete consists of up to 8 percent.
This size depends on the largest grain.
Concrete and steel are two types of materials that are used today more than any other material for building various constructions, and it can be said that without these two, the progress of human societies would not be possible in the present form. They are used alone or as a supplement. Steel is easier to use than concrete because it is produced under carefully controlled conditions and its features and properties are determined and controlled by multiple experiments. However, concrete is produced and used in completely different conditions and based on different parameters such as type of cement, type of materials and weather conditions.
Use of different materials in concrete production
Lack of sufficient knowledge of the properties of concrete components, as well as production and consumption procedures, can lead to irreversible losses. Today, different types of concrete are produced and used with different materials, and each has its own properties and applications. Currently, different types of cement are produced, which contain pozzolan, fly ash, blast-furnace slag, iron furnaces, sulfur, polymers, various fibers, and various additives.
Today, the use of softer concrete that can withstand many deformations without failure has been considered. Research and studies are conducted to provide the desirable softness in concrete and various fibers and even to remove reinforcement.
The purpose of using fibers in concrete is to increase the tensile and bending strength, control the expansion of cracks and increase the strength of concrete so that the concrete piece can withstand many deformations in a cracked section after the maximum stress point against loads.
Concrete with different fibers has been used in recent years in the structures such as pavements, airports, huge foundations with many deformations and especially in the concrete cover of tunnels. In the construction of tunnel coverings, fiber concrete is formed by spraying on the wall.
To remove cracks in the tunnels, which are made in several prefabricated pieces, the mass concrete/fiber-reinforced concrete is used. This type of concrete removes cracks during curing and transportation of pieces and installing them to complete the section of metro tunnels.
In the very new type of fiber-reinforced concrete, which can be used to achieve maximum softness in concrete, the method of pouring gout on the fibers is used such that the fibers are first poured and the empty space between them is filled with the grout mortar. With these materials, protective layers can be created without cracks and almost impenetrable.
In recent years, limited use of non-metallic reinforcements has begun. However, research is ongoing on their wider application and the long-term performance of this type of reinforcement. These reinforcements, known as Fiberglass Reinforced Plastic (FRP), are made of various fibers such as Glass Fiber Reinforced Plastic (GFRP), Aramid Fiber Reinforced Polymer (AFRP) and Carbon Fiber Reinforced Polymer (CFRP) in sticky resin.
Steel Corrosion in Concrete
The steel corrosion in concrete is one of the major problems of the construction industry in different countries of the world. This has led to high costs, even in developed countries. This problem has been very severe in developing countries as well as the countries bordering the Persian Gulf, and many concrete structures have been corroded and damaged in a short period of time. Studies in these areas show that if the right materials are selected, and the technically and climatically suitable concrete is designed, the skilled people are applied, and finally, if sufficient and appropriate curing is applied, many concrete problems will be solved.
Considering Concrete Degradation Factors
Concrete that has been exposed to harsh conditions in the Persian Gulf, as well as in refineries or is exposed to the climatic conditions of other regions may be degraded due to the following conditions:
Very high temperatures in blast furnaces in refineries and cracking due to this factor, sulfate attack as a result of sulfuric gases (for example, the efflorescence that appears in Fars refinery that reduces the strength of concrete).
Degradation occurs when the concrete is simultaneously under water, and air pressures.
Drying and wetting due to water leakage or washing the concrete structure with saline seawater, hydrocarbons spilled on the concrete surface, are factors that cause water to infiltrate into the pores of cement paste and aggregates and thus increase concrete permeability.
Infiltration of chlorine ions and Sulfate attacks cause corrosion of reinforcement and consequent cracking. Heavy vehicles also produce cracks in concrete.
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