It is a mixture of sand, gravel, slag, crushed stone, cement, water and used in all kinds of construction works. It's been used since ancient times. To prepare the concrete, one part of cement, two parts of sand, three parts of gravel or crushed stone is taken. It is also possible to mix slag into the concrete according to where it will be poured. The weight of one cubic meter of cement used in home construction is 75 kg. It is up. The concrete starts to freeze two to three hours after being mixed with water. 28 from day of pouring achieves almost maximum strength after day. When freezing, it is more damaged than severe cold. High resistance to pressures.
Concrete is one of the most used materials after water in building materials of the world. There are many reasons for this. Here are a few of these reasons: economic, low cost, components have been found with more than in nature, durability is high, easy to process, resistant to fire, does not require much energy in production, environmentally friendly and important is the construction of aesthetic buildings to allow different engineering work data. In its most primitive form, concrete was used when the Egyptian pyramids were built five thousand years ago, the Great Wall was built, and even during the Roman period, many buildings were built.
Concrete production as used today began in 1848 when the first cement factory was established in the UK. Then, in 1903, ready-mixed concrete was used in construction in Germany. The first concrete mixers were used in 1916.
Composition of concrete: The most important substance constituting concrete is cement, which is the binder. Cement reacts with water to bind aggregate grains. Aggregate forms approximately 75 of concrete. It is called coarse and thin depending on grain size. Coarse or coarse aggregate can often be obtained by crushing from quarries or naturally. it is important to note that it is clean of harmful substances. These harmful substances can be soft grains, clay, soluble salts and organic substances. Sand or fine aggregate can be obtained by sieving naturally fractionated material containing silica or limestone, as well as by crushing and grinding from rocks. Another important material constituting concrete is water. Water should not contain harmful substances. Usually drinkable water is sufficient.
Types of concrete structures
Reinforced concrete: Generally, the tensile strength of concrete is about 10% of the compressive strength. In practice, this is compensated by placing steel bars in the concrete. Thus, tensile stresses are also taken. Concrete and steel have the same coefficient of elongation as temperature and have a very good bond strength (adherence), making them an ideal couple. Concrete protects self-reinforcing steel against fire and rust. Usually steel equipment is used in the tensile parts of concrete. The birth of reinforced concrete can be attributed to the construction of a small reinforced concrete boat of French Joseph L. Lambot. However, it can be said that the first practical use was started with the French Joseph Monier in l867. Reinforced concrete is the most common form of construction today.
Prestressed concrete: The basic principle of this is to expose the concrete to pressure and the steel to tensile stresses. Tensile stresses in steel create pressure stresses in concrete. It is then foreseen that the tensile stresses that will occur in the concrete will be compensated with the previous pressures. In this way, the whole of the concrete section is utilized by operating the pressure on each side. Exposure of concrete to pressure stresses minimizes cracking in concrete. The prestress is applied for two purposes. One is to produce desirable stresses and deformations, the other is to compensate for undesirable.
With this type of structure, it is possible to make more delicate lightweight concrete structures. Pretension to steel can be given before concrete casting or after concrete hardening. In the first, prestressing cables are stretched, concrete is then poured and expected to harden. After the bond between the concrete and the steel is fully exposed, the prestressing cable is cut. In the other type, concrete is poured by leaving gaps in the concrete for steel. After the concrete is hardened, the steel cables are stretched and connected to the concrete at their ends. The relationship between concrete and steel can be achieved by connecting the tensioned cable along the length of the concrete as well as at the ends. The birth of prestressing began with American Jackson Jackson at l886, but the first application was made by French Eugene Freyssinet at l928.
Concrete shells: One of the newest application areas of concrete is thin, curved surface carrier systems. They can be cylindrical, hyperbolic, elliptical and parabolic, or can be very complex. The most suitable example of load bearing is the known eggshell's ability to carry a uniform spring load. The first applicators of this type of construction were Franz Dischinger and Ulrich Finsterwalder. Pre-cast concrete: Pre-poured structural elements prepared in various lengths and shapes are transported to the place where the structure will be installed and the construction is made by combining with each other. Concrete pipes are already made by this method. They may be reinforced or prestressed.
With the development of technology, new technologies have been developed in concrete construction. Today, chemical and mineral additives and fibers are used in the production of concrete and more durable concrete is produced.
In concrete production, cement, water, aggregate and necessary chemical and mineral additives are added in certain proportions and they are mixed homogeneously in concrete. The concrete which has soft consistency when first made is hard as it dries and gained durability. A quality concrete protects its chemical and physical integrity throughout its lifetime against environmental influences and loads. The indicator of quality in concrete is not primarily resistant to pressure, but also resistant to the loads and environmental impacts during its economic life.
In addition, the durability and quality of concrete are strictly dependent on the following properties: material used (ie cement, aggregate, water, chemical and mineral admixtures), water and cement ratio, production methods, proper design, degree of compression, air content, maintenance (ie time, humidity and temperature).
Determination of raw material quality within the properties of concrete is done by various tests. These tests carried out in authorized laboratories take into consideration the legal regulations in force as well as the standards published by domestic and foreign organizations. Here are a few of these standards:
- TS EN 12350-1 Concrete - Fresh concrete tests - Part 1: Sampling
- TS EN 12350-2 ... Section 2: Slump test
- TS EN 12350-3 ... Section 3: Parental experiment
- TS EN 12350-4 ... Section 4: Degree of compressibility
- TS EN 12350-5 ... Section 5: Expansion table test
- TS EN 12350-6 ... Section 6: Density
- TS EN 12350-7 ... Chapter 7: Determination of air content - Pressure methods
- TS EN 12350-8 ... Section 8: Self-compacting concrete - Crumbling test
- TS EN 12350-9 ... Section 9: Self-compacting concrete - Sump-V funnel test
- TS EN 12350-10 ... Section 10: Self-compacting concrete - L box test
- TS EN 12350-11 ... Section 11: Self-compacting concrete - Decomposition test in sinking-screening
- TS EN 12350-12 ... Section 12: Self-compacting concrete - J-ring test
