Concrete , usually Portland cement concrete , is a composite material consisting of fine and coarse aggregates bonded together with cemented liquid (cement paste) over time - most often lime-based cement binder, such as Portland cement, but occasionally with other hydraulic cements, such as calcium aluminate cement. It is distinguished from other types of non-minute concrete that bind several forms of aggregate together, including asphalt concrete with asphalt binder, which is often used for road surfaces, and polymer concrete using polymers as binders.
When the aggregate is mixed together with dried Portland cement and water, the mixture forms a liquid puree which is readily poured and shaped into shape. Cement reacts chemically with water and other materials to form a hard matrix that binds the material together into a material such as durable stone that has many uses. Often, additives (such as pozzolans or superplasticizers) are included in the mixture to improve the physical properties of wet or finished mixtures. Most concrete is poured with a reinforcing material (such as rebar) grown to provide tensile strength, resulting in reinforced concrete.
The famous concrete structures include the Hoover Dam, the Panama Canal and the Roman Pantheon. The earliest large-scale concrete technology users were ancient Romans, and concrete was used extensively in the Roman Empire. The Colosseum in Rome is built mostly of concrete, and the concrete dome of the Pantheon is the largest concrete dome in the world. Currently, large concrete structures (eg, dams and multi-storey car parks) are usually made with reinforced concrete.
After the Roman Empire collapsed, the use of concrete became scarce until the technology was redeveloped in the mid-18th century. Around the world, concrete has exceeded the steel in the tonnage of materials used.
Video Concrete
Etimologi
The word concrete comes from the Latin " concretus " (meaning concise or solid), the perfect passive participle of " concrescere ", from " con - "(together) and" crescere "(grow).
Maps Concrete
History
Prehistoric
Small-scale production of materials such as concrete dates from 6500 BC, spearheaded by Nabatiea traders or Bedouins, who occupy and control a series of oases and develop a small empire in southern Syria and northern Jordan. They discovered the advantages of hydraulic lime, with some cementing properties, in 700 BC. They built a kiln to supply mortar for the construction of houses of debris walls, concrete floors, and waterproof waterproof tanks. They keep the secret of the tank because it allows Nabataea to flourish in the desert. Some of these structures survive to this day.
Classic Era
In the days of Ancient Egypt and then Rome, the builders again found that adding volcanic ash to the mix allowed it to set under water.
German archaeologist Heinrich Schliemann discovers concrete floors, made of limestone and gravel, in the royal palace of Tiryns, Greece, estimated to be around 1400-1200 BC. Lime is used in Greece, Crete, and Cyprus in 800 BC. The Assyrian Jerwan Aqueduct (688 BC) utilizes waterproof concrete. Concrete is used for construction in many ancient structures.
The Romans used the concrete extensively from 300 BC to 476 AD, spanning over seven hundred years. During the Roman Empire, Roman concrete (or opus caementicium ) was made of lime, pozzolane and aggregates of pumice. Its extensive use in many Roman structures, an important event in the history of architecture called the Roman Architectural Revolution, freed Roman construction from the limitation of stone and brick material. This allows a revolutionary new design in terms of complexity and structural dimension.
Concrete, as the Romans know it, is a new and revolutionary material. Arranged in the form of arches, domes and domes, it quickly hardened into a rigid mass, free of many internal stresses and tensions that disrupt builders of similar structures in stone or brick.
The modern test shows that opus caementicium has the same compressive strength as the modern Portland-cement concrete (about 200 kg/cm 2 Ã, [20 MPa; 2,800Ã, psi]). However, in the absence of reinforcement, its tensile strength is much lower than modern reinforced concrete, and its mode of application is also different:
Modern structural concrete differs from Roman concrete in two important details. First, the consistency of the mixture is liquid and homogeneous, allowing it to be poured into forms rather than requiring hand coating along with aggregate placement, which, in Roman practice, often consists of debris. Second, integral steel reinforcement provides modern concrete assemblies of great strength in tension, whereas Roman concrete can only rely on the strength of concrete bonds to withstand tension.
The long-term durability of Roman concrete structures has been found due to the use of pyroclastic stone and ash (volcanic ash), where the crystallization of strÃÆ'¤tlingite and the fusion of the calcium-aluminum-silicate-hydrate cementing binder helps give the concrete a greater degree of fracture resistance even in the active seismic environment. Roman concrete was significantly more resistant to erosion by sea water than modern concrete; it used pyroclastic materials that react with seawater to form the Al-tobermorite crystals over time.
The widespread use of concrete in many Roman structures ensures that many survive to this day. The Baths of Caracalla in Rome is just one example. Many Roman waterways and bridges, such as the magnificent Pont du Gard in southern France, have stone walls on a concrete core, just like the Pantheon dome.
Medieval
After the Roman Empire, the use of lime and pozzolana was greatly reduced until the technique was almost forgotten between the 500 and the 14th century. From the 14th century until the middle of the 18th century, the use of cement gradually returned. The Canal du Midi was built using concrete in 1670.
Industrial era
Perhaps the biggest step forward in the modern use of concrete is Smeaton's Tower, built by British engineer John Smeaton in Devon, England, between 1756 and 1759. This third Eddystone lighthouse pioneered the use of hydraulic lime in concrete, using gravel and powdered bricks as aggregates.
The method for producing Portland cement was developed in England and patented by Joseph Aspdin in 1824. Aspdin chose the name because of its resemblance to the Portland stone, excavated on the Isle of Portland in Dorset, England. His son, William, continued into the 1840s, earning him recognition for the development of a "modern" Portland cement.
Reinforced concrete was discovered in 1849 by Joseph Monier. In 1889 the first reinforced concrete bridge was built, and the first large concrete dam was built in 1936, the Hoover Dam and Grand Coulee Dam.
Composition
Many types of concrete are available, distinguished by the proportions of the main ingredients below. In this way or by substitution for the cement and aggregate phases, the finished product may be adapted to the application. Strength, density, and chemical and heat resistance are variables.
Aggregates consist of large pieces of material in concrete mixes, generally rough gravel or crushed stone such as limestone, or granite, along with fine materials such as sand.
Cement, Portland's most common cement, is associated with the general term "concrete." Various other materials can be used as cement in concrete as well. One of the most familiar of these alternative cement is asphalt concrete. Other cement materials such as fly ash and slag cement, sometimes added as mineral mixing (see below) - are either pre-mixed with cement or directly as concrete components - and become part of the binder for aggregates.
To produce concrete from most of the cement (not including asphalt), water is mixed with dry powder and aggregate, which produces a semi-liquid formed slurry, usually by pouring it into shape. The concrete solidifies and solidifies through a chemical process called hydration. Water reacts with cement, which binds other components together, creating a material like a strong stone.
Mixing chemicals are added to achieve varied properties. These materials can accelerate or slow down the rate at which the concrete hardens, and provides many other useful properties including increased tensile strength, air entrainment and water resistance.
Reinforcement is often included in concrete. Concrete can be formulated with high compressive strength, but always has a lower tensile strength. For this reason it is usually reinforced with a strong material in tension, usually a steel rebar.
Mineral admixtures have become more popular in recent decades. The use of recycled materials as concrete material has gained popularity due to increasingly stringent environmental regulations, and the discovery that such materials often have complementary and valuable properties. The most striking of these are fly ash, a by-product of coal-fired power plants, blast slag clay grains, steel-making byproducts, and silica fumes, a by-product of industrial electric arc furnaces. The use of these materials in concrete reduces the amount of resources required, since the mineral mixing acts as a substitute for partial semen. This replaces some cement production, a very costly and environmentally problematic process, while reducing the amount of industrial waste to be disposed of. The mineral mixture may be mixed with cement during production to be sold and used as a cement mixture, or mixed directly with other components when the concrete is produced.
mixed design depends on the type of structure being built, how the concrete is mixed and shipped, and how it is placed to form the structure.
Cement
Portland cement is the most commonly used type of cement. It is the base material of concrete, mortar, and lots of plaster. British bricklayer Joseph Aspdin patented Portland cement in 1824. It was named for its color similarity to the Portland chalk, excavated from British Island Portland and used extensively in London architecture. It consists of a mixture of calcium silicate (alite, belite), aluminate and ferrite - a compound that combines calcium, silicon, aluminum and iron in a form that will react with water. Portland cement and similar materials are made by heating limestone (calcium source) with clay or flakes (source of silicon, aluminum and iron) and grinding this product (called clinker ) with sulfate sources (most often gypsum ).
In modern cement kiln many advanced features are used to lower fuel consumption per ton of clinker produced. Disposal of semen is a very large, complex, and inherently dusty industrial installation, and has emissions that must be controlled. Of the various materials used to produce a certain amount of concrete, cement is the most energetically expensive. Even complex and efficient furnaces require 3.3 to 3.6 gigajoules of energy to produce a ton of clinker and then grind them into cement. Many kilns can be triggered by waste that is hard to remove, the most commonly used tire. Extremely high temperatures and long periods of time at these temperatures allow the cement kiln to efficiently burn and even tough fuel use.
Water
Combine water with a cement material to form a cement paste with a hydration process. The cement paste aggregates together, fills the cavity inside, and makes it flow more freely.
As stated by the Abrams law, the lower water-to-cement ratio yields stronger and more durable concrete, while more water gives concrete flowing faster with higher deterioration. The dirty water used to make concrete can cause problems when regulating or causing premature structure failure.
Hydration involves many different reactions, often occurring at the same time. As the reaction progresses, the product of the cement hydration process gradually binds together the individual sand and pebble particles and other components of the concrete to form a solid mass.
Reaction:
- Chemical notation of cement: C 3 S H -> C-S-H CH
- Standard notation: Ca 3 SiO 5 H 2 O -> (CaO) Ã, Â · (SiO 2 ) Ã, Â · (H 2 O) (gel) Ca (OH) 2
- Balanced: 2Ca 3 SiO 5 7H 2 O -> 3 (CaO) Ã, Â · 2 (SiO 2 ) Ã, Â · 4 (H 2 O) (gel) 3Ca (OH) 2 (approximate ratio of CaO, SiO < sub> 2 and H 2 O in CSH may vary)
Aggregates
The fine and coarse aggregates form most of the concrete mixture. Sand, natural gravel, and crushed stone are used primarily for this purpose. Recycled aggregates (from construction, dismantling, and excavation waste) are increasingly used as partial replacements for natural aggregates, while a number of aggregates produced, including cooled air slag furnaces and bottom ash are also permitted.
The aggregate size distribution determines how many binders are required. Aggregates with very evenly distributed sizes have the greatest gaps while the addition of aggregates with smaller particles tends to fill this gap. The binder must fill the gap between the aggregate and insert the aggregate surface together, and is usually the most expensive component. Thus variations in aggregate size reduce the cost of concrete. Aggregates are almost always stronger than binders, so their use does not negatively affect the strength of concrete.
Aggregate redistribution after solidification often creates inhomogeneity due to the influence of vibration. This can cause a power gradient.
Ornamental stones such as quartzites, small river rocks, or broken glass are sometimes added to the concrete surface for the "aggregate finish" decoration, which is popular among landscape designers.
In addition to decorative, open aggregates can add to the robustness of the concrete.
Reinforcement
The concrete is strong in compression, because the aggregate efficiently carries the compression load. However, it is weak in tension as the cement holding the aggregate in place may crack, allowing the structure to fail. Reinforced concrete improves both reinforcing steel, steel fibers, glass fibers, or plastic fibers to carry tensile loads.
Chemical mix
Mixing chemicals are substances in the form of powders or liquids added to the concrete to provide certain characteristics that can not be obtained with ordinary concrete mixtures. In normal use, the mixed dose is less than 5% by the mass of cement and added to the concrete during batching/mixing. (See the section on Concrete Production, below.) Common types of admixtures are as follows:
- Accelerators speed up the hydration (hardening) of concrete. The material used is CaCl
2 , Ca (NOT 3 ) 2 and NaNO 3 . However, the use of chloride may cause corrosion of reinforced steel and is prohibited in some countries, so nitrates may be preferred. Accelerating admixtures are particularly useful for modifying concrete properties in cold weather. - Retarder slows concrete hydration and is used in large or difficult castings where partial arrangement before casting is finished is undesirable. The typical polyol retardol is sugar, sucrose, sodium gluconate, glucose, citric acid, and tartaric acid.
- Air entraining agents add and insert small air bubbles in the concrete, which reduces damage during the freeze-thaw cycle, increasing endurance. However, entrained air requires trade off with strength, because every 1% of air can decrease compressive strength by 5%. If too much air is trapped in the concrete as a result of the mixing process, Defoamers can be used to push air bubbles to clot, climb onto wet concrete surfaces and then spread.
- Plasticizer improves the working power of plastic or "fresh" concrete, allowing it to be placed more easily, with less consolidation effort. A typical plasticizer is lignosulfonate. Plasticizers can be used to reduce the water content of concrete while maintaining workability and are sometimes called water reducers due to this use. Such treatment increases the strength and durability characteristics. Superplasticizers (also called high-range water-reducers ) are a class of plasticizers that have fewer harmful effects and can be used to enhance workability more than practical with traditional plasticizers. The compounds used as superplasticizers include sulfonated naphthalene formaldehyde condensate, sulfonated melamine formaldehyde condensate, acetone formaldehyde condensate and polycarboxylate ethers.
- Pigments can be used to change the color of concrete, for aesthetics.
- Corrosion inhibitors are used to minimize corrosion of steel and steel rods on concrete.
- Bonding bonds are used to create bonds between old and new concrete (usually a kind of polymer) with wide temperature tolerances and corrosion resistance.
- Pumping aids improves pumping ability, thickens paste and reduces separation and bleeding.
Mixture of minerals and cement mix
Inorganic materials having a pozzolan or latent hydraulic properties, these highly refined materials are added to concrete mixtures to enhance the properties of concrete (mixing minerals), or as a substitute for Portland cement (mixed cement). Products incorporating limestone, fly ash, blast furnace slag, and other useful materials with pozzolanic properties into the mixture, are being tested and used. This development is due to cement production being one of the largest producers (around 5 to 10%) of global greenhouse gas emissions, as well as lowering costs, increasing concrete properties, and recycling waste.
- Fly ash: A by-product of a coal-fired power plant, used to replace part of Portland cement (up to 60% mass). The nature of fly ash depends on the type of coal burned. In general, fly ash containing silica is pozzolanic, while calcareous fly ash has latent hydraulic properties.
- Ground-ground granulated slag powder (GGBFS or GGBS): A by-product of steel production is used to replace part of Portland cement (up to 80% mass). It has latent hydraulic properties.
- Silica fume: A by-product of the production of silicon alloys and ferrosilicon. Silica fumes are similar to fly ash, but have a particle size 100 times smaller. This results in a higher surface to volume ratio and a much faster pozzolanic reaction. Silica fume is used to increase the strength and durability of concrete, but generally requires the use of superplasticizers to work.
- High reactivity Methaolin (HRM): Metakaolin produces concrete with strength and endurance similar to concrete made with silica fume. While silica fume is usually dark gray or black, the high reactivity of metakaolin is usually bright white, making it the preferred choice for concrete architecture where appearance is important.
- Carbon nanofibres can be added to the concrete to increase the compressive strength and gain a higher Young's modulus, and also to improve the electrical properties required for strain monitoring, damage evaluation and self-health monitoring of the concrete. Carbon fibers have many advantages in terms of mechanical and electrical properties (eg higher strength) and self-monitoring behavior due to high tensile strength and high conductivity.
- Carbon products have been added to make electrically conductive concrete, for deicing purposes.
Production
Concrete production is the process of mixing together various materials - water, aggregates, cement, and any additives - to produce concrete. Concrete production is time-sensitive. Once the ingredients are mixed, the worker must put the concrete in place before it hardens. In modern use, most concrete production takes place in a large industrial facility type called a concrete plant, or often a batch plant.
In general use, concrete plants consist of two main types, ready-to-use plants and mixed plants center. A mixed factory is ready to mix all ingredients except water, while a center mix factory mixes all ingredients including water. A central blend factory offers more accurate control of the quality of concrete through better measurement of the amount of water added, but should be placed closer to the workplace where the concrete will be used, since hydration begins at the plant.
A concrete plant consists of a large storage hopper for a variety of reactive materials such as cement, storage for bulk materials such as aggregates and water, mechanisms for addition of various additives and amendments, machines to accurately weigh, move and mix some or all of these materials, to remove the concrete mixture, often to the concrete mixer truck.
Modern concrete is usually prepared as a viscous liquid, so it can be poured into a shape, which is a container established in the field to provide the desired concrete shape. Formwork of concrete can be prepared in several ways, such as Coating and Steel Plate construction. Alternatively, the concrete may be mixed into the dryer, non-fluid forms and used in the factory setting to produce Precast concrete products.
A wide range of equipment is used to process concrete, from hand tools to heavy industrial machinery. Whatever is used by the equipment builder, the goal is to produce the desired building material; materials must be properly mixed, placed, shaped, and stored within the time limit. Any disruption in pouring concrete may cause the material to be initially placed to be adjusted before the next batch is added above. This creates a horizontal field of weakness called cold joint between two batches. Once the mixture is in the proper place, the preservation process should be controlled to ensure that the concrete reaches the desired attribute. During the concrete preparation, various technical details may affect the quality and nature of the product.
When initially mixed, Portland cement and water quickly form a chain gel of mutually crystal tangles, and the gel component continues to react from time to time. Initially the gel is a liquid, which improves workability and aids in material placement, but as a concrete set, the crystal chains combine into a rigid structure, preventing the gel fluidity and fixing the aggregate particles in place. During the drying process, the cement continues to react with residual water in the hydration process. In properly formulated concrete, once this preservation process has terminated the product has the desired physical and chemical properties. Among the usually desirable qualities, are mechanical strength, low moisture permeability, and chemical and volumetric stability.
Mixing
Complete blending is essential for uniform high quality concrete production. For this reason equipment and methods should be able to effectively mix concrete materials containing the specified aggregates to produce a uniform mixture of the lowest slump that is practical for the job.
Different paste mixing has shown that mixing of cement and water into a paste before incorporating these materials with aggregate can increase the compressive strength of the resulting concrete. Pasta is generally mixed in high velocity, shear type mixer at w/cm ratio (water to cement) 0.30 to 0.45 with mass. Premix cement pastes can include mixing such as accelerators or retarders, superplasticizers, pigments, or silica fume. The mixed paste is then mixed with aggregate and remaining residual water and final mixing is completed in conventional concrete mixing equipment.
Working Power
Workability is the ability of a fresh concrete (plastic) mixture to fill forms/prints correctly with desired work (vibrations) and without reducing the quality of concrete. Working power depends on water content, aggregate (shape and size distribution), cement content and age (hydration level) and can be modified by adding a chemical mixture, such as a superplasticizer. Increasing moisture content or adding a chemical mixture improves the ability of concrete work. Excess water causes increased bleeding or aggregate segregation (when cement and aggregate begin to separate), with the resulting concrete decreasing in quality. The use of aggregate mixtures with unwanted gradations can result in a very hard mix design with very low deterioration, which is not easily made more applicable with the addition of water in reasonable quantities. Unwanted gradations can mean using large aggregates that are too large for formwork sizes, or that have too few smaller aggregate values ​​to serve to fill the gap between larger values, or use too little or too much sand for the same. reasoning, or using too little water, or too much cement, or even using jagged crushed stone instead of fine rounded aggregates like gravel. Any combination of these and other factors can produce a mixture that is too hard, that is, that does not flow or spread smoothly, it is difficult to fit into the formwork, and that is difficult to complete the surface.
Working ability can be measured by concrete slump testing, a simple measure of plasticity of fresh batches of concrete following the ASTM C 143 or EN 12350-2 test standard. Deterioration is usually measured by filling "Abrams cone" with samples from fresh batches of concrete. The cone is placed with the width down to the surface, non-absorbent. It is then filled with three layers of the same volume, with each layer compacted with a steel rod to consolidate the coating. When the cone is removed carefully, the closed material slumps in a certain amount, due to gravity. The relatively dry sample has deteriorated very little, has a value of deterioration of one or two inches (25 or 50 mm) from one foot (305 mm). Relatively wet concrete samples may drop as much as eight inches. Working ability can also be measured by flow table test.
The deterioration can be increased by adding a chemical mixture such as a plasticizer or superplasticizer without changing the water-cement ratio. Some other mixing, especially air-entraining mixing, can increase the mixed deterioration.
High flow concrete, such as self-consolidated concrete, was tested by other flow measurement methods. One of these methods involves placing a cone on a narrow end and observing how the mixture flows through the cone while it is gradually lifted.
After mixing, the concrete is a liquid and can be pumped to the location where it is needed.
Curing
The concrete must be kept moist during the curing process to achieve optimum strength and durability. During the hydration process takes place, allowing calcium-silicate hydrate (C-S-H) to form. Over 90% of the final strength of the mixture is usually achieved within four weeks, with the remaining 10% being achieved for years or even decades. Conversion of calcium hydroxide in concrete to calcium carbonate from CO 2 absorption for several decades further strengthens the concrete and makes it more resistant to damage. This carbonation reaction, however, decreases the pH of the cement pore solution and can corrode the reinforcing reinforcement.
Hydration and hardening of concrete during the first three days is very important. Extremely rapid drying and shrinkage due to factors such as evaporation from wind during placement can cause an increase in tensile stress when not getting enough strength, resulting in larger crack depreciation. The initial strength of the concrete can be increased if it is kept moist during the curing process. Minimize stress before curing minimizes cracking. High-strength concrete is designed to hydrate faster, often with increased use of cement that increases shrinkage and cracking. The power of concrete change (increased) to three years. It depends on the dimension of cross-section elements and the conditions of exploitation of the structure. The addition of short-cut polymer fibers can increase (decrease) the stress-induced stress during the curing process and increase the strength of the initial and final compression.
The right preservative concrete leads to increased strength and lower permeability and avoids cracks where the surface dries prematurely. Care should also be taken to avoid freezing or overheating due to exothermic cement arrangements. Incorrect preservatives can cause scaling, reduce strength, poor abrasion resistance and cracks.
Technique
During the curing period, the concrete is ideally maintained at controlled temperature and humidity. To ensure full hydration during preservation, concrete slabs are often sprayed with a "preservative compound" that makes a water-retaining film on top of the concrete. Typical films are made of wax or related hydrophobic compounds. After the concrete is healed enough, the film is allowed to blur from the concrete through normal use.
The traditional conditions for preservation involve by spraying or soaking the surface of the concrete with water. The image on the right shows one of the many ways to achieve this, the pool - soaking the concrete settings in water and wrapping in plastic to prevent dehydration. Other common preservation methods include wet goggles and plastic sheets that cover fresh concrete.
For higher strength applications, accelerated preservation techniques can be applied to concrete. One common technique is to heat the concrete poured with steam, which serves to keep it moist and to raise the temperature, so that the hydration process proceeds faster and more thoroughly.
Custom types
Pervious
The translucent concrete is a mixture of coarse aggregate, cement, water and fine-to-no aggregate. This concrete is also known as "no-fines" or porous concrete. Mixing ingredients in a carefully controlled process creates a paste that coats and binds the aggregate particles. Hardened concrete contains an interconnected air cavity with a total of about 15 to 25 percent. Water flows through the voids on the sidewalk to the ground beneath. Mixed air entrainment is often used in a frozen-melt climate to minimize the possibility of frost damage.
Nanoconcrete
Nanoconcrete is made by mixing high energy (HEM) from cement, sand and water. To make sure mixing is sufficiently thorough to make the nano-concrete, the mixer must apply the total mixing power to the 30-600 watt mixture per kilogram mixture. This mixing should continue long enough to produce specific clean energy spent on a mixture of at least 5000 joules per kilogram of mixture. A plasticizer or superplasticizer is then added to the activated mixture which can later be mixed with the aggregate in a conventional concrete mixer. In the HEM process, intense mixing of cement and water with sand provides energy dissipation and increases the shear stress on the surface of cement particles. This intense mixing serves to divide the cement particles into a very fine nanometer-scale size, which provides a very thorough mixing. This results in an increase in the volume of water interacting with cement and acceleration of colloidal colloidal preparation of Siliate Silicates (C-S-H).
The initial natural process of cement hydration with the formation of a colloidal globe of about 5 nm diameter spreads to the entire volume of water-cement matrix as the energy spent on mixed approaches and exceeds 5000 joules per kilogram.
High energy-activated fluid blends can be used by itself for the casting of small architectural details and decorative items, or foaming (expanded) for lightweight concrete. HEM Nanoconcrete hardens under conditions of low temperature and below zero and has an increase in gel volume, which reduces capillarity in solid and porous materials.
Microbe
Bacteria such as Bacillus pasteurii Bacillus pseudofirmus Bacillus cohnii Sporosarcina pasteuri and artobacter crystallopoietes i> increase the strength of concrete compression through their biomass. Not all bacteria increase the strength of concrete significantly with their biomass. Bacillus sp. CT-5. can reduce the corrosion of reinforcement in reinforced concrete up to four times. Sporosarcina pasteurii reduces water and chloride permeability. B. pasteurii increases acid resistance. Bacillus pasteurii and B. sphaericuscan induce precipitation of calcium carbonate at the crack surface, adding to compression strength.
Polymer
Concrete polymers are a mixture of aggregates and various polymers and can be strengthened. Cement is more expensive than lime-based cement, but polymer concrete still has advantages, they have significant tensile strength even without reinforcement, and they are mostly resistant to water. They are often used for repair and development of other applications such as water channels.
Security
Concrete grinding can produce harmful dust. The National Institute of Occupational Safety and Health in the United States recommended the installation of local exhaust ventilation valves to electric concrete grinders to control the spread of the dust.
Properties
Concrete has a relatively high compressive strength, but its tensile strength is much lower. For this reason it is usually reinforced with a strong material in tension (often steel). The elasticity of the concrete is relatively constant at low stress levels but begins to decline at a higher stress level when the cracking of the matrix develops. Concrete has a very low thermal expansion coefficient and shrinks when mature. All concrete structures are cracked to some extent, due to shrinkage and tension. Concrete that is subjected to long-lasting strength tends to creep.
Tests can be made to ensure that the concrete properties conform to the specifications for the application.
Different mixtures of concrete materials produce different strengths. The value of concrete strength is usually determined as lower lower compression strength either from cylindrical or cubic specimens as determined by standard test procedures.
Different concrete strengths are used for different purposes. Very low power - 14 MPa (2,000 psi) or less-concrete can be used when the concrete should be lightweight. Lightweight concrete is often achieved by adding air, foam, or lightweight aggregates, with side effects of reduced strength. For most routine uses, 20 MPa (2,900 psi) to 32Ã, MPa (4,600Ã, psi) concrete is often used. Concrete 40Ã, MPa (5,800Ã, psi) is readily available commercially as a more durable option, though more expensive. Higher strength concrete is often used for larger civilian projects. Strengths above 40 MPa (5,800 psi) are often used for certain building elements. For example, the lower floor columns of high-rise concrete buildings may use 80 MPa concrete (11,600 psi) or more, to keep the column size small. Bridges can use long beams of high strength concrete to lower the number of spans required. Sometimes, other structural needs may require high strength concrete. If the structure must be very rigid, concrete with very high strength can be determined, even stronger than necessary to bear the burden of service. Strengths as high as 130 MPa (18,900 PSI) have been used commercially for this reason.
Under construction
Concrete is one of the most durable building materials. It provides superior fire resistance compared to wood construction and gain strength over time. Structures made of concrete can have a long life. Concrete is used more than any other artificial material in the world. In 2006, about 7.5 billion cubic meters of concrete was made annually, more than one cubic meter for every person on Earth.
Bulk structure
Due to exothermic chemical reactions of cement during regulation, large concrete structures such as dams, navigation locks, large mattress foundations, and large breakwaters generate excessive heat during hydration and associated expansion. To reduce this effect post-cooling is usually applied during construction. Early example in Hoover Dam, placing a pipe network between vertical concrete placement to circulate the cooling water during the curing process so as not to overheat. Similar systems are still used; depending on the volume of castings, the concrete mixture used, and the ambient air temperature, the cooling process may last for months after the concrete is placed. A variety of methods are also used to cool concrete mixtures in bulk concrete structures.
Another approach to bulk concrete structures that minimize the heat by-products of cement is the use of roller-compacted concrete, which uses a dry mixture that has a much lower cooling requirement than conventional wet placement. It is stored in a thick layer as a semi-dried material then rolled into a solid, strong mass.
The final surface
The surface of raw concrete tends to be porous, and has a relatively unappealing appearance. Many different touches can be applied to improve the appearance and maintain the surface against coloring, water penetration, and freezing.
Examples of enhanced performance include marked concrete in which wet concrete has an impressionable pattern on the surface, to give a paved, rocky or brick-like effect, and may be accompanied by coloration. Another popular effect for floor and table tops is polished concrete where the concrete is flat optically polished with abrasive diamond and sealed with polymer or other sealant.
The other end can be achieved by sculpting, or more conventional techniques such as painting or covering it with other materials.
Proper treatment of concrete surfaces, and therefore their characteristics, is an important stage in the construction and renovation of architectural structures.
Prestressed Structure
Prestressed concrete is a reinforced concrete form built at compressive pressure during construction to resist tensile stress experienced in use. This can greatly reduce the weight of the beam or slab, by better distributing the pressure within the structure to optimally utilize the amplifier. For example, horizontal rays tend to sag. Strengthening the prestress at the bottom of the block negates this. In pre-tension concrete, the prestress is achieved by using steel or polymer or polarized tendons or bars worn by tensile force before casting, or for postdate concrete, after casting.
More than 55,000 miles (89,000 km) of highways in the United States are paved with this material. Reinforced concrete, prestressed concrete and precast concrete are the most widely used types of functional concrete extensions in modern times. See Brutalism.
Cold weather placement
Extreme weather conditions (extreme heat or cold, windy conditions, and humidity variations) can significantly alter the quality of the concrete. Many precautions are observed in cold weather placement. The low temperature significantly slows down the chemical reactions involved in cement hydration, thus affecting the development of strength. Preventing freezing is the most important precaution, since the formation of ice crystals can cause damage to the crystal paste crystal paste structure. If the surface of the concrete pour is insulated from the outside temperature, the heat of hydration will prevent freezing.
The American Concrete Institute (ACI) definition of cold weather, ACI 306 , is:
- The period when more than three consecutive days, average daily air temperature dropped below 40? F (~ 4.5 ° C), and
- The temperature remains below 50? F (10Ã, Â ° C) for more than half of any 24-hour period.
In Canada, where temperatures tend to be lower during winter, the following criteria are used by CSA A23.1:
- When the air temperature is <= 5Ã, Â ° C, and
- When it is possible that the temperature may drop below 5Ã, Â ° C within 24 hours after installing the concrete.
The minimum strength before exposing concrete to extreme cold is 500 psi (3.5 MPa). CSA A 23.1 specifies a compressive strength of 7.0 MPa to be considered safe for exposure to freezing.
Path
Concrete roads are more fuel efficient to drive, more reflective and last longer than other paving surfaces, yet have a much smaller market share than other paving solutions. Modern paving design methods and practices have changed the economics of paving concrete, so that well-designed and placed concrete pavements will be cheaper at initial cost and significantly cheaper over the lifecycle. Another key benefit is that translucent concrete can be used, which eliminates the need to place storm ducts near the road, and reduces the need for slightly tilted roads to help rainwater flow. No longer needing to dispose of rain water through the use of water channels also means that less electricity is needed (more pumping is otherwise required in the water distribution system), and no polluted rainwater is no longer mixed with contaminated water. Instead, it was soon absorbed by the soil.
Energy efficiency
Energy requirements for low-cost concrete transport because it is locally produced from local resources, usually produced within 100 kilometers of the work site. Similarly, relatively little energy is used in producing and combining raw materials (although large amounts of CO 2 are produced by chemical reactions in the manufacture of cement). The overall energy of concrete contained in about 1 to 1.5 megajoules per kilogram is therefore lower than most of the structural and construction materials.
Once in place, the concrete offers great energy efficiency during the lifetime of a building. The leaky concrete walls are much lower than those made of wooden frames. Air leak account for most of the energy loss from home. The properties of thermal mass of concrete increase the efficiency of both residential and commercial buildings. By storing and releasing the energy required for heating or cooling, the thermal mass of the concrete provides benefits throughout the year by reducing changes in temperature inside and minimizing heating and cooling costs. While insulation reduces energy loss through building envelopes, thermal mass uses walls to store and release energy. Modern concrete wall systems use external insulation and thermal mass to create energy-efficient buildings. Isolation of concrete forms (ICFs) are hollow blocks or panels made of insulating foam or stacked rafts to form the shape of the building wall and then filled with reinforced concrete to create the structure.
Fire safety
Concrete buildings are more resistant to fire than those built using steel frames, because concrete has a lower thermal conductivity than steel and can last longer under the same fire conditions. Concrete is sometimes used as a fire protector for steel frame, for the same effect as above. Concrete as a fire shield, for example Fondu fyre, can also be used in extreme environments such as launch pads of missiles.
Options for non-combustible construction include floor, ceilings and roofs made of precast cast-in-place and hollow-core concrete. For walls, concrete stone technology and Ismetation Concrete Forms (ICFs) are additional options. ICFs are hollow blocks or panels made of fire-resistant insulation foam that are stacked to form a building wall shape and then filled with reinforced concrete to create the structure.
Concrete also provides excellent resistance to externally applied forces such as strong winds, hurricanes, and tornadoes due to lateral stiffness, resulting in minimal horizontal movement. But this stiffness can work against some types of concrete structures, especially where relatively higher flexing structures are required to withstand more extreme forces.
Earthquake safety
As discussed above, the concrete is very strong in compression, but weak in tension. Larger earthquakes can produce very large shear loads on the structure. This shear load is subject to structure for tensile and compression loads. Unbranded concrete structures, like other opaque masonry structures, may fail during severe earthquakes. The opaque masonry structure is one of the biggest risks of earthquakes globally. This risk can be reduced through seismic retrofitting in risky buildings, (eg school buildings in Istanbul, Turkey).
Degradation
Concrete can be damaged by many processes, such as the expansion of steel reinforcement products, trapped water freeze, fire or radiant heat, aggregate expansion, seawater effect, bacterial corrosion, washing, erosion by rapidly flowing water, physical damage and chemical damage carbonatation, chloride, sulfate and distilled water). Aspergillus Alternaria and Cladosporium micro fungus is capable of growing on concrete samples used as a barrier to radioactive waste in Chernobyl reactors; washing aluminum, iron, calcium and silicon.
Influence of modern usage
Concrete is widely used to create architectural structures, foundations, brick/block walls, sidewalks, bridges/elevated bridges, highways, runways, parking structures, dams, ponds/reservoirs, pipes, footholds for gates, fences and poles and even boats. Concrete is used in large numbers almost everywhere there is a need for infrastructure. Concrete is one of the most commonly used building materials in animal houses and for storage structures of dirt and silage in agriculture.
The amount of concrete used worldwide, tonnes for tonnes, is twice the size of steel, wood, plastic, and aluminum. The use of concrete in the modern world is only surpassed by natural water.
Concrete is also the basis of a large commercial industry. Globally, the ready-mixed concrete industry, the largest segment of the concrete market, is projected to exceed $ 100 billion in revenues by 2015. In the United States alone, concrete production is a $ 30-billion industry per year, considering only the value of ready mixed concrete sold annually. Given the size of the concrete industry, and the fundamental way concrete is used to shape the infrastructure of the modern world, it is difficult to overstate the role played by this material today.
Environment and health
Concrete manufacture and use produce various environmental and social consequences. Some are dangerous, some acceptable, and some both, depending on circumstances.
The main component of concrete is cement, which also provides environmental and social effects. The cement industry is one of the three major producers of carbon dioxide, the main greenhouse gas (the other two being energy production and the transportation industry). In 2001, Portland cement production contributed 7% to anthropogenic global CO 2 emissions, largely due to sintering of limestone and clay at 1,500 ° C (2,730 ° F). Researchers have suggested a number of approaches to increasing sequestration of carbon relevant to concrete production.
Concrete is used to create hard surfaces that contribute to surface runoff, which can lead to severe soil erosion, water pollution, and flooding, but instead can be used to divert, dam, and control flooding.
Concrete is a contributor to the urban island heat effect, although less than asphalt.
Workers who cut, grind or polish concrete at risk of breathing air silica, which can cause silicosis. Concrete dust released by building dismantling and natural disasters can be a major source of harmful air pollution.
The presence of some substances in the concrete, including useful and unwanted additives, can cause health problems due to toxicity and radioactivity. Fresh concrete (before drying is finished) is highly alkaline and should be handled with the right protective equipment.
Recycling
Recycling of concrete is an increasingly common method for disposing of concrete structures. Concrete debris has been routinely sent to landfills for disposal, but recycling is increasing due to increased environmental awareness, government law and economic benefits.
Concrete, which must be free of garbage, wood, paper and other materials, is collected from the crushing and inserted through a crushing machine, often together with asphalt, brick and stone.
Reinforced concrete contains rebar and other metal reinforcements, which are released with magnets and recycled elsewhere. The remaining aggregate pieces are sorted by size. Larger pieces can be through the destroyer again. Smaller pieces of concrete are used as pebbles for new construction projects. Aggregate base pebbles are placed as the lowest layer on the road, with fresh concrete or asphalt placed on top of it. Crushed recycled concrete can sometimes be used as a dry aggregate for new concrete if free of contaminants, although the use of recycled concrete boundary strength and is not allowed in many jurisdictions. On March 3, 1983, a government-funded research team (VIRL.codep study) estimated that nearly 17% of landfills around the world are byproducts of concrete-based waste.
World record
The world record for the largest concrete pour in a single project is the Three Gorges Dam in Hubei Province, China by the Three Gorges Corporation. The amount of concrete used in dam construction is estimated to reach 16 million cubic meters for 17 years. The previous record was 12.3 million cubic meters held by the Itaipu hydropower station in Brazil.
The world record for concrete pumping was set on August 7, 2009 during the construction of the Parbati Hydroelectric Project, near the village of Suind, Himachal Pradesh, India, when the concrete mixture was pumped through a vertical altitude of 715 m (2,346 ft)..
The world record for a continuously poured concrete raft reached in August 2007 in Abu Dhabi by an Al Habtoor-CCC Joint Venture contracting company and a concrete supplier is the Unibeton Ready Mix. Pour (part of the foundation of the Abu Dhabi Landmark Tower) is 16,000 cubic meters of concrete poured in two days. The previous record, 13,200 cubic meters was poured in 54 hours despite a severe tropical storm requiring sites to be covered with tarpaulins to allow work to continue, achieved in 1992 by a consortium with Japan and South Korea Hazama Corporation and Samsung C & T Corporation for the construction of Petronas Tower in Kuala Lumpur, Malaysia.
The world record for the largest concrete floor that is constantly poured over 8 November 1997, in Louisville, Kentucky by the design-build company EXXCEL Project Management. The monolithic placement consists of 225,000 square feet (20,900 m 2 ) of concrete placed in a 30-hour period, completed with a flatness tolerance of F F 54.60 and the tolerance levelness of F L 43,83. This surpassed the previous record of 50% in total volume and 7.5% in total area.
The record for the largest continuously placed underwater concrete pour was completed on October 18, 2010, in New Orleans, Louisiana by contractor C. J. Mahan Construction Company, LLC of Grove City, Ohio. This placement consists of 10,251 cubic meters of concrete placed in a period of 58.5 hours using two concrete pumps and two batches of special concrete batches. Once maintained, this placement allows cofferdam of 50,180 square feet (4,662 m 2 ) to be dried about 26 feet (7.9 m) below sea level to enable the construction of the Inner Navigation Port Sill & amp; The Monolith project will be completed in a dry place.
See also
References
Bibliography
- Matthias Dupke: Textilbewehrter Concrete als Korrosionsschutz . Diplomica Verlag, Hamburg 2010, ISBNÃ, 978-3-8366-9405-6.
External links
- Concrete Chemistry on Periodic Video Table (University of Nottingham)
- Ã, "Concrete". New Student Reference Work . 1914.
- Why Roman concrete is still standing strong while the modern version decays
Source of the article : Wikipedia
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