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Civil Engineering Essay

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The material used for construction or the materials used to produce other materials which may be used in construction is called construction material. construction material are: Cement,sand ,water. Concrete, Lime, Stones, Paints and Varnishes, Wood and Timber, Engineering Metals, Bituminous materials and Plastics, Rubber and Glass, Miscelleneous materials,

http://www.aboutcivil.org/engineering-materials.html
Cement

Bricklayer Joseph Asp din of Leeds, England first made portland cement early in the 19th century by burning powdered limestone and clay in his kitchen stove.

Portland cement, the basic ingredient of concrete, is a closely controlled chemical combination of calcium, silicon, aluminum, iron and small amounts of other ingredients sand to which gypsum is added in the final grinding process to regulate the setting time of the concrete. Lime and silica make up about 85% of the mass. Common among the materials used in its manufacture are limestone, shells, and chalk or marl combined with shale, clay, slate or blast furnace slag, silica sand, and iron ore.

Strength of cement

Also known as the mother of all engineering, it is the oldest, most simple and useful of all engineering sciences. Civil engineering is field of engineering sciences, related to construction, design and maintenance of buildings, dams, bridges, tunnels, highways etc.

sand

Sand is an extremely needful material for the construction but this important material must be purchased with all care and vigilance. Sand which is used in the construction purpose must be clean, free from waste stones and impurities. It is important to know what type of sand is beneficial for construction purpose as sand is also classified into three different forms that make it suitable for specific type of construction.

Sand is classified as: Fine Sand (0.075 to 0.425 mm), Medium Sand (0.425 to 2 mm) and Coarse Sand (2.0 to4.75 mm). However this classification of sand is further has types of sand in particular and on that basis only they are being incorporated in the construction. Read out the detailing of the types of sand:

Pit Sand (Coarse sand)

Pit sand is classified under coarse sand which is also called badarpur in common language. This type of coarse sand is procured from deep pits of abundant supply and it is generally in red-orange colour. The coarse grain is sharp, angular and certainly free from salts etc which is mostly employed in concreting.

River Sand

River sand is procured from river streams and banks and is fine in quality unlike pit sand. This type of sand has rounded grains generally in white-grey colour. River sand has many uses in the construction purpose such as plastering.

Sea Sand

As the name suggest, sea sand is taken from seas shores and it is generally in distinct brown colour with fine circular grains. Sea sand is avoided for the purpose construction of concrete structure and in engineering techniques because it contains salt which tends to absorb moisture from atmosphere and brings dampness. Eventually cement also loses its action when mixed with sea sand that is why it is only used for the local purpose instead of structural construction.

There are different standards for the construction purpose which must be checked and considered for the better construction. The requirement according to which sand is chosen should be like: * For plastering purpose the overall fine sand used must not be less than 1.5 while silt is preferred to not less than 4 percent. * For brick work fine sand used must not be less than 1.2 to 1.5 and silt is preferred is 4 percent generally. * Concreting work require coarse sand in modulus of 2.5 to 3.5 with not less than 4 percent silt content. * http://www.sereneinteriors.com/building-construction/types-of-sand-construction.html water

Pure and hygienic water is not only important for our life but also needed for quality construction. From the foundation till the completion of construction we must ensure the quality of water used. Here are few tips to know about water. Water is one of the most important elements in construction but people still ignore quality aspect of this element. The water is required for preparation of mortar, mixing of cement concrete and for curing work etc during construction work. The quality and quantity of water has much effect on the strength of mortar and cement concrete in construction work.

Quality of Water

The water used for mixing and curing should be clean and free from injurious quantities of alkalis, acid, oils, salt, sugar, organic materials, vegetable growth and other substances that may be deleterious to bricks, stone, concrete or steel. Potable water is generally considered satisfactory for mixing. The pH value of water should be not less than 6.

Effects of Bad Quality Water on Cement Concrete

It has been observed that certain common impurities in water affect the quality of mortar or concrete. Many times in spite of using best material i.e. cement, coarse sand, coarse aggregate etc. in cement concrete, required results are not achieved. Most of Engineers/Contractors think that there is something wrong in cement, but they do not consider quality of water being used. Some bad effects of water containing impurities are following. * Presence of salt in water such as Calcium Chloride, Iron Salts, inorganic salts and sodium etc. are so dangerous that they reduce initial strength of concrete and in some cases no strength can be achieved. There is rusting problem in steel provided in RCC.

 Presence of acid, alkali, industrial waste, sanitary sewage and water with sugar also reduce the strength of concrete.  Presence of silt or suspended particle in water has adverse effect on strength of concrete. Presence of oil such as linseed oil, vegetable oil or mineral oil in water above 2 % reduces the strength of concrete up to 25 %. 5. Presence of algae/vegetable growth in water used for mixing in cement concrete reduce of the strength of concrete considerably and also reduce the bond between cement paste and aggregate.

Concrete.

Concrete is a composite construction material composed primarily of aggregate, cement, and water. There are many formulations, which provide varied properties. The aggregate is generally a coarse gravel or crushed rocks such as limestone, or granite, along with a fine aggregate such as sand. The cement, commonly Portland cement, and other cementitious materials such as fly ash and slag cement, serve as a binder for the aggregate. Various chemical admixtures are also added to achieve varied properties. Water is then mixed with this dry composite, which enables it to be shaped (typically poured) and then solidified and hardened into rock-hard strength through a chemical process called hydration. The water reacts with the cement, which bonds the other components together, eventually creating a robust stone-like material. Concrete has relatively high compressive strength, but much lower tensile strength. For this reason it is usually reinforced with materials that are strong in tension (often steel). Concrete can be damaged by many processes, such as the freezing of trapped water.

Types of Concrete.

Mix design

Modern concrete mix designs can be complex. The choice of a concrete mix depends on the need of the project both in terms of strength and appearance and in relation to local legislation and building codes. The design begins by determining the requirements of the concrete. These requirements take into consideration the weather conditions that the concrete will be exposed to in service, and the required design strength. The compressive strength of a concrete is determined by taking standard molded, standard-cured cylinder samples. Many factors need to be taken into account, from the cost of the various additives and aggregates, to the trade offs between, the “slump” for easy mixing and placement and ultimate performance.

A mix is then designed using cement (Portland or other cementitious material), coarse and fine aggregates, water and chemical admixtures. The method of mixing will also be specified, as well as conditions that it may be used in. This allows a user of the concrete to be confident that the structure will perform properly. Various types of concrete have been developed for specialist application and have become known by these names.. Concrete mixes can also be designed using software programs. Such software provide the user an opportunity to select their preferred method of mix design and enter the material data to arrive at proper mix designs.

Old concrete recipes

Concrete has been used since ancient times. Regular Roman concrete for example was made from volcanic ash (pozzolana), and hydrated lime. Roman concrete was superior from other concrete recipes (for example, those consisting of only sand and lime)[1] used by other nations. Besides volcanic ash for making regular Roman concrete, brick dust can also be utilized. Besides regular Roman concrete, the Romans also invented hydraulic concrete, which they made from volcanic ash and clay.

Modern concrete

Regular concrete is the lay term describing concrete that is produced by following the mixing instructions that are commonly published on packets of cement, typically using sand or other common material as the aggregate, and often mixed in improvised containers. The ingredients in any particular mix depends on the nature of the application. Regular concrete can typically withstand a pressure from about 10 MPa (1450 psi) to 40 MPa (5800 psi), with lighter duty uses such as blinding concrete having a much lower MPa rating than structural concrete. Many types of pre-mixed concrete are available which include powdered cement mixed with an aggregate, needing only water.

Typically, a batch of concrete can be made by using 1 part Portland cement, 2 parts dry sand, 3 parts dry stone, 1/2 part water. The parts are in terms of weight – not volume. For example, 1-cubic-foot (0.028 m3) of concrete would be made using 22 lb (10.0 kg) cement, 10 lb (4.5 kg) water, 41 lb (19 kg) dry sand, 70 lb (32 kg) dry stone (1/2″ to 3/4″ stone). This would make 1-cubic-foot (0.028 m3) of concrete and would weigh about 143 lb (65 kg). The sand should be mortar or brick sand (washed and filtered if possible) and the stone should be washed if possible. Organic materials (leaves, twigs, etc.) should be removed from the sand and stone to ensure the highest strength.

High-strength concrete

High-strength concrete has a compressive strength greater than 40 MPa (5800 psi). High-strength concrete is made by lowering the water-cement (W/C) ratio to 0.35 or lower. Often silica fume is added to prevent the formation of free calcium hydroxide crystals in the cement matrix, which might reduce the strength at the cement-aggregate bond. Low W/C ratios and the use of silica fume make concrete mixes significantly less workable, which is particularly likely to be a problem in high-strength concrete applications where dense rebar cages are likely to be used.

To compensate for the reduced workability, superplasticizers are commonly added to high-strength mixtures. Aggregate must be selected carefully for high-strength mixes, as weaker aggregates may not be strong enough to resist the loads imposed on the concrete and cause failure to start in the aggregate rather than in the matrix or at a void, as normally occurs in regular concrete. In some applications of high-strength concrete the design criterion is the elastic modulus rather than the ultimate compressive strength.

Stamped concrete

Stamped concrete is an architectural concrete which has a superior surface finish. After a concrete floor has been laid, floor hardeners (can be pigmented) are impregnated on the surface and a mold which may be textured to replicate a stone / brick or even wood is stamped on to give an attractive textured surface finish. After sufficient hardening the surface is cleaned and generally sealed to give a protection. The wear resistance of stamped concrete is generally excellent and hence found in applications like parking lots, pavements, walkways etc.

High-performance concrete

High-performance concrete (HPC) is a relatively new term used to describe concrete that conforms to a set of standards above those of the most common applications, but not limited to strength. While all high-strength concrete is also high-performance, not all high-performance concrete is high-strength. Some examples of such standards currently used in relation to HPC are:

Properties of concrete.

Uses of concrete.

Concrete is widely used for making architectural structures, foundations, brick/block walls, pavements, bridges/overpasses, motorways/roads, runways, parking structures, dams, pools/reservoirs, pipes, footings for gates, fences and poles and even boats. Famous concrete structures include the Burj Khalifa (world’s tallest building), the Hoover Dam, the Panama Canaland the Roman Pantheon.

Lime.
Manufacture of lime

Lime stones are burnt in either clamps or kilns.1. Clamps:For small quantity of limestone, burning is done in a clamp. On a clear surface about 5 meters in diameter, layers of broken limestones and fuel are laid to form a heap about 4 meters high.First and the last layers should be of the fuel. In case coal is used as fuel, it could be well mixed up with limestones and lay in a heap. Sides of the heap, which incline slightly inwards, are plastered over with mud to stop loss of heat. A little opening at the top is provided for draught. The clamp is then fired at the bottom.Disappearance of blue flame at the top is an indication of the burning of lime having completed. The clamp is then allowed to cool down and pieces of quick lime are then handpicked.Clamp burning of lime is uneconomical as the fuel consumption is more due to loss of heat and as some lime powder is lost in fuel ash. Also the quick lime carries any admixture of ash.|

2. Kiln for large quantity of lime, permanent structures of kilns are constructed.A. Intermittent kiln:Whenever the lime is desired intermittently or the supply of stones or fuel is not regular then the intermittent kiln is used. An intermittent kiln in which the fuel is not in contact with the lime is shown in the figure.Big pieces of limestones are used to make a sort of archon with which smaller pieces of limestone are loaded. Fire is lighted below the arch formed with big pieces of limestone. It is only the flame not the fuel that comes in contact with the stones. Burning should be gradual so that the stones forming the arch do not get split. It normally takes two days to burn and one day to cool the charge.

B. Continuous kiln:Wood or charcoal could be used as a fuel. Limestones or kankars free from earth or impurities are broken into small pieces to about 5cm gauge. Alternate layers of 75 mm stone and 6mm coal dust are fed into the kiln. Top should be covered with mud, leaving a hole of 0.5 meter diameter in the center. Burning proceeds continuously and the kiln is not allowed to cool down. Burnt material is drawn out daily and fresh charge of stone and fuel is added from top. Over burnt pieces are discarded whereas the under burnt ones are reloaded into the kiln. Remaining material is slaked or ground in grinding mill for use. |

a. Eminently rich lime:

It slakes rapidly. It consists of less than 5% of impurities such as silica and alumina (in clay form) and high %age of CaO. It is slow in setting and hardening and setting depends on CO2 from atmosphere, therefore rich lime is used for plastering but not mortar making. It may be used for inferior and temporary structures. B. Lean and poor lime:

It contains more than 5% clayey impurities and other impurities like silica, alumina, iron and magnesium oxides, exceeds 11%. Due to large amount of impurities it slakes slowly. It also sets and hardens very slowly. It is used both for plastering and mortar making for inferior class of work.

Advertisements| 1. Composition:Fat lime is produced from sea shell, coral deposits etc or from lime stone containing impurities like free sand and soluble silica combined with alumina, magnesium, carbonate etc. If the proportion of free sand is large, the resulting lime becomes progressively poor and is called poor or lean lime.2. Behavior in slaking:Fat lime slakes rapidly when water is added giving out considerable heat and making hissing and cracking noise and increases 2 to 3 times its original volume. Fat lime if exposed to air, it absorbs moisture and CO2 from the atmosphere and becomes inert CaCO3 or chalk again and loses its cementing power. For developing the cementing power, quick lime must be slaked with water as early as possible, after it is obtained from the kiln.|

3. Shrinking:Fat lime has a greater tendency to shrink and crack as it dries. To prevent this, a large quantity of sand (2 to 3 times) must be mixed with it to prepare mortar.4. Hardening or setting:Fat lime is hydrated calcium oxide and sets by the absorption of CO2 from the air.Ca (OH) 2 + CO2 ==> CaCO3 + H2OCrystals of CaCO3 are formed and the water goes by evaporation. Thus fat lime hardens only where it comes in contact with air, as in plaster work.In the interior of thick walls, it does not acquire strength as CO2 i.e. air cannot reach there. Mixing of sand (2 to 3 times) forms pores for access of CO2 and helps hardening.5. Strength:Crystals of CaCO3 formed by fat lime are not very strong. Fat lime, therefore, does not possess much strength and is used for plastering walls, while washing etc in exposed positions.

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