Concrete and cementmanufaturing and.pptx

concrete and cement
manufacturingunits
history

1. INTRODUCTION TO CEMENT HISTORY Assyrians and Babylonians were perhaps the first to use clay as cementing material. In ancient monuments, e.g. forts, places of worship and defence structures, stones have been invariably used as a construction material with lime as the binder. Records show that Egyptians have used lime and gypsum as cementing materials in the famous pyramids. Vitruvius, a Roman scientist, is believed to be the first to have the know how about the chemistry of the cementitious lime. One of the most notable examples of Roman work is the Pantheon. It consists of a concrete dome 43.43m in span. The calcareous cements used by the Romans were either composed of suitable limestones burned in kilns or were mixtures of lime and puzzolanic materials (volcanic ash, tuff) combining into a hard concrete. Vitruvius’s work was followed by the researches made by M. Vicat of France. Joseph Aspedin of Yorkshire (U.K.) was the first to introduce Portland cement in 1824 formed by heating a mixture of limestone and finely divided clay in a furnace to a temperature high enough to drive off the carbonic acid gas. In 1845, Issac C. Johnson invented the cement by increasing the temperature at which the mixture of limestone and clay were burned to form clinker. This cement was the prototype of the modern Portland cement. From then onwards, a gradual improvement in the properties and qualities of cement has been made possible by researchers in U.S.A., U.K., France and Germany. Cements in a general sense are adhesive and cohesive materials which are capable of bonding together particles of solid matter into a compact durable mass

2. DEFINITION A building material made by grinding calcined limestone and clay to a fine powder, which can be mixe d withwater and poured to set as a solid mass or used as an ingredient in making mortar or concrete. b. Portland cement. c. Concrete. 2. A substance that hardens to act as an adhesive; glue. 3. Something that serves to bind or unite: "Custom was in early days the cement of society" (Walter Ba gehot ). 4. Geology A chemically precipitated substance that binds particles of clastic rocks. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry, or with sand and gravel, produces concrete. Cement is the most widely used material in existence and is only behind water as the planet's mostconsumed resource Cements used in construction are usually inorganic, often lime or calcium silicate based, and can be characterized as either hydraulic or non-hydraulic, depending on the ability of the cement to set in the presence of water (see hydraulic and non-hydraulic lime plaster

3. Non-hydraulic cement does not set in wet conditions or under water. Rather, it sets as it dries and reacts with carbon dioxide in the air. It is resistant to attack by chemicals after setting. Hydraulic cements (e.g., Portland cement) set and become adhesive due to a chemical reaction between the dry ingredients and water. The chemical reaction results in mineral hydrates that are not very water-soluble and so are quite durable in water and safe from chemical attack. This allows setting in wet conditions or under water and further protects the hardened material from chemical attack. The chemical process for hydraulic cement found by ancient Romans used volcanic ash( pozzolana ) with added lime (calcium oxide). The word "cement" can be traced back to the Roman term opus caementicium , used to describe masonry resembling modern concrete that was made from crushed rock with burnt lime as binder. The volcanic ash and pulverized brick supplements that were added to the burnt lime, to obtain a hydraulic binder, were later referred to as cementum , cimentum , cäment , and cement. In modern times, organic polymers are sometimes used as cements in concrete.

4. CHEMICIAL REACTIVITYFirst calcium oxide (lime) is produced from calcium carbonate (limestone or chalk) by calcination at temperatures above 825 °C (1,517 °F) for about 10 hours at atmospheric pressure: CaCO3 → CaO + CO2 The calcium oxide is then spent (slaked) mixing it with water to make slaked lime (calcium hydroxide): CaO + H2O → Ca(OH)2 Once the excess water is completely evaporated (this process is technically called setting), the carbonation starts: Ca(OH)2 + CO2 → CaCO3 + H2O This reaction takes time, because the partial pressure of carbon dioxide in the air is low. The carbonation reaction requires that the dry cement be exposed to air, so the slaked lime is a non-hydraulic cement and cannot be used under water. This process is called the lime cycle.

5. Conversely, hydraulic cement hardens by hydration when water is added. Hydraulic cements (such as Portland cement) are made of a mixture of silicates and oxides, the four main components being: Belite (2CaO·SiO2); C2S : Dicalcium Silicate(25%) Alite (3CaO·SiO2); C3S: Tricalcium Silicate-50% Tricalcium aluminate (3CaO·Al2O3) (historically, and still occasionally, called ' celite ');C3A (10%) Brownmillerite (4CaO·Al2O3·Fe2O3). Tetracalcium Aluminoferrite (10%) Gypsum (5%) The silicates are responsible for the cement's mechanical properties—the tricalcium aluminate and brownmillerite are essential for formation of the liquid phase during the kiln sintering (firing). The chemistry of these reactions is not completely clear and is still the object of research.

6. Cement starts to set when mixed with water, which causes a series of hydration chemical reactions. The constituents slowly hydrate and the mineral hydrates solidify. The interlocking of the hydrates and hardening rapidly gives cement its initial set and early strength.. Contrary to popular belief, hydraulic cement does not set by drying out—proper curing requires maintaining the appropriate moisture content during the curing process. If hydraulic cements dry out during curing, the resulting product can be significantly weakened. A minimum temperature of 5 °C is recommended Early strength of cement is higher with increased percentages of C3S. C3S: Tricalcium Silicate Dicalcium Silicate - Hydrates and hardens slowly. - Contributes largely to strength increase at ages beyond one week. - Responsible for long term strength : Tricalcium Aluminate - Liberates a large amount of heat during the first few days of hydration and hardening. -Also contributes slightly to early strength development. Gypsum added to the cement slows down the hydration rate of C3A. Cements with low percentages of C3A are especially resistant to soils and waters containing sulfates. Tetracalcium Aluminoferrit

7. 1)Portland cement OPC Portland cement is by far the most common type of cement in general use around the world. This cement is made by heating limestone (calcium carbonate) with other materials (such as clay) to 1,450 °C (2,640 °F) in a kiln, in a process known as calcination that liberates a molecule of carbon dioxide from the calcium carbonate to form calcium oxide, or quicklime—which then chemically combines with the other materials in the mix to form calcium silicates and other cementitious compounds. The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum into a powder to make ordinary Portland cement, the most commonly used type of cement (often referred to as OPC). Portland cement is a basic ingredient of concrete, mortar, and most non-specialty grout. The most common use for Portland cement is to make concrete. Concrete is a composite material made of aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast in almost any shape, an