Manufacturing process of concrete - Research Paper Example

? Concrete – History, Manufacturing Process, Properties and Application, List of Contents Concrete – Introduction History of Concrete Manufacturing process of concrete Properties of concrete Applications and Uses of Concrete Concrete Concrete is a composite construction material that is composed from different materials like cement, fly ash, aggregate, gravel, water and chemical admixtures. The word came from Latin language concretus that means compact and condensed. Concrete is a hardened building material that becomes solid and hard when it is mixed with water and placement due to hydration. It takes the shape of stone like hard material when water reacts with the cement and other components of concrete. Concrete has been used for wide variety of uses like construction of pavements, pipes. Architectural structures, gates, plots, building blocks and gate footings etc. (Robert and Hutchinson, 1999) It is widely believed that concrete is used for different purposes more than any other man made material. It is produced in heavy quantity and powers the industries providing employment to millions of people. According to the estimates over 5 billion concrete is produced and used everyday around the world for different construction purposes. Concrete plays such important role in the society that the modern day living could not be imagined without concrete. The essay aims to discuss concrete in details highlights its different aspects. The essay strives to trace the origins of concrete to unveil its history and identifies its properties, uses, applications and manufacturing process to provide extensive information and detailed knowledge about concrete. History of Concrete The history of concrete could be traced back to the ancient era. The work concrete has Latin origin that reflects that it was also used by the ancient Romans. Some historians also believe that ancient Romans were the first nation to make use of this substance. Some of the constructions done by the Romans that exist after the centuries are also made up of concrete like Pantheon in Rome etc. The concrete invented by the Romans is known by the name of hydraulic cement based concrete. The cement mostly used in concrete construction today is called Portland cement (Stella, 1996). Earlier clay was also used as bonding material to prepare the concrete by the Assyrians and Babylonian. The Egyptians introduced the use of lime and gypsum cement to make concrete. In 1756, the first modern concrete was invented by the British engineer John Smeaton. He used pebbles as coarse aggregate substances and mixing powered bricks in to the cement for the formation of concrete. In 1984, English inventor by Joseph Aspdin first time made the Portland cement that still play major role in the composition of modern day concrete. It is believed that the invention of Portland cement is the first and major landmark achieved in the history of modern concrete because it was the first true artificial cement produced by burning of limestone and clay together (Stella, 1996). Due to burning some chemical changes occurred in the properties of limestone and clay and their combination become stronger cement as compared with that produced with the plain crushed limestone. Along with cement aggregates are also used in the composition of concrete like sand, crushed stones, slag and ashes etc. Along with time several new materials were added as aggregate to bring variations in concrete. For instance, the reinforced concrete or Ferro-concrete was introduced in which metal like steel is imbedded. This concrete was invented in 1849 by a Parisian gardener Joseph Moneir. He made several garden pots and tubs with the concrete in which he used meshed iron as aggregate. His invention was exhibit in 1867 in Paris Exposition in which he not only show the use of reinforced concrete for making tubs and pots but also for the construction of railways, pipes, bridges and arches (Robert and Hutchinson, 1999). The invention o f the reinforced concrete was another important development in the history of concrete because it combines the tensile or bendable strength of metal that add strength to the concrete enabling it to withstand heavy loads. Due to the strength added to concrete it became possible to construct heavy structures with the help of concrete. The modern day construction is highly dependent upon concrete technology that has evolved as most important element of advanced constructions of buildings, structures and different types of objects. Today there have been several types of concrete invented that are categorized according to their installation methods and composition (Lancaster, 2005). Manufacturing process of concrete There are several steps involved in the manufacturing process of concrete including material selection and preparation of cement, mixing, and transportation to the site or compacting, curing and quality control. The process of concrete manufacturing simply follows these steps after which it becomes ready to use for the construction of any structure or object. First of all the required components for the concrete manufacturing are selected. Usually the proportion of one part cement to two fine aggregate to four part coarse aggregate is uses for concrete manufacturing. However, it is not necessary to follow this proportion in all the cases because the proportion of the components could be altered in order to adapt to the required strength of the structure. The cement for binding the compounded could be made from different materials like limestone, clay, silica or shale. The aggregates are almost 75 percent of the total volume of the concrete and they add strength to it. After the selection of the concrete components in the desired ratio and volume, they are ground together and a fine power is made. The material is then heated in high temperature to burn away all the impurities. In this process all the components are partially fuse together and a substance called clinker is formed. This substance is cooled and ground until it attains a fine consistency. A tube or ball mill is used for cooling down the clinker. When the clinker gets finely consistent cement is combined with the aggregates, fibres and water. At this stage, constant stirring motion is used so that all the aggregates could be evenly coated with the cement mixture. Constant attiring also assures that all the components are blended together completely. Fibres are chosen for the concrete according to the required strength and glass or plastic is generally used to make the concrete suitable for the tensile loads. All the materials meant to give any additional characteristic to the concrete are added to the materials in the mixing stage so that all the materials could be well blend with each other (Stella, 1996). After mixing the material is transported to the site where the concrete is placed and compacted. This process occurs just after the mixing process in order to avoid the separation of any ingredient from the mixture and to prevent the entrance of air bubbles into the mixture. An internal or external vibrator is used for compacting of the concrete or it is also done with the help of vibrating tables in which there are two shafts rotating in opposite directions for creating vertical vibration. After placement, the concrete is cured so that it could be prevented from drying too fast (Neville and Brooks, 1987). The moisture level at the time of hardening of the concrete determines the durability and strength of the concrete. When the concrete dries it decreases in size because the cement solidifies and reduces the size of the concrete. The concrete becomes week if the concrete is prevented from contracting and tensile stresses also develop in the concrete so the concrete is kept damp for several days when it is set for hardening. After curing the necessary quality assurance checks and tests are conducted using quality assurance charts and other tools that assure the strength of the concrete before it is used for the construction purpose (Lancaster, 2005). Properties of concrete The concrete could be examined according to its properties including strength, elasticity, tension and shrinkage cracking and expansion and shrinkage. The concrete has high compressive strength however its tensile length is usually relatively low due to which it is often reinforces with the strong in tension and durable materials like steel etc. The simple tensile strength of concrete is usually around 10-15 percent of its compressive strength so when the concrete is loaded in compression without compensation it fails from the tensile stresses. In order to cope up with this problem the elements of the concrete subjects to the tensile stresses are reinforced with the strong n tension materials. At low stress levels the elasticity of concrete remains constant however as the stress becomes higher the elasticity begins decreasing due to the occurrence of matrix cracking. The elasticity of the concrete is basically determined by the aggregated used in the manufacturing of the concrete. The elasticity of concrete is calculated using following equation provided by the American concrete institute. (Where wc = weight of concrete (pounds per cubic foot) and f'c = compressive strength of concrete at 28 days) (Neville and Brooks, 1987) The coefficient of thermal expansion of concrete remains at low level but it starts increasing when the concrete shrinks. The provision for concrete expansion is still very important because if no such provision is made there could be creation of large force that will cause cracks in such part of the structures that are not able to withstand the force. The thermal expansion coefficient of the concrete made from the Portland cement is 0.000008 to 0.000012 however; it could vary as the concrete gets mature and continues to shrink. The density of concrete varies according to the materials used for its manufacturing however generally it remains around 2,400 kg/m?. (Robert and Hutchinson, 1999) Due to the shrinking and tension the concrete structures often crack and it is a fact that all structures made from concrete crack up to some extent. It cracks because of the tensile stress produced from the shrinking and stresses occurred during the setting or use of the concrete. There are different methods invented by the experts to overcome the problem of cracks in the concrete. Fine fibres are often used along with the metal and other reinforcement elements so that the size and limits of the cracks could be limit down at lower levels. In some structures, joints and concealed caw cuts are also used in to concrete so that they could manage and hide the cracks. Applications and Uses of Concrete There are wide range of uses and applications of concrete. Due to its chemical composition it gets stone like consistency after missing with water and becomes ideal for building different structures and systems like roads, railways, bridges, water supply and sewerage systems. There are many different applications of concrete. It has been used for construction since ancient times. The modern day concrete has proved its application for construction, rebuilding, mending and decoration etc. It been used for several uses like the construction of dams, bridges, pools, houses, basements, tiles, pavement blocks, benches and lamp posts etc (Neville and Brooks, 1987). Different types of concretes have different applications like ready mixed concrete is the durable and hard type of concrete that is used for the construction of the durable and crack resistant structures. Another type is cast in place concrete that is the unhardened state of concrete. It is placed in mould and is used for foundations and slabs on grounds, walls, beams, roofs and pavement etc. The concrete is also used for decoration purpose. The life expectancy and durability of concrete is used to be higher than any other flooring material due to which it is often used for flouring and to add colour and texture in the pathways, interiors and driveways etc. The fibre cement concrete is made by mixing sand, cement and fibres. It has wood like appearance and is used for decorative shapes and trim applications (Lancaster, 2005). Concrete is also used for vegetation roofs in offices, hospitals and residential buildings. It provides prolonged building benefits to the structures because it functions as thermal mass and acoustical barrier. The Portland cement made concrete is used in the airport pavements, highways and secondary roads. There are several other popular and important application of concrete including Brick ledge application, construction of Brick/block walls and bases for gates, fences and poles, Beams, drain tiles, piers, steps and high Performance Admixtures (Robert and Hutchinson, 1999). References Neville, A. M. and Brooks J. J. (1987). Concrete Technology, NY: John Wiley & Sons, Inc. Robert M., Hutchinson, P. (1999). "On the Structure of the Roman Pantheon", Art Bulletin, Vol. 68 (1), p26 Lancaster, L. (2005). Concrete Vaulted Construction in Imperial Rome - Innovations in Context, Cambridge University Press Stella L. M. (1996). “Ancient Concrete Structures”, Concrete International, 18(2), pp. 56–58 Read More