The Chemistry of Cement - Coursework Example

Cement & Portland cement Introduction Cement refers to a finely ground substance mainly produced by pulverization of clinker in a rotary kiln, which hardens gradually when mixed with water. Facilitation of hardening characteristic in this case results from numerous integrated materials including lime and shale as main components besides other additives whose respective roles are indispensable during kilning process (Thomas & Jennings, 2008). Currently, there are varied types of cements manufactured for specific purposes besides the ordinary ones meant for conventional roles in the construction sector. Their differences vary in the mode of manufacturing as well as how they behave once exposed to natural elements, for instance, water and atmospheric air. Main contributing factors that vary characteristics of any given type of cement include Tricalcium Aluminate (C3A) content and extent of fineness (Thomas & Jennings, 2008). The purpose of this study entails highlighting varied and essential aspects involved in the making of cement. Chemistry of Cement Cement to obtain required characteristics essential in combining diverse materials into a solid compact, its making encompasses mixing of numerous chemical ingredients. Most of these ingredients entail grounding (raw milling) and intimate mixing in a mixer. Afterwards, blended and reactive materials proceed to the rotary kiln where heating takes place at extremely elevated temperatures (Thomas & Jennings, 2008). Essential and main chemical components that comprise Portland cement include, Tricalcium Silicate, Ca3SiO5 – Alite This component’s role encompasses providing cement strength up to 28Th day and hydrates steadily giving out heat. Equation involved in this process include, 2C3S + 6H2O C3S2.3H2O + 3Ca (OH) 2 + Heat Dicalcium Silicate, Ca2SiO4 – Belite This composition is responsible in providing cement’s strength after the 28Th day whereby it hydrates moderately compared to the latter component giving also low amount of heat in comparison. 2C2S + 2H2O C3S2.3H2O + Ca (OH)2 + Heat Tricalcium Aluminate, Ca3Al2O6 – Aluminate Its role encompasses setting besides contributing slightly to the strength of cement once it has formed a strong and compact solid. Compared to other chemical compositions, it is readily attacked by Sulfate water once in contact with it producing much heat than the latter discussed cement elements. Setting process caused by C3A leads to the development of plastic stage, hence hindering the ordinary formation of concrete. Its chemical formula is, C3A + 6H2O C3A.6H2O + Much heat Tetracalcium Aluminoferrite, 4Ca2AlFeO5­ – Ferrite The presence of this component leads to the setting of lower rate than that of C3A and its concrete of solid compact is free from Sulfate attack once in contact with the solution. C4AF + H2O C4AHF Calcium oxide, CaO – Lime This is the main component or quantity of material, which is in abundance during kilning process. Calcium Sulfate Dihydrate, CaSO4.2H2O – Gypsum This component’s role is more of an additive than a material because it moderates the rate of setting to achieve an even and strong concrete formation. Cement Production First step encompasses preparation of material to their required size and condition. Mainly, this is size reduction of materials, which are bulky in size and cannot fit well in the rotary kiln besides ensuring intimate reaction of varied chemical components (ZKG, 2010). This process is raw milling mostly taking place in the field before transportation of lime (ZKG, 2010). Once materials arrive in the factory, mixing or blending of varied components takes place. This is to ensure uniform and intimate reaction of materials once they are in the kiln, which is always at high temperatures. However, these temperatures usually vary significantly in diverse sections. These include dehydration (- 4500C), Calcination (4500C to 9000C), solid-state reaction (9000 – to 13000C), clinkering section (13000C to 15500C) and finally cooling zone (Thomas & Jennings, 2008). After formation and cooling of clinker in silo, milling commences with addition of other essential additives whose role is to ensure cement attains its required condition before stored in silosg (ZKG, 2010). Milling entails feeding the clinker into a four-chamber or cemernt mill coupled with addition of gypsum and other components to produce a very fine powder, which is cement (Taylor et al. 2008). After milling, the fine powder based on materials may stay in the silo for sometime before packaging takes place. This is to allow final residue process take places effectively whereby afterwards packaging or bagging takes place before kept in warehouses ready for distribution and transportation to market. Figure 1: Climatetechwiki. (n.d). Cement Manufacturing Process. Types of Cement 1. Ordinary Portland cement (OPC) This is calcium silicate cement commonly used for all conventional purposes in the construction sector (Emmitt, Barry & Gorse, 2010). According to Emmitt, Barry & Gorse (2010), its calcining or kilning process requires approximately high temperatures of 13000C. Main components used in the making of this type embrace are lime and clay besides Gypsum, which acts as an additive meant to regulate mode of setting process (Emmitt, Barry & Gorse, 2010). 2. Rapid hardening Portland cement Main difference between this type of cement and OPC is the extent of finely ground powder mostly characterized by rapid setting (Emmitt, Barry & Gorse, 2010). This leads to more strength whereby within a duration of three days is comparable to that of OPC (Emmitt, Barry & Gorse, 2010). 3. Sulphate-Resisting Portland Cement Contrary to OPC, the lowest cont of C3A in this cement, this is usually below 5% increases its tendency to resist effects of sulphate conditions (Emmitt, Barry & Gorse, 2010). Hence, this makes it suitable for constructing structures, which in alkaline environment. 4. White Portland Cement Main components used to manufacture this type of cement encompass china clay and pure chalk, hence making them best for white concrete finishes (Emmitt, Barry & Gorse, 2010). Due to its color and high quality, it is expensive compared to other discussed types due to specific areas where masons prefer using them. 5. Low heat Portland cement Mostly preferred in constructions of dams and other related structures where other types might be unsuitable because heat of hydration causes them to undergo unwanted shrinkage (Emmitt, Barry & Gorse, 2010). 6. Water repellent Cement This is a combination of metallic soap and OPC or white Portland type (Emmitt, Barry & Gorse, 2010). Hence, from its name this cement usually exhibits low rate of water absorption, which makes it preferred for cast concrete (Emmitt, Barry & Gorse, 2010). 7. High alumina cement It is a combination of bauxite and chalk in equal quantities, which makes it fall off once used in hot moist settings (Emmitt, Barry & Gorse, 2010). Applications of Cement Common applications of cement include, Filling cracks that have developed in concrete structures Plastering and joints Making posts, for instance those of roadside lamps, telephone and railways (Brandt, 2009). Road constructions Cement Admixtures Conclusion References Brandt, A. M. (2009). Cement-Based Composites: Materials, Mechanical Properties and Performance, Second Edition. Boca Raton, Florida: CRC Press. Emmitt, S., Barry, R., & Gorse, C. A. (2010). Barry's advanced construction of buildings. Chichester, U.K: Wiley-Blackwell. Taylor, P. C., National Cooperative Highway Research Program., American Association of State Highway and Transportation Officials., United States., & National Research Council (U.S.). (2008). Specifications and protocols for acceptance tests on processing additions in cement manufacturing. Washington, D.C: Transportation Research Board. Thomas, J. & Jennings, H. (2008). The science of concrete. Retrieved from Zement Klk Gips International – ZKG. (2010). Grinding trends in the cement industry. Retrieved from Read More