CE 308: Structural Materials PDF

CE 308: Structural Materials 1. Cement Production Dr. Raid Alrashidi Civil Engineering Department, Jubail Industrial College Semester 461 Learning Objectives 1. To explain the raw materials used in manufacturing of cement 2. To explain brief...

CE 308: Structural Materials 1. Cement Production Dr. Raid Alrashidi Civil Engineering Department, Jubail Industrial College Semester 461 Learning Objectives 1. To explain the raw materials used in manufacturing of cement 2. To explain briefly the manufacturing process of cement 3. To explain the role of each chemical component of cement 2 Hydraulic and Nonhydraulic Cements Hydraulic cement – sets and hardens by reacting chemically with water to form a water-resistant product. The presence of air is not required for the hardening process. Example: Portland cement. Nonhydraulic cement - reacts with water to form a product which is not stable in water. The hydration product may then react with air to form a water-resistant product. Example: Quick Lime. mud I 3 Invention of Portland Cement Greeks and Romans had used a blend of lime and pozzolanic materials to produce a hydraulic cement. Modern Portland cement was invented by Joseph Aspdin, an English mason who obtained a patent for his product in 1824. He named his patent as “Portland cement” because it produced a concrete that resembled the color of the natural limestone quarried on the Isle of Portland, in England. 4 Portland Cement Production Portland cement is manufactured first by combining precise proportions of raw materials. The raw materials are generally a mixture of calcareous (calcium oxide, CaO) and argillaceous (silica SiO2 and alumina Al2O3). Raw materials used in manufacture of cement contain appropriate portion of the following: Lime (CaO) Silica (SiO2) s 5 Alumina (Al2O3) if 6 8 Iron (Fe2O3) 0 5 6 A 5 The cement industry commonly uses shorthand notation for these compound Sources of Raw Materials Common raw materials sources used in cement production 6 Steps in the Manufacture of the Portland Cement 1. Raw materials are quarried and produced and crashed The raw materials are crushed into 125 mm size, then to smaller size ~ 20 mm, and stored 7 Steps in the Manufacture of the Portland Cement 2. The crushed raw materials are ground to a powder and blended The raw materials, in the desired proportions, are passed through a grinding mill, using either a wet or dry process. The powdered raw materials are either blended in dry condition (dry process) or mixed with water to form slurry and blended (wet process) Nowadays, the dry process is commonly used. 8 Steps in the Manufacture of Portland Cement 3. The ground materials then sent to a rotating kiln for burning Kiln system has four stages: preheating, burning, cooling and clinker storage. In the kiln, the materials are melted at temperature of (1400 °C to 1650 °C) At temperature of ~ 1480 °C, a series of chemical reactions cause the materials to fuse and form cement clinkers. 9 Steps in the Manufacture of Portland Cement In 4. The clinkers are cooled and then ground (pulverized) After the clinker is ground, a small amount of gypsum is added to control the setting time of cement in the concrete and to allow for transport. Clinker with gypsum are mixed and ground together to a desirable fineness that passes through a (< 45 μm diameter) No. 325 mesh, leading to a final product called portland cement. Clinker 10 Video on Cement Manufacturing Please use this link to watch a video on cement production https://www.youtube.com/watch?v=TdxPxfeEUSQ 11 Chemical Composition of Cement After the raw materials were interacted (burned) in the kiln, four main chemical compounds were formed, and The final product of a Portland cement contains the following four chemical compounds, which make up over 90% by weight: Other components of Portland cement are: 1. Gypsum , which is added to control the rate of setting of cement, 2. Impurities, such as magnesium oxide (MgO). 12 Role of Compound Composition Hydration is the chemical reaction of cement with water to form a hardened paste. The reaction is exothermic (heat is generated.) 1. C3S Hydrates and hardens rapidly Largely responsible for initial set and early strength 2. C2S Hydrates and hardens slowly Contributes largely to strength increase at ages beyond one week 3. C3A Hydrates rapidly and liberates a large amount of heat Contributes slightly to the early strength A cement with a high C3A content is more susceptible to sulfate attacks, which cause expansion and cracking 4. C4AF Contributes little to strength. However, its presence reduces the clinkering temperature in the production of cement, and thus helps to reduce cost. 13