Cement Production
INTRODUCTION
Cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed rock with burnt lime as binder. The volcanic ash and pulverized brick additives that were added to the burnt lime to obtain a hydraulic binder were later referred to as cementum, cimentum, cäment, and cement.
Cement is made by grinding together limestone and shales (a mixture of aluminosilicates) and heating the mixture to about 1500oC. The chemical reaction releases carbondioxide and partially melts the components to form solid lumps called clinker. The clinker is ground to powder, and a small quantity of calcium sulfate is mixed in. This mixture is known as Portland Cement.
Chemically, its main components are 26% dicalcium silicates ( Ca2SiO4); 51% tricalcium silicates (Ca3SiO5); and 11% tricalcium aluminate (Ca3Al2O6). When water is added, a number of complex hydration reactions take place. A typical idealized reaction can be represented as
2 Ca2SiO4(s) + 4 H2O(l) Ca3Si2O7. 3H2O(s) + Ca(OH)2(s).
The hydrated silicate, called tobermorite gel, forms strong crystals that adhere by means of strong silicon-Oxygen bonds to the sand and aggregate (small rocks) that are mixed with the cement. Because the other product in this reaction is Calcium hydroxide, the mixture should be treated as a corrosive material while it is hardening.
Cements used in construction can be characterized as being either hydraulic or non-hydraulic. Hydraulic cements (e.g., Portland cement) harden because of hydration, a chemical reaction between the anhydrous cement powder and water. Thus, they can harden underwater or when constantly exposed to wet weather. The chemical reaction results in hydrates that are not very water-soluble and so are quite durable in water. Non-hydraulic cements do not harden underwater; for
Cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed rock with burnt lime as binder. The volcanic ash and pulverized brick additives that were added to the burnt lime to obtain a hydraulic binder were later referred to as cementum, cimentum, cäment, and cement.
Cement is made by grinding together limestone and shales (a mixture of aluminosilicates) and heating the mixture to about 1500oC. The chemical reaction releases carbondioxide and partially melts the components to form solid lumps called clinker. The clinker is ground to powder, and a small quantity of calcium sulfate is mixed in. This mixture is known as Portland Cement.
Chemically, its main components are 26% dicalcium silicates ( Ca2SiO4); 51% tricalcium silicates (Ca3SiO5); and 11% tricalcium aluminate (Ca3Al2O6). When water is added, a number of complex hydration reactions take place. A typical idealized reaction can be represented as
2 Ca2SiO4(s) + 4 H2O(l) Ca3Si2O7. 3H2O(s) + Ca(OH)2(s).
The hydrated silicate, called tobermorite gel, forms strong crystals that adhere by means of strong silicon-Oxygen bonds to the sand and aggregate (small rocks) that are mixed with the cement. Because the other product in this reaction is Calcium hydroxide, the mixture should be treated as a corrosive material while it is hardening.
Cements used in construction can be characterized as being either hydraulic or non-hydraulic. Hydraulic cements (e.g., Portland cement) harden because of hydration, a chemical reaction between the anhydrous cement powder and water. Thus, they can harden underwater or when constantly exposed to wet weather. The chemical reaction results in hydrates that are not very water-soluble and so are quite durable in water. Non-hydraulic cements do not harden underwater; for
References: 1. Hewlett, Peter (2003). Lea 's Chemistry of Cement and Concrete. Butterworth-Heinemann. 2. Justnes, H.; Ronin, V. Performance of Energetically Modified Cement (EMC) and Energetically Modified Fly Ash (EMFA) as Pozzolan. SINTEF. Retrieved 5 November 2013. 3. Van Oss, Hendrik G.; Padovani, Amy C. (2002). "Cement Manufacture and the Environment, Part I: Chemistry and Technology". Journal of Industrial Ecology. 4. Van Oss, Hendrik G.; Padovani, Amy C. (2003). "Cement Manufacture and the Environment, Part II: Environmental Challenges and Opportunities". Journal of Industrial Ecology. 5. Geoff Ratner – Canham, and Tina Overton. ‘’Descriptive Inorganic Chemistry’’. 3rd edition (2002).