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The construction material known as cement is defined as a binding force that undergoes a chemical reaction to hold two ingredients together . It also can be used to create the structures themselves. The construction of cement begins with a mixture of limestone and sand. They place this mixture in a kiln and heat it to 1480 degrees Celsius (The Chemistry). As it is heated, CO2 is driven off and the chemical properties of the limestone and sand change. This, as mentioned before, is known as the calcining reaction. The limestone turns into lime (The Chemistry). The final product is ground finely. This is cement. The release of CO2 is one of the dangerous environmental risks that the creation of cement creates. To harden the cement, it is mixed with water. This reaction, the hydration reaction, goes on for years hardening the cement until the reaction ends. Modern cement contains five common compounds, unlike more archaic or natural cement. The powdered cement is comprised mainly of lime (CaO), silica (sand, SiO2), alumina (Al2O3), iron (III) oxide (Fe2O3), and magnesium oxide (MgO) (Maslow 1). The compound of alumina is a white powder used to create pure aluminum metal (Queensland). It is found naturally in bauxite and has to be refined (Queensland). In addition to these compounds, others can be added to change the desired properties of the cement to increase durability or shorten the drying time. One such compound is a superplasticizer. These special polymers increase the strength by decreasing the water needed to create workable cement (Vaughan). Another additive used in cement is a retarding agent. Obviously these agents delay the setting time required to harden cement. In addition to that, however, it increases the long-term strength of the cement. It also protects the cement from the adverse effects of high-temperature weather. One such retarding agent is sugar (Vaughan). Yes, sugar. When it is necessary to retard the hardening of cement, a water-reducing admixture can be used. Concrete with this admixture can be less strong than others (Maslow 17). Accelerating agents are also used in the construction of some cement. This additive obviously speeds the setting time of the cement. In addition to this, it offers more early strength. It also protects the cement from the adverse effects of low-temperature weather. One such additive is calcium chloride (Vaughan). Another common additive is an air-entraining agent. They improve the durability and workability, as well as reduce problems with the freeze-thaw cycle. These are made from special detergents (Vaughan). |
