Materials are the major item used in construction. In construction, various materials are used in various building components in combinations with other materials. The choice of materials used depends on factors such as the component specification, quality of material, availability of the materials, cost restrictions, etc. The materials under study are commonly used both in building, civil engineering as well as heavy engineering constructions. This study is limited to the following construction materials; cement, sharp sand, chippings, timber, and reinforcement bars.
It is a major constituent of concrete which is responsible for the hardening of the constituent materials of concrete through the process of hydration when mixed with water. Cement consists of about 12% of the total weight of concrete (Varghese, 2006). The construction industry is becoming dynamic in its requirements which have to lead to the existence of various types of cement in order to meet up with these requirements.
“There are many varieties of cement and numerous ways of classification. One of the simplest classifications is by the chemical constituent that is responsible for the setting or hardening of the cement. On this basis, the silicate and aluminate cement, wherein the setting agents are calcium silicates and aluminates, constitute the most important group of modern cement. Included in this group are the portland, aluminous, and natural cement” (Akers, 2001). Portland cement is the most commonly used cement in the construction industry today.
Manufacturing of cement
In the manufacture of cement, the raw materials are first mined and then ground to a powder before blending in predetermined proportions. The blend is fed into the upper end of a rotary kiln heated to 26000F to 30000F by burning oil, gas, or powdered coal. Because cement production is an energy-intensive process, reheaters and the use of alternative fuel sources, such as old tires, are used to reduce the fuel cost. (Burning tires provide heat to produce the clinker and the steel belts provide the iron constituent.)
Exposure to the elevated temperature chemically fuses the raw materials together into hard nodules called cement clinker. After cooling, the clinker is passed through a ball mill and ground to a fineness where essentially all of it will pass a No. 200 sieve (75 µm). During the grinding, gypsum is added in small amounts to control the temperature and regulate the cement setting time.
The material that exits the ball mill is Portland cement. It is normally sold in bags containing 50 Kg of cement. Four major compounds [lime (CaO), iron (Fe2O3), silica (SiO2), and alumina (Al2O3)] and two minor compounds [gypsum (CaSO4.2H2O) and magnesia (MgO)] constitute the raw materials (Akers, 2001).
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