Cement and Types of Cements...

Cement and Types of Cements Any substance which bonds materials is normally considered as cement. There are many types of cements. However in construction, the term cement generally refers to bonding agents that are mixed with water or other liquid, or both, to produce a cementing paste. Initially, a mass of particles coated with the paste is in a plastic state which can be formed, or moulded, into various shapes. Such a mixture is normally considered a cementitious material since it can bond other materials together. After a time, due to chemical reactions, the paste sets and the mass harden. When these particles consist of fine aggregate (sand) then mortar is formed. When these particles consist of fine and coarse aggregates then concrete is the result. In its simplest form, concrete is a mixture of paste and aggregates. The paste, composed of portland cement and water, coats the surface of the fine and coarse aggregates. Through the chemical reaction which is called hydration, the paste hardens and gains strength to form the rock-like mass known as concrete. Within this process lies the key to a remarkable trait of concrete is that it is plastic and malleable when newly mixed, strong and durable when hardened. Concrete’s durability, strength and relatively low cost make it the backbone of buildings and infrastructure worldwide houses, schools and hospitals as well as airports, bridges, highways and rail systems. It is the most-produced material on the mother earth. Even construction professionals sometimes incorrectly use the terms cement and concrete interchangeably. Cement is actually an ingredient of concrete. It is the fine powder which, when mixed with water, sand, and gravel or crushed stone (fine and coarse aggregate), forms the rock-like mass known as concrete. Though the history of cementing materials is...

Fly ash

                       Fly ash Fly ash is a product of combustion of coal. It is normally produced while burning coal in a boiler of a power plant and is generally captured before the flue gas goes to the chimney. The other ash from the boiler is bottom ash which is removed from the bottom of coal fired boiler. Depending upon the type of the coal used, the composition of the fly ash vary widely  but all the types of fly ash include silicon dioxide (SiO2) (both amorphous and crystalline) and calcium oxide (CaO). Fly ash is a fine glass like powder. The particle size of the ash is in microns. The composition of fly ash in case of bituminous coals is as follows: SiO2 – 20%- 60% Al2O3 – 7% – 35% Fe2O3 – 12% – 40% CaO – 2% – 12% LOI – 0%- 12% Fly ash contains environmental toxins in significant amounts. These toxins include arsenic (45 ppm); barium (805 ppm); beryllium (5 ppm); boron (310 ppm); cadmium (3 ppm); chromium (135 ppm); chromium VI (90 ppm); cobalt (35 ppm); copper (110 ppm); fluorine (30 ppm); lead (55 ppm); manganese (250 ppm); nickel (75 ppm); selenium (8 ppm); strontium (775 ppm); thallium (10 ppm); vanadium (250 ppm) and zinc (180 ppm). The use of fly ash as an engineering material is due to its pozzolanic nature, spherical shape, and relative uniformity. The following are the various uses of fly ash: Portland cement and and in materials for grout Embankments and structural fill Waste stabilization and solidification Raw feed for cement clinkers Mine reclamation Stabilization of soft soils Sub base for road Aggregates Flowable fill Mineral filler in asphaltic concrete Roofing tiles Filler in wood and plastic products Fly ash is used as a...