Coal- Its Composition, Classification, Formation and Indian Occurences

Introduction

The term COAL generally applied to a sedimentary formation of highly carbonaceous character that is derived from vegetable matter involving of set of processes such as burial, compaction, and biochemical transformation.

The principal constituents of coal are fixed carbon, moisture, volatile matter and mineral matter. The fixed carbon is actually a part of hydrocarbons that are the source material of coal.

Chemical Composition of Coal

Coal is composed chiefly of carbon, oxygen, hydrogen, nitrogen, traces of Sulphur and  phosphorus, carbon being major components. Besides these, coals may contain varying proportions of mineral matter which may be residues of the mineral constituents of the plants from which coals are derived.

The chemical composition of coal may be in the following ranges:

• Carbon (60 to 90%)
• Oxygen (2 to 20%)
• Hydrogen (1 to 12%)
• Nitrogen (1 to 3%)

Among the mineral matter, silica is quite common; besides variable proportions of alumina, iron oxides, salts of sodium, potassium, calcium and mineral grains of beryllium, nickel, cobalt and sometimes traces of uranium, molybdenum, gallium and vanadium may also be present in some cases.

Classification of Coal

Various types of pulverized fuel ashes (IS 4305)

Ash is generated by the burning of ground or pulverized or crushed coal or lignite-fired boilers. It can be fly ash, bottom ash, pond ash, or mound ash. As per IS 4305, it may be of the following types:

Siliceous Pulverized Fuel Ash — Pulverized fuel ash with reactive calcium oxide less than 10 percent, by mass. Such fly ash is normally produced from burning anthracite or bituminous coal and has pozzolanic properties.

Calcareous Pulverized Fuel Ash — Pulverized fuel ash with reactive calcium oxide not less than 10 percent by mass. Such fly ash is normally produced from lignite or sub-bituminous coal and has both pozzolanic and hydraulic properties.

Reactive Calcium Oxide (CaO) — That fraction of the calcium oxide which, under normal hardening conditions, can form calcium silicate hydrates or calcium aluminate hydrates.

Fly Ash — Pulverized fly ash extracted from flue gases by any suitable process such as by cyclone separator or electrostatic precipitator. 

Bottom Ash — Pulverized fuel ash collected from the bottom of boilers by any suitable process. 

Pond Ash — Fly ash or bottom ash or both mixed in any proportion and conveyed in the form of water slurry and deposited in a pond or lagoon. 

Mound Ash — Fly ash or bottom ash or both mixed in any proportion and conveyed or carried in dry form and deposited dry. 

Source: IS 3812:2003

Everything about Ordinary Portland Cement (OPC)

Hydration of Cement - A brief information for beginners

Introduction

When water is added to cement, a chemical reaction occurs known as the hydration of cement.

• It is an exothermic reaction; heat evolved during it, known as heat of hydration.
• The product of this hydration of cement is Tobermorite Gel (`CaSO_{4}SiO_{2}H_{2}O`).
• It is called Tobermorite Gel due to its structural similarity to a naturally occurring mineral, Tobermorite.
• Commonly, it is referred to as C-S-H Gel.

Factors affecting the hydration of cement

Types Of Cementitious Materials

What are the cemetitious materials present in the concrete?