It is a common type of powdery cementitious building material made from finely pulverized alumina, iron oxide, lime, magnesia, and silica burnt together in a kiln. When mixed with water and sand (or gravel) it turns into masonry mortar (or concrete) and, after a series of complex internal reactions (hydration), sets like a stone.

Invented in 1824 by the UK bricklayer Joseph Aspdin (1779-1855), it gets its name from its resemblance upon hardening to the famous Portland limestone obtained from quarries on the Isle of Portland.

Ingredients used in the process in making Portland cement are usually materials such as limestone, marl, shale, iron, ore, and clay.

The process of manufacture of cement consists essentially of grinding the raw materials, mixing them intimately in certain proportions and burning in a large rotary kiln at a temperature of up to about 1450^oC when the material sinters and partially fuses into balls known as clinker. The clinker is cooled and ground to a fine powder, with some gypsum added, and the resulting product is the commercial Portland cement so widely used throughout the world.

EN 197-1 defines 5 classes of common cement that comprise Portland cement as a main constituent. They are as stated below:-

The definition according to ASTM-C150 is as below:-

Type I - For use when the special properties specified for any other type are not required.

Type IA - Air-entraining cement for the same uses as Type I, where air-entrainment is desired.

Type II - For general use, more especially when moderate sulfate resistance or moderate heat of hydration is desired.

Type IIA - Air-entraining cement for the same uses as Type II, where air-entrainment is desired.

Type III - For use when high early strength is desired.

Type IIIA - Air-entraining cement for the same use as Type III, where air-entrainment is desired.

Type IV - For use when a low heat of hydration is desired.

Type V - For use when high sulfate resistance is desired.

Blended hydraulic cements are produced by intimately and uniformly intergrinding or blending two or more types of fine materials. The primary materials are portland cement, ground granulated blast furnace slag, fly ash, silica fume, calcined clay, other pozzolans, hydrated lime, and pre-blended combinations of these materials.

The raw materials consisting of combinations of limestone, shells or chalk, and shale, clay, sand, or iron ore are mined from a quarry near the plant.

Gypsum plays a very important role in regulate the setting of cement. The amount of gypsum added to the cement clinker has to be very carefully matches, in particular an excess of gypsum leads to an expansion and consequent disruption of the set cement paste.

The compounds present in Portland cement react with water to form a cementitious crystalline structure that adheres to the sand and aggregate. This helps in binding the mass together and increases its strength till it becomes very hard.

When concrete hydrates, it hardens and gains strength. This hydration process continues over a long period of time. It occurs quickly at the outset and slows down as time passes. It would require a wait of several years before the strength of concrete can really be measured. Since this is impractical, a time period of 28 days was introduced by specification-writing authorities as the time where all concrete should be tested. In this period, a substantial percentage of the hydration has already taken place.

No. There is no universal international standard for Portland cement because every country has their own standard.

This is the term used to describe the stiffening of the cement paste, although the definition of the stiffness of the paste which is considered set is somewhat arbitrary. Broadly speaking, setting refers to a change from a fluid to a rigid stage. Although, during setting, the paste acquires some strength, for practical purposes it is important to distinguish setting from hardening, which refers to the gain of strength of a set cement paste.

In common with many chemical reactions, the hydration of cement compounds is exothermic, energy of up to 500J/g (120 cal/g) of cement being liberated. Because the thermal conductivity of concrete is comparatively low, it acts as an insulator, and in the interior, serious cracking may result. This behavior is, however, modified by the creep of concrete or by insulation of the surfaces of the concrete mass.

Concrete “shrinks” slightly as it hardens. A normal shrinkage rate is approximately 1/8” per 100 linear feet. This shrinkage is caused by loss of excess water from the mix. Obviously, the “wetter” the mix, the higher the shrinkage rate. Control joints should be placed in the concrete at intervals equal to 2.5 times (in feet) the thickness of the slab. For example, a slab 4” thick should have control joints every 10 feet.

These defects are generally a result of improper finishing of the concrete. As discussed earlier, the prime factor affecting concrete strength is water/cement ratio. If excess water is added to the surface of the concrete during placement and finishing, the water/cement ratio on the surface may be drastically increased. This condition greatly reduces the strength of the concrete on the surface. Unfortunately, this is where the wear takes place.

Fly ash, known also as pulverized-fuel ash (PFA), is the ash precipitated electrostatically or mechanically from the exhaust gases of coal-fired power station. It is the most common artificial pozzolana.

No, the color of cement does not effect the strength of cement in anyway. It just gives a proper finish to the concrete. There is a general misconception that the cement that is darker in color has greater strength, this is not true and the cement that is lighter in color not only has the same strength but also has a more pleasing finish than the cement that is darker in color.

17. Addition of fly ash in concrete is detrimental to its strength?

Not true. It might lower the early strength development depending on replacement level, but the late strength will be higher resulted from pozzolanic reaction between calcium hydroxide and fly ash.

The silo needs to be suitable for holding cement. It needs to be of sufficient size to accept full tanker loads of cement, and have some additional capacity to maintain your production whilst your next load is being delivered. In addition to these basic requirements, all cement silos are advised to be fitted with the following safety equipment: pressure relief valve & dust collector (both ducted to 1m of ground level).

As cement is likely to react with moisture or carbon dioxide in the air, it is advised to consume cement soonest possible after delivery. However, if cement being stand exceeded 3 months, it is suggested that the cement be tested for an increase in Loss of Ignition and other tests as required.