The truth about the world's most argued flyover

Cement is the second basic ingredients along with aggregates and water. cement interacts with water to develop a binding material that acts as a glue to bind the aggregates. As a matter of fact, cement is not the only binding material being used, but it is the most commonly used material.

In this article we will be discussing the cement (portland cement, to be specific) and its role in a concrete mix.

Portland cement

Portland cement was developed by Joseph Aspdin in 1824, so named because its color and quality are similar to a kind of limestone, Portland stone (Portland, England).

Manufacturing process of Portland cement

Portland cement is made by blending an appropriate mixture of limestone and clay or shale

together, and by heating them to 1450◦C in a rotary kiln. Currently, the capability of a rotary

kiln can reach 10,000 metric tons daily.

Cement production line - Hai Luo Cement Company, China

The sequence of operations, in which the preliminary steps are a variety of blending and crushing operations. The raw feed must have a uniform composition and be of fine enough size that reactions among the components can be completed in the kiln. Subsequently, the burned clinker is ground with gypsum to form the familiar gray powder known as Portland cement.

The basic raw materials used for manufacturing Portland cement are limestone, clay, and iron ore. For geeks who would like to get the full chemical reaction that leads to the cement formation, I prepared this article specially for you. For the rest of us we will now move on to the reaction between cement and water in the process of "Hydration"

Hydration

Hydration of cement is the reaction between cement particles and water, including chemical and physical processes. The properties of fresh concrete, such as setting and hardening, are the direct results of hydration. The properties of hardened concrete are also influenced by the process of hydration. Hence, to understand the properties and behavior of cement and concrete, some knowledge of the chemistry of hydration is necessary.

Hydration of pure cement compounds

Clinker is anhydrous (without water) having come from a hot kiln. Cement powder is also anhydrous if we ignore the small amount of water in any gypsum added at the clinker grinding stage. The reaction with water is termed "hydration". This involves many different reactions, often occurring at the same time. As the reactions proceed, the products of the hydration process gradually bond together the individual sand and gravel particles, and other components of the concrete, to form a solid mass.

By the process of hydration (reaction with water) Portland cement mixed with sand, gravel and water produces the synthetic rock we call concrete. Concrete is as essential a part of the modern world as are electricity or computers.

The mechanism of hydration of the cement as whole is very complex and has not been fully understood yet. So far, the only approach to studying the hydration of Portland cement is to investigate the reaction mechanism of individual compounds separately. This assumes that the hydration of each compound takes place independently and no interaction occurs. Although this assumption is not valid completely, it helps to understand the chemistry of hydration.

When water is added, the reactions which occur are mostly exothermic, that is, the reactions generate heat. We can get an indication of the rate at which the minerals are reacting by monitoring the rate at which heat is evolved using a technique called conduction calorimetry. 

An illustrative example of the heat evolution curve produced is shown below.

Schematic of the rate of hydration or heat evolution as a function of time.

Now again, for geeks who would like to dive deeper into the chemistry of hydration, I am humbly inviting you to visit this page dedicated for the subject.