Animated Solution for Chemistry - s and p-Block Elements: The major component/ingredient of Portland cement is

Have you ever looked at a towering skyscraper or a massive bridge and wondered what holds it all together? The answer lies in a fine, unassuming grey powder known as Portland cement. But don't let its simple appearance fool you; chemically, it is a highly engineered mixture of calcium silicates and aluminates.

In this walkthrough, we are going to dissect the composition of Portland cement and identify its major ingredient—a classic, high-yield concept for JEE Chemistry.

The Chemical Roster

Portland cement is manufactured by heating limestone (a source of calcium) with clay (a source of silica, alumina, and iron oxide) in a rotary kiln at extremely high temperatures. This intense heat causes the raw materials to fuse and form complex compounds.

If we look at the final composition, we find several key players. Dicalcium silicate ($2\text{CaO}\cdot {\text{SiO}}_2$) makes up about $26\%$ of the mixture. It hydrates slowly and is responsible for the ultimate, long-term strength of the cement.

Then we have tricalcium aluminate ($3\text{CaO}\cdot {\text{Al}}_2{\text{O}}_3$), which constitutes around $11\%$. This compound reacts very rapidly with water, which is why a small amount of gypsum is added to the cement to prevent it from setting too quickly (a phenomenon known as flash setting).

The Undisputed King

While the minor components play crucial roles, they are not the stars of the show. The undisputed king of Portland cement is tricalcium silicate ($3\text{CaO}\cdot {\text{SiO}}_2$).

Tricalcium silicate alone constitutes a whopping $51\%$ of the entire mixture! Because it is present in such a massive proportion, it is the major component of Portland cement.

When water is added to the cement, tricalcium silicate hydrates rapidly. It is the primary compound responsible for giving the cement its initial, rapid strength during the first few days of setting.

Returning to our original question, we were asked to identify the major component or ingredient of Portland cement.

Given the composition: - Tricalcium silicate: $\sim 51\%$ - Dicalcium silicate: $\sim 26\%$ - Tricalcium aluminate: $\sim 11\%$ - Tetracalcium aluminoferrite: $\sim 9\%$

It is crystal clear that tricalcium silicate is the major ingredient. Therefore, the correct option is (b).

Next time you see a construction site, remember the complex chemistry happening right before your eyes. The rapid hardening of that grey slurry is all thanks to the dominance of tricalcium silicate!