Question

What is clinker? Why is gypsum added to it?

Short answer

A: Clinker is a nodular material produced in the process of manufacturing cement from raw materials such as limestone, clay, and other components. Gypsum (calcium sulfate dihydrate) is added to clinker during the grinding process to control the setting and hardening of cement, allowing for better workability and improved strength and durability of the hardened cement.

Step-by-step solution

Definition of Clinker

Clinker is a nodular material produced in the process of manufacturing cement, developed from the raw materials such as limestone, clay, and other components of the cement mixture (like fluxes). When these raw materials are heated at high temperatures (around 1400 to 1500°C), they undergo a series of chemical reactions to form new compounds that solidify and harden into clinker. Clinkers are then ground into a fine powder to create cement.

Gypsum's Role in Cement Making

Gypsum (calcium sulfate dihydrate) is added to clinker during the grinding process to control the setting and hardening of cement. Cement made from clinker alone would set too quickly, making it difficult to work with and compromising its structural strength. Gypsum helps to extend the setting time of cement, allowing for better workability and the opportunity for proper hydration to occur, which in turn results in improved strength and durability of the hardened cement. Typically, 3% to 5% gypsum by weight is added during the grinding process, depending on the desired setting time and strength requirements of the cement product.

Summing Up

In summary, clinker is a nodular material formed during the cement manufacturing process which, when ground into a fine powder, creates cement. Gypsum is added to clinker to control the setting and hardening of cement, improving its workability and final strength characteristics.