What is cement made of

Hello and welcome to "thecivilengineer18.com", your go-to source for all things Civil Engineering. In this article, we will explore what cement is made of, and to better understand this, we need to delve into the history of cement.

The use of binding materials for construction dates back to ancient times. The Egyptians used mud and straw as binding material, while the Romans used lime mortar, a mixture of lime, volcanic ash and small rocks that hardened after drying. After the decline of the Roman Empire, interest in binding materials waned until the 18th century when John Smeaton created a new mixture of lime and clay, which was the starting point for modern-day cement. Later in the mid-19th century, Joseph Aspdin introduced a new process of clinker formation, which is still used today to produce modern cement. The final product is a fine powder that hardens when treated with water, resembling the Portland rocks that can be obtained from the Portland island of England, hence the name Portland cement.

Today, there are a variety of cement available in the market, but they are blends of Portland cement. Among which Ordinary Portland Cement (OPC) is the most common. OPC is made up of three primary ingredients: limestone/lime, clay/shale, and gypsum.

Limestone/lime is the primary ingredient in cement production, mined from underground and mountains. Limestone contains calcium carbonate (CaCo3), which when heated at high temperatures (1,450 Celsius) with other raw materials like clay or shale, leads to clinker formation. Clinker is nothing but boulders of cement that are powdered as cement. During the clinker formation, the calcium carbonate gets converted into calcium oxide (CaO) and carbon dioxide (CO2). Then the calcium oxide reacts with others to form the Tricalcium Silicates (C3S), which reacts with water leading to the formation of the Calcium Silicate Hydrates (CSH) and Calcium Hydroxide (CaOH).

Clay/shale provides the silica and alumina for the formation of the Tricalcium Silicates (C3S), which are formed when lime and clay/shale are heated at high temperatures. The hydraulic properties of the cement are greatly affected by the amount of clay content in the clinker formation process.

Gypsum is added to the cement to prevent immediate setting/hardening of the cement, allowing for longer working hours of the concrete.

Other types of cement include Portland Pozzolana Cement (PPC), Rapid Hardening Cement, Extra Rapid Hardening Cement, Low Heat Cement, Sulfate-Resistant Cement, Blast Furnace Slag Cement, High Alumina Cement, White Cement, Colored Cement, Air-Entraining Cement, Expansive Cement, Hydrophobic Cement, and Portland Limestone Cement.

PPC is made up of materials that are used for OPC, but with a replacement of 15% to 35% of pozzolanic material (fly ash) in place of clinker material such as lime and clay. The final composition of PPC is 15% to 35% pozzolanic material (fly ash), 4% gypsum, and the rest is clinker. PPC is ideal for the construction of hydraulic structures such as dams, dykes, retaining walls, sewage pipes, and marine structures. It is also suitable for masonry mortar as well as wall plastering works.

Rapid hardening cement is obtained by blending aluminum sulfate during the clinker formation process and more finely powdered limestone than normal OPC. Aluminum sulfate increases the rate of the cement's hydration process. Rapid hardening cement is used where construction needs to speed up, such as road pavement where traffic management is critical.

We hope this article has been informative and helpful in understanding what cement is made of.


Popular Posts