Cement | Types of cement | History of cement | cement chemistry

 Cement

One of the most significant building materials is cement, which is a binding agent that sets and hardens to cling to building components like stones, bricks, and tiles. Cement is a fine powdered substance formed primarily of limestone (calcium), sand or clay (silicon), bauxite (aluminium), and iron ore, although it can also contain shells, chalk, marl, shale, clay, blast furnace slag, and slate. In cement manufacturing factories, raw materials are processed and heated to form a rock-hard substance, which is subsequently ground into a fine powder and sold. When cement is mixed with water, a chemical reaction occurs, forming a paste that sets and hardens to link separate building elements structures.

Cement is an important component of urban infrastructure. It's used to manufacture concrete and mortar, as well as to safeguard infrastructure by tying the building blocks together. Cement, water, sand, and gravel are mixed in specific amounts in concrete, whereas cement, water, and lime aggregate are used in mortar. Both are used to bond rocks, stones, bricks, and other building units, as well as to fill or seal gaps and create beautiful patterns. Cement mixed with water silicates and aluminates to form a water-repellent hardened aggregate used for waterproofing.

Cement is divided into two kinds based on the method of hardening and setting.

1.       Hydraulic Cement

2.       Non-hydraulic Cement

There are many different varieties of cement, based on its composition and features. The following are the other types of cement:

1.       Ordinary Portland Cement (OPC)

2.       Portland Pozzolana Cement (PPC)

3.       Rapid Hardening Cement

4.       Quick Setting Cement

5.       Low Heat Cement

6.       Sulphate Resisting Cement

7.       Blast Furnace Cement

8.       High Alumina Cement

9.       White Cement

10.   Colored Cement

11.   Air Entraining Cement

12.   Expansive Cement

13.   Hydrophobic Cement

History

Cement has been used in many forms since the dawn of human civilization, albeit it differs from the polished product available today. From volcanic ashes, crushed pottery, burnt gypsum, and hydrated lime to the first hydraulic cement used by the Romans in the middle ages, cement development continued until the 18th century, when James Parker patented Roman cement, which became popular but was eventually replaced by Portland cement in the 1850s.

In the nineteenth century, Frenchman Louis Vicat established the chemical composition of Portland cement, and Egor Cheliev publicised the methods of creating cement, as well as its uses and benefits in Russia. In England, Joseph Aspdin introduced Portland cement, and his son, William Aspdin, developed the "modern" Portland cement, which was quickly in high demand. However, Isaac Charles Johnson is widely regarded as the true father of Portland cement, having published the technique of generating meso-Portland cement in the kiln.

Rosendale cement was discovered in New York in the nineteenth century. Though its stiffness made it popular at first, market demand quickly dwindled due to its long curing period, and Portland cement reclaimed its position as the market leader. Catskill Aqueduct, on the other hand, developed a novel combination of Rosendale-Portland cement that is both highly durable and requires less drying time, and is now often used for highway and bridge building.

To suit the needs of today's world, cement has undergone extensive research, experimentation, and substantial advances, such as the development of strong concrete for roads and highways, hydraulic mortars that withstand sea water, and stucco for moist areas. Blast furnace cement, Portland fly-ash cement, Portland pozzolan cement, pozzolan-lime cement, slag-lime cement, and other modern cements, the majority of which are known as Portland cement or blends.

Cement chemistry

Cement is divided into two types based on how it is set and hardened: hydraulic cement, which hardens when water is added, and non-hydraulic cement, which hardens by carbonation with carbon in the air and so cannot be used underwater.

The following steps (lime cycle) are used to make non-hydraulic cement:

1. Calcination: Lime is produced from limestone at over 825°C for about 10 hours. (CaCO₃ → CaO + CO₂)
2. Slaking: Calcium oxide is mixed with water to make slaked lime. (CaO + H₂O → Ca(OH)₂)
3. Setting: Water is completely evaporated.
4. The cement is exposed to dry air and it hardens after time-consuming reactions. (Ca(OH)₂ + CO₂ → CaCO₃ + H₂O)

On the other hand, hydraulic cement is mainly made up of silicates and oxides:

1. Belite (2CaO·SiO₂);
2. Alite (3CaO·SiO₂);
3. Tricalcium aluminate/ Celite (3CaO·Al₂O₃)
4. Brownmillerite (4CaO·Al₂O3·Fe₂O₃)

In cement facilities, the ingredients are processed in the kiln. The complete chemistry of the reactions is currently being studied.

Ordinary Portland cement

Nowadays, the most often used cement is Portland cement or Portland cement blends, which is a hydraulic cement (i.e., it hardens when water is added). These are typically the primary ingredients in the production of concrete, a load-bearing construction material. Portland cement may be used underwater and is excellent for wet areas. Portland blast furnace slag cement, Portland fly-ash cement, Portland pozzolan cement, Portland-silica fume cement, masonry cement, expansive cement, white blended cement, coloured cement, and extremely finely ground cement are some of the several varieties or blends of Portland cement.

Composition of Portland cement

85% Portland cement clinker (37-72% of 3CaO.SiO₂; 6-47% 2CaO.SiO₂; 2-20% 2CaO.Al₂O₃; 2-19% 4CaO. Al₂O₃.Fe₂O₃), 1.5-3.5% gypsum by SO₃ content, up to 15% admixtures.

How is Portland cement made?

Limestone and other raw materials such as silicate, bauxite, iron ore, and others are heated in a cement plant so that carbon dioxide molecules are liberated from the limestone to make quicklime, which then reacts with the other components to form calcium silicates and other products. Clinker, a rock-hard material, is created in this way. The ultimate product, Portland cement, is made by mixing gypsum with clinker and grinding it into a fine powder.

The World's Cement Manufacturing Industries

In 2010, the United States, China, and India were the top three cement producers in the world. China alone produces around 45 percent of all cement produced around the world. Cement usage continues to rise globally since it is a non-recyclable substance that requires new cement for every new construction or repair. Cement manufacturing is a critical component of progress, particularly in Asian and Eastern European countries.

There are around 2273 operational cement production plants in the globe, according to the worldwide cement directory. LafargeHolcim, Anhui Conch, China National Building Materials, HeidelbergCement, Cemex, Italcementi, China Resources Cement, Taiwan Cement, Eurocement, and Votorantim are some of the biggest cement manufacturers. According to estimates from 2015, total global cement consumption reached 18 million metric tonnes, with the majority of this ascribed to North America's growing national economy.

 

The United States, France, Italy, and Germany are the main cement producers among developed capitalist countries. Iran, which is now the leading cement producer in the Middle East, is ranked third in the world. Cement production is also progressing in Asian and African countries.

Carbon dioxide is emitted during the kiln process in cement plants, which is one of the key greenhouse gases that contributes to global warming. Leading sectors are currently attempting to introduce technologies that use recyclable materials and renewable energy sources in order to reduce, if not eliminate, the detrimental environmental implications of cement usage. "Green cement" is a sustainable construction material that has been developed as a consequence of considerable research into mitigating the effects of global warming.

 

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