Cement, one of the most significant building materials, is a binding agent that solidifies and hardens to bond to building components such as stones, bricks, and tiles. Cement is a very fine powdery substance composed primarily of limestone (calcium), sand or clay (silicon), bauxite (aluminum), and iron ore, although it may also contain shells, chalk, marl, shale, clay, blast furnace slag, and slate. In cement manufacturing plants, raw materials are processed and heated to form a rock-hard substance that is then pulverized into a fine powder for sale. When cement is mixed with water, a chemical reaction occurs, resulting in a paste that sets and hardens to link separate construction elements.
Cement is an essential component of the urban infrastructure. It is used to manufacture both concrete and mortar, as well as to secure infrastructure by binding building blocks together. Concrete is composed of cement, water, sand, and gravel in certain quantities, whereas mortar is composed of cement, water, and lime aggregate. Both are used to bind rocks, stones, bricks, and other building materials, fill or seal gaps, and create beautiful patterns. Cement mixed with water silicates and aluminates forms a hardened mass that repels water and is used for waterproofing.
Cement, while distinct from the polished product found today, has been employed in a variety of applications from the beginning of human civilization. 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 gained popularity before being replaced by Portland cement in the 1850s.
In the nineteenth century, Frenchman Louis Vicat provided the groundwork for the chemical composition of Portland cement, while in Russia, Egor Cheliev revealed the methods of creating cement, its uses, and benefits. Joseph Aspdin introduced Portland cement to the market in England, and his son, William Aspdin, created the “modern” Portland cement, which was quickly in high demand. However, Isaac Charles Johnson is often regarded as the true founder of Portland cement, having made significant contributions by publishing the technique of generating meso-Portland cement in the kiln.
In the nineteenth century, Rosendale cement was discovered in New York. Though its stiffness made it fairly popular at first, market demand quickly fell because of its long curing period, and Portland cement was once again the preference.
Today’s cement has undergone extensive experimentation, testing, and substantial advancements to satisfy the needs of the modern world, such as the development of strong concretes for roads and highways, hydraulic mortars that can withstand seawater, and stucco for damp environments. Modern cement comes in a variety of forms, the majority of which are known as Portland cement or mixes, such as blast furnace cement, Portland fly-ash cement, Portland pozzolan cement, pozzolan-lime cement, and slag-lime cement.
Cement is classified 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 through carbonation with carbon in the air, making it unsuitable for use underwater.
Non-hydraulic cement is manufactured using the following steps (lime cycle):
Calcination: Lime is generated by heating limestone at temperatures above 825°C for approximately 10 hours. (CaCO3 to CaO + CO2)
Slaking: Calcium oxide is combined with water to produce slaked lime. CaO + H2O yields Ca(OH)2.
Setting: Water has completely evaporated.
The cement is exposed to dry air and hardens after several time-consuming processes. Ca(OH)2 + CO2 = CaCO3 + H2O.
Hydraulic cement, on the other hand, is mostly composed of oxides and silicates.
Belite (2CaO·SiO2), Alite (3CaO·SiO2), and Tricalcium aluminate/Celite (3CaO·Al2O3).
Brownmillerite (4 CaO·Al2O·Fe2O3)
Cement companies use kilns to process their materials. The entire chemistry of the reactions is still being researched.
The most prevalent type of cement used today is hydraulic cement (which hardens when water is added), also known as Portland cement or Portland cement mixes. These are typically the primary ingredients required in the production of concrete, a load-bearing construction material. Portland cement is suited to wet environments and can be utilized underwater.Portland cement comes in a variety of forms and blends, including Portland blast furnace slag cement, Portland fly-ash cement, Portland pozzolan cement, Portland-silica fume cement, masonry cement, expansive cement, white blended cement, colored cement, and extremely finely ground cement.
Portland cement consists of 85% Portland cement clinker (37-72% 3CaO.SiO2; 6-47% 2CaO.SiO2; 2-20% 2CaO.Al2O3; 2-19% 4CaO. Al2O3.Fe2O3), 1.5-3.5% gypsum by SO3 content, and up to 15% admixtures. For more details, read: Eight Main Cement Ingredients and Their Functions.
In a cement manufacturing plant, limestone and other raw materials such as silicate, bauxite, iron ore, and so on are heated until carbon dioxide molecules are liberated from the limestone to form quicklime, which combines with the other ingredients to form calcium silicates and other products. Thus, clinker, a rock-hard material, is created. Gypsum is added to the clinker and then processed into a fine powder, yielding the finished product known as Portland cement.
Cement Manufacturing Industries around the World
As of 2010, the United States, China, and India were the world’s top three cement manufacturers. China alone accounts for around 45% of global cement output.
Cement usage continues to expand globally since it is a non-recyclable substance that requires new cement for each new construction or repair. Cement manufacturing is a key driver of economic growth, particularly in Asia and Eastern Europe.
According to the global cement directory, there are around 2273 operational cement production units worldwide. Some of the leading cement manufacturers are LafargeHolcim, Anhui Conch, China National Building Materials, HeidelbergCement, Cemex, Italcementi, China Resources Cement, Taiwan Cement, Eurocement, and Votorantim. According to 2015 figures, total global cement consumption reached 18 million metric tons, the majority of which was attributable to North America’s increasing national economy.
The top cement producers in developed capitalist countries are the United States, France, Italy, and Germany. Iran, being the leading producer in the Middle East, ranks third in the world for cement production. Asian and African countries have also made progress in cement output.
The kiln process in cement plants emits carbon dioxide, one of the principal greenhouse gases responsible for global warming. To reduce, if not eliminate, the negative environmental effects of cement use, leading firms are currently attempting to implement solutions that use recycled materials and renewable energy sources. “Green cement” is a sustainable construction material that is the outcome of substantial research into mitigating the consequences of global warming.
Cement is mainly classified into two categories depending on the hardening and setting mechanism. These are:
Hydraulic Cement and
Non-hydraulic Cement
Cement is a binding substance that bonds aggregates and reinforcing elements together. As technology advanced, so did the quality and variety of cement. As a result, several cement varieties exist for different construction applications.
There are several types of cement, in addition to these primary ones, based on their composition and features.
The following are the other cement types:
Ordinary Portland Cement (OPC) and
Portland Pozzolana Cement (PPC)
Rapid hardening Cement is quick to set and requires little heat. Cement is sulfate resistant. Cement Blast Furnace Cement with high alumina Cement can be white or colored. Air Entraining Cement: Expansive. Hydrophobic cement.
Brief descriptions of these cement types with their uses are given below:
Hydraulic Cement
Hydraulic cement, as the name implies, hardens when exposed to water. The main raw materials used to make non-hydraulic cement are limestone, clay, and gypsum. This raw material is burned at extremely high temperatures to produce Hydraulic Cement.
Hydraulic cement (cement that not only hardens when exposed to water but also creates a water-resistant product) is made by pulverizing clinkers that are primarily composed of hydraulic calcium silicates and frequently contain one or more kinds of calcium sulfate as an interground addition.
Non-hydraulic Cement
The non-hydraulic cement does not require water to harden. It absorbs carbon dioxide (CO2) from the air. This sort of cement requires dry conditions to solidify. Non-hydraulic cement is made from limestone, gypsum plasters, and oxychloride. For example, slaked lime is not a hydraulic cement.
OPC Cement
Hydraulic cement that hardens on contact with water. It is highly versatile and can be used in a variety of applications including concrete, mortar, plaster, foundations, walls, roofs, beams and columns. OPC is the most common type of cement, but it has a high carbon footprint, an energy-intensive manufacturing process, and slow curing times compared to other types of cement.
PCC Cement
A synthetic cement that is the reaction of OPC and pozzolanic materials such as volcanic ash, fly ash, and slag. PPC is more cost-effective than OPC, more environmentally friendly, and has higher resistance to alkaline reactions and marine corrosion. Suitable for quick construction. B. Mass concrete placement for bridges, RCC placement for structures, and plastering work. However, PPC is not suitable for mass concrete because it has slower setting times and heat-related problems than OPC.