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Know Your Cement

Cement Production In India
  • What is cement?
  • History of Cement
  • Types of cement
  • Cement Industry
  • Innovation

Intro

Cement serves the purpose of a binder, a substance widely used in construction that sets and hardens and can bind other materials together in it. Manufactured strictly with precise processes it is very fine mineral powder. Mixed with water, this powder transforms into a paste known for its binding properties which gets harder when submerged in water. Cement has different properties depending upon its makeup. This is because not only the composition of cement but also the fineness may potentially vary.

Depending on what material is mixed with cement, it results in the following variants:
  • Cement mixed with water, sand and gravel, forms concrete. It is the main component of concrete. It's an economical, high-quality construction material used in construction projects worldwide.
  • Cement mixed with water and sand forms cement plaster.
  • Cement mixed with water, lime and sand, forms mortar.

Cement is usually grey but also found in white, which is usually more expensive than grey cement.

Chemistry of Cement

Cement is an organic material obtained by mixing together materials such as limestone, sand, clays and iron ores; burning them at a clinker temperature and grinding the resulting clinker. It develops strength by chemical reaction with water by formation of hydrates.

Hydrate products shape the binding component that binds together building blocks of concrete: gravels. Cement and supplementary cementing materials (SCMs) are the vital ingredients that lock sand and gravel together into an inert concrete matrix. They usually represent 10% to 15% of a concrete mix. So cement quality largely affects the strength and durability of the overall concrete itself. Hence, various properties of cement need to be checked before approving it for a project.

Bricklayer Joseph Aspdin of Leeds, England was the first to make Portland Cement early in the 19th century by burning powdered limestone and clay on his kitchen stove. With this basic method, he laid the foundation for an industry that annually processes a great deal of limestone, clay, cement rock, and other materials into a powder so fine that it passes through a sieve capable of holding water.

Typical Concrete Mix:
  • 6% Air
  • 11% Cement and SCMs
  • 41% Gravels or crashed sand stones
  • 26% Sand
  • 16% Water

The very first dwelling, the solid-rock caves were used as a home in the ancient age. Since then civilisation has started to build, create and construct. To construct and bind two different elements, two different stones, a material was needed. Assyrians and Babylonians used a fine mesh of soil, mud and moulded it into clay.

Discovery of gypsum mortars by the Egyptians created an architectural revolution but gypsum would not work once the humidity increased. Strength, viscosity and setting time were still an issue. The Romans, later on, started using a combination of gypsum and lime to create structures with remarkable durability. The foundation was formed using concrete.

The volcanic soil of Pozzuoli led to the creation of Pozzolana cement. It had material that would blend, bind and set-in. In 1817, Louis Vicat started to explore how optimum proportions of limestone and silica would create a hydraulic binder-like substance that would be christened Cement.

The following are the types of cement that are in practice:

Rapid Hardening Cement

  • Known to attain high strength in early days.
  • Composition - Increased Lime content
  • Uses of Cement - it is used in concrete where form works are removed at an early stage.

Quick setting cement

  • Composition - Small percentage of aluminium sulphate as an accelerator and reducing percentage of Gypsum with fine grinding
  • Uses of Cement - Used in works to be completed in very short period and concreting in static and running water

Low Heat Cement

  • Composition - Manufactured by reducing tricalcium aluminate
  • Uses of Cement - It is used in massive concrete construction like gravity dams

Sulphate resisting cement

  • Composition - It is prepared by maintaining the percentage of tricalcium aluminate below 6% which increases power against sulphates
  • Uses of Cement - It is used in construction exposed to severe sulphate action by water and soil in places like canal linings, culverts, retaining walls, siphons etc.

Blast Furnace Slag Cement

  • Composition - It is obtained by grinding the clinkers with about 60% slag and resembles more or less in properties to Portland Cement
  • Uses of Cement - It can be used for economic considerations.

High Alumina Cement

  • Composition - It is obtained by melting a mixture of bauxite and lime and grinding with the clinker. It is a rapid hardening cement with initial and final setting time of about 3.5 and 5 hours respectively
  • Uses of Cement - It is used in works where concrete is subjected to high temperatures, frost, and acidic action.

White Cement

  • Composition - It is prepared from raw materials free from Iron oxide.
  • Uses of Cement - It is more costly and is used for architectural purposes such as precast curtain walls and facing panels, terrazzo surfaces etc.

Coloured cement

  • Composition - It is produced by mixing mineral pigments with ordinary cement.
  • Uses of Cement - They are widely used for decorative works in floors

Pozzolanic Cement

  • Composition – It is prepared by grinding Pozzolanic clinker with Portland Cement
  • Uses of Cement - It is used in marine structures, sewage works, and for laying concrete under water such as bridges, piers, dams etc.

Air Entraining Cement

  • This cement has high workability and strength
  • Composition - It is prepared by mixing water repelling chemicals
  • Uses of Cement – This type of cement considerably increases the water resistance of a concrete.

Hydrographic cement

  • Composition - Manufactured by reducing tricalcium aluminate
  • Uses of Cement - It is used in massive concrete construction like gravity dams

Expanding Cement

  • Composition – It is prepared by adding an expanding medium like sulpho-aluminate and a stabilising agent to the ordinary cement.
  • Uses of Cement – It is used for construction of water retaining structures and also for repairing damaged concrete surfaces.

Acid-resistant cement

Composition -
  • Acid-resistance aggregates such as quartz, quartzites, etc.
  • Additive such as sodium fluosilicate Na2SiF6
  • Aqueous solution of sodium silicate or soluble glass.

Difference between OPC & PPC cement

Ordinary Portland Cement (OPC) is commonly used worldwide for many years now but an alternative option which is Portland Pozzolana Cement has also risen to prominence in recent times.

OPC

Concrete, mortars stucco and other common construction essentials require a basic component called OPC when they require cement in the mixture.

Identified as hydraulic cement, it is a type of cement that hardens as a reaction to being mixed with water. Not only that, it also becomes resistant once it cures. It is produced through pulverizing Portland Cement clinkers, which consist of hydraulic calcium silicates, producing a fine powder.

The cost of producing OPC is very low and available at the best quality because of the readily available raw material in the area where it is produced. Being a low cost cement it is widely used in the production of concrete, which is the most popular material used for construction in the world for roads, houses, buildings, dams, and the like. OPC is also used for mortars and in making grouts.

PPC

Another form of Portland Cement is Portland Pozzolana Cement (PPC). It is produced when pozzuolans are used in the mixture. PPC is a cement extender that not only helps in improving its strength but also its durability which further reduces the cost of producing concrete.

Initially, Volcanic ash was the first form of pozzuolana used, this now also includes natural and artificial siliceous or siliceous, aluminous materials such as clay, slag, silica fume, fly ash, and shale. Some of these are effective “waste” materials from other processes but are ideal for producing PPC. With the production of PPC, the use of overall OPC is greatly reduced in the mixture (by close to 50 percent) to produce the same results.

In a nutshell, OPC is produced simply by grinding to a powder limestone and secondary materials; PPC is the result of adding pozzuolan or similar materials such as volcanic ash, clay, slag, silica, fume, fly ash, or shale with OPC. PPC can greatly reduce the amount of OPC used in concrete.

Cement Industry in India

India comes second in terms of largest producers of cement in the world. The Indian cement industry is an important part of its economy that provides employment and sustains a workforce of a million people. Ever since it was deregulated in 1982, the Indian cement industry has received huge investments, both from Indian as well as foreign investors.

India’s future in the development of the infrastructure and construction sector and the cement sector is very positive. Some of the recent significant government initiatives such as development of 98 smart cities are expected to give a major boost to the sector. A significant factor that aids the growth of this sector is the readily available raw materials for making cement, such as limestone and coal.

Innovation

Cement is the world’s most widely used building material. It’s also the product of an energy-intensive process that accounts for about five percent of global greenhouse gases driving climate change. These emissions cause great harm to developing countries as they urbanise and build roads, develop new buildings, and other infrastructure in the decades ahead.

The strategy in the cement industry is to support adoption of a low carbon growth path, and aid the industry adopt the most efficient and sustainable technologies, develop innovative products, and explore favourable technologies for alternative fuels, including wind and solar.

Number of processes, product and management innovations can contribute to future sustainability.

Examples of sustainable process changes include:
  • Advanced techniques for using waste and biomass fuels in kilns, including better ways to monitor air pollutant emissions from kilns using such fuels
  • New kiln concepts, such as improved fluidised bed combustion, lower temperature processes, or use of microwaves or plasma in the cement-making process
  • Co-production of cement and electricity, e.g., innovative methods to burn coal to generate electricity and turn coal by-products (i.e. ash) into cement
  • Use of low-carbon, hydrogen-rich fuels for CO2 emission reduction
  • Carbon capture and sequestration
  • Lower-cost methods to reduce air pollution to a level of near-zero emissions