Cement is a binding agent used in construction that starts as a finely ground powder. When mixed with water, it undergoes hydration , a chemical process that allows it to harden into a strong mass, even underwater. The most common type is portland cement , made by burning a mix of limestone and clay. The manufacturing of portland cement involves crushing and grinding raw materials, blending them, burning the mix in a kiln, and grinding the resulting clinker with gypsum. There are different kinds of portland cement, including ordinary, modified, high-early-strength, low-heat, and sulfate-resistant. The production of cement contributes to carbon dioxide emissions, with efforts being made to increase energy efficiency and explore alternative formulations.

What materials are used to make cement?

Cement consists of lime (calcium oxide) mixed with silica (silicon dioxide) and alumina (aluminum oxide). Lime comes from a calcareous raw material, while the other oxides are from an argillaceous (clayey) material. Additional raw materials like silica sand, iron oxide, and bauxite may be added in smaller amounts to get the desired composition. Limestone and chalk are the commonest calcareous raw materials, but coral or shell deposits can also be used. Common argillaceous raw materials include clays, shales, slates, and estuarine muds. Portland cement is composed of tricalcium silicate, dicalcium silicate, tricalcium aluminate, and a tetra-calcium aluminoferrite. Gypsum is added during grinding to control the setting time.

How is cement made in factories?

Cement manufacture involves crushing and grinding raw materials, blending them, burning the mix in a kiln, and grinding the burned product or clinker with gypsum. The raw materials, such as limestone, chalk, clays, shales, and slate, are extracted and transported to the crushing plant. They are then crushed and ground using ball or tube mills, which can be done wet or dry. The materials are blended in correct proportions and burned in rotary kilns at temperatures reaching 1,350 to 1,550 °C (2,460 to 2,820 °F). The resulting clinker is cooled and ground with about 5% gypsum to control setting time.

How does cement become hard when mixed with water?

Cement hardens through a process called hydration , where calcium silicates react with water to form calcium silicate hydrate (C–S–H) and calcium hydroxide (CH). The calcium silicates, (C_2S) and (C_3S), are the most important hydraulic constituents in this process. The chemical reactions are: [2C_3S + 6H = C_3S_2H_3 + 3CH] [2C_2S + 4H = C_3S_2H_3 + CH] Initially, the compounds dissolve, releasing heat, followed by a dormant period. Hardening begins after this period as C–S–H and CH are produced, binding the cement together. The setting and hardening is continuous, with an initial set at roughly 45 minutes and a final set within 10–12 hours.

What is the difference between cement and concrete?

Cement and concrete are often confused, but cement is actually a key ingredient in concrete. Cement is a fine powder that, when mixed with water, hardens and acts as a binder. The most common type is Portland cement , made from heating limestone and clay. There are also other special types of Portland cement, such as colored cements, air-entraining cements, low-alkali cements, masonry cements, waterproof cement, hydrophobic cement, and oil-well cements. Concrete is a construction material composed of cement, water, and aggregates like sand, gravel, or crushed stone, which provide bulk and strength. The quality and ratio of water to cement are crucial for the strength and workability of concrete. Concrete is used in the construction of roads, bridges, foundations, and infrastructure.

What are some important uses of cement in construction?

Cement is a binding agent that is a key ingredient in mortar and concrete . Mortar, a mixture of cement and sand, is used to bind bricks, blocks, and stone in walls or as surface coverings. Concrete, a mix of cement, sand, and aggregates, serves various construction purposes, including roads, bridges, building foundations, retaining walls, and large-scale infrastructure like dams and tunnels . Cement is also used to manufacture prefabricated components like bricks, tiles, shingles, pipes, and beams . Mixtures of soil and portland cement create bases for roads.

Cement

Images

Concrete is being poured from a cement truck into a trench with rebar at the bottom, as workers guide the flow for a house foundation.

Eddystone Lighthouse: Sir James N. Douglass's version

At a Glance

cement summary

Cement

building material

Written by

Thomas O. MasonAll

Fact-checked by

Britannica Editors

Last updated

Nov. 7, 2026 •History

Top Questions

What is cement?
Cement is a binding agent used in construction that starts as a finely ground powder. When mixed with water, it undergoes hydration, a chemical process that allows it to harden into a strong mass, even underwater. The most common type is portland cement, made by burning a mix of limestone and clay.

The manufacturing of portland cement involves crushing and grinding raw materials, blending them, burning the mix in a kiln, and grinding the resulting clinker with gypsum. There are different kinds of portland cement, including ordinary, modified, high-early-strength, low-heat, and sulfate-resistant.

The production of cement contributes to carbon dioxide emissions, with efforts being made to increase energy efficiency and explore alternative formulations.
3 Britannica Sources
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What materials are used to make cement?
Cement consists of lime (calcium oxide) mixed with silica (silicon dioxide) and alumina (aluminum oxide). Lime comes from a calcareous raw material, while the other oxides are from an argillaceous (clayey) material. Additional raw materials like silica sand, iron oxide, and bauxite may be added in smaller amounts to get the desired composition.

Limestone and chalk are the commonest calcareous raw materials, but coral or shell deposits can also be used. Common argillaceous raw materials include clays, shales, slates, and estuarine muds. Portland cement is composed of tricalcium silicate, dicalcium silicate, tricalcium aluminate, and a tetra-calcium aluminoferrite. Gypsum is added during grinding to control the setting time.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How is cement made in factories?
Cement manufacture involves crushing and grinding raw materials, blending them, burning the mix in a kiln, and grinding the burned product or clinker with gypsum.

The raw materials, such as limestone, chalk, clays, shales, and slate, are extracted and transported to the crushing plant. They are then crushed and ground using ball or tube mills, which can be done wet or dry. The materials are blended in correct proportions and burned in rotary kilns at temperatures reaching 1,350 to 1,550 °C (2,460 to 2,820 °F). The resulting clinker is cooled and ground with about 5% gypsum to control setting time.
1 Britannica Source
1. cement: Crushing and grinding
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How does cement become hard when mixed with water?
Cement hardens through a process called hydration, where calcium silicates react with water to form calcium silicate hydrate (C–S–H) and calcium hydroxide (CH). The calcium silicates, (C_2S) and (C_3S), are the most important hydraulic constituents in this process. The chemical reactions are:

[2C_3S + 6H = C_3S_2H_3 + 3CH]

[2C_2S + 4H = C_3S_2H_3 + CH]

Initially, the compounds dissolve, releasing heat, followed by a dormant period. Hardening begins after this period as C–S–H and CH are produced, binding the cement together. The setting and hardening is continuous, with an initial set at roughly 45 minutes and a final set within 10–12 hours.
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1. cement: Setting time
2. cementation
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What is the difference between cement and concrete?
Cement and concrete are often confused, but cement is actually a key ingredient in concrete. Cement is a fine powder that, when mixed with water, hardens and acts as a binder. The most common type is Portland cement, made from heating limestone and clay. There are also other special types of Portland cement, such as colored cements, air-entraining cements, low-alkali cements, masonry cements, waterproof cement, hydrophobic cement, and oil-well cements.

Concrete is a construction material composed of cement, water, and aggregates like sand, gravel, or crushed stone, which provide bulk and strength. The quality and ratio of water to cement are crucial for the strength and workability of concrete. Concrete is used in the construction of roads, bridges, foundations, and infrastructure.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What are some important uses of cement in construction?
Cement is a binding agent that is a key ingredient in mortar and concrete. Mortar, a mixture of cement and sand, is used to bind bricks, blocks, and stone in walls or as surface coverings. Concrete, a mix of cement, sand, and aggregates, serves various construction purposes, including roads, bridges, building foundations, retaining walls, and large-scale infrastructure like dams and tunnels. Cement is also used to manufacture prefabricated components like bricks, tiles, shingles, pipes, and beams. Mixtures of soil and portland cement create bases for roads.
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Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Cement, in general, adhesive substances of all kinds, but, in a narrower sense, the binding materials used in building and civil engineering construction. Cements of this kind are finely ground powders that, when mixed with water, set to a hard mass. Setting and hardening result from hydration, which is a chemical combination of the cement compounds with water that yields submicroscopic crystals or a gel-like material with a high surface area. Because of their hydrating properties, constructional cements, which will even set and harden under water, are often called hydraulic cements. The most important of these is portland cement.

This article surveys the historical development of cement, its manufacture from raw materials, its composition and properties, and the testing of those properties. The focus is on portland cement, but attention also is given to other types, such as slag-containing cement and high-alumina cement. Construction cements share certain chemical constituents and processing techniques with ceramic products such as brick and tile, abrasives, and refractories. For detailed description of one of the principal applications of cement, see the article building construction.

Applications of cement

Cements may be used alone (i.e., “neat,” as grouting materials), but the normal use is in mortar and concrete in which the cement is mixed with inert material known as aggregate. Mortar is cement mixed with sand or crushed stone that must be less than approximately 5 mm (0.2 inch) in size. Concrete is a mixture of cement, sand or other fine aggregate, and a coarse aggregate that for most purposes is up to 19 to 25 mm (0.75 to 1 inch) in size, but the coarse aggregate may also be as large as 150 mm (6 inches) when concrete is placed in large masses such as dams. Mortars are used for binding bricks, blocks, and stone in walls or as surface renderings. Concrete is used for a large variety of constructional purposes. Mixtures of soil and portland cement are used as a base for roads. Portland cement also is used in the manufacture of bricks, tiles, shingles, pipes, beams, railroad ties, and various extruded products. The products are prefabricated in factories and supplied ready for installation.

The manufacture of cement is extremely widespread, as concrete is the most widely used of all construction materials in the world today.

Cement

Applications of cement

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