History of Cement

Ancient History Cement’s history dates back at least 12,000 years. The earliest known use of cement-like materials is from a whitewashed floor found in Turkey, made from burned limestone and clay. In the Fertile Crescent, early civilizations discovered that lime from burnt limestone could be used to make mortar. By 800 BC, the Phoenicians had developed hydraulic lime from a mix of burnt lime and volcanic ash, or pozzolana, which hardened underwater and was stronger than previous materials.

The Romans advanced masonry techniques significantly, creating “opus caementitium,” a form of concrete using lime, sand, and crushed rock. This innovation allowed the construction of impressive structures like the Colosseum, Pantheon, and Hagia Sophia, which still endure today.

The Middle Ages During the Middle Ages, cement development slowed. While hydraulic cements were used for fortresses and canals, detailed knowledge of cement was kept secret within guilds and passed orally. Concrete as a modern material did not yet exist, with typical mortars consisting of lime and sand. Alchemists of the time explored material properties but often used coded language.

The Industrial Revolution The late 18th century Industrial Revolution sparked significant advancements in cement technology. Key figures such as John Smeaton discovered the relationship between lime’s hydraulicity and clay content, while others like James Parker, Louis Vicat, and Egor Cheliev made further contributions to cement development.

The Birth of Portland Cement In 1824, Joseph Aspdin, a British bricklayer, created the precursor to modern cement by heating a mixture of limestone and clay, then grinding it and mixing it with water. He named it Portland Cement after the strong building stone from the Isle of Portland in Dorset, UK. His son, William Aspdin, later produced the first cement containing alite, a key component in modern Portland cement.

In 1845, Isaac Johnson improved the process by firing the mixture at higher temperatures (1400-1500°C), producing what is essentially today’s Portland cement. The use of Portland cement expanded rapidly from 1850, with concrete becoming popular for various applications including sculptures, bridges, and sewage systems. By the end of the 19th century, hollow concrete blocks for housing construction were introduced.

The advent of reinforced concrete in the 1840s in France revolutionized construction, allowing for larger and taller structures and reducing steel’s dominance. In 1878, Germany approved the first standard for Portland cement, establishing testing methods and minimum properties.

The 20th century saw global cement production surge. Rotary kilns replaced vertical shaft kilns, improving efficiency and producing stronger cement. Innovations included calcium aluminate cements for better sulfate resistance, the blending of Rosendale cement with Portland cement, and the use of cementitious materials for nuclear waste storage.

The Future of Cement and Concrete

Advancements The future of cement and concrete is focused on improving sustainability, strength, and applications. New technologies incorporate fibers and special aggregates for advanced products like roof tiles and countertops. Offsite manufacturing, driven by digitalization and AI, aims to reduce waste and enhance efficiency. Emerging cements and concretes that absorb CO2 over their lifetimes are being developed to reduce the carbon footprint of construction materials.

Types of Modern Cement

Portland Cement Portland cement is produced by heating limestone and clay minerals to 1450°C in a kiln to form clinker, which is then ground with gypsum. It is a key component in concrete and mortar, which can be molded into various shapes and provides structural support once hardened. Portland cement can be gray or white.

Portland Cement Blends

  • Portland Blastfurnace Cement: Contains up to 70% ground granulated blast furnace slag, with the rest being Portland clinker and gypsum. It provides high ultimate strength, reduced early strength, and lower heat evolution, making it an economical alternative for sulfate-resisting and low-heat cements.
  • Portland Flyash Cement: Includes up to 30% fly ash, which is pozzolanic and maintains strength. Fly ash reduces water content in concrete, preserving early strength and offering cost advantages where high-quality fly ash is available.
  • Portland Pozzolan Cement: Contains fly ash and other pozzolans, including natural volcanic ash. These are widely used in regions with abundant volcanic materials.
  • Portland Silica Fume Cement: Incorporates 5-20% silica fume for exceptionally high strengths. Silica fume is typically added at the concrete mixer.
  • Masonry Cements: Used for bricklaying mortars and stuccos, not for concrete. These are complex blends of Portland clinker and other ingredients like limestone, hydrated lime, and air entrainers. Variants include Plastic Cements and Stucco Cements.
  • Expansive Cements: Contain Portland clinker and expansive clinkers to counteract drying shrinkage, suitable for large floor slabs without contraction joints.
  • White Blended Cements: Made with white clinker and supplementary materials such as high-purity metakaolin.
  • Colored Cements: Used for decorative purposes, sometimes made by adding pigments to Portland cement or as blended hydraulic cements where pigment addition is restricted.

Non-Portland Hydraulic Cements

  • Pozzolan-Lime Cements: Historic mixtures of ground pozzolan and lime, still used in ancient structures. They develop strength slowly but can achieve very high ultimate strength.
  • Slag-Lime Cements: Activated by alkalis, such as lime, and have properties similar to pozzolan-lime cements.
  • Supersulfated Cements: Contain ground granulated blast furnace slag, gypsum, and a small amount of Portland clinker or lime. They develop strength through ettringite formation and resist aggressive agents like sulfates.
  • Calcium Aluminate Cements: Made from limestone and bauxite, containing monocalcium aluminate and mayenite. Used in high-temperature refractory concretes.
  • Calcium Sulfoaluminate Cements: Contain ye’elimite and are used in expansive cements and ultra-high early strength cements. They offer lower energy requirements and CO2 emissions compared to Portland cement.
    Natural Cements: Produced by burning argillaceous limestones, resulting in variable properties.
  • Geopolymer Cements: Created from alkali metal silicates and aluminosilicate mineral powders, such as fly ash and metakaolin.
    Fuels and Raw Materials Cement production requires 3,000 to 6,500 MJ of fuel per tonne of clinker. Most kilns use coal and petroleum coke, with some using natural gas or fuel oil. Waste materials with calorific value can partially replace fossil fuels if they meet specifications, and materials like sewage sludge can also serve as raw materials in the kiln.

Fuels and Raw Materials Cement production requires 3,000 to 6,500 MJ of fuel per tonne of clinker. Most kilns use coal and petroleum coke, with some using natural gas or fuel oil. Waste materials with calorific value can partially replace fossil fuels if they meet specifications, and materials like sewage sludge can also serve as raw materials in the kiln.