Modern Cement
Modern hydraulic development began with the start of the Industrial Revolution (around 1800), driven by three main needs: Hydraulic cement render (stucco) for finishing brick buildings in wet climatesHydraulic mortars for masonry construction of harbor works, etc., in contact with seawater
Development of strong concretes
Modern cement is often Portland cement or Portland cement blends, but the industry also uses other types of cement.
Portland Cement
Portland cement, a form of hydraulic cement, is by far the most common type of cement in general use around the world. This cement is made by heating limestone (calcium carbonate) with other materials (such as clay) to 1,450 °C (2,640 °F) in a kiln, in a process knownas calcination that liberates a molecule of carbon dioxide from the calcium carbonate to form calcium oxide, or quicklime, which then chemically combines with the other materials in the mix to form calcium silicates and other cementitious compounds. The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum into a powder to make ordinary Portland cement, the most commonly used type of cement (often referred to as OPC). Portland cement is a basic ingredient of concrete, mortar, and most non-specialty grout. The most common use for Portland cement is to make concrete. Concrete is a composite material made of aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast in almost any shape, and once it hardens, can be a structural (load bearing) element. Portland cement may be grey or white.
Portland cement blend
Portland cement blends are often available as inter-ground mixtures from cement producers, but similar formulations are often also mixed from the ground components at the concrete mixing plant.Portland blast-furnace slag cement, or blast furnace cement
(ASTM C595 and EN 197-1 nomenclature respectively), contains up to 95% ground granulated blast furnace slag, with the rest Portland clinker and a little gypsum. All compositions produce high ultimate strength, but as slag content is increased, early strength is reduced, while sulfate resistance increases and heat evolution diminishes. Used as an economic alternative to Portland sulfate-resisting and low-heat cement.Portland-fly ash cement
contains up to 40% fly ash under ASTM standards (ASTM C595), or 35% under EN standards (EN 197–1). The fly ash is pozzolanic, so that ultimate strength is maintained. Because fly ash addition allows a lower concrete water content, early strength can also be maintained. Where good quality cheap fly ash is available, this can be an economic alternative to ordinary Portland cement.Portland pozzolan cement
includes fly ash cement since fly ash is a pozzolan, but also includes cement made from other natural or artificial pozzolans. In countries where volcanic ashes are available (e.g., Italy, Chile, Mexico, and the Philippines), these cement are often the most common form in use. The maximum replacement ratios are generally defined as for Portland-fly ash cement.
Portland silica fume cement.
The addition of silica fume can yield exceptionally high strengths, and cement containing 5–20% silica fume is occasionally produced, with 10% being the maximum allowed addition under EN 197–1. However, silica fume is more usually added to Portland cement in the concrete mixer.
Masonry cement
are used for preparing bricklaying mortars and stuccos, and must not be used in concrete. They are usually complex proprietary formulations containing Portland clinker and a number of other ingredients that may include limestone, hydrated lime, air entertainers, retarders, waterproofs, and coloring agents. They are formulated to yield workable mortars that allow rapid and consistent masonry work. Subtle variations of masonry cement in North America are plastic cement and stucco cement. These are designed to produce a controlled bond with masonry blocks.
Expansive cement
contain, in addition to Portland clinker, expansive clinkers (usually sulfoaluminate clinkers), and are designed to offset the effects of drying shrinkage normally encountered in hydraulic cement. This cement can make concrete for floor slabs (up to 60 m square) without contraction joints.
White blended cement
may be made using white clinker (containing little or no iron) and white supplementary materials such as high-purity metakaolin. Colored cement serves decorative purposes. Some standards allow the addition of pigments to produce colored Portland cement. Other standards (e.g., ASTM) do not allow pigments in Portland cement, and colored cement is sold as blended hydraulic cement.
Very finely ground cement
are cement mixed with sand or with slag or other pozzolan-type minerals that are extremely finely ground together. Such cement can have the same physical characteristics as normal cement but with 50% less cement, particularly due to its increased surface area for the chemical reaction. Even with intensive grinding, they can use up to 50% less energy (and thus fewer carbon emissions) to fabricate than ordinary Portland cement.
Other Cement
Pozzolan-lime cement is a mixture of ground pozzolan and lime. These are the cement the Romans used, and are present in surviving Roman structures like the Pantheon in Rome. They develop strength slowly, but their ultimate strength can be very high. The hydration products that produce strength are essentially the same as those in Portland cement.
Slag-lime cement—ground granulated blast-furnace slag—is not hydraulic on its own, but is "activated" by the addition of alkalis, most economically using lime. They are similar to pozzolan lime cement in their properties. Only granulated slag (i.e., water-quenched, glassy slag) is effective as a cement component.
Supersulfated cement contains about 80% ground granulated blast furnace slag, 15% gypsum or anhydrite, and a little Portland clinker or lime as an activator. They produce strength by formation of ettringite, with strength growth similar to a slow Portland cement. They exhibit good resistance to aggressive agents, including sulfate. Calcium aluminate cement is hydraulic cement made primarily from limestone and bauxite. The active ingredients are monocalcium aluminate CaAl2O4 (CaO · Al2O3 or CA in cement chemist notation, CCN) and mayenite Ca12Al14O33 (12 CaO · 7 Al2O3, or C12A7 in CCN). Strength forms by hydration to calcium aluminate hydrates. They are well-adapted for use in refractory (high-temperature resistant) concretes, e.g., for furnace linings.
Calcium sulfoaluminate cement is made from clinkers that include ye'elimite (Ca4(AlO2)6SO4 or C4A3S in Cement chemist's notation) as a primary phase. They are used in expansive cement, ultra-high early strength cement, and "low-energy" cement. Hydration produces ettringite, and specialized physical properties (such as expansion or rapid reaction) are obtained by adjustment of the availability of calcium and sulfate ions. Their use as a low-energy alternative to Portland cement has been pioneered in China, where several million tonnes per year are produced. Energy requirements are lower because of the lower kiln temperatures required for reaction, and the lower amount of limestone (which must be endothermically decarbonated) in the mix. In addition, the lower limestone content and lower fuel consumption lead to a CO2 emission of around half that associated with Portland clinker. However, SO2 emissions are usually significantly higher.
"Natural" cement corresponding to certain cement of the pre-Portland era, is produced by burning argillaceous limestones at moderate temperatures. The level of clay components in the limestone (around 30–35%) is such that large amounts of belite (the low-early strength, high-late strength mineral in Portland cement) are formed without the formation of excessive amounts of free lime. As with any natural material, such cement has highly variable properties. Geopolymer cement is made from mixtures of water-soluble alkali metal silicates, and aluminosilicate mineral powders such as fly ash and metakaolin. Polymer cement is made from organic chemicals that polymerize. Producers often use thermoset materials. While they are often significantly more expensive, they can give a waterproof material that has useful tensile strength. Sorel Cement is a hard, durable cement made by combining magnesium oxide and a magnesium chloride solution
Fiber mesh cement or fiber reinforced concrete is cement that is made up of fibrous materials like synthetic fibers, glass fibers, natural fibers, and steel fibers. This type of mesh is distributed evenly throughout the wet concrete. The purpose of fiber mesh is to reduce water loss from the concrete as well as enhance its structural integrity. When used in plasters, fiber mesh increases cohesiveness, tensile strength, impact resistance, and reduces shrinkage; ultimately, the main purpose of these combined properties is to reduce cracking.