Types of modern cement

Non-Portland hydraulic cements
Pozzolan-lime cements. Mixtures of ground pozzolan and lime are the cements used by the Romans, and can be found in Roman structures still standing (e.g. 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 produced by Portland cement. Slag-lime cements. Ground granulated blast furnace slag is not hydraulic on its own, but is "activated" by addition of alkalis, most economically using lime. They are similar to pozzolan lime cements in their properties. Only granulated slag (i.e. water-quenched, glassy slag) is effective as a cement component. Supersulfated cements. These contain 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 cements are hydraulic cements 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 cements are 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 cements, in ultra-high early strength cements, and in "low-energy" cements. 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 High Temperature Cement has been pioneered in China, where several million tonnes per year are produced.[40][41] 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 leads to a CO2 emission around half that associated with Portland clinker. However, SO2 emissions are usually significantly higher. "Natural" cements correspond to certain cements of the pre-Portland era, 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, High Temperature Insulation such cements have highly variable properties. Geopolymer cements are made from mixtures of water-soluble alkali metal silicates and aluminosilicate mineral powders such as fly ash and metakaolin.

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Types of modern cement

Portland cement blends

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.[35] Portland blastfurnace cement contains up to 70% 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 cements.Portland flyash cement contains up to 35% fly ash. 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 cements made from other natural or artificial pozzolans. In countries where volcanic ashes are available (e.g. Italy, Chile, Mexico, the Philippines) these cements are often the most common form in use.. High Temperature Insulation  Portland silica fume cement. Addition of silica fume can yield exceptionally high strengths, and cements containing 5–20% silica fume are occasionally produced.

However, silica fume is more usually added to Portland cement at the concrete mixer. Masonry cements 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 entrainers, retarders, waterproofers and coloring agents. They are formulated to yield workable mortars that allow rapid and consistent masonry work. Subtle variations of Masonry cement in the US are Plastic Cements and Stucco Cements. These are designed to produce controlled bond with masonry blocks. Expansive cements contain, in addition to Portland clinker, expansive clinkers (usually sulfoaluminate clinkers), and are designed to offset the effects of drying shrinkage that is normally encountered with hydraulic cements. This allows large floor slabs (up to 60 m square) to be prepared without contraction joints. White blended cements may be made using white clinker and white supplementary materials such as high-purity metakaolin. Colored cements are used for decorative purposes.
High Temperature Cement

In some standards, the addition of pigments to produce "colored Portland cement" is allowed. In other standards (e.g. ASTM), pigments are not allowed constituents of Portland cement, and colored cements are sold as "blended hydraulic cements". Very finely ground cements are made from mixtures of cement with sand or with slag or other pozzolan type minerals that are extremely finely ground together. Such cements can have the same physical characteristics as normal cement but with 50% less cement particularly due to their increased surface area for the chemical reaction. Even with intensive grinding they can use up to 50% less energy to fabricate than ordinary Portland cements.

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Types of modern cement

Portland cement

Main article: Portland cement

Cement is made by heating limestone (calcium carbonate) with small quantities of other materials (such as clay) to 1450 °C in a kiln, in a process known as calcination, whereby a molecule of carbon dioxide is liberated from the calcium carbonate to form calcium oxide, or quicklime, which is then blended with the other materials that have been included in the mix. 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 in the production of concrete. Concrete is a composite material consisting of aggregate (gravel and sand), cement, High Temperature Cement and water. As a construction material, concrete can be cast in almost any shape desired, and once hardened, can become a structural (load bearing) element. Portland cement may be grey or white.
[edit]Energetically Modified Cement ("EMC Cement")


Proving Energetically Modified Cement's "self-healing" capabilities...



PHOTO A: Proving Energetically Modified Cement's "self-healing" capabilities. Mechanically-induced cracking in concrete comprising EMC Cement, caused by RILEM 3-point bending induced after ~3 weeks of water curing (September, 2012). Cracks had an average width of 150-200 μm.
The photo above depicts a concrete test-beam made from EMC Cement undergoing RILEM 3-point bending at Luleå University of Technology in Sweden (February, 2013). This treatment induces cracks so as to test for EMC Cement's "self-healing" capabilities.



PHOTO B: Former cracks in concrete comprising EMC Cement, taken 5 months after PHOTO A. The photograph shows that the former cracks had undergone a complete "self healing" process without any intervention, by virtue of newly-synthesized CSH gel — itself a product of the ongoing pozzolanic reaction.
Concrete (total cmt: 350 kg/m³) containing 40% Portland cement and 60% EMC Cement made from fly ash was used. Cracks of average width 150-200 μm were induced after ~3 weeks of water curing. This is depicted in PHOTO A.

Control cubes were tested for compressive strength at different ages.

As expected, without any intervention the high volume pozzolan concrete exhibited the gradual filling-in of the cracks with newly-synthesized CSH gel (a product of the ongoing pozzolanic reaction). These were completely filled-in after ~4.5 months. This is depicted in PHOTO B.

During the observation period, continuous strength-development was also recorded by virtue of the ongoing pozzolanic reaction. This, together with the observed "self healing" properties, both have a positive impact on concrete durability.

All photos courtesy of Dr. V. Ronin
An alternative fabrication technique EMC (Energetically Modified Cement) produces cementitious materials made from pozzolanic minerals that have been treated using a patented milling process ("EMC Activation").[13] The resultant concretes can have the same, if not improved, physical characteristics as "normal" concretes — at a fraction of the Portland cement. Note, although Energetically Modified Cement is able to replace Portland cement in concrete to high levels, it cannot fully replace it.
Energetically Modified Cement is better known as "EMC Cement". EMC Cement may be classified both as an "Alternative Cementitious Material" and as a "Supplemental Cementitious Material", on account of the range of the Portland cement replacement-ratios offered. Colloquially, EMC Cement may be referred-to also as a "Green Cement", on account of the significant energy and carbon dioxide savings yielded by EMC Activation as compared to Portland cement production.
The trade name for EMC Cement is "CemPozz". At the 45th World Exhibition of Invention, Research and Innovation, held in Bruxelles, Belgium, EMC Activation was awarded the Gold Medal "with mention" by the EUREKA Organisation (the pan-European research & development funding and coordination organization, comprising all 27 EU Member States). High Temperature Insulation

Put simply, EMC Activation is a patented, cost– and energy–efficient, near zero-emission technology for the high replacement of Portland cement in concrete.

Materials that are used to replace Portland cement in concrete (such as fly ash, blast furnace slag, natural pozzolans – e.g. volcanic ash – and silica sand) are mechanically activated in proprietary milling systems.EMC Activation increases the amount of Portland cement that can be replaced over and above "traditional" replacement methods (which typically replace an average of circa. 15% of the Portland Cement in concrete). By contrast, up to 70% of the Portland cement in concrete can be replaced using EMC Cement.
EMC Activation generates high-energy particle impacts. This leads to deep transformations in the particle micro-structure in the form of (among others) sub-micro cracks, dislocations and lattice defects that significantly increase reactivity, with no material increase in overall powder fineness.
EMC Cements comply with relevant normative standards and specifications. For example, where EMC Cement is made from fly ash, high Portland cement replacements (i.e., the replacement of at least 50% Portland cement) yield concretes that exhibit consistent field results.This is also the case for EMC Cement made from natural pozzolans (e.g., volcanic ash).

For example, volcanic ash deposits situated in Southern California of the United States were tested by independent consultants, according to the relevant normative standards. EMC Activation was then applied to the raw materials. At 50% Portland cement replacement, the resulting concretes exceeded the normative requirements. At 28 days, the compressive strength was recorded at 4,180 psi / 28.8 MPa (N/mm²). The 56-day strength exceeded the requirements for 4,500 psi (31.1 Mpa) concrete, even taking into account the safety margin as recommended by the American Concrete Institute.

EMC Cement presents dramatic savings both in terms of carbon dioxide and energy-savings. The figures vary slightly depending on the source material used. For example, if volcanic ash is used, the resulting compound has to be dried. This drying process consumes about 150,000 Btu per ton of EMC Cement produced.

All in all, as compared to a total energy consumption of ~1,000 to 1,400 KWh for each ton of Portland cement produced:
For each ton of EMC Cement made from fly ash, the energy requirement is usually ~25 KWh. There are no direct CO2 emissions.
For each ton EMC Cement made from volcanic ash, the energy requirement (including drying, as above) is no more than ~80KWh, with direct emissions of only 8 kgs CO2 per ton.

The performance of concretes made from EMC Cement can also be custom designed. Hence, concretes can range from those exhibiting superior strength and durability that reduce the carbon footprint at up to ~70% as compared to concretes made from Portland Cement, through to the production of rapid and ultra-rapid hardening, high-strength concretes (for example, over 70 MPa / 10,150 psi in 24 hours and over 200 MPa / 29,000 psi in 28 days).This allows EMC Cement to yield High Performance Concretes (HPCs).
EMC Cement exhibits a high resistance to chloride and sulfate ion attack, together with a low Alkali–Silica Reactivity (ASR).These features allow concretes made from EMC Cement to exhibit superior durabilities as compared to concretes made from Portland cement. For example, an early project using EMC Cement was the construction of a road bridge in Karungi, Sweden, with Swedish construction firm Skanska. The Karungi road bridge has successfully withstood the tests of time, despite Karungi's harsh subarctic climate and extremely divergent diurnal temperatures.

EMC Activation and EMC Cements are well-proven to an "industrial scale". In the United States, EMC Cement has been approved for usage by PennDOT (Pennsylvania Department of Transportation), TxDOT (Texas Department of Transportation) and CalTrans (California Department of Transportation). As a result, hundreds of miles of highway paving have been laid, together with assorted highway bridges, using concretes made from EMC Cement — including large sections of Interstate 10, which is the main U.S. Interstate highway linking Miami, Florida with Los Angeles, California.
Another notable project in the United States includes the extension of the passenger terminals at the Port of Houston, Texas. This project fully exploits EMC Cement's known propensity to yield concretes that exhibit high-resistances to chloride– and sulfate–ion permeability (i.e., increased resistance to sea waters), as compared to concretes made from Portland cement.

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History of the origin of cement

Modern cements
Modern hydraulic cements began to be developed from the start of the Industrial Revolution (around 1800),

driven by three main needs:
Hydraulic cement render (stucco) for finishing brick buildings in wet climates.
Hydraulic mortars for masonry construction of harbor works, etc., in contact with sea water.
Development of strong concretes.

In Britain particularly, good quality building stone became ever more expensive during a period of rapid growth, and it became a common practice to construct prestige buildings from the new industrial bricks, and to finish them with a stucco to imitate stone. Hydraulic limes were favored for this, but the need for a fast set time encouraged the development of new cements. Most famous was Parker's "Roman cement". This was developed by James Parker in the 1780s, and finally patented in 1796. It was, in fact, nothing like any material used by the Romans, but was a "Natural cement" made by burning septaria – nodules that are found in certain clay deposits, and that contain both clay minerals and calcium carbonate. The burnt nodules were ground to a fine powder. This product, made into a mortar with sand, set in 5–15 minutes. The success of "Roman Cement" led other manufacturers to develop rival products by burning artificial mixtures of clay and chalk.

John Smeaton made an important contribution to the development of cements when he was planning the construction of the third Eddystone Lighthouse (1755–9) in the English Channel. He needed a hydraulic mortar that would set and develop some strength in the twelve hour period between successive high tides. He performed an exhaustive market research on the available hydraulic limes, visiting their production sites, and noted that the "hydraulicity" of the lime was directly related to the clay content of the limestone from which it was made. Smeaton was a civil engineer by profession, and took the idea no further. Apparently unaware of Smeaton's work, the same principle was identified by Louis Vicat in the first decade of the nineteenth century. Vicat went on to devise a method of combining chalk and clay into an intimate mixture, and, burning this, produced an "artificial cement" in 1817. James Frost, working in Britain, produced what he called "British cement" in a similar manner around the same time, but did not obtain a patent until 1822. In 1824, Joseph Aspdin patented a similar material, which he called Portland cement, because the render made from it was in color similar to the prestigious Portland stone.

Setting time and "early strength" are important characteristics of cements. Hydraulic limes, "natural" cements, and "artificial" cements all rely upon their belite content for strength development. Belite develops strength slowly. Because they were burned at temperatures below 1250 °C, they contained no alite, which is responsible for early strength in modern cements. The first cement to consistently contain alite was made by Joseph Aspdin's son William in the early 1840s. This was what we call today "modern" Portland cement. Because of the air of mystery with which William Aspdin surrounded his product, others (e.g., Vicat and I.C. Johnson) have claimed precedence in this invention, but recent analysis[11] of both his concrete and raw cement have shown that William Aspdin's product made at Northfleet, Kent was a true alite-based cement. However, Aspdin's methods were "rule-of-thumb": Vicat is responsible for establishing the chemical basis of these cements, and Johnson established the importance of sintering the mix in the kiln.

William Aspdin's innovation was counterintuitive for manufacturers of "artificial cements", because they required more lime in the mix (a problem for his father), a much higher kiln temperature (and therefore more fuel), and the resulting clinker was very hard and rapidly wore down the millstones, which were the only available grinding technology of the time. Manufacturing costs were therefore considerably higher, but the product set reasonably slowly and developed strength quickly, thus opening up a market for use in concrete. The use of concrete in construction grew rapidly from 1850 onward, and was soon the dominant use for cements. Thus Portland cement began its predominant role.. High Temperature Cement

In the US the first large scale use of cement was Rosendale cement a natural cement mined from a massive deposit of a large dolostone rock deposit discovered in the early 19th century near Rosendale, New York. Rosendale cement was extremely popular for the foundation of buildings (e.g., Statue of Liberty, Capitol Building, Brooklyn Bridge) and lining water pipes. But its long curing time of at least a month made it unpopular after World War One in the construction of highways and bridges and many states and construction firms turned to the use of Portland cement. Because of the switch to Portland cement, by the end of the 1920s of the 15 Rosendale cement companies, only one had survived. But in the early 1930s it was soon discovered that, while Portland cement had a faster setting time it was not as durable, especially for highways, to the point that some states stopped building highways and roads with cement. High Temperature Insulation

 Bertrain H. Wait, an engineer whose company had worked on the construction of the New York Cities Catskill Aqueduct, was impressed with the durability of Rosendale cement, and came up with a blend of both Rosendale and synthetic cements which had the good attributes of both: it was highly durable and had a much faster setting time. Mr. Wait convinced the New York Commissioner of Highways to construct an experimental section of highway near New Paltz, New York, using one sack of Rosendale to six sacks of synthetic cement, and it was proved a success and for decades the Rosendale-synthetic cement blend became common use in highway and bridge construction.

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History of the origin of cement

Early uses

It is uncertain where it was first discovered that a combination of hydrated non-hydraulic lime and a pozzolan produces a hydraulic mixture (see also: Pozzolanic reaction), but concrete made from such mixtures was first used by the Ancient Macedonians and three centuries later on a large scale by Roman engineers. High Temperature Cement.

 They used both natural pozzolans (trass or pumice) and artificial pozzolans (ground brick or pottery) in these concretes. Many excellent examples of structures made from these concretes are still standing, notably the huge dome of the Pantheon in Rome and the massive Baths of Caracalla. The vast system of Roman aqueducts also made extensive use of hydraulic cement. High Temperature Insulation

Although any preservation of this knowledge in literary sources from the Middle Ages is unknown, medieval masons and some military engineers maintained an active tradition of using hydraulic cement in structures such as canals, fortresses, harbors, and shipbuilding facilities.The technical knowledge of making hydraulic cement was later formalized by French and British engineers in the 18th century.

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Cement

For other uses, see Cement (disambiguation).
Not to be confused with Concrete.

Lafarge cement plant in Contes, France.
In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed rock with burnt lime as binder. The volcanic ash and pulverized brick additives that were added to the burnt lime to obtain a hydraulic binder were later referred to as cementum, cimentum, cäment, and cement. High Temperature Cement

Cement used in construction is characterized as hydraulic or non-hydraulic. Hydraulic cements (e.g., Portland cement) harden because of hydration, chemical reactions that occur independently of the mixture's water content; they can harden even underwater or when constantly exposed to wet weather. The chemical reaction that results when the anhydrous cement powder is mixed with water produces hydrates that are not water-soluble. Non-hydraulic cements (e.g. gypsum plaster) must be kept dry in order to retain their strength. High Temperature Insulation

The most important uses of cement are as an ingredient in the production of mortar in masonry, and of concrete, a combination of cement and an aggregate to form a strong building material.

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