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Cement

Contacts to production companies worldwide make it possible for us to offer CEMENT to you. As a standard we offer Portland Cement coming directly from the production companies via railways or trucks directly to the ports. Pls ask us for a customized offer and send us an LOI with exact specification and desired amount.

Portland cement (often referred to as OPC, from Ordinary Portland Cement) is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stuccoand most non-specialty grout. It usually originates from limestone.It is a fine powderproduced by grinding Portland cement clinker (more than 90%), a limited amount of calcium sulfate (which controls the set time) and up to 5% minor constituents as allowed by various standards such as the European Standard EN197-1: Portland cement clinker is a hydraulicmaterial which shall consist of at least two-thirds by mass of calcium silicates (3 CaO·SiO₂and 2 CaO·SiO₂), the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. The ratio of CaOto SiO₂ shall not be less than 2.0. The magnesium oxide content (MgO) shall not exceed 5.0% bym ass.
(The last two requirements were already set out in the German Standard, issued in 1909).

ASTMC 150 defines portland cement as "hydraulic cement (cement that not only hardens by reacting with water but also forms a water-resistant product) produced by pulverizing clinkers consisting essentially of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulfate as an inter ground addition."Clinkers are nodules (diameters, 0.2-1.0 inch [5–25 mm]) of a sintered material that is produced when a raw mixture of predetermined composition is heated to high temperature.
The low costand widespread availability of the limestone, shales, and other naturally occurring materials make portland cement one of the lowest-cost materials widely used over the last century throughout the world. Concrete is one of the most versatile construction materials available in the world.

Portland cement clinker is made by heating, in a kiln, a homogeneous mixture of raw materials to a calciningtemperature, which is about 1450 °C for modern cements. The aluminium oxide and iron oxide are present as a fluxand contribute little to the strength. For special cements, such as Low Heat (LH) and Sulfate Resistant (SR) types, it is necessary to limit the amount of tricalcium aluminate(3 CaO·Al₂O₃) formed. The major raw material for the clinker-making is usually limestone (CaCO₃) mixed with a second material containing clay as source of alumino-silicate. Normally, an impure limestone which contains clay or SiO₂ is used. The CaCO₃ content of these limestones can be as low as 80%. Secondary raw materials (materials in the rawmix other than limestone) depend on the purity of the limestone. Some of the materials used are clay, shale, sand, iron ore, bauxite, fly ashand slag. When a cement kilnis fired by coal, the ash of the coal acts as a secondary raw material. (Source: Wikipedia)

Types of Cement

General

There are different standards for classification of Portland cement.The two major standards are the ASTMC150 used primarily in the U.S. and European EN-197.EN 197 cement types CEM I, II, III, IV, and V do not correspond to the similarly named cement types in ASTM C 150.

ASTM C150
There are five types of Portland cements with variations of the first three according to ASTMC150.

Type I
Portland cement is known as common or general purpose cement. It is generally assumed unless another type is specified. It is commonly used for general construction especially when making precast and precast-prestressed concrete that is not to be in contact with soils or ground water. The typical compound compositions of this type are:
55% (C₃S), 19% (C₂S), 10% (C₃A), 7% (C₄AF), 2.8% MgO, 2.9% (SO₃), 1.0% Ignition loss, and 1.0% free CaO

A limitation on the composition is that the (C3A) shall not exceed fifteen percent.

Type II
is intended to have moderate sulfateresistance with or without moderate heat of hydration. This type of cement costs about the same as Type I. Its typical compound composition is:
51% (C₃S), 24% (C₂S), 6% (C₃A), 11% (C₄AF), 2.9% MgO, 2.5% (SO₃), 0.8% Ignition loss, and 1.0% free CaO.

A limitation on the composition is that the (C₃A) shall not exceed eight percent which reduces its vulnerability to sulfates.This type is for general construction that is exposed to moderate sulfate attack and is meant for use when concrete is in contact with soils and ground water especially in the western United States due to the high sulfur content of the soil. Because of similar price to that of Type I, Type II is much used as a general purpose cement, and the majority of Portland cement sold in North America meets this specification.

Note: Cement meeting (among others) the specifications for Type I and II has become commonly available on the world market.

Type III
has relatively high early strength. Its typical compound composition is:
57% (C₃S), 19% (C₂S), 10% (C₃A), 7% (C₄AF), 3.0% MgO, 3.1% (SO₃), 0.9% Ignition loss, and 1.3% free CaO.

This cement is similar to Type I, but ground finer. Some manufacturers make a separate clinker with higher C₃S and/or C₃A content, but this is increasingly rare, and the general purpose clinker is usually used, ground to a specific surfacetypically 50-80% higher. The gypsum level may also be increased a small amount.

This gives the concrete using this type of cement a three day compressive strength equal to the seven day compressive strength of types I and II. Its seven day compressive strength is almost equal to types I and II 28 day compressive strengths. The only downside is that the six month strength of type III is the same or slightly less than that of types I and II. Therefore the long-term strength is sacrificed a little. It is usually used for precast concrete manufacture, where high 1-day strength allows fast turnover of molds. It may also be used in emergency construction and repairs and construction of machine bases and gate installations.

Type IV
Portland cement is generally known for its low heat of hydration. Its typical compound composition is:
28% (C₃S), 49% (C₂S), 4% (C₃A), 12% (C₄AF), 1.8% MgO, 1.9% (SO₃), 0.9% Ignition loss, and 0.8% free CaO

The percentages of (C₂S) and (C₄AF) are relatively high and (C₃S) and (C₃A) are relatively low. A limitation on this type is that the maximum percentage of (C₃A) is seven, and the maximum percentage of (C₃S) is thirty-five. This causes the heat given off by the hydration reactionto develop at a slower rate. However, as a consequence the strength of the concretedevelops slowly. After one or two years the strength is higher than the other types after full curing.

This cement is used for very large concrete structures, such as dams, which have a low surface to volume ratio. This type of cement is generally not stocked by manufacturers but some might consider a large special order. This type of cement has not been made for many years, because Portland-pozzolan cements and ground granulated blast furnace slagaddition offer a cheaper and more reliable alternative.

Type V
is used where sulfate resistance is important. Its typical compound composition is:
38% (C₃S), 43% (C₂S), 4% (C₃A), 9% (C₄AF), 1.9% MgO, 1.8% (SO₃), 0.9% Ignition loss, and 0.8% free CaO.

This cement has a very low (C₃A) composition which accounts for its high sulfate resistance. The maximum content of (C₃A) allowed is five percent for Type V Portland cement. Another limitation is that the (C₄AF) + 2(C₃A) composition cannot exceed twenty percent. This type is used in concrete that is to be exposed to alkali soil and ground water sulfates which react with (C₃A) causing disruptive expansion. It is unavailable in many places although its use is common in the western United States and Canada. As with Type IV, Type V Portland cement has mainly been supplanted by the use of ordinary cement with added ground granulated blast furnace slag or tertiary blended cements containing slag and fly ash.
 

Types Ia, IIa, and IIIa have the same composition as types I, II, and III. The only difference is that in Ia, IIa, and IIIa an air-entraining agent is ground into the mix. The air-entrainment must meet the minimum and maximum optional specification found in the ASTM manual. These types are only available in the eastern United States and Canada but can only be found on a limited basis. They are a poor approach to air-entrainment which improves resistance to freezing under low temperatures.
 

Types II(MH) and II(MH)a have recently been added with a similar composition as types II and IIa but with a mild heat. The cements were added to ASTM C-150 in 2009 and will be in publication in 2010.

EN 197

EN197-1 defines 5 classes of common cement that comprise Portland cement as a main constituent.
These classes differ from the ASTM classes.

Constituents that are permitted in Portland-composite cements are artificial pozzolans (blastfurnace slag, silica fume, and fly ashes) or natural pozzolans (siliceous or siliceous aluminous materials such as volcanic ash glasses, calcined clays and shale).