Javedan Corporation Limited

Portland cement is the most common type of cement in general usage in many parts of the world, as it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout. It is a fine powder produced 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). As defined by the European Standard EN197.1, "Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates (3CaO.SiO₂ and 2CaO.SiO₂), the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. The ratio of CaO to SiO₂ shall not be less than 2.0. The magnesium content (MgO) shall not exceed 5.0% by mass." (The last two requirements were already set out in the German Standard, issued in 1909). Portland cement clinker is made by heating, in a kiln, a homogeneous mixture of raw materials to a sintering temperature, which is about 1450 °C for modern cements. The aluminium oxide and iron oxide are present as a flux and 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 (3CaO.Al₂O₃) formed. The major raw material for the clinker-making is usually limestone (CaCO₃). Normally, an impure limestone which contains 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 secondary raw materials used are: clay, shale, sand, iron ore, bauxite, fly ash and slag. When a cement kiln is fired by coal, the ash of the coal acts as a secondary raw material.

Slag Cement is recycling of blast furnace slag has been used for a long time in the cement industry. It is often used in composite cement. Slag is not hydraulic by it self, but if an activator (e. g. lime) is present, it takes part of the hydration reactions and makes a substantial contribution to the hydration product.

Blast furnace slag can also be used as a raw material for the manufacture of Portland cement clinker. In general slag contains 30-50 % lime, 30-40 % silica, 10-25 % aluminia, 0-20 % magnesia and minor elements, e. g. Sulfur, iron, manganese, titanium, sodium, potassium etc.

In this project we will investigate the effects of slag as a raw material on the microstructure, chemistry and reactivity of Portland cement clinker.

Sulphate Resistant Cement is especially designed for aggressive environments. The concrete made from this cement is typically used in foundations, basements, and waste-water systems as well as for standard ready mixed concrete. The composition of this cement is different than the average cement due to the limited content of calcium aluminate in the clinker and limited content of clinker in cement. This is significant for limiting the reaction between tricalcium aluminate (C3A) and sulphate which damages concrete. The portland clinker within sulphate resistant cement is specifically produced at Cement Works Mokra for this product and for special cement being used for concrete roads.

Sulphate resistant concrete is designed for aggressive and corrosive environments. The biggest customers are large ready-mix companies and the manufacturers of pre-cast elements such as pipes. Currently, there are no European standards for sulphate resistant cement. For this reason, sulphate resistant cement CEM III/A 32,5 R is being produced, certified and brought to the Czech market according to general European harmonized standard for cements EN 197-1 and according to tighten requirements