Cement, Energy and Environment

as Reactive Belite Cement. When , however, the silicates pair of Alite and Belite is broken and replaced by Calcium Sulfa-aluminate (CSA) and belite, a modified Portland cement known as Calcium Sulfa-aluminate cement is obtained. While making high belite cements it is necessary to reduce the lime saturation factor (LSF) of the raw feed. The substitution of a high lime by a low lime cement therefore leads to energy saving and also to a reduction of C0 2 emission from the decarbonation of the limestone. A reduction in LSF leads automatically to an increase in Belite content and a decrease in Alite content, with the added benefit that formation of C 2 S (65.1% CaO) occurs at lower temperature than the formation of C 3 S (having 73.7% CaO). When the LSF is reduced to 75%, a virtually alite free clinker is formed. The depletion in the CaC0 3 content reduces the energy demand by 15-20% for a Lime Saturation Factor of 80-85% and allows satisfactory clinker formation at lower temperatures by 100-150 deg C. Substitution of some natural raw materials by suitable waste materials also leads to further decrease in the energy demand. To produce low energy cement with adequate strength development and LSF below 85%, Belite must be formed with improved reactivity. Dicalcium silicate (C 2 S) exists in several polymorphic forms that are stable in different temperature ranges. Stabilization of the active forms of dicalcium silicate (a' and a-C 2 S) in the Belite clinkers can be realized by very quick cooling , at least 500 deg C/min in the range 1300- 700 deg C, or by inclusion of appropriate minor elements and mineralizer. Mineralizer is a substance that when added in small dosages during clinkerisation influences either kinetics and/or thermodynamics favorably towards lower energy consumption. In case of calcium sulfa-aluminate cements two sulfate phases C4A 3 S* and CS* instead of high-temperature C 3 S and C 3 A are stabilized along with C 2 S. Therefore raw mixes for C4A 3 S* clinkers also differ from those for Portland cement in that they contain significant amounts of sulfates; therefore , reactions and products are quite different from those normally found in Portland cement production. The total lime requirement to produce such a modified Portland cement is about 50 wt% as against about 65% for Portland cement, and can be synthesized at a lower temperature of 1200 deg C, rather than between 1400 to 1450 deg C as in case of Portland cement. It is conceived that cement containing a calcium sulfa– aluminate and a reactive C 4AF can derive its early strength and other physical properties from formation of calcium sulfa-aluminate hydrates. Although calcium sulfa-aluminate-based cements are increasingly being used in specialized applications where high early strengths and self– stressing or shrinkage compensation are required, their more general application to concrete is limited to China, where a wide range of C 4A 3 S* -based cements have been developed and normalized under the name of the "Third Cement Series". Lastly, the concept of Mineralized Clinker Cement relies on effecting clinker mineralization by controlled introduction of sulfate and fluoride into the kiln system , thereby lowering the clinker formation temperature. Based on the above information it can be realized that marginal grade limestone deposits available at the group manufacturing locations, which are not usable currently, can be utilized successfully for making reactive belite cements. Considering the global thrust on sustainable development and resource crunch of limestone, making of reactive belite cements is expected to be a norm for every cement manufacturer rather than a choice in near future. Therefore initiating actions in this direction proactively can help the group with first movers' advantage. Similarly high sulfate containing limestone available at some of group units can be gainfully exploited for making calcium sulfa-aluminate cements or mineralized clinker cements . Portland Limestone cement: Portland-limestone cements are a type of blended cement similar to PPC & PSC but incorporating limestone in cement in the range of 6-35% instead of fly ash or slag. Depending upon addition levels there are two types containing 6- 20% and 21-35% limestone fines respectively as per European standard EN 197-1 :2000. Portland Limestone cement (PLC) is quite popular in American and European Countries since its use leads to reduced levels of C0 2 emissions and