Cement, Energy and Environment

22 Table-3 Chemical Properties of Poirtland Cement and Sulfoauminate Belite Cement Chemical Composition & properties Portland Cement Sulfoaluminates Belite Cement Loss on Ignition 1.40 0.60 CaO (wt.%) 63.70 48.12 SiO 2 (wt.%) 19.17 17.17 Al 2 O 3 (wt.%) 5.67 15.25 Fe 2 O 3 (wt.%) 3.48 6.16 MgO (wt.%) 1.49 1.66 SO 3 (wt.%) 3.01 7.88 Free Lime(wt.%) 0.10 0.00 Sp Gravity ( kg/m 3 ) 3.16 3.21 SurfaceArea (m 2 /kg) 443 643 Insoluble Residue(wt.%) 1.66 3.06 Initial Setting Time (min) 125 35 Final Setting Time (min) 205 45 The rapid setting of sulfoaluminate cement is mainly due to quick conversion of C 4 A 3 S to hydration product during early age hydration. On hydration the gypsum react with C 4 A 3 S and from ettringite (C 6 AS 3 H 32 ) to regulate the technical properties of Sulfoaluminate Belite cements. 4 CaO3Al 2 O 3 SO 3 +8CaSO 4 +6CaO+93H 2 O → 3 (CaOAl 2 O 3 CaSO 4 31H 2 O) The formation of the ettringite is very fast in this case, as a result in reduced workability of the cement and required retarder. The C 2 S present in this cement add the strength and durability. The mortars of such cements also has comparable compressive strength and total porosity when compared with Portland Cement. The mortar prepared from the Sufoalluminate Belite cement release less quantity of Ca(OH) 2 than the Portland cement mortar on hydration, thus reduces the porosity of the concrete. The higher content of gypsum in the Sufoalluminate Belite cement also decrease the carbonation of concrete. The Sufoalluminate Belite cement exhibits better protection for the steel reinforcement corrosion. Presently these cements are produced commercially some of the countries such as China, Japan, Russia successfully. These cements are best suitable for the construction in the coastal areas owing to their sulphate resistance property. The influence of MgO on the composition structure and properties of alite calcium strontium sulphoaluminate cement were investigated. The results show that when the mass fraction of MgO is 1-5% the early strength of cement can be enhanced significantly. The optimal content of MgO in cement clinker is 2% and the compressive strength of the cement at 3, 28 days are 64.3 and 103.6 MPa respectively. The suitable amount of MgO can promote the formation of cl.5Sr 2 S A 3 , while the formation of cl.5Sr 2 S A 3 can be hindered if the content of MgO is excessive. The existence of MgO can improve the formation of C 3 S, increasing the mechanical properties of the cement. Compared to Portland cement the Calcium Strontium Sulphoaluminate cement has higher capacity to dissolve MgO which indicate that the low quality high magnesium limestone can be effectively used in cement production. 6.0 Conclusion: From the above analysis it can be concluded that fort use of high MgO limestone in Cement production the following measures can be taken.  Screening of dolomitic limestone and blending with low MgO limestone to control the MgO in the Raw meal . It should not be more than 5% limestone.  The raw meal should be the finer for the better reactivity in pyroprocessing  The Lime Saturation factor and Alumina Modulus should be low incase of high MgO Raw Mixes. Lowering the C3A and increasing C4AF contents could readily counteract the autoclave expansion due to high MgO content in cement.  Maintaining the (Al 2 O 3 +MgO)/ Fe 2 O 3 in the raw meal <1.2 control the formation of periclase in clinker.  Use of CaF 2 and Gypsum as mineralizer reduces considerably the formation of larger size pericalse crystals, thus control the expansion of the cement.  The rapid cooling of Portland clinker causes the MgO in the solution in the glass form and reduced autoclave expansion.  The cement ground finer more than 400 m 2 /kg reduced the autoclave expansion.  With the longer days of curing the cement concrete, the autoclave expansion decreases considerably.  With Production of blended cement and composite cement the MgO content up to 10 % in cement can be adjusted for production of sound cement.