GAJ Composite Cement
All hydraulic hardening binding materials produced by the grinding of the Portland cement clinker, two or more of the above-regulated blended materials and an appropriate amount of gypsum are known as Portland cement composite (so-called composite cement), code-named P • C. The total mixing quantity of cement blended materials should be more than 15% but not more than 50%. Kiln dust of less than 8 per cent may be used to replace part of the blended materials; the mixing amount of the blended materials should not overlap with Portland blast furnace slag cement when blended with slag. With respect to Composite Portland Cement (GB 12958-1999) as the national standard, the content of magnesium oxide in cement clinker should be no more than 5.0 per cent. If the cement is qualified for soundness by autoclave method, the magnesium oxide content of the clinker may be up to 6.0 per cent. The sulfur trioxide content in cement must not exceed 3.5%. Composite cement has six strength levels as 32.5, 32.5R, 42.5. 42.5R, 52.5 and 52.5R. Its requirements in fineness, setting time and volume stability are the same as those of ordinary silicate cement.
The main features of composite cement are related to the types and amount of the two or more admixtures in it and are similar to those of slag silicate cement, pozzolanic silicate cement and fly ash silicate cement, i.e., certain admixture provides the cement with features of its own.