The superior performance of blended cements over those of PC is mainly due to the following: i) The pozzolanic reaction of SCMs with free lime (CH) produced by cement hydration, which reduces gypsum formation; ii) The reduction of C3A content, i.e. dilution effect; iii) The reduction of pH value therefore, the ettringite becomes less expansive; iv (The formation of additional amounts of CSH, which produces a coating film on the alumina-rich and other reactive phases, thereby hindering the formation of secondary and lastly ettringite; and v) The formation of secondary CSH also results in pore size refinement, which reduces the permeability as well as the ingress of aggressive ions.

It all depends on what do you mean by the word "composite". If you meant it to be fiber or nano filler reinforced cement, then the property improvement is the same as usual polymer matrix composite and nano composites, due to the high aspect ratio of the reinforcing fibers.

If, however, you meant it to be polymer added cement, the polymer fills the interstices of the cement particles. When the polymer completely fills the existing voids, then you can create macrodefect-free cement. Macrodefect-free cement can create concrete 5-10 times stronger compressive strength than usual concrete without the additives. It is very important that the amount of additives are adjusted in such a way that it just fills all the voids. Too much or too less is not effective. Also, if the polymer additive is the latex, upon evaporation of the solvent, the voids are again created. Therefore, the most effective elimination of the void is the addition of reactive monomer that does not shrink too much upon polymerization.

composite cement may be indicated to that fibrous cement . Composite cement may be indicated to blended one . I think composite cement indicate to cement reinforced with fiber . Superior characteristics are due to the large capccity for tension accomodation. Conventional cement is stronge enough in copression bat not in tension . It is a brittle material , while coposite cement may be regarded flexible enough ti resist tesile stresses .