The effect of the variation in C(4)A(3) (S) over bar content (expressed as C(4)A(3) (S) over bar/C5S2 (S) over bar weight ratio ranging from 1:5 to 3:1) on the ternary system C(4)A(3) (S) over bar-C5S2S2 (S) over bar-C (S) over bar having a constant C (S) over bar/C(4)A(3) (S) over bar ratio of 0.5, has been studied. At the fixed w/s ratio of 0.4 the mechanical strength of the system at early ages (1-28 days) increased with higher C(4)A(3) (S) over bar content. However, depending on the curing conditions, compositions containing more than 50% C(4)A(3) (S) over bar showed expansion, cracking and loss of strength at later ages, due to the insufficient water used. Moreover compositions with more than 20% C(4)A(3) (S) over bar and increasing C(4)A(3) (S) over bar content gave progressively lower mechanical strength, when hydrated with the fixed water/reactants (C(4)A(3) (S) over bar + C (S) over bar) ratio of 0.86, i.e. 10% more than the stoichiometric water requirement. Thus, both C(4)A(3) (S) over bar content and w/s ratio must be optimized in order to achieve satisfactory performances at early and later ages. The best behaviour was obtained with cements containing 30-40% C(4)A(3) (S) over bar hydrated with a w/s ratio ranging from about 0.35 to 0.50.
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