The study was concerned with examining the effect of thewater-to-cement ratio over the range of 0.19 to 0.50 on the composition andmorphology of hydrated cement pastes. The strength after setting increases withdecreasing w/c while the content of hydration products decreases. At the sametime the homogeneity of the hydration products tends to increase and theoccurrence of crystalline hydrates (particularly that of portlandite) decreases.At the lower w/c values, higher-calcium forms of the C-S-H phase, in whichCa(OH)2 is dispersed, arise at the lower w/c values. Crystallineportlandite exhibits a preferen-tial direction of fracture, thus creatingconditions for potential ready crack propagation and therefore also for apossible lowering of strength. Crystalline Ca(OH)2 is then theweakest part of the set system and represents a limit of its mechanicalproperties. The differences in the content and form of Ca(OH)2present in set materials based on Portland cement may have unexpected effects ontheir performance properties.
