  Colloidal gels are widely applied in industry due to their rheological
character -- no flow takes place below the yield stress. Such property enables
gels to maintain uniform distribution in practical formulations; otherwise,
solid components may quickly sediment without the support of gel matrix.
Compared with pure gels of sticky colloids, therefore, the composites of gel
and non-sticky inclusions are more commonly encountered in reality. Through
numerical simulations, we investigate the gelation process in such binary
composites. We find that the non-sticky particles not only confine gelation in
the form of an effective volume fraction, but also introduce another
lengthscale that competes with the size of growing clusters in gel. The ratio
of two key lengthscales in general controls the two effects. Using different
gel models, we verify such a scenario within a wide range of parameter space,
suggesting a potential universality in all classes of colloidal composites.
