Skin formation in adhesive mortars evaluated by MRI and interfacial rheology

The formation of a dry skin on fresh adhesive mortars is an undesirable side effect of polymeric admixtures that are indispensable to this type of material. This investigation adapted a classical interfacial rheology technique to study the evolution of the skin's properties. The introduced technique and magnetic resonance imaging (MRI) were used to evaluate the effects of cellulose ether (CE) content and degree of substitution's (DS) on skin formation of mortars prepared with two types of cements. MRI results of water distribution within the sample over time indicated a dryer zone formed at the exposed surface that is dependent on CE content. Oscillatory interfacial measurements pointed out that skin's storage modulus (G') was firstly dominated by water loss, presenting smaller increasing rate with higher CE content, then an inversion occurred due to polymer properties predominance. Wind conditions accelerated the effects of CE on G' kinetics of the skin.