Use of nonionic, water-dispersible polyisocyanates as concrete additives

In a process for preparing a mortar/concrete composition by mixing an inorganic binder, an aggregate, water, the improvement which involves incorporating into the mortar/concrete composition either before or during the mixing operation a hydrophilic, strength-enhancing water-dispersible polyisocyanate in solvent-free form which

• a) has an average isocyanate functionality of 1.8 to 4.0,
• b) contains from 4.0 to 25.0 wt. % of an isocyanate component comprising a group selected from the group consisting of aliphatically-bound isocyanate groups and cycloaliphatically bound isocyanate groups, calculated as NCO;
• molecular weight=42, and
• c) contains 5 to 80 wt. % of ethylene oxide units present within polyether chains, calculated as C.sub.2 H.sub.4 O;
• molecular weight=44, in which
• d) the polyether chains contain an average of 5 to 50 ethylene oxide units
• wherein the water-dispersible polyisocyanate can be used in an amount up to 10 wt. % based on the weight of the binder.