Cementitious mixt. contg. no fine fraction aggregate - with added poly-electrolyte for improved strength, and used in form of soln. or dispersion

Cementitions mixt. comprising hydraulic binder, water and aggregate such as pulverised ash, contg. as fine fraction is claimed in which 0.001-0.25 (0.01-0.5) wt% of a polyelectrolyte is added wrt the wt. of the cement. The polyelectrolyte is added as a low viscosity soln. in water or a dispersion in a hydrocarbon oil, esp. a low viscosity aliphatic oil. A lower density concrete can be made without loss of strength. Suitable polyelectrolytes are polyacrylamide, polyethylene oxide are carboxyl-vinyl polymers esp. of mol. wts. 1.10x106. Esp. suitable is a 2 wt% of partly hydrolysed polyacrylamide. The current may be Portland cement as a sulphate contg. cement. Other additives may also be made to the mixt.