The effect of particles size distribution of the coarse aggregates on the water demand of the concrete mix was studied and analyzed using the concept of particles size distribution in so far as they deviate from the avera size or fineness modulus as indicated by the standard deviation of the sample.
Six concrete mixes 1:2:4 by weight (320 kg/m3 cement content) were designed for a given slump of (30-60) mm. The main variable being the gradation of the coarse aggregates.
The results showed that an increase in the S.D of the coarse aggregate particle distribution resulted in an increase in the water demand of the mix, this was further substantiated by a decrease in the resulting compressive strength. An extra 38 similar concrete mixes were selected randomly from the literature for further supporting evidence.

Keywords: Particle size distribution, Water demand, standard deviation, average size of aggregate