Real World Example:
Let’s consider a ready mix truck containing 10 cubic yards of air-entrained concrete mixture (containing
564 lbs. of portland cement per cy) that has been proportioned at the maximum design w/cm of 0.45
(dashed arrows on Fig. 2). Upon arrival to the jobsite and prior to placement, 33 gallons of water are
added to the 10 cubic yard load, resulting in a w/cm of approximately 0.50 (solid arrows on Fig. 2). The
resulting 28-day compressive strength of the mixture prior to the water addition was approximately 4250
psi and the resulting compressive strength realized was approximately 3750 psi. This equates to a drop
of 500 psi or a strength loss of nearly 12%.