Materials

Water-Cement Ratio

The weight of mixing water divided by the weight of cement — the main control on concrete strength.

The water-cement ratio is the single most important number in a concrete mix. Water beyond what the cement needs to hydrate leaves capillary pores when it evaporates, so a higher ratio produces weaker, more permeable concrete. Typical structural mixes run from about 0.40 to 0.55.

Adding water on site to restore slump raises the ratio and lowers strength, even though the concrete looks better to place. A water-reducing admixture achieves the same workability without that cost.

How much of the FE Civil exam is Materials?