7.7 : Water Cement Ratio

The water-cement ratio is pivotal in defining concrete's quality. This ratio, a balance between the weight of water and cement in the mix, shapes the concrete's strength, durability, and resistance to environmental factors. As identified by Abrams’ law, less water in the mix equates to stronger concrete. However, water is essential not only for the chemical process of hydration but also for the concrete's workability and compaction. While hydration chemically binds water and cement, physical absorption of water into the cement gel is also necessary for complete hydration.

Excess water used for easier workability leads to capillary voids once it evaporates, which in turn raises porosity and permeability, thus reducing strength. Standard concrete applications maintain water-cement ratios from 0.45 to 0.60. Lower ratios result in denser, stronger concrete that shrinks less but may require additives to achieve the desired fluidity for placement. It's crucial to use enough water to ensure the concrete's malleability without compromising its cured qualities. The art of concrete mix design involves finding this delicate balance to produce a material that meets specific workability requirements while retaining its integrity once set.