Water Cement Ratio

The water to cement (w/c) ratio is a basic parameter in concrete technology. The theoretical water to cement ratio strictly necessary for the hydration reaction is called stoichiometric ratio and is extremely low: about 0.23, the exact value depending on the kind of cement. Of course this ratio is too low for providing to concrete a suitable fresh-state workability, hence higher w/c are currently used, even up to 0.8. However, water in excess respect to the w/c ratio 0.23 does not react with cement and progressively evaporates, leaving the concrete more porous and, hence, weaker. According to the scheme in Figure 4, with increasing water the cement particles are more distant from each other and the final rods network is less cross linked, hence pores are present
The w/c ratio has great influence on the concrete compressive strength.
For this reason, any addition of water respect to the original concrete formulation is potentially dangerous.