Which property is most affected by high water-cement ratios in concrete?

The property most affected by high water-cement ratios in concrete is compressive strength. When the water-cement ratio increases, it generally leads to an excess of water in the mix. This additional water dilutes the amount of cement available for bonding, resulting in the formation of a weaker paste upon curing. Consequently, the concrete will have a lower density and reduced strength once it hardens.

Compressive strength is a critical measure, as it reflects the ability of concrete to withstand axial loads without failure. Higher water-cement ratios can significantly compromise this strength, making the concrete more susceptible to cracking, deformation, and ultimate failure under load.

Other properties such as longevity, visual aesthetics, and thermal conductivity may also be influenced by the water-cement ratio, but compressive strength is primarily the most directly impacted. Longevity might decrease due to the potential for structural failures or increased porosity, visual aesthetics could be affected by the mix's finish, and thermal conductivity might vary slightly, but none are as fundamentally affected as compressive strength.