When the water-to-cement (W/C) ratio is decreased, how does durability of concrete change?

Decreasing the water-to-cement (W/C) ratio generally leads to an increase in the durability of concrete. A lower W/C ratio means that there is less water relative to cement in the mixture, which results in a denser and more cohesive concrete matrix after curing. This density enhances the concrete's ability to resist various forms of deterioration, such as penetration of water, chloride ions, and other aggressive chemicals, which can lead to corrosion of reinforcing steel and other structural damage.

Additionally, a lower W/C ratio typically results in improved compressive strength. When concrete has higher strength, it often possesses better resistance to freeze-thaw cycles, scaling from de-icing chemicals, and other environmental impacts, all of which contribute to its long-term durability.

In contrast, increasing the W/C ratio may lead to a more porous concrete structure, which can absorb water and harmful substances more easily, compromising its durability over time. Thus, the correlation between a lower W/C ratio and enhanced durability is well-established in concrete technology and is a critical consideration in structural engineering.