What happens to the strength of concrete when the water-to-cement (W/C) ratio is decreased?

As the water-to-cement (W/C) ratio decreases, the strength of concrete generally increases. This relationship is primarily due to the fact that a lower W/C ratio results in a denser microstructure within the concrete. Water is essential for the hydration process of cement, allowing it to develop its strength. However, excess water can lead to the formation of voids and unhydrated particles in the hardened concrete.

When there is less water relative to the amount of cement, the concrete will have a higher cement content per unit volume, leading to more complete hydration and a reduction in the capillary pores that can compromise strength. As a result, the interlocking of cement particles improves, enhancing the overall compressive strength of the concrete.

In contrast, increasing the W/C ratio would lead to lower strength due to the increased porosity and reduced effective cement content, while fluctuations in the W/C ratio may prevent consistent and reliable strength characteristics. Therefore, maintaining an optimal W/C ratio is crucial in structural applications to ensure that concrete achieves its desired strength and durability characteristics.