Which method can improve the durability of concrete?

Reducing the water-to-cement ratio is a well-established method for improving the durability of concrete. The water-to-cement ratio affects the strength and permeability of the concrete. A lower ratio typically results in denser concrete with fewer voids, which leads to reduced permeability. This, in turn, can impede the ingress of harmful substances such as chlorides and sulfates that can cause corrosion of reinforcing steel and deterioration of the concrete matrix.

Increased durability translates into a longer service life for the concrete structure, as it is more resistant to cracking, freezing and thawing cycles, and chemical attacks. Additionally, a lower water-to-cement ratio generally results in higher compressive strength, enhancing the overall performance of the concrete.

The other methods listed, such as increasing aggregate size or using more cement, do not directly address the fundamental characteristics of the concrete mix relative to its water content. While using more cement may improve strength, it can also lead to thermal cracking and increased costs without specifically targeting durability through reduced porosity. Adding more water, contrary to improving durability, would compromise the concrete's strength and increase the risk of shrinkage and cracking. Therefore, maintaining an optimal water-to-cement ratio is crucial for achieving durable concrete.