What does coarse aggregate consist of in concrete mixtures?

Coarse aggregate in concrete mixtures primarily consists of larger particles, typically gravel or crushed stone that are larger than ¼ inch in diameter. This component is crucial because it contributes to the overall strength and durability of the concrete. The larger size of these aggregates helps to provide volume and stability to the concrete structure, aiding in load distribution and reducing shrinkage during the curing process.

Coarse aggregates also play a role in reducing the cost of concrete, as they typically make up a significant portion of the mixture. The size and type of coarse aggregate used can influence the workability, strength, and overall performance characteristics of the concrete.

Other materials listed, such as sand and fine particles, fibers for reinforcement, and cement particles, serve different purposes in concrete mixtures. Sand and fine particles are part of the fine aggregate that works together with the coarse aggregate to fill voids and improve the mixture's cohesion, while fibers are often added for specific reinforcement needs but are not classified as aggregates. Cement particles are the binding component that reacts with water to harden and set the concrete. Thus, the focus on gravel or crushed stone as the defining feature of coarse aggregate makes this the correct understanding in the context of concrete composition.