What material is recognized as the 'glue' in concrete?

Cement is recognized as the 'glue' in concrete because it is the binding agent that holds the aggregates together, creating a solid and durable material. When mixed with water, cement undergoes a chemical reaction known as hydration, allowing it to harden and bind the sand, gravel, or crushed stone particles in the mix. This process is crucial for the development of concrete's strength and structural integrity.

In contrast, chalk is not used in significant quantities in concrete and does not serve as a binding agent. Caulking is a material used for sealing gaps or joints but is not a component of concrete itself. Wood, while it can serve various purposes in construction, does not function as an adhesion agent in concrete mixtures. Thus, cement's role as the key binder differentiates it from these other materials.