In this section, we focus on the short-time mechanical properties of concrete that relate to its function as a building material. By “short time” we refer to a loading period that is typically more than a minute but not exceeding a day. Concrete is a conglomerate obtained by mixing Portland cement, a coarse aggregate (typically gravel or crushed rock), a ne aggregate (sand), and water. Cement is the ingredient that, with the help of water, hardens and transforms the mixture into a synthetic rock. In addition to cement, chemical and natural admixtures can be used to improve the workability of the wet mix and to increase the strength, durability, and re resistance of the hardened concrete. Admixtures may also be used to control the tendency of the concrete to change volume with time.