APortland cement (PC) is cement made from limestone and clay that is quarried and crushed. The crushed rock is combined with other ingredients such as iron ore or fly ash and ground, mixed, and fed to a cement kiln. It’s then heated to 2700°F, producing off-gases, primarily CO2. The resulting material, called “clinker”, is cooled and then cement plants grind it and mix it with small amounts of gypsum and limestone. Portland cement can contain some hazardous components such as silica and hexavalent chromium.
Portland cement-based concrete is a mixture of PC, water, and aggregate (sand, gravel). The PC mixed with water acts as a binder for the aggregate.