What is concrete made from and does it have limestone in it?

Concrete is made up of three basic components: water, aggregate (rock, sand, or gravel), and Portland cement. Cement, usually in powder form, acts as a binding agent when mixed with water and aggregates. This combination, or concrete mix, will be poured and harden into the durable material with which we are all familiar. The cement and water form a paste that coats the aggregate and sand in the mix. The paste hardens and binds the aggregates and sand together. Water is needed to chemically react with the cement (hydration) and too provide workability with the concrete. The amount of water in the mix in pounds compared with the amount of cement is called the water/cement ratio. Sand is the fine aggregate. Gravel or crushed stone is the coarse aggregate in most mixes.
Limestone is common a rock that makes up about ten percent of all sedimentary rocks. Cement is simply one of the ingredients of concrete, and limestone is also used in cement.