How It Is Made
After the aggregates, water, and the cement are combined, the mixture remains in a fluid condition for about four to six hours which permits transporting, placing and finishing in its final location, then the mixture starts to harden. All portland cements are hydraulic cements that set and harden through a chemical reaction with water. During this reaction, called hydration, crystals radiate outwards from cement grains and mesh with other adjacent crystals or adheres to adjacent aggregates. The building up process results in progressive stiffening, hardening, and strength development.
Once the concrete is thoroughly mixed and workable it should be placed in forms before the mixture becomes too stiff. During placement, the concrete is consolidated to compact it within the forms and to eliminate potential flaws, such as honeycomb and air voids.