Concrete is a mixture of cementitious materials, water, aggregate, usually sand and gravel or crushed stone. There is a common misunderstanding that cement and concrete are one and the same. Cement is a powdered ingredient that provides the glue that binds the aggregates together in a mass called concrete.
Ready mixed concrete is that which is delivered to the customer in a freshly mixed and unhardened state. Due to the ability to customize its properties for different applications and its strength and durability to withstand a wide variety of environmental conditions, ready mixed concrete is one of the most versatile and popular building materials.
Concrete mixtures are proportioned to obtain the required properties for the application. It should have the correct consistency, or slump, to facilitate handling and placing and adequate strength and durability to withstand applied loads in the anticipated environment and service conditions. The design quantities of concrete ingredients are accurately weighed and mixed, either in a mixer at the concrete plant or in a concrete truck mixer. It is delivered in a truck mixer or agitation unit, which keeps the concrete uniformly mixed until it is discharged at the placement location. Concrete remains plastic for several hours depending on the type of mixture and conditions during placement so that there is sufficient time for it to be placed and finished. Concrete normally sets or hardens within two to twelve hours after mixing and continues to gain strength for months or even years if it is properly cured during the first few days.