Ready-Mix concrete is the most versatile and widely used material in worldwide construction today. Its flexible recipe characteristics allow for an end product that can assume almost any color, shape, texture and strength to meet the many requirements of end uses that range from bridges, foundations, skyscrapers, pavements, dams, houses, parking garages, water treatment facilities, airports, tunnels and power plants, hospitals and schools. This versatility gives concrete designers a spectrum of unlimited potential.
There are five primary ingredients that constitute a basic concrete mix:
• Cement
• Coarse Aggregate (CA)
• Fine Aggregate (FA)
• Water
• Admixtures
The water and cement are combined and a chemical reaction is produced called hydration. This paste or binder represents between 25 to 40 percent of the volume of the mix that coats each particle of aggregate and serves as the agent that binds the aggregates together. The aggregates represent 60 to 75 percent of the mix by volume, with the remaining volume (4% - 8%) consisting of entrapped air that was generated by using air entraining admixtures. Once fully hydrated, the plastic concrete will then harden and take on the shape of the form in which it was placed.
The quality of a concrete mix is generally determined by ratio of water to cement. The water cement ratio is determined by dividing the weight of the water by the weight of the cement. It physically only requires approximately 0.29 lbs of water to hydrate 1.0 lbs of Portland cement; any amount in excess of this is generally used to gain workability. Higher quality concrete is produced by lowering the water-cement ratio as much as possible without sacrificing the workability or finishability of the fresh concrete. Specialty admixtures such as high range water reducers can aid in achieving this condition without sacrificing quality.
Other materials commonly used in the production of ready-mix concrete include fly-ash, a waste byproduct from coal burning power plants, silica fume, a waste byproduct generated from the manufacture of silicon and ferro-silicon metals, and ground granulated blast furnace slag, a byproduct of the iron and steel manufacturing process. All of these products have cemetitious properties that enhance the strength, durability and permeability of the concrete.
The U.S. alone consumes approximately 340 million cubic yards of concrete fueling a $35 billion industry which employs over 2 million workers and covering 55,000 miles of roadways.
Some different types of concrete include Lightweight Concrete, High Performance Concrete, Self Compacting/Consolidating Concrete and Architectural Concrete.