Types of Portland cement and Uses
Portland cement was named for the Isle of Portland, a peninsula in the English Channel where it was first produced in the 1800’s. Since that time, a number of developments and improvements have been made in the production process and cement properties. The production process for portland cement first involves grinding limestone or chalk and alumina and silica from shale or clay. The raw materials are proportioned, mixed, and then burned in large rotary kilns at approximately 2500°F until partially fused into marble-sized masses known as clinker. After the clinker cools, gypsum is added, and both materials are ground into a fine powder which is portland cement.
Three types of portland cement are used for several applications:
- Type I cement is the general purpose and most common type. Unless an alternative is specified, Type I is usually used.
- Type II cement releases less heat during hardening. It is more suitable for projects involving large masses of concrete–heavy retaining walls, or deadmen for suspension bridges.
- Type III cement produces concrete that gains strength very rapidly.
It is very finely ground and sets rapidly, making it useful for cold weather jobs.
- Good water is essential for quality concrete.
- It should be good enough to drink–free of trash, organic matter and excessive chemicals and/or minerals.
- The strength and other properties of concrete are highly dependent on the amount of water and the water-cement ratio.
- Aggregates occupy 60 to 80 percent of the volume of concrete.
- Sand, gravel and crushed stone are the primary aggregates used.
- All aggregates must be essentially free of silt and/or organic matter.
- Admixtures are ingredients other than portland cement, water, and aggregates.
- Admixtures are added to the concrete mixture immediately before or during mixing.
Air Entraining agents:
are the most commonly used admixtures for agricultural concrete.
produce microscopic air bubbles throughout the concrete.
Entrained air bubbles:
improve the durability of concrete exposed to moisture and freeze/thaw action.
Improve resistance to scaling from deicers and corrosive agents such as manure or silage.