Resources
Concrete 101

Composition of Concrete
Concrete is composed of four main ingredients: cement, water, fine aggregate (sand), and coarse aggregate (rock). Sometimes recycled cementitious materials known as slag and fly ash are substituted for cement, causing varying effects on the concrete’s plastic and hardened properties. Admixtures can also be supplemented to the mix in order to reduce curing time, increase workability, increase strength, or to change the material properties. Varying proportions of these main ingredients are what create the many types of concrete.

Air Entrainment

Reinforcement

Slump

Water-Cement Ratio

Interior vs. Exterior

Hot vs. Cold Weather
Concrete is sensitive to temperature, setting quicker in hot weather and slower in cold weather. Admixtures are often added to slow the set time during hot weather (retarder) and to speed up the set time in cold weather (accelerator).
When pouring fresh concrete, hot weather may cause difficulties such as:
- Accelerated slump loss
- Increased set time
- Increased water demand
- Difficulties controlling entrained air
Be careful when adding water to the concrete at the jobsite as it can adversely affect the concrete causing decreased strength, durability, and increasing the tendency to crack.