We often hear people use the terms “cement” and “concrete” interchangeably, but they are indeed very different things. This is your concrete guide to what concrete is. First, let’s discuss the difference between cement and concrete: Cement is a powder that acts as a binding agent. It is mixed with water and aggregates (sand, gravel, or crushed stone) to form a paste. This paste hardens over time, eventually becoming concrete. So, basically, concrete is the final product of a cement, water, and aggregate mixture. Think of cement as the flour that goes into your cake mix.
Cement is typically made from a mixture of minerals such as limestone, clay, gypsum, and/or iron oxide. These minerals are ground together to make a powder called raw meal. The raw meal powder is heated up in a kiln to create clinker, which is then ground again into a very fine powder. This then becomes the main binding ingredient for concrete.
Water mixed with the fine powder cement is what creates the backbone of concrete. Aggregates bulk up the structure of the mix and sad help with the entire binding process. Air can be added to the mix to create pockets throughout the concrete. This aids in the freeze/thaw cycle, which will reduce cracking and spalling because it allows for some expansion room. The ratios of these ingredients depend mostly on climate factors and the uses and needs of the concrete. The concrete mixture for a backyard patio will be a little different than the concrete mixture for a highway overpass, for example.
For a good concrete mix, there are several factors to consider. Strength refers to the ability to withstand stress and heavy loads. Durability refers to wear resistance from climate exposure and chemical factors. Workability is how well the mix can be poured and molded into the desired shape. Setting time considerations refer to when the concrete is ready for use. Density refers to the consistency of the concrete both in surface texture and throughout the entire mix. Shrinkage should be minimal as it cures to avoid potential cracks during the setting process, and the water-to-cement ratio needs to be balanced to ensure proper setting. Freeze/thaw cycle refers to how the concrete will withstand this repeated event each year without losing its integrity. Sulfate resistance takes into account the sulfates in soil, which can damage the concrete through too much expansion. Finally, long-term stability factors are considered in order for the concrete to maintain its disposition and properties over time.
Reinforced concrete is made with bars for added tensile strength and is used for weight-bearing structures such as bridges and buildings. Lightweight concrete commonly used for walls or flooring or to protect steel structures. Plain concrete is typically what you see in basic pavements and driveways. Precast concrete is often made in a controlled environment then transferred to a job site. Air-entrained concrete is infused with air particles and is used mostly in areas with high freeze/thaw cycles. A normal-strength concrete mix typically combines a good balance of strength, workability, and durability.