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What is Concrete?Concrete & Portland Cement Information
Learn about the basic ingredients of concrete, mix designs, and types of cement.
Contrary to popular belief, concrete and cement are not the same thing; cement is actually just a component of concrete. Concrete is made up of three basic components: water, aggregate (rock, sand, or gravel) and Portland cement. Cement, usually in powder form, acts as a binding agent when mixed with water and aggregates. This combination, or concrete mix, will be poured and harden into the durable material with which we are all familiar.
Following is a group of articles that will be helpful when trying to understand more about concrete and cement. Topics include issues relating to concrete basics, mix design, installation, and decorative concrete.
Components of the Basic Concrete Mix
There are three basic ingredients in the concrete mix:
- Portland Cement
- Aggregates (rock and sand)
Portland Cement - The cement and water form a paste that coats the aggregate and sand in the mix. The paste hardens and binds the aggregates and sand together.
Water- Water is needed to chemically react with the cement (hydration) and too provide workability with the concrete. The amount of water in the mix in pounds compared with the amount of cement is called the water/cement ratio. The lower the w/c ratio, the stronger the concrete. (higher strength, less permeability)
Aggregates- Sand is the fine aggregate. Gravel or crushed stone is the coarse aggregate in most mixes.
Portland Cement--What Is It?
Portland Cement is a type of cement, not a brand name. Many cement manufacturers make Portland Cement.
Portland cement, the basic ingredient of concrete, is a closely controlled chemical combination of calcium, silicon, aluminum, iron and small amounts of other ingredients to which gypsum is added in the final grinding process to regulate the setting time of the concrete.
The Portland Cement Association's How cement is made provides detailed information of the process.
1. The concrete mix is workable. It can be placed and consolidated properly by yourself or your workmen.
2. Desired qualities of the hardened concrete are met: for example, resistance to freezing and thawing and deicing chemicals, watertightness (low permeability) , wear resistance, and strength. Know what you are trying to achieve with the concrete.
3. Economy. Since the quality depends mainly on the water to cement ratio, the water requirement should be minimized to reduce the cement requirement (and thus reduce the cost).
Take these steps to reduce the water and cement requirements:
- use the stiffest mix possible
- use the largest size aggregate practical for the job.
- Use the optimum ratio of fine to coarse aggregate.
Discuss how to achieve your goals for the concrete with your ready mix supplier.
Reinforcement to the Concrete Mix
Fibers can be added to the concrete mix in lieu of welded wire mesh.
The problem with welded wire mesh is that it often ends up on the ground from being stepped on as the concrete is being placed. (particularly if no support blocks are used). Another problem is that mesh does not prevent or minimize cracking-it simply holds cracks that have already occurred together.
If you could look into a section of concrete poured with fibers you would see millions of fibers distributed in all directions throughout the concrete mix. As micro cracks begin to appear due to shrinkage as water evaporates form the concrete (plastic shrinkage), the cracks intersect with the fibers which block their growth and provide higher tensile strength capacity at this crucial time.
Click here for how fibers are an important part of "how to build high quality slabs on grade."
Concrete Contractors: Find A Concrete Product Supplier or Distributor