The aggregate is a collection of inert granular material that makes up to 60% to 80% of a typical concrete mix. There are many different types of aggregates that are commonly found in concrete, such as sand, gravel, or crushed stone. Cement is also similar to aggregate because it contains sand, one of the most commonly used aggregates. However, cement is slightly thicker than aggregate because it is finely ground rock, usually limestone or shale.
Although the terms cement and concrete are often used interchangeably, cement is actually an ingredient in concrete. Concrete is a mixture of aggregates and paste. Paste is water and portland cement, while aggregates are sand and gravel or crushed stone. As concrete ages, it grows stronger due to a process called hydration, where cement and water harden and bind aggregates together into a rock-like mass.
Portland cement is not a trade name, but rather the generic term for the type of cement used in virtually all concrete, just as stainless steel is a type of steel and sterling silver is a type of silver. Cement makes up 10 to 15 percent of the concrete mix, by volume. The absorption and surface moisture of aggregates are simple but critically important aspects of producing concrete that consistently achieves the specified or desired strength. Concrete is made by mixing materials with water and aggregates, which are the most common elements on Earth, so no specific or difficult processes are required to manufacture it.
It's important to use aggregates that meet ASTM C 33, Standard Specifications for Concrete Aggregates. Due to the variety of mixes of different colors and textures available, exposed aggregate concrete is very versatile and can be combined with all types of exterior and landscaping designs. Concrete with exposed aggregates is a special mixture that is poured in almost the same way as regular concrete, but its upper surface is subsequently removed to expose the aggregate below. A properly proportioned concrete mix will possess the desired workability for fresh concrete and the durability and strength required for hardened concrete.
If made correctly, concrete can last up to 50 years with strong steel reinforcing bars inside the material. If their absorption is not satisfied, these sponges steal water from the designated amount of mixing water, reducing concrete settling. Recycled concrete will have a higher absorption and a lower specific gravity than conventional aggregates. The use of non-potable water or water of unknown purity jeopardizes the quality and workability of concrete. Cement doesn't have much strength on its own; however, when mixed with water and aggregates, it becomes concrete and gains greater strength.
The use of aggregates for construction purposes is much more sustainable than the use of cement or concrete. A mixture with an excess of cement paste will be easy to place and will produce a smooth surface; however, the resulting concrete is more likely to crack and be uneconomical. Concrete production is similar to cement because it also requires heat to melt all ingredients, emitting greenhouse gases that correlate with its overall environmental impact. In general, using less water produces higher quality concrete as long as the concrete is properly placed, consolidated and cured. Concrete also has similar prices to aggregates, depending on the type of aggregate used in the mix.
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