In our Case Study article, we mention that 5000 PSI concrete was used to finish the elevated walkway at the Dexter Southfield School.
Concrete is made up of three main ingredients: water, Portland cement, and aggregates. The ratio of the ingredients changes the properties of the final product, which allows the engineer to design concrete that meets specific needs. Admixtures can be added to adjust the concrete mixture for specific performance criteria.
There are many different types, strengths, and compositions of concrete, each with characteristics that make them appropriate for different applications.
Strength is typically determined by compression testing, and is expressed in pounds per square Inch (PSI). Normal concrete mixes range from 2500 PSI to 5000 PSI, with engineered design mixes of 10,000 PSI or higher used in specialized applications. Lower strengths are also available for grouts and other low stress applications. The following are common uses for various strength concrete formulations:
- 2500 PSI concrete may be used in driveways, walkways, and even floor slabs on grade. This concrete is usually the cheapest available from batch plants. However, many concrete professionals prefer a higher strength product due to warranty concerns. Further, some building codes may not allow its use for all of these applications.
- 3000 PSI concrete is a standard multipurpose mixture for general use in construction. It is durable, has sufficient cement to provide good finishing characteristics, and can be placed fairly wet without sacrificing quality.
- 3500 PSI concrete is used for applications where surface spalling is not acceptable, and significant loading is expected. One example would be paving curbs, where heavy traffic may drive on the surface. Other uses include building footings, bond beams, grade beams, and floor slabs where heavy loads may be moved or stored.
- 4000 PSI concrete is used for heavy traffic pavement, heavy use floor slabs like shops and warehouses, and concrete footings designed to support heavy loads.
- 5000 PSI, like the strength used at the Dexter Southfield School, and higher concrete mixes are usually used for specialized construction projects where high impact resistances, very low wear rates, or extreme conditions are expected.