Frequently Asked Questions
Q: I have heard that concrete can be made
to a wide variety of strengths. What are typical strength ranges
of concrete and where is it appropriate to use them?
A: Concrete can be proportioned to
meet a wide variety of strength requirements. It is important to
note that there is more than one type of strength property used
to design concrete projects. The most commonly used design properties
|Flexural strength testing
- Flexural strength, used for design of pavements (slab-on-grade).
- Compressive strength, used for design of foundations, building
elements (walls, columns, slabs), bridges (abutments, columns,
Flexural strength increases proportionally with compressive strength
(as the compressive strength goes up, so does the flexural strength).
This property is used specifically for pavement design the flexural
strengths of interest fall in a range of 3.9 MPa (570 psi) to 5.1
MPa (750 psi). These flexural strengths correspond approximately
to compressive strengths of 28 MPa (4000 psi) to 48 MPa (7000psi).
While concrete can attain much higher flexural strengths, it is
not required for pavements, and use of higher strengths would have
an adverse effect on the economics of the project with little benefit
The compressive strength of structural concrete begins at 17 MPa (2500
psi) and can be produced commercially at 138 MPa (20,000 psi) or more.
With such a wide range of strengths to choose from, the following
guidance is provided to assist in making an appropriate choice for
|Compressive strength testing
- Residential and light commercial building projects typically
strengths ranging from 17 MPa (2500 psi) to 34 MPa (5000 psi). Keep
that the lower strength concrete is only appropriate for mild environmental
exposures, and interior concrete protected from the elements. Severe
environmental exposures (freezing and thawing cycles and deicer
exposure) require a minimum strength of 4000 psi to assure durability.
codes commonly provide guidance for the minimum requirements, but
cases do not address long term durability issues.
- Heavy commercial and special structures (high rise buildings,
long span bridges, slabs exposed to heavy abrasion, etc.) typically
require concrete strengths of 28 MPa (4000 psi) or more. The actual
required strength may be controlled by the structural loading,
durability requirements, special property requirements (low permeability,
high abrasion resistance, etc.) or a combination of these factors.
Concrete design professionals should always be consulted for guidance
regarding these important structures.
Kosmatka, Steven H., Kerkhoff, Beatrix, Panarese, William C., Design
and Control of Concrete Mixtures, EB001, Portland Cement
Association, 2002, 372 pages.
Tarr, Scott M., Farny, James A., Concrete
Floors on Ground, EB075, Fourth Edition, Portland Cement
Association, 2008, 252 pages