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? Sterling Fence Inc is very aware of the importance fo concrete strength.
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| Flexural strength testing |
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 are:
- 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, decks), etc.
Flexural Strength
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 in performance.
Compressive Strength
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| Compressive strength testing |
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 specific projects:
- Residential and light commercial building projects typically use concrete
strengths ranging from 17 MPa (2500 psi) to 34 MPa (5000 psi). Keep in mind 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 chemical
exposure) require a minimum strength of 4000 psi to assure durability. Local
codes commonly provide guidance for the minimum requirements, but in many 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.
References:
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