Properties of Concrete
These tables show the structural properties of concrete
Compressive Strength
The most important property of structural concrete is the compressive strength at 28 days (f'c). Common compressive strengths of structural concrete range from 25-85MPa (3500-12000psi). Ultra-high-performance concretes can exceed 85MPa, but they are not widely used on typical structures. Most building codes use the compressive strength as a benchmark and provide empirical relations for stiffness and tensile strength.
Unit Conversion
Concrete properties are usually measured in units of pressure. In Canada, concrete is typically specified in MPa. In the US, it is typically specified in psi or ksi. 1 MPa is approximately 145 psi or 0.145 ksi
Modulus of Elasticity
The stiffness of concrete material is determined using the Modulus of Elasticity (Young's Modulus). It can be directly measured, but most building codes provide an empirical equation that relates compressive strength to modulus of elasticity.
CSA A23.3
The table below shows the modulus of elasticity for various concretes.
| f'c | (3300√fc+6900)(yc/2300)1.5 cl. 8.6.2.2 | 4500√fc cl. 8.6.2.3 |
|---|---|---|
| 25 MPa (3.6 ksi) | 24943 MPa (3618 ksi) | 22500 MPa (3263 ksi) |
| 30 MPa (4.4 ksi) | 26621 MPa (3861 ksi) | 24648 MPa (3575 ksi) |
| 35 MPa (5.1 ksi) | 28165 MPa (4085 ksi) | 26622 MPa (3861 ksi) |
| 40 MPa (5.8 ksi) | 29602 MPa (4293 ksi) | 28460 MPa (4128 ksi) |
| 45 MPa (6.5 ksi) | 30951 MPa (4489 ksi) | 30187 MPa (4378 ksi) |
| 50 MPa (7.3 ksi) | 32228 MPa (4674 ksi) | 31820 MPa (4615 ksi) |
| 55 MPa (8 ksi) | 33442 MPa (4850 ksi) | 33373 MPa (4840 ksi) |
| 60 MPa (8.7 ksi) | 34602 MPa (5019 ksi) | 34857 MPa (5056 ksi) |
| 65 MPa (9.4 ksi) | 35714 MPa (5180 ksi) | 36280 MPa (5262 ksi) |
| 70 MPa (10.2 ksi) | 36785 MPa (5335 ksi) | 37650 MPa (5461 ksi) |
| 75 MPa (10.9 ksi) | 37818 MPa (5485 ksi) | 38971 MPa (5652 ksi) |
| 80 MPa (11.6 ksi) | 38817 MPa (5630 ksi) | 40249 MPa (5838 ksi) |
| 85 MPa (12.3 ksi) | 39785 MPa (5770 ksi) | 41488 MPa (6017 ksi) |
| 90 MPa (13.1 ksi) | 40725 MPa (5907 ksi) | 42691 MPa (6192 ksi) |
ACI 318 and LATBSDC
The table below shows the modulus of elasticity for various concretes.
| f'c | 57000√fc | 40000√fc+106 |
|---|---|---|
| 4000 psi (28 MPa) | 3605 ksi (24856 MPa) | 3530 ksi (24338 MPa) |
| 4500 psi (31 MPa) | 3824 ksi (26366 MPa) | 3683 ksi (25393 MPa) |
| 5000 psi (34 MPa) | 4031 ksi (27793 MPa) | 3828 ksi (26393 MPa) |
| 5500 psi (38 MPa) | 4227 ksi (29144 MPa) | 3966 ksi (27345 MPa) |
| 6000 psi (41 MPa) | 4415 ksi (30440 MPa) | 4098 ksi (28255 MPa) |
| 6500 psi (45 MPa) | 4595 ksi (31681 MPa) | 4225 ksi (29130 MPa) |
| 7000 psi (48 MPa) | 4769 ksi (32881 MPa) | 4347 ksi (29972 MPa) |
| 7500 psi (52 MPa) | 4936 ksi (34033 MPa) | 4464 ksi (30778 MPa) |
| 8000 psi (55 MPa) | 5098 ksi (35149 MPa) | 4578 ksi (31564 MPa) |
| 8500 psi (59 MPa) | 5255 ksi (36232 MPa) | 4688 ksi (32323 MPa) |
| 9000 psi (62 MPa) | 5407 ksi (37280 MPa) | 4795 ksi (33060 MPa) |
| 9500 psi (66 MPa) | 5556 ksi (38307 MPa) | 4899 ksi (33777 MPa) |
| 10000 psi (69 MPa) | 5700 ksi (39300 MPa) | 5000 ksi (34474 MPa) |
| 10500 psi (72 MPa) | 5841 ksi (40272 MPa) | 5099 ksi (35156 MPa) |
Concrete Shear Strength
The shear strength of concrete is dependant on many factors including f'c, aggregate, reinforcing, and member size.
A rule of thumb for the shear strength of normalweight concrete, Vc is ϕ2√fc (psi) or ϕ0.16√fc (MPa), however, Vc can vary from 0 to 2x that value depending on the specific conditions. The material factor (ϕ) is 0.75 for ACI318 non-seismic-loads. However, the governing building code should be consulted for specifics.
Concrete Tensile Strength
The tensile strength of concrete is dependant on many factors including f'c, mix design and SCMs, reinforcing, and member size. Additionally, tensile strength is usually ignored in reinforced-concrete design. However, it is sometimes relied on for plain (unreinforced) concrete structures.
A rule of thumb for the tensile strength of normalweight concrete for flexure is ϕ5√fc (psi) or ϕ0.41√fc (MPa). The material factor (ϕ) is 0.6 for ACI 318. However, the governing building code should be consulted for specifics.
Concrete strength guide
Low strength (5-20MPa or 1000-3000psi)
Low strength concrete typically has a strength under 20MPa. It is widely available from ready-mix suppliers and bagged products. Low strength concrete has limited structural value for buildings but may be used in applications such as rat slabs and nonstructural slabs-on-grade, soil enhancement, and small misc footings.
Normal strength (25-45MPa or 3500-6500psi)
Normal strength concrete typically has a strength in the range of 25-45MPa. This concrete is widely available from ready mix suppliers and bagged products. Normal strength concretes are typically used for flatwork such as slabs and footings, as well as beams, columns, and walls in shorter buildings.
High strength (45-85MPa or 6500-12000psi)
High strength concrete typically has a strength in the range of 45-85MPa, although strengths above 65MPa may be difficult to obtain in some markets. This concrete is tyipcally used for vertical elements in tall buildings such as columns and shear walls.
Ultra high strength (more than 85MPa or 12000psi)
Ultra-high performance concrete with strength exceeding 85MPa is typically reserved for special uses and structures. It is not economical to use in most typical buildings.
Calcs.app