Mean value of axial tensile strength of concrete an age of t days – 3.1.2
The mean value of axial tensile strength of concrete an age of t days is:
| fctm(t) = (βcc(t))α⋅fctm | (3.4) |
where:
- fctm : is the mean value of axial tensile strength of concrete at 28 days (look at the table below)
- βcc(t) : is a coefficient which depends on the age of the concrete
| βcc(t) = exp { s [1 – (28/t)1/2] } | (3.2) |
with
- t : the age of the concrete
- s : a coefficient which depends on the type of cement:
= 0,20 for CEM 42,5 R, CEM 52,5 N and CEM 52,5 R (Class R)
= 0,25 for CEM 32,5 R and CEM 42,5 N (Class N)
= 0,38 for CEM 32,5 N (Class S) - α = 1 for t < 28 days
= 2/3 for t ≥ 28 days.
The following application calculates the mean tensile strength fctm(t) from your inputs. Intermediate results will also be given.
| Strength classes for concrete | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| fck (MPa) | 12 | 16 | 20 | 25 | 30 | 35 | 40 | 45 | 50 | 55 | 60 | 70 | 80 | 90 |
| fck,cube (MPa) | 15 | 20 | 25 | 30 | 37 | 45 | 50 | 55 | 60 | 67 | 75 | 85 | 95 | 105 |
| fcm (MPa) | 20 | 24 | 28 | 33 | 38 | 43 | 48 | 53 | 58 | 63 | 68 | 78 | 88 | 98 |
| fctm (MPa) | 1,6 | 1,9 | 2,2 | 2,6 | 2,9 | 3,2 | 3,5 | 3,8 | 4,1 | 4,2 | 4,4 | 4,6 | 4,8 | 5 |
| fctk,0,05 (MPa) | 1,1 | 1,3 | 1,5 | 1,8 | 2 | 2,2 | 2,5 | 2,7 | 2,9 | 3 | 3,1 | 3,2 | 3,4 | 3,5 |
| fctk,0,95 (MPa) | 2 | 2,5 | 2,9 | 3,3 | 3,8 | 4,2 | 4,6 | 4,9 | 5,3 | 5,5 | 5,7 | 6 | 6,3 | 6,6 |
| Ecm (GPa) | 27 | 29 | 30 | 31 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 41 | 42 | 44 |
| εc1 (‰) | 1,8 | 1,9 | 2 | 2,1 | 2,2 | 2,25 | 2,3 | 2,4 | 2,45 | 2,5 | 2,6 | 2,7 | 2,8 | 2,8 |
| εcu1 (‰) | 3,5 | 3,2 | 3 | 2,8 | 2,8 | 2,8 | ||||||||
| εc2 (‰) | 2 | 2,2 | 2,3 | 2,4 | 2,5 | 2,6 | ||||||||
| εcu2 (‰) | 3,5 | 3,1 | 2,9 | 2,7 | 2,6 | 2,6 | ||||||||
| n | 2 | 1,75 | 1,6 | 1,45 | 1,4 | 1,4 | ||||||||
| εc3 (‰) | 1,75 | 1,8 | 1,9 | 2 | 2,2 | 2,3 | ||||||||
| εcu3 (‰) | 3,5 | 3,1 | 2,9 | 2,7 | 2,6 | 2,6 | ||||||||
