1. Estimation of service life-span of concrete structures
Exercise 11

2. Strength classes in by50

3. Workability classes

5. Concrete family -consept
Requires the same characteristics:
Same cement
Same aggregate
Same additional binders
Can have admixtures, as long as they don’t substantially affect the strength
K15 – K60 (C12 – C50)
Same age at testing

6. In applying the concept of concrete families, a reference concrete is chosen. The reference concrete is usually the most commonly produced, or one from the mid-range of the concrete family.
Combining data into families can reduce the time taken to detect any significant changes in production quality.
All members’ compressive strength results need to be converted to that of the reference concrete. Two methods of transposing can be used:
Strength method based on a straight line relationship between strength and water/cement ratio
Strength method based on a proportional effect

7. Example: The strength of the studied concrete is converted to correspond to the strength of the reference concrete.
Reference concrete K30, target strength of 36 MPa Studied concrete K45, target strength of 55 MPa Convert the strength to correspond to the strength of the reference concrete when the compressive strength results for the studied concrete was at 53 MPa MPa = -2 MPa →36 – 2 = 34 MPa

8. Conformity Control (kelpoisuuden valvonta)
In the assessment of conformity control, three criterion need to be satisfied. When a family member is tested, the original compressive strength result has to conform to criterion 2 in Table 14 of SS EN The member’s result will be converted to equivalent values of the reference concrete and assessed for conformity (Criterion 1, Table 14 of SS EN 206-1).
Criterion 1 and 2 for initial and continuous production according to SS EN 206-1: 2009
Initial
Continuous

9. Conformity Control (kelpoisuuden valvonta)
In addition, it has also to be assessed that each individual member belongs to the family (Criterion 3, Table 15 of SS EN 206-1). In the case where a member fails to meet criterion 3, it is removed from the family and assessed individually for conformity.

10. Curing - X0 and XC1 60 % of the nominal strength
- others 70 % of the nominal strength except
XF2 and XF4 80 % of the nominal strength
Estimation of the strength development for example with the Sadgroven maturity function

11. Sadgrove :
t20 = ((T + 16 oC)/36 oC) * t

12. Durability - against what?
Physical erosion
Carbonation
Chlorides
Freeze/thaw resistance
Chemical durability

13. Carbonation Ca(OH)2 + CO2 → CaCO3 Concrete pH 12,5 - 14,0
Carbonation pH < 9,0
Is not dangerous in ”easy” conditions (for example, indoors)
protective passivity layer on steel surface is broken
iron + water + oxygen → rust
A: Fe → Fe2+ + 2e-
C: 4e- + 2H2O + O2 → 4OH-

14. 2 Fe (OH)- → 2 Fe(OH)2
3 Fe(OH)2 → Fe3O4 + 2 H2O + H2
Rust demands more space than initial products → concrete breaks

15. Chlorides Are usually not harmful to concrete
Free chlorides in the pore water are effective in initiating chloride-induced corrosion of the reinforcement

16. Steel Thickness of the concrete cover Concerns all reinforcement
Corrosion susceptible reinforcement * presents a 10 mm additional coverage requirement
* Thickness of the reinforcement 4 mm or more
* long-term stress state (in service state) over 400 MN/m2 (cold-worked steel)

17. Freeze-thaw resistance
Rate of freezing and thawing
Temperature
Degree of moisture saturation
Number of cycles
Chlorides

18. Freeze-thaw resistance
Air-entrained concrete
2 % → 6 % (8 %)
Spacing factor (huokosjako)
Specific surface area

19. Chemical attack Has to be foreseen in the design process
Environment of the concrete
Reactions with external substances
Humidity
Migration with water / drying
Acids
Sulphates SO42-
SO42- + Ca(OH)2 = gypsum
SO42- + gypsum + calsiumaluminatehydrate = ettringite

20. Exposure classes
The designer must choose an appropriate exposure class for the structure in terms of the following stress or load factors:
Corrosion caused by carbonation
Corrosion caused by chlorides
Corrosion caused by chlorides in sea water
Freezing-and-thawing stress
Chemical load

21. Factors influencing the service life of concrete
- Strength class
- Amount of cement and cement/additional binders
- water/cement -ratio
- Air content
- Curing
- Age
Service operations
Environment

22. Service life of concrete
Service life requirement can be designed with either tabular data (taulukkomitoitus) or calculations
Use of tabular data
50 or 100 years
Carbon dioxide
Chlorides
Sea water and thawing agents (salts)
Freeze-thaw stress
Chemical load

23. Tabular data Simple, fast Does not enable optimization
Useful with strenght classes ≤ K40, in other cases may lead to too thick concrete covers
Only for service lifes of 50 or 100 years

24. DESIGNING WITH TABULAR DATA 50 YEARS
Feasible when the strength grade is close to the minimum
The requirement of minimum cement content must be fulfilled
Only option in classes XA

26. Minimum cover of concrete using tabular data
Permitted negative deviation generally 10 mm

27. Exposure classes XS and XD

28. Calculating the service life
50…200 years
Uses reference service life-span of 50 years
For all exposure classes
Estimated seperately for each class and the shortest of these will be the determining one
Materials, porosity
Design structural details
Performance of work
Interior climate
Exterior exposure to weather
Working load
Maintenance measures

29. 1.
Calculate the service life for a K30 foundation with regard to carbonation for which a CEM I A cement was used and the air content of the concrete was measured at 2,0 %.

30. Working life with regard to carbonation

31. Exposure classes X for foundations XO no risk of corrosion or chemical attack - XC carbonation + XS chlorides, sea water - XD chlorides, from other sources - XF freezing and thawing + XA chemical loads +

32. Exposure class for carbonation XC
Exposure class for carbonation XC??? XC2 Minimum cover of concrete 20 mm (+tolerance)

33. The working life is calculated using the equation:
tL = tLr x A x B x C x D x E x F x G tLr is the reference service life-span of 50 years tL is the service life

34. Materials, porosity
Design structural details
Performance of work
Interior climate
Exterior exposure to weather
Working load
Maintenance measures

35. A materials, porosity
A1 K30 0,95
A2 CEM I A 1,00
A3 2 % 1,08

36. B Design, structural details
B1 30 mm concrete 1,44
B2 Coating no coating 1,0

37. E Exterior exposure to weather
C Curing
1,0
D Interior climate -
E Exterior exposure to weather
E1 XC2 foundations and 1,4
other underground
structures
E2…E4: if the structure is protected from rain,
coefficients E2, E3 and E4 shall be given
the value ,0

38. F Working load -
G Inspection and maintenance frequency
G1 None 0,85

39. What did we get?
tL = tLr x A x B x C x D x E x F x G = 50 x (0,95*1,00*1,08) x (1,44*1,0) x (1,0) x (1,4) x (0,85) = 50 x 1,76 = 88 years

40. 2
A: 80,5 years

41. 3.
Design a foundation for a service life of 100 years using tabular data.

42. Foundation for a service life of 100 years using tabular data
Table 4.2 (from by50 Concrete code 2004)
Exposure classes?

43. Corrosion caused by carbonation, XC

44. Minimum amount of cement 230 kg/m3
Strength grade K35

45. Chemical load, XA

48. Minimum amount of cement 320 kg/m3
Strength grade K45
Max w/c ratio 0,45 -> w = 144 kg/m3

49. F- and P-factors
The F-factor describes the freeze-thaw resistance in a non-saline environment: In which w/c is the effective water/cement ratio a is the measured air content

51. F-factor

52. F-factor
Calculated life span is the product of F-factor and 50 years (k x t50 years) Using tabular data 50 years XF1 1,0 and XF3 1,5 100 years XF1 2,0 and XF3 3,0

53. P-factor
The P-factor describes the freeze-thaw resistance in a saline environment: