Estimation of service life-span of concrete structures Exercise 11

Strength classes in by50

Workability classes

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

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

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. 53-55 MPa = -2 MPa →36 – 2 = 34 MPa

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 206-1. 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

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.

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

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

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

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-

2 Fe2+ + 4 (OH)- → 2 Fe(OH)2 3 Fe(OH)2 → Fe3O4 + 2 H2O + H2 Rust demands more space than initial products → concrete breaks

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

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)

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

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

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

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

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

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

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

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

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

Exposure classes XS and XD

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

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 %.

Working life with regard to carbonation

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 +

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

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

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

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

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

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 1 1,0

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

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

2 A: 80,5 years

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

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

Corrosion caused by carbonation, XC

Minimum amount of cement 230 kg/m3 Strength grade K35

Chemical load, XA

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

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

F-factor

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

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