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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
t1
Slide 5
t1 omina betonilaatuinaan tai eri perheinä tulee käsitellä betonit joiden sisältämillä lisäaineilla voi olla vaikutusta pur. luj. esmes huokost
Tiivistystavaltaan eril. bet. (maakost, itsetiiv, tärytettävät) tulee käsitellä omina perheinääntikkanen; 7.12.2012
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 MPaStudied concrete K45, target strength of 55 MPaConvert the strength to correspond to the strength of the reference concrete when the compressive strength results for the studiedconcrete 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
InitialContinuous
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 examplewith the Sadgroven maturity function
Durability - against what?
• Physical erosion• Carbonation• Chlorides• Freeze/thaw resistance• Chemical durability
• 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-
Carbonation
2 Fe2+ + 4 (OH)- 2 Fe(OH)23 Fe(OH)2 Fe3O4 + 2 H2O + H2
Rust demands more space than initialproducts 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 coveragerequirement
* Thickness of the reinforcement 4 mm ormore* 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 SO4
2-
• SO42- + Ca(OH)2 = gypsum
• SO42- + gypsum + calsiumaluminatehydrate =
ettringite
Exposure classes
The designer must choose an appropriateexposure class for the structure in terms of the following stress or load factors:1. Corrosion caused by carbonation2. Corrosion caused by chlorides3. Corrosion caused by chlorides in sea water4. Freezing-and-thawing stress5. 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) orcalculations
Use of tabular data50 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 YEARSFeasible when the strength grade is close to the minimumThe requirement of minimum cement content must be fulfilledOnly option in classes XA
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 thesewill be the determining one
A. Materials, porosityB. Design structural detailsC. Performance of workD. Interior climateE. Exterior exposure to weatherF. Working loadG. 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 %.
Exposure classes X for foundations
XO no risk of corrosion orchemical attack -
XC carbonation +XS chlorides, sea water -XD chlorides, from other sources -XF freezing and thawing +XA chemical loads +
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 yearstL is the service life
A. Materials, porosityB. Design structural detailsC. Performance of workD. Interior climateE. Exterior exposure to
weatherF. Working loadG. Maintenance measures
C Curing
E Exterior exposure to weather
E1 XC2 foundations and 1,4other undergroundstructures
E2…E4: if the structure is protected from rain,coefficients E2, E3 and E4 shall be giventhe value 1 1,0
D Interior climate -1,0
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
Foundation for a service life of 100 years using tabular dataTable 4.2 (from by50 Concrete code 2004)
Exposure classes?
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
0,4)1()/(2,7;25,0max
1
1 4,0
4 5,0
acw
F
F-factor
Calculated life span is the product of F-factorand 50 years (k x t50 years)
Using tabular data 50 years XF1 1,0 and XF3 1,5100 years XF1 2,0 and XF3 3,0