Cause estimation of cracked RC structures

General

(１) Cause estimation shall be carried out accurately before evaluation of crack, judgment of the necessity for repair and strengthening and their selection.

(２) Cause estimation shall be carried out based on standard investigation and/or detailed investigation.

Cause of crack

Causes of cracking are listed in Table 3.1.

Causes of cracking （Table-3.1）Major classification Sub classification Sub-sub Cause (No)

Ａ：(Material)

Ｂ：(Construction)

Ｃ：(Environment)

Ｄ：(Structure and

External Force）

Ｅ：Others

MaterialConcreteSteelFormworkPhysicalChemicalLoadStructural designSupport condition

Cement JointAggregate Bar arrangementConcrete FormworkMixing SupportTransport Cold jointConcreting PC GroutCompaction Temp./R.H.Curing Chemical reactionLong term loading Structural designShort term loading Support condition

Ａ１～Ａ１０

Ｂ１～Ｂ１８

Ｃ１～Ｃ８

Ｄ１～Ｄ７

Typical crack patterns for different causes

Ａ Materials

A Materials

Cement False Setting (of Cement)

Heat of Hydration (of Cement)

Abnormal Expansion of Cement

Clay included in Aggregate

Low Quality Aggregate

Reactive Aggregate (Alkali-Aggregate Reaction)

Aggregate

Used M

aterials

Wall which has restrained at the base(thickness of wall is more than 50 cm)

Example: retaining wall, culvert, etc.

Wall

Restraining Member

External restraint（Penetrated Crack）

Internal restraint（Surface crack）

Member with large cross section, such as a foundation girder

Ａ２：Heat of Hydration (of Cement) Ａ５：Low Quality Aggregate

Cracks generate like pop-out

Reticular crackscracks of a column along the steel in axial direction

Ａ６：Reactive Aggregate(Alkali-Aggregate Reaction)

Rim of Reaction Product

Deposition of alkali-silica gel

Chloride in Concrete

Settlement and Bleeding of Concrete

Drying Shrinkage of Concrete

Autogeneous Shrinkage of Concrete

concrete

A Materials

Restraint by steel bar(Slab)

Shrinkage cracks generated on the upper surface of the slab due to the plastic settlement.

Settlement and Bleeding of Concrete

Drying Shrinkage of Concrete

Example of drying shrinkage crack of external wall

Example of crack at handrail of road

Drying Shrinkage of Concrete

Stress concentration within the periphery of windows, embedded material, etc.

Ｂ Construction

B Construction

Mixing Non-uniform Dispersion of Admixture

Long-Time Mixing

Inappropriate Placing Sequence

Change of Mix Proportion at Pumping

Rapid Placing

Transport

concrete Placing

Insufficient Compaction

Loading or Vibration before Hardening

Rapid Drying during Initial Curing

Early Age Frost Damage

Inappropriate Joint Treatment

Compaction

Curing

ConstructionJoint

concrete

B Construction

Segregation due to excessive compaction

Ｂ６：Inappropriate Compaction

Water leakage at construction joint

Ｂ10：Inappropriate Joint Treatment

Arrangement of Steel

Bad Placement of Reinforcement

Lack of Cover

Water Leakage (from formwork, into subgrade)

Deformation of Formwork

Early Removal of Formwork

Formwork

Settlement of Support

Steel

Support

Formw

ork

B Construction

Inappropriate Joint or Discontinuity

Insufficient GroutingPC Grout

Others

Cold Joint

B Construction Ｂ17：Inappropriate Joint or Discontinuity

A cold joint forms.

Concrete lining in the tunnelRC building wall

Examples of cold joint

LightLight

Significant Significant

Ｃ Environment

C Environment

Temperature and Humidity

Change of Environmental Temperature and/or Humidity

Difference of Temperatures and Humidity between two surfaces of member

Repeated Cycles of Freezing and Thawing

Fire

Surface Heating

Physical

Ｃ１：Change of Environmental Temperature and/or Humidity

Ｃ１： Change of Environmental Temperature and/or Humidity

Chemical Reaction

Chemical Reaction of Acid and/or Salt

Corrosion of Embedded Steel due to Carbonation

Corrosion of Embedded Steel due to Chloride Attack

Chem

ical

Ｃ６：Chemical Reaction of Acid and/or Salt

The concrete surface is eroded due to a chemical reaction. Most of the cracks occur along the steel bars, and some parts of the concrete may peel off.

Ｃ７：Corrosion of Embedded Steel due to Carbonation

＊Ｂ１２：Lack of Cover: Cracks occur along the steel bar

C8. Corrosion of rebar due to chloride attackA7. Chloride in concrete

Rust spills out from the cracks and it often stains the concrete surface. In the case of severe corrosion of steel bars, peeling of the concrete may occur. The corrosion of exposed steel is always severe.

Ｃ８：Corrosion of Embedded Steel due to Chloride Attack

Ｄ Structure and External Force

D Structure and External Force

Long-Term Load

Long-Term Load within Design load

Long-Term Load over Design Load

Short-Term Load over Design Load

Short-Term Load within Design Load

Short-Term Load

Load Insufficient Cross Section or Quality of Steel

Differential Settlement of StructureFreezing Heave

Structural Design

Support Condition

Ｄ６：Differential Settlement of Structure

Example of cracks in a rigid frame pier due to differential settlement.

settlement

support

settlement

displacement displacement

The systematical procedure of Cause Estimation based on the results of standard investigationMajor Classifications of Causes

Materials (A), Construction (B), Service Environment (C), Structure and External Force (D)

Classification Based on the Crack Generation Period, Regularity, and Extent of Cracks (Table 3.1) Generating Period, Regularity, Extent (reticular, surface layer, penetration)

Classification Based on the Deformation and Limit of Consideration (Table 3.2) Deformation of Concrete (drying shrinkage, expansion, settlement,

bending, and shearing), Limit of Consideration

Classifications Based on the Mixture Proportion and Weather Condition (Tables 3.3 and 3.4) Mixture Proportion (rich and poor), Weather Conditions during Placing Concrete

Detection of Common Cause

Classification Based on the Crack Generation Period, Regularity, and Extent of Cracks (Table 3.1)

The systematical procedure of Cause Estimation based on the results of standard investigation Major Classifications of Causes

Materials (A), Construction (B), Service Environment (C), Structure and External Force (D)

Classification Based on the Crack Generation Period, Regularity, and Extent of Cracks (Table 3.1) Generating Period, Regularity, Extent (reticular, surface layer, penetration)

Classification Based on the Deformation and Limit of Consideration (Table 3.2) Deformation of Concrete (drying shrinkage, expansion, settlement,

bending, and shearing), Limit of Consideration

Classifications Based on the Mixture Proportion and Weather Condition (Tables 3.3 and 3.4) Mixture Proportion (rich and poor), Weather Conditions during Placing Concrete

Detection of Common Cause

Classification Based on the Deformation and Limit of Consideration (Table 3.2)

The systematical procedure of Cause Estimation based on the results of standard investigation Major Classifications of Causes

Materials (A), Construction (B), Service Environment (C), Structure and External Force (D)

Classification Based on the Crack Generation Period, Regularity, and Extent of Cracks (Table 3.1) Generating Period, Regularity, Extent (reticular, surface layer, penetration)

Classification Based on the Deformation and Limit of Consideration (Table 3.2) Deformation of Concrete (drying shrinkage, expansion, settlement,

bending, and shearing), Limit of Consideration

Classifications Based on the Mixture Proportion and Weather Condition (Tables 3.3 and 3.4) Mixture Proportion (rich and poor), Weather Conditions during Placing Concrete

Detection of Common Cause

Classifications Based on the Mixture Proportion(Table 3.3)

Classifications Based on the Weather Condition (Tables 3.4)

The systematical procedure of Cause Estimation based on the results of standard investigation Major Classifications of Causes

Materials (A), Construction (B), Service Environment (C), Structure and External Force (D)

Classification Based on the Crack Generation Period, Regularity, and Extent of Cracks (Table 3.1) Generating Period, Regularity, Extent (reticular, surface layer, penetration)

Classification Based on the Deformation and Limit of Consideration (Table 3.2) Deformation of Concrete (drying shrinkage, expansion, settlement,

bending, and shearing), Limit of Consideration

Classifications Based on the Mixture Proportion and Weather Condition (Tables 3.3 and 3.4) Mixture Proportion (rich and poor), Weather Conditions during Placing Concrete

Detection of Common CauseMain cause of cracks

Example: Cracks generated in the box type RC rigid frame

>the crack spacing: 2 to 5 m

Investigation Results:

>The crack width: from 0.2 to 1 mm

>The finding of cracks: approximately 2 weeks after placing of concrete

>cement content per unit volume of concrete: 350 kg/m3 temperature at casting: 33℃

Cracks Joints

The systematical procedure of Cause Estimation based on the results of standard investigation Major Classifications of Causes

Materials (A), Construction (B), Service Environment (C), Structure and External Force (D)

Classification Based on the Generation Period, Regularity, and Extent of Cracks (Table 3.1) Generating Period, Regularity, Extent (reticular, surface layer, penetration)

Classification Based on the Deformation and Limit of Consideration (Table 3.2)

Deformation of Concrete (shrinkage, expansion, settlement,bending, and shearing), Limit of Consideration

Classifications Based on the Mixture Proportion and Weather Condition (Tables 3.3 and 3.4) Mixture Proportion (rich and poor), Weather Conditions during Placing Concrete

Detection of Common Cause

Major Classifications of Causes1) A Materials, B Construction, D Structure and External Force

The systematical procedure of Cause Estimation based on the results of standard investigation Major Classifications of Causes

Materials (A), Construction (B), Service Environment (C), Structure and External Force (D)

Classification Based on the Generation Period, Regularity, and Extent of Cracks (Table 3.1) Generating Period, Regularity, Extent (reticular, surface layer, penetration)

Classification Based on the Deformation and Limit of Consideration (Table 3.2)

Deformation of Concrete (shrinkage, expansion, settlement,bending, and shearing), Limit of Consideration

Classifications Based on the Mixture Proportion and Weather Condition (Tables 3.3 and 3.4) Mixture Proportion (rich and poor), Weather Conditions during Placing Concrete

Detection of Common Cause

Classification Based on the Generation Period, Regularity, and Extent of Cracks (Table 3.1) Major Classifications of Causes>>> Table 3.1

1) A Materials, B Construction, D Structure and External Force

2) A2，A8，A10，B2，B3，B4・・・

Classification Based on the Generation Period, Regularity, and Extent of Cracks>>>Table 3.1

The systematical procedure of Cause Estimation based on the results of standard investigation Major Classifications of Causes

Materials (A), Construction (B), Service Environment (C), Structure and External Force (D)

Classification Based on the Generation Period, Regularity, and Extent of Cracks (Table 3.1) Generating Period, Regularity, Extent (reticular, surface layer, penetration)

Classification Based on the Deformation and Limit of Consideration (Table 3.2)

Deformation of Concrete (shrinkage, expansion, settlement,bending, and shearing), Limit of Consideration

Classifications Based on the Mixture Proportion and Weather Condition (Tables 3.3 and 3.4) Mixture Proportion (rich and poor), Weather Conditions during Placing Concrete

Detection of Common Cause

Classification Based on the Deformation and Limit of Consideration (Table 3.2)

Major Classifications of Causes>>> Table 3.11) A Materials, B Construction, D Structure and External Force

2) A2，A8，A10，B2，B3，B4・・・

Classification Based on the Generation Period, Regularity, and Extent of Cracks>>>Table 3.1

Classification Based on the Deformation and Limit of Consideration >>> Table 3.23) A2，A9，A10，B2，B3，B8・・・

The systematical procedure of Cause Estimation based on the results of standard investigation Major Classifications of Causes

Materials (A), Construction (B), Service Environment (C), Structure and External Force (D)

Classification Based on the Generation Period, Regularity, and Extent of Cracks (Table 3.1) Generating Period, Regularity, Extent (reticular, surface layer, penetration)

Classification Based on the Deformation and Limit of Consideration (Table 3.2)

Deformation of Concrete (shrinkage, expansion, settlement,bending, and shearing), Limit of Consideration

Classifications Based on the Mixture Proportion and Weather Condition (Tables 3.3 and 3.4) Mixture Proportion (rich and poor), Weather Conditions during Placing Concrete

Detection of Common Cause

Classifications Based on the Mixture Proportion(Table 3.3)

Classifications Based on the Weather Condition (Tables 3.4)

Major Classifications of Causes>>> Table 3.11) A Materials, B Construction, D Structure and External Force

2) A2，A8，A10，B2，B3，B4・・・

Classification Based on the Generation Period, Regularity, and Extent of Cracks>>>Table 3.1

Classification Based on the Deformation and Limit of Consideration >>> Table 3.23) A2，A9，A10，B2，B3，B8・・・

4) A2，A6，A9，A10，B2，B8・・・

Classifications Based on the Mixture Proportion and Weather Condition >>>Tables 3.3 and 3.4

Major Classifications of Causes>>> Table 3.11) A Materials, B Construction, D Structure and External Force

2) A2，A8，A10，B2，B3，B4・・・

Classification Based on the Generation Period, Regularity, and Extent of Cracks>>>Table 3.1

Classification Based on the Deformation and Limit of Consideration >>> Table 3.23) A2，A9，A10，B2，B3，B8・・・

4) A2，A6，A9，A10，B2，B8・・・

Classifications Based on the Mixture Proportion and Weather Condition >>>Tables 3.4 and 3.5

Major Classifications of Causes>>> Table 3.11) A Materials, B Construction, D Structure and External Force

2) A2，A8，A10，B2，B3，B4・・・

Classification Based on the Generation Period, Regularity, and Extent of Cracks>>>Table 3.1

Classification Based on the Deformation and Limit of Consideration >>> Table 3.23) A2，A9，A10，B2，B3，B8・・・

4) A2，A6，A9，A10，B2，B8・・・

Classifications Based on the Mixture Proportion and Weather Condition >>>Tables 3.4 and 3.5

B2 (Long-time mixing):the concrete transporting distance from plant to construction site was not long (about 12 km) >>>A2 (Heat of Hydration of Cement) ，>>>A10 (Autogeneous Shrinkage of Concrete)

Exercise 1: Explain the cause of cracksReinforced concrete structure built in 1972Location: Osaka prefecturePeeling and crack along with re-bar of beamCracks became obvious from 1990 to 2000Design strength of concrete is 18MPa

Exercise 2: Explain the cause of cracks

Exercise 3: Explain the cause of cracks5 stories RC structure built in 1965Span of trabecular direction is 20m and ridge direction is 100mLocation: Inner part of Kanto regionPushed out peeling can be seen at the top of wall. Asphalt at joint between water proofing cinder concretes (thickness 100mm) is also pushed out.Design strength of concrete is 21MPaExposed concrete building

Parapet of top floor

Pushed out asphalt

Span of trabecular direction

Cinder concrete

JointBricks

Pushed out peelingInterior

Insulation

Water proofing

Slab of top floor

Pushed out peeling

Exercise 4: Explain the cause of cracks and explain why cracks occur partially in the member