Different factors cause the failure of concrete structure such as errors from design stage to construction stage and to occupancy. The main causes of failure of concrete structures are discussed.
What Factors Causes Failure of Concrete Structures?
The main factors that affect the failure of concrete structures are:
- Incorrect selection of materials
- Errors in design calculation and detailing
- Improper construction techniques and insufficient quality control and supervision
- Chemical attacks on concrete structures
- External mechanical factors
Fig.1: Failure of Concrete Structures Due to Various Factors
Incorrect Selection of Concrete Materials Causes Failure of Structure
To build a structure that meet safety and strength requirements, it is necessary to execute construction process according to the applicable codes and specifications.
Normally, the selection of materials required for given project should be acceptable according to code specifications to use suitable materials.
If materials are selected properly and meet code requirements, then they will meet the conditions of the place where the material is placed such as soil conditions.
Failure in the material selection is one of the major factors that detrimentally affect the strength and safety of structure and eventually could lead to failure.
Various detrimental factors such as presence of sulfide in soil or ground water and the occurrence of freezing and thawing should be carefully considered while materials are selected to prepare concrete mixture.
Fig.2: Materials Used in Construction of Concrete Structure
Errors in Design Calculation and Detailing of Concrete Structures
It is considerably important to practice substantial care while design calculation is conducted otherwise undesired events and costly structural improvement would prevail.
That is why it is recommended to conduct an entire design check to guarantee that reinforced concrete section sizes, thicknesses, and reinforcement spacing and sizes are sufficient to support the most critical load combinations.
Not only does the check need to involve entire stability of the structure but also its serviceability and robustness. Regarding detailing, it is the most well-known factor that leads to initiate cracks and sometimes failure of the structure.
It is advised to use correct, robust and efficient arrangement for the structure. The building should be constructed in such a way that prevents water to remain on the structure and consequently deteriorate the structure. Movement joints should be placed properly to avoid crack development.
Code specifications regarding reinforced concrete elements shall be followed correctly. For example, concrete cover which protects steel bars from aggressive attacks and fire, maximum and minimum reinforcement ratio, steel bar spacing which restricts cracks, lap length and anchorages.
Improper Construction Techniques and Insufficient Quality Control and Supervision Causes Failure
Improper construction methods, poor workmanship, low quality material and insufficient supervision of construction process would cause several problems that reduces the performance of concrete structures substantially and subsequent failure. Table-1 provides construction issues and their influence on the failure of the structure.
Table-1: Construction Issues That Influence Failure of Concrete Structure
|Types of Construction Errors||Effect of Construction Errors on Concrete Structure|
|Incorrect placement of steel||This error makes concrete cover smaller which in turn leave the steel bars unprotected. Disposition of steel bars may lead the member to fail when it is loaded completely.|
|Inadequate cover to reinforcement||If required cover thickness is not provided, then aggressive elements can penetrate the member and eventually reinforcement bars will deteriorate and concrete spalling will occur.|
|Incorrectly made construction joints||Poor compaction and inadequate preparation are common problems of joint construction. If such joints are not constructed properly, it would become a path for moisture to penetrate concrete.|
|Grout leakage||When joints of formworks are not sealed properly, then grout and fine material would move out of concrete mixture. As a result, a considerably porous concrete will be produced.|
|Poor compaction||This would create porous honeycombed concrete which should be tackled immediately by removing it and then recast that part of the element.|
|Segregation of concrete mixture||Segregation would distort concrete texture and sometimes increase porosity.|
|Poor curing||The required strength of concrete cannot be attained if curing is not executed properly.|
|High quantity water content||Excessive water content makes concrete permeable, porous and reduces its strength. So, this problem should be avoided.|
Chemical Attacks on Concrete Structures
There are different types of chemical attacks that considerably affect strength of the structure. Various types of chemical attacks and their influence on the structure are discussed in Table-2.
Table-2: Types of Chemical Attacks and Their Effects on Concrete Structures
|Types of Chemical Attacks||Effect of Chemical Attacks on Concrete Structure|
|Chloride||Chloride ions penetrate concrete during and after construction. High concentration of chloride corrodes steel bars and deteriorates concrete.|
|Sulfate||It disintegrates concrete and create path for harmful substances to attack reinforcements.|
|Carbonation||Carbonation attack and deteriorate steel bars|
|Alkali silica reaction||Alkali silica reaction produces a gel which its volume increases and consequently disintegrates concrete.|
|Acids||It strongly affect concrete and removes part of set cement|
External Mechanical Factors Causing Concrete Structure Failure
There are various types of exterior or mechanical factors that influence concrete failure for example restraints against movement, abrasion, wetting and drying, freezing and thawing, overloading, structural alteration, fire resistance and settlement.