Structural Cracks

WHAT ARE STRUCTURAL CRACKS?

Structural cracks can endanger the safety and stability of concrete structures and can occur due to factors such as foundation movement, inadequate structural design, overloading of the structure during usage, congested or inadequate reinforcement design, and poorly compacted or inadequate concrete mixes.

These cracks can be classified according their appearance:

Flexural cracks start at the tension face of a beam or column often due to overloading, and propagate towards the elements neutral axis;

Shear cracks are caused by structural loading or movement of supports (e.g. due to foundation settlement) or lateral displacement of frames and columns;

Transverse cracks are caused by concrete shrinkage, thermal contraction and structural loading, and are transverse to the main reinforcement. Where reinforcement runs in two directions - slabs - cracks that are transverse to secondary bars will tend to coincide with the main bars.

When any of these cracks appear in prestressed concrete, these are signs of a serious structural defect.

How do Structural cracks damage concrete structures?

Structural cracking in concrete structures can lead to a range of issues that compromise the integrity, durability, and functionality of the structure such as:

REDUCTION IN LOAD-BEARING CAPACITY

Cracks in concrete can reduce the load-bearing capacity of the structure. This is particularly critical in beams, columns, and slabs where the transmission of loads through the concrete is essential for structural stability. Cracks provide a path for stresses to concentrate, potentially leading to failure under loads that the structure was originally designed to withstand.

CORROSION OF REINFORCEMENT

One of the most significant issues arising from cracks in concrete structures is the corrosion of reinforcement steel. Cracks allow water, oxygen, and harmful chemicals (such as chlorides from de-icing salts or sea spray) to penetrate the concrete and reach the reinforcing steel. This can initiate corrosion, which expands the steel and exerts pressure on the surrounding concrete, leading to further cracking and eventual spalling of the concrete cover.

WATER INGRESS

Cracks can allow water to leak through the structure, leading to damage in parts of the structure that should remain dry. In the case of water-retaining structures like dams, tanks, and basements, water leakage can compromise the structure's functionality and cause damage to other building components or contents.

REDUCED DURABILITY

The ingress of water and aggressive chemicals through cracks accelerates the deterioration of concrete and its reinforcement. This reduces the structure's durability and can lead to premature failure necessitating costly repairs or even replacement.

FREEZE-THAW DAMAGE

Water entering cracks can freeze and expand, exerting pressure on the concrete and enlarging the cracks. This freeze-thaw cycling can cause significant damage to the structure over time.

AESTHETIC DAMAGE

Besides structural implications, cracks can also be aesthetically displeasing. This can be particularly problematic in architectural concrete where the appearance is critical.

REDUCED STRUCTURAL INTEGRITY

Large or critical structural cracks can directly compromise the integrity of the structure, leading to structural failures or collapse if not properly addressed.

LOSS OF STIFFNESS AND DEFORMATION

Structural cracks can lead to a loss of stiffness in the structure, causing excessive deformation under load. This can affect the serviceability of the structure, leading to issues like excessive deflections or vibrations.

What causes Structural cracks?

• Creep

• Stress concentrations.

• Fatigue.

• Overloading.

• Vibration.

• Structural movement such as foundation settlement.

• Low concrete strength.

• Premature formwork removal.

• Insufficient reinforcement design or construction.

How can I identify Structural cracks in concrete structures?