Deterioration of reinforced concrete structures can happen for a number of reasons. Physical and Chemical processes can impact durability and structural performance of the concrete. Defects in design, materials, workmanship, curing and maintenance can all impact the service life, safety and reliability of an element. In this article, we will review some of the most common types of deterioration mechanisms in concrete.

Why concrete structures fail? Concrete has long been known as a reliable construction material, but deficiencies in material selection, detailing, and design can affect the service life of Concrete. Deterioration of concrete structures can become a challenge for the owners of these structures. It is important to identify these defects on time, and plan appropriate repair strategies. In this article, we will review some of the most famous deterioration mechanisms. In doing so, we have focused on the Ontario Structure Inspection Manual (OSIM, 2008). In addition, the review of the following two documents is highly recommended in learning defects and deterioration of concrete (Reference 1 and Reference 2).

Deterioration of Concrete

Before we begin this review, It is good to review the definition of the following two terms according to the OSIM (2008):

  • Defect: An identifiable, unwanted condition that was not part of the original intent of design.
  • Deterioration: A Defect that has occurred over a period of time

Different defects can be involved in the deterioration of concrete.  The following review provides a brief summary on the most common defects observed in the existing structures. Normally, one or a number of these defects can be seen in structures; therefore, it is necessary to identify them properly. One needs to understand these different defects properly in order to get more realistic evaluation of the structure.


What is it?

Scaling is referred to the loss of the surface portion of concrete (or mortar) as a result of the freezing and thawing (OSIM, 2008). It is a physical action that usually leaves the aggregates clearly exposed. (PCA, 2001).

How it happens?

Scaling happens when the hydraulic pressure from water freezing within concrete exceeds the tensile strength of concrete. Scaling is more common in non-air-entrained concrete, but can also occur in air-entrained concrete in the fully saturated condition.


What is it?

Disintegration is the physical deterioration (such as scaling) or breaking down of the concrete into small fragments or particles.

How it happens?

It usually starts in the form of scaling. It may be also caused by de-icing chemicals, sulphates, chlorides or by frost action.


What is it?

Erosion is the deterioration of concrete surface as a result of particles in moving water scrubbing the surface.

How it happens?

When concrete surface is exposed to the water-borne sand and gravel, the surface gets deteriorated by particles scrubbing against the surfaces. Flowing ice particles can also cause the problem. It is an indicator of poor durability of concrete for that specific exposure.


What is it?

Corrosion is the deterioration of steel reinforcement in concrete. Corrosion can be induced by chloride or carbonation. The corrosion can result in cracking in the concrete cover, delamination in concrete decks, etc.

How it happens?

When the concentration of chloride ions above the surface of reinforcement reaches the threshold limit (which is the amount required to break down the passive film) corrosion begins. The volume of resulting material (rust) is 6-7 times, which increases the stress around the rebar, and causes fracture and cracking. The cracks extend to the surface of concrete over time; that is when we can visually see the sign of rust over the surface of concrete.



What is it?

“Delamination is defined as a discontinuity of the surface concrete which is substantially separated but not completely detached from concrete below or above it.” (OSIM, 2008). Delamination is often identified by the hollow sound by tapping or chain dragging of concrete surface.

How it happens?

The corrosion of reinforcement and subsequent cracking of the cover can cause delamination. When the rebar have small spacing, the cracking extends in the plane of the reinforcement parallel to the exterior surface of the concrete.


What is it?

Spalling can be considered an extended delamination. In fact, when the delamination continues, the concrete fragments detach from a larger concrete mass.

How it happens?

If delamination is not repaired on time, the progress of damages as a result of external loads, corrosion, and freezing and thawing can break off the delaminated pieces.


What is it?

It is the internal cracking of concrete mass as a result of a chemical reaction between alkalis in the cement and silica in the aggregates. The AAR/ASR cracking are very famous for their crack patterns.

How it happens?

The alkalis in the cement can react with the active silica in the aggregates to form a swelling gel. When this gel absorbs water, it expands, and applies pressure to surrounding environment which makes the concrete crack.


What is it?

A crack is a linear fracture in concrete which extends partly or completely through the member.

How it happens?

Some people believe that concrete is born with cracks; that its ingredients, and how it is produced – from the batching plant to pouring, setting, and curing – is influenced by so many factors that cracking of concrete does not come as a big surprise; and to a great extent, that might be true. Cracking of concrete can happen in different stages: It can happen before hardening of concrete, and it can happen in an old concrete structure:

Before Hardening

+ Settlement within concrete mass

+ Plastic shrinkage

After Hardening

+ Drying shrinkage

+ Thermal contraction

+ Sub-grade settlement

Concrete Cracks