8 Common Defects in Concrete Structures & How to Prevent Them

Causes of Concrete Structure Defects

The following categories apply to the causes of defects in concrete structures:

1. Structural weakness caused by design defects, loading requirements violations, or unintentional overloading.
2. Deficiency in structural integrity as a result of design defects.
3. Damage caused by fires, floods, earthquakes, and cyclones, among other things.
4. Chemical attack-related damage.
5. Marine environment-related damage.
6. Concrete moves as a result of its physical characteristics.

Defects in Structures as a result of Design and Detailing

In this scenario, the design must be thoroughly checked and corrective steps devised by the design team. Once this is accomplished, the procedures for implementing the remedial steps would be identical to those used for other types of defects.

Structural Inadequateness as a result of Construction Defects

Defective building techniques account for the largest share of beam distress. These flaws can be narrowly classified as follows:

1. Defects caused by poor raw material quality.
2. Non-adoption of a concrete mix that has been planned.
3. Utilization of a deficient construction plant for the production, transportation, and placement of concrete.
4. Poor workmanship.
5. Inadequate attention to detail.

It is critical to choose the proper form of cement for the concrete that will be used in the structure in question. Ordinary Portland cement is the most frequently used form of cement.

As long as the condition of the cement meets the applicable minimum requirements at the time of use, there should be no problems with ordinary Portland cement. Where concrete is exposed to an aggressive climate, special cements such as sulphate-resistant Portland cement, blast furnace slag cement, and low C3A cement may be required. It is necessary to consider the aggregates’ quality, especially in terms of alkali-aggregate reaction; fortunately, cases of defects / failures attributed to alkali-aggregate reaction are extremely rare in India.

The use of salty water in the concrete manufacturing process may also lead to the concrete’s degradation. Concrete mixes can be successfully built using a wide range of aggregates. A reasonable degree of consistency in aggregate grading should be maintained.

The most significant single cause of failure is an excessive amount of water in the concrete mix. The precision with which the various components are weighed is highly dependent on the efficiency of the available weigh batching method.

Spring-loaded dials on weigh batchers lead to India’s excessive variation in the consistency of weigh-batched concrete. Other factors that contribute to poor workmanship include segregation, incorrect spacing, insufficient or excessive mortar leakage through shuttering joints, insufficient concrete cover, and insufficient curing.

Appropriate reinforcement detailing, including sufficient cover, is critical to the effective placement of concrete. Inadequate detailing results in reinforcement congestion to the point that concrete cannot be installed or compacted correctly, even though the concrete is workable.

Reinforcement detailing should be focused on a thorough understanding of how concrete positioning and compaction would be accomplished.

Additional factors that contribute to bad design detailing

1. Corners of re-entrants.
2. Sections undergo abrupt changes.
3. Inadequate detailing of joints.
4. Limits on deflection.
5. Drips and scuppers are poorly detailed.
6. Drainage is insufficient or improper.
7. Expansion joints with inadequate detailing

Concrete Defects: Types, Causes, and Prevention

The following sections discuss the various forms of defects that may occur on a hardened concrete surface and how to avoid them:

1. Cracking

Cracks in concrete can occur for a variety of reasons, but when they are very large, it is dangerous to use the concrete framework.

Numerous causes of cracking include inadequate curing, the absence of expansion and contraction joints, the use of a high slump concrete mix, and an unsuitable sub-grade.

To stop cracking, use a low water-cement ratio and a high proportion of coarse aggregate in the concrete mix. Calcium chloride-containing admixtures must be avoided. The surface should be protected from excessive evaporation of moisture. Loads can be applied to the surface of the concrete only after it has reached its full strength.

 

2. Crazing

Crazing, alternatively referred to as pattern cracking or map cracking, is the uneven formation of closely spaced shallow cracks.

Crazing occurs as a result of the top surface of concrete rapidly hardening due to high temperatures, an excess of water in the mix, or inadequate curing. Avoiding pattern cracking requires careful curing, dampening the sub-grade to prevent water absorption from the concrete, and protecting the surface from sudden temperature changes.

3. Blistering

Blistering is the development of hollow bumps of varying sizes on the surface of finished concrete as a result of trapped air under the finished concrete surface.

It may occur as a result of excessive vibration in the concrete mix, excessive entrapped air in the mix, or improper finishing.

Blistering can also occur as a result of excessive water evaporation on the top surface of concrete.

It can be avoided by using a proper proportion of additives in the concrete mix, by covering the top surface to prevent evaporation, and by using proper placement and finishing techniques.

4. Delamination

Delamination is also a condition that resembles blistering. Additionally, in this situation, the top surface of concrete separates from the underlying concrete.

Delamination occurs when the top layer of concrete hardens before the underlying concrete does. This is because the water and air evaporating from the underlying concrete collide between these two surfaces, resulting in the formation of space.

As with blistering, delamination can be avoided through the use of proper finishing techniques. It is preferable to begin finishing after the bleeding process has ended.

5. Dusting

Dusting, alternatively referred to as chalking, is the disintegration of fine and loose powdered concrete onto hardened concrete.

This occurs as a result of an accumulation of water in concrete. It results in water bleeding from the concrete; as a result, fine particles such as cement or sand rise to the top, resulting in dust at the top level.

To prevent dusting, use a low slump concrete mix to achieve a hard, wear-resistant concrete surface. Utilize water-reducing admixtures to achieve the desired slump. Additionally, it is recommended to use superior finishing techniques, which should begin immediately after extracting the bleed water from the concrete surface.

6. Curling

Curling occurs when a concrete slab is distorted into a curved form by upward or downward displacement of the edges or corners.

It is caused primarily by variations in the moisture content or temperature of the slab surface (top) and the slab base (bottom).

Curling of a concrete slab may be either upward or downward. When the top surface is dry and cooled prior to the bottom surface, the top surface starts to contract and upward curling occurs. When the bottom surface is dried and cooled as a result of the high temperature and high moisture content, it shrinks ahead of the top surface, resulting in downward curling.

To avoid curling, use a low shrinkage concrete mix, provide control joints, strengthen the edges with strong reinforcement, or provide thick edges.

7. Efflorescence

Efflorescence is the deposition of salt deposits on the surface of concrete. Generally, formed salts are white in color.

This is because the water used to make the concrete mix contains soluble salts. As concrete hardens, these soluble salts are raised to the top surface by hydrostatic pressure, and salt deposits form on the surface after full drying.

It can be avoided by combining with clean, pure water and using chemically ineffective aggregates. Additionally, cement does not contain more than 1% alkalis by weight.

8. Scaling and Spalling

Scaling and spalling both result in deterioration of the concrete surface and flaking of the concrete. The primary cause of these types of cases is water penetration through the concrete surface. Steel becomes corroded as a result, and spalling or scaling can occur

ScalingOther possible factors include the use of a non-air entrained concrete mix, insufficient curing, and the use of low strength concrete. This form of defect can be avoided by using well-designed concrete mixes, applying air entrainment admixtures, properly finishing and curing the concrete, and having a good slope to drain surface water.

References: Defects in Concrete Structures

Read Also: 4 Serious Types of Cracks in Concrete Columns