Concrete cover is a crucial factor in safeguarding reinforcement steel bars against corrosive elements. Therefore, great care must be taken when designing and constructing the thickness of concrete cover. Typically, the specified thickness of concrete cover depends on the type of reinforced concrete member and the environmental conditions in which the structure is built. In this article, we will delve into the concrete cover specifications provided by commonly used codes.
The determination of concrete cover thickness is influenced by various factors such as the nature of the structure, construction method, environmental conditions, and the quality of the concrete used. To establish the appropriate concrete cover thickness, it is necessary to refer to specific codes and standards. These codes provide guidelines tailored to different regions and construction practices.
The American Concrete Institute (ACI) code is one such reference. It outlines specifications for concrete cover thickness based on the particular requirements of the structure. The ACI code takes into account factors such as loadings, exposure conditions, and desired durability to ensure adequate protection of the reinforcing steel within the concrete.
In Europe, the European Code provides its own set of regulations for determining concrete cover thickness. This code considers factors like structural design, environmental exposure, and local construction practices. By following the guidelines of the European Code, engineers and builders can determine the appropriate concrete cover thickness for their specific project.
Similarly, the British standard offers its own specifications for concrete cover thickness. These standards are designed to ensure the structural integrity and durability of concrete elements. By adhering to the British standard, construction professionals can ascertain the appropriate concrete cover thickness based on the unique requirements of their project.
In cases where structures are subjected to significantly severe conditions, special specifications may be required. These specifications take into account extreme environmental factors, aggressive chemicals, or other harsh conditions that could potentially impact the structure’s integrity. By considering these special specifications, engineers can determine the necessary concrete cover thickness to provide adequate protection for the reinforcing steel and maintain the overall safety and durability of the structure.
In summary, the determination of concrete cover thickness involves referencing specific codes and standards. Codes such as the ACI code, European Code, British standard, and special specifications for severe conditions provide guidance tailored to various factors and requirements. These codes ensure that the concrete cover thickness is appropriate for the specific structure, construction method, environmental conditions, and quality of the concrete utilized in the project.
Concrete Cover Specifications as per ACI code
The American Code Institute (ACI 318-11) furnishes guidelines regarding the minimum thickness of concrete cover for various components in reinforced concrete structures. These prescribed minimum covers can be found in Table 1. However, there are certain circumstances outlined in the ACI code where these minimum cover thicknesses may not suffice, necessitating an increase in the required thickness. These conditions include exposure to corrosive environments, the need for fire protection, and provisions for future extensions. To ensure that a concrete cover thickness of at least 50mm is achieved, it is advisable to establish a minimum cover thickness of 65mm, accounting for potential construction errors. It is worth noting that the ACI code allows for the use of cover thicknesses smaller than those specified in Table 1 for precast concrete members.
Table-1: Minimum Cover Thickness for Cast-in-Place Concrete
| Type of structure | Concrete over, mm |
| Concrete cast against and permanently in contact with ground | 75 |
| Concrete in contact with ground or water | |
| No. 19 through No. 57 bars | 50 |
| No. 16 bar and smaller | 40 |
| Concrete not exposed to weather or in contact with ground | |
| Slabs, walls, joists | |
| No. 43 and No. 57 bars | 40 |
| No. 36 bar and smaller | 20 |
| Beams, columns | |
| Primary reinforcement, ties, stirrups, spirals | 40 |
| Shells, folded plate members | |
| No. 19 bar and larger | 20 |
| No. 16 bar and smaller | 13 |
Concrete Cover Specifications as per European Code
The Euro Code offers comprehensive guidelines and specifications for determining the appropriate thickness of concrete cover. These recommendations are based on precise calculations and take into account various factors such as the water-to-cement ratio, concrete strength, and minimum cement content. One crucial aspect addressed by the code is the type of weather conditions to which the structure will be exposed. This information can be easily referenced in Table-2, which provides the minimum concrete cover thickness required, as well as other relevant parameters, depending on the specific weather condition. By consulting this table, one can ascertain the appropriate concrete cover thickness needed for a given situation.
Table-2: Minimum concrete cover according to the European code and British specifications
| Exposure condition | Maximum W/C ratio | Minimum cement content, Kg/m3 | Minimum concrete cover, mm | Concrete grade |
| Dry | 0.65 | 260 | 15 | C30/37 |
| Humid | ||||
| No frost | 0.60 | 280 | 20 | C30/37 |
| Frost | 0.55 | 280 | 25 | C35/45 |
| De-icing salts | 0.5 | 300 | 40 | C35/45 |
| Seawater | ||||
| No frost | 0.55 | 300 | 40 | C35/45 |
| Frost | 0.50 | 300 | 40 | C35/45 |
| Aggressive chemicals | ||||
| Slightly | 0.55 | 280 | 25 | – |
| Moderately | 0.50 | 300 | 30 | – |
| Highly | 0.45 | 300 | 40 | – |
Several researchers, including Browne et al. and Van Daver, have conducted studies demonstrating that the concrete cover in a significant number of structures is often less than what is specified in the design. For instance, Browne et al. found that the average cover thickness in the structures they observed was 13.9mm, significantly lower than the specified 25mm. This discrepancy has prompted the European code to address the issue by recommending an increase in the minimum cover thickness. The code incorporates a permitted standard deviation, ranging from 5-10mm for cast-in-situ concrete and 0-5mm for precast concrete, to account for variations in cover thickness. By incorporating these adjustments, the European code aims to ensure that the minimum cover requirements are met despite the observed tendency for cover thickness to be below design specifications.
Concrete Cover Specifications as per British standard
The determination of concrete cover thickness according to the British standard takes into consideration various factors such as weather conditions prevailing during the construction of a structure. This standard also considers the strength of the concrete and its overall quality, which is influenced by factors like the cement content and water-to-cement ratio used in the concrete mix. To provide guidance on minimum concrete cover thickness, Table-3 is provided within the British standard. This table serves as a reference for ensuring adequate concrete cover for different structural elements based on the aforementioned factors. By adhering to these guidelines, construction professionals can help ensure the durability and long-term performance of the structure.
Table-3: Thickness and properties of concrete cover according to British standard
| Environmental conditions | Concrete grade, MPa | ||||
| 30 | 35 | 40 | 45 | 50 | |
| Water/ cement ratio | |||||
| 0.65 | 0.60 | 0.55 | 0.50 | 0.45 | |
| Minimum cement content, Kg/m3 | |||||
| 25 | 20 | 20 | 20 | 20 | |
| Concrete cover thickness | |||||
| Moderate1 | 25 | 20 | 20 | 20 | 20 |
| Moderate2 | — | 35 | 30 | 25 | 20 |
| Hard3 | — | — | 40 | 30 | 25 |
| Very hard4 | — | — | 50 | 40 | 30 |
| Maximum condition5 | — | — | — | 60 | 50 |
To safeguard a concrete surface against harsh weather conditions or challenging environments, it is essential to provide adequate protection. This can involve applying coatings or sealants that act as a barrier, shielding the concrete from external elements such as heavy rain, extreme temperatures, or other detrimental factors.
Concrete surfaces that are exposed to rain, freezing temperatures, or submersion in water require specific protection measures. These may include using waterproofing techniques or utilizing protective coatings designed to resist water infiltration. Additionally, it is crucial to consider the adjacent soil conditions to prevent any adverse effects on the concrete.
When concrete surfaces are constantly exposed to rain and subjected to wetting and drying cycles, it is crucial to implement protective measures to ensure their durability. This can involve utilizing water-resistant coatings or sealants that provide a barrier against moisture penetration. By safeguarding the concrete from excessive moisture exposure, potential issues such as cracking or deterioration can be mitigated.
Concrete structures that face exposure to seawater spray, salt-induced melting ice, or freezing conditions demand specific protective measures. These can include utilizing corrosion-resistant materials, applying anti-corrosion coatings, or incorporating additives in the concrete mixture to enhance its resistance to saltwater or freezing conditions. Such precautions help prevent degradation and maintain the structural integrity of the concrete.
Concrete surfaces that experience abrasion from sources such as seawater containing solid particles, moving water with a pH of 4.5, or constant contact with machinery or vehicles necessitate protective strategies. These may involve utilizing abrasion-resistant coatings or incorporating additives into the concrete mixture to enhance its durability and resistance to wear. By safeguarding the concrete against abrasion, its longevity and performance can be significantly improved.
Special specifications for structures subjected to considerably sever conditions
Offshore structures face direct exposure to seawater, making it crucial to implement effective measures to prevent corrosion of the embedded steel bars. These structures are vulnerable to three primary regions of severe weather conditions: air, splash zone, and immersion in water. Among these conditions, the splash zone poses the greatest risk as the structure is constantly exposed to a combination of seawater and air. To address this challenge, ACI 357 offers recommendations for determining the appropriate cover thickness in severe weather conditions. These recommendations consider factors such as the concrete strength, location of the structure, and the maximum water-to-cement ratio. Detailed guidance can be found in Table 4 of ACI 357.
Table-4: ACI 357 recommendations for cover thickness in offshore structure
| Location | Maximum w/c ratio | Minimum concrete strength at 28 days | Cover thickness | |
| Reinforced steel | Prestressed | |||
| Air | 0.4 | 35 | 50 | 75 |
| Splash zone | 0.4 | 35 | 65 | 90 |
| Immersed in water | 0.45 | 35 | 50 | 75 |
In addition to ACI 357, the British standard offers guidance on selecting the appropriate thickness of concrete cover for private structures. The determination of concrete cover thickness involves considering various factors, such as the degree of mixing for different concrete grades, the expected lifespan of the structure, and the chloride diffusion factor within the concrete. These parameters play a crucial role in ensuring the durability and long-term performance of the concrete elements in private constructions. By taking into account these considerations, the British standard aims to provide recommendations that support the overall quality and longevity of private structures.