When designing any component in structural and civil engineering, considerations in costs frequently arise as a major topic of discussion. Whether it is a discussion of construction, material costs, engineering time, or labor expenses, there will always be considerable effort dedicated to reducing the economical impact of a particular design. One approach to achieving this is to minimize repairs to existing facilities by incorporating self-healing capabilities rather than performing outright repairs. As far fetched as this may sound, within the topic of concrete design, this technology has been in the works since the 1990’s with the concept of Self Healing Concrete (SHC).
Self-healing concrete offers greater flexibility in design by providing alternative options compared to traditional concrete. Depending on the required applications, SHC brings with it several advantages over conventional concrete, such as infrastructure longevity, maintenance reduction, and less recurring costs. This innovative material utilizes mechanisms like internal capsules or bacteria that react when cracks occur, enabling the concrete to repair itself and maintain its structural strength. From extending the lifespan of bridges and highways to reducing the frequency of costly repairs in high-rise buildings, the profound implications of self-healing concrete represents a significant leap forward in engineering and design. In this article, we will explore the two primary types of self-healing concrete—autogenous and autonomous—examining their properties and what sets them apart from traditional concrete
Autogenous Self-Healing Concrete
There are two different types of self healing concrete, the first being autogenous self healing concrete. This type of concrete has the ability to heal itself with natural chemical reactions that take place to heal the damage. Within this type of concrete, the healing properties function in the form of embedded systems or materials to close small cracks. Once small cracks are produced on the concretes surface, the internal materials of the concrete become exposed to environmental conditions, like water or carbon dioxide. Once exposed, small unreacted particles embedded in the concrete begin to react under the new conditions to begin the repair process. There are three types of embedded particles that react to these exposed conditions through one or a combination of the following mechanisms, Hydration of unreacted Cement, Formation of calcium carbonate, and internal Sealants.
Hydration of Unreacted Cement:
When cracks are formed, unhydrated cement particles become exposed to moisture, which then react with water to form additional calcium carbonate or calcium silicate hydrate. This additional material is then filled into the cracks, helping to seal them.
Formation of Calcium Carbonate:
Exposure of calcium-rich materials to carbon dioxide in the atmosphere can lead to the formation of calcium carbonate, which can fill and seal cracks.
Internal Sealants:
Some formulations include internal sealants, like microcapsules or hydrogels, that release healing agents when cracks occur, helping to close them.
Autonomous Self-Healing Concrete
The second type of self healing concrete is Autonomous self healing concrete. This type of concrete refers to a type of self-healing concrete designed to repair itself independently, often without any external stimuli or interventions. Unlike autogenous, which relies on the concrete’s inherent properties to heal itself through processes like hydration of unreacted cement or carbonation, autonomous self-healing concrete typically involves more proactive mechanisms. Rather than embedding the concrete with unreacted particles waiting for cracks to expose them to environmental stimuli, It is embedded with micro capsules that are specifically designed to fill and seal the cracks with healing agents when they occur. There are three types of methods that Autonomous self healing concrete uses to undergo its self healing methods, Embedded Healing Agents, Microbial Systems and Smart Materials.
Embedded healing Agents:
Microcapsules containing healing agents like polymers, adhesives, or bacterial spores are incorporated into the concrete. When cracks form, these capsules break open and the healing materials are released and react to fill and seal the cracks.
Microbial systems:
Bacteria or other microorganisms are embedded in the concrete, which produce healing substances (e.g., calcium carbonate) when exposed to water and air. These bacteria are often encapsulated in the concrete and activate by crack formation.
Smart Materials:
It is possible for advanced formulations to incorporate smart materials that respond to environmental conditions, such as moisture or temperature changes, to initiate the healing process. Such material could involve examples such as hydrogels or Bentonite Clay.
Regular applications for Self-Healing Concrete
Concrete is a fundamental and widely used building material essential in structural and civil designs, especially in situations where post-construction inspection of some areas can prove to be challenging. Self-healing concrete is particularly advantageous in applications where environments involve less practical situations to regularly maintain or repair. It could also be an environment where the concrete is exposed to irregular forces, making it naturally prone to developing cracks. Any of these situations mentioned introduces the requirement for a material that will either be highly resistant to the surrounding conditions or to be engineered with the capabilities to self repair simple damage. Such locations where self healing concrete would be favored can be any of the following;
Critical Infrastructure:
The use of autonomous self-healing concrete in bridges can manage the stress and damage from heavy traffic and environmental conditions, ensuring long-term structural integrity and reducing the need for frequent inspections and repairs. Within tunnels, autonomous systems can effectively address cracks and maintain safety in underground environments where repair access is limited.
High -Rise Buildings:
The use of autonomous self-healing concrete in bridges can manage the stress and damage from heavy traffic and environmental conditions, ensuring long-term structural integrity and reducing the need for frequent inspections and repairs.
Marine Structures:
Autonomous self-healing concrete is ideal for marine environments where proactive healing can address damage from saltwater, waves, and environmental stress, protecting critical infrastructure.
Parking Garages:
In parking structures, autonomous self-healing concrete can manage cracks caused by vehicle traffic and de-icing chemicals, reducing maintenance and extending the structure’s operational life.
Factories and Power Plants:
In industrial settings, autonomous self-healing concrete helps maintain the structural integrity of facilities exposed to heavy loads, vibration, and harsh operational conditions.
Preservation Projects:
When restoring historical buildings or monuments, autonomous self-healing concrete can provide a modern solution to repair damage while preserving the structure’s historical value and reducing the need for invasive repairs.
Dams and Reservoirs:
Autonomous self-healing concrete can address cracks in water-retaining structures proactively, helping to maintain effective water containment and reduce the risk of leaks.
Pavements and Roads:
In roads and pavements subject to heavy traffic and environmental wear, autonomous self-healing concrete helps manage damage proactively, improving durability and reducing repair frequency.
Comparing to Conventional Concrete – Disadvantages of SHC
As mentioned earlier, the concept of self healing concrete had been conceptualized in the 1990’s making it a fairly newer construction material in comparison to conventional concrete, which has had many variations used by humans since around 6500BC. As grand of a material that SHC is with it’s many benefits, there are still some disadvantages that come with it. It in itself being a rather newer technology brings disadvantages of integration within existing building codes and standards. This integration of self healing concrete into facilities using conventional concrete can be difficult and may be slow, causing delays in its adoption and limiting its immediate benefits in the construction industry. Some other disadvantages can be any of the following:
Lower Initial Cost:
Conventional concrete typically has a lower initial cost compared to self-healing concrete, which can be more expensive due to the specialized additives or technologies involved. For projects with tight budgets, Conventional concrete may be the more cost-effective option.
Established Standards and Practices:
Traditional concrete is well-understood and widely used, with established standards, practices, and performance data. This reliability can be advantageous for projects that require proven, standard methods without the uncertainty of newer technologies.
Simpler Construction Techniques:
Traditional concrete does not require the integration of advanced materials or systems, making it easier to work with using conventional construction techniques. This can simplify the construction process and reduce the need for specialized training.
Less Complexity in Repairs:
In cases where self-healing mechanisms fail or are less effective, traditional concrete allows for straightforward repairs using well-established methods. This can be advantageous when dealing with severe or complex damage.
Compatibility with Existing Infrastructure:
Traditional concrete may be preferred for repairs or extensions to existing infrastructure, especially if the surrounding structures use conventional materials and methods. This ensures compatibility and consistency in the repair process.
Predictable Performance:
Traditional concrete’s performance is well-documented and predictable, which can be beneficial for projects requiring precise control over material properties and behavior. Self-healing concrete’s performance can vary depending on the specific healing mechanisms used.
Less Dependency on Environmental Conditions:
Self-healing concrete often relies on specific environmental conditions, such as moisture for bacteria or hydration for chemical reactions. Traditional concrete does not have these dependencies and can be used in a broader range of conditions.
Easier Customization:
Traditional concrete mixes can be easily customized to achieve specific properties, such as strength, durability, or aesthetics, without the need for specialized self-healing components. This allows for greater flexibility in meeting project requirements.
In Conclusion
In writing this post, my interest in learning more about this interesting material has increased. I will be writing a few more posts diving deeper into how each of the two types of Self Healing Concrete Functions. Follow along to learn more about this relatively new and interesting construction material.