self healing concrete for modern construction

SELF HEALING CONCRETE

   As revolutionary as it was and still is, modern concrete (Lime-based) has a short lifespan caused by the formation of cracks shortening the longevity of a particular construction. That’s how the concept of self-healing finds its way to concrete. the natural way of hydrates to seal cracks over time, and the artificial way to seal cracks which needs a man-made intervention. 

   PURPOSE 

• increase concrete’s durability

• huge positive impact on both the environment and economics

• improve the architectural designs

• change the shape of internal spaces so that it serves many functions and provides flexibility.

A self-healing material is described as a material that is capable of repairing itself back to the original state. The concept of self-healing concrete (SHC) that happens over time (autogenic) has been noticed for over 20 years. It can be observed in many old structures which have remained standing for long periods of time in spite of the fact that they have limited maintenance. This observation concludes that the cracks heal when moisture interacts with non-hydrated cement clinker in the crack. Nevertheless, in present-day constructions the cement is lowered as a result of modern construction methods. Hence, the amount of available non-hydrated cement is less and therefore, the natural healing effect is reduced.

The principal phases of the natural healing ability are the inflammation and hydration of cement pastes; followed by the precipitation of calcium carbonate (CaCO3), and lastly the obstruction of flow paths as a result of the deposition of water impurities or the movement of some concrete bits that get detached throughout the cracking process.  

Many factors are considered in the natural way of healing, such as; temperature, degree of damage, freeze-thaw cycles, the age of the concrete and the mortar state.As for the artificial way to repair cracks in concrete, which is man-made self-healing process was first invented in 1994. The main method and first approach was to use a healing agent (adhesive) which is encapsulated inside a micro capsule, once a crack forms, it causes the micro capsules to break, releasing the healing agent, hence healing the crack. The adhesives can be stored in short fiber or in longer tubes.

PROCESS OF HEALING CONCRETE

There are many approaches to create smart concrete and enhance its properties while reducing the cost of overall use of the material. Also known as Bio-Concrete; this kind of concrete uses a simple process to close the formed crack. The main mechanism is achieved by making a concrete mixture that contains (i) a precursor like calcium lactate (Ca(C3H5O2)2) and, (ii) bacteria planted in micro capsules (or just added to the mixture) that will later germinate, once the water reaches the crack. As soon as the bacteria germinate, they produce limestone (CaCo3) caused by the multiplying bacteria. Dr. Richard Cooper of Bath’s Department of Biology & Biochemistry says that incorporating bacteria in concrete adds a double layer shield in order to prevent corrosion in steel. Not to mention that it employs oxygen present which would then benefit the process of steel corrosion.

The bacteria which are applied in this kind of concrete are Spore-forming and alkali-resistant bacteria. Bacteria from this group are the most suitable as they are spore-forming and can live for more than 200 years in dry conditions [6 – p.102]. Therefore, using bacteria as a healing mechanism is one of the best mechanisms to produce this kind of concrete because of its sustainable organic properties.

FACTOR AFFECTING SELF HEALING CONCRETE

There are many factors that intervene with the usage of this kind of concrete. As it is noticed; it is not yet used in all new constructions as it is still being under development. Recently Self-healing bacteria-based concrete has been successfully tested on a full-scale. However, the cost of using it is still not determined as it is hard to predict a full cost. The cost efficiency is one of the most important factors and will determine whether the material will have limited usage restricted to spots that are hard to fix and important constructions such as bridges and highways.Other than cost, long-term efficiency is one of the important factors as well alongside the size of the formed cracks which must not exceed 150 millimeters of depth to establish an ideal result.All in all, some factors that will definitely determine whether SHC will be used as a replacement of concrete are; the economical factor, long-term efficiency, prospect suppliers and safety factors.

CONCLUSION

•  self healing concrete appears to be much more efficient than usual concrete.

•  It will definitely reshape how architects think and design.

•  we notice that it has more advantages than disadvantages and will transform concrete from an Eco-harming into an Eco-friendly material, 

• it reduces the CO2 emissions significantly. 

• the most promising approach is the bio-concrete which is bacteria-based due to its simplicity in comparison with other mechanisms. 

• For the meanwhile, architects must develop new design methods; ones that allow flexibility in changing functions easily for instance by providing movable partitions which allow creating bigger or smaller spaces depending on the current needs.