Since more than a decade, TU Delft has been working on the development of bacteria based self-healing concrete. The self-healing ability of the material is based on a biological mechanism in which a limestone producing bacteria is added to the material to repair cracks.
The purpose of this study was to understand and compare the efficiency of different methods and materials used for incorporating bacteria into mortar. The aim of the study was to create a self-healing mortar mix for practical applications. Concrete is a widely used construction material. Most structural elements are made using concrete and covered by a protective layer of mortar, called plaster. Cracks usually propagate from the surface to the inside, which means that the plaster is the first to crack. If the mortar is made self-healing, then the concrete underneath can be better protected from the elements, and this could effectively increase the lifespan of the structure.
For this project, fibre reinforced mortar is healed using bacteria (Bacillus Cohnii) which is applied to the concrete using internal (different types of embedded capsules) and external methods (paste applied to the cracks). This is done to check the effectiveness of the bacteria in repairing damaged concrete and to observe which method of application works best. The effectiveness is analysed using optical and electron (BSE) microscopy and a permeability test to observe the water tightness of the sample after cracking.
Additionally, characterization tests are performed on the capsules and performance tests are carried on the mortar samples, to better understand their behaviour. This study would help in making concrete structures more durable which would make them more sustainable and cheaper in the long term. This study found that crack healing is dependent on the crack width and the number of capsules present in the material near the crack. The compressive and flexural strength at 28 and 84 days was found to be higher in samples embedded with alginate capsules and PLA capsules. External healing was found to be a good method for healing existing materials but the healing was found to be dependent on the amount of paste that adhered to the crack wall