Abstract
The principal objective of the research is to contribute towards attaining the goal of developing self-healing cementitious concrete composites by incorporating bacteria as healing agent. Since the root cause of the majority of structural failure is attributed to concrete cracking, there is a compelling economic incentive to develop a concrete that can treat and repair the damage all by itself. Even though some research has been carried out in this area, a major breakthrough in identifying the types of bacteria, modes to protect this bacteria from high pH concrete environment and nutrients for effective healing are yet to materialise. For the present study, three different bacteria namely, Sporosarcina ureae, Sporosarcina pasteurii and Bacillus subtilis subsp. spizizenii and two protective vehicles such as zeolite and pumice were selected to determine the best combination among them for self-healing. Normal and fibre reinforced mortar and engineered cementitious composite (ECC) specimens were employed for the study. In order to develop self-healing bacterial concrete based materials, it is crucial to understand whether the introduction of mineral producing bacteria and nutrients adversely affect the properties. Thus, various concentrations of bacteria and nutrients were tested to determine the best possible combinations without sacrificing concrete properies. Evaluation of healing effect was determined by comparing compressive strength, sorptivity and rapid chloride permeability (RCPT), four point bending and ultrasonic pulse velocity (UPV) properties of sound and damaged specimens at different ages. Healing associated with crack closure was visualised and analysed using scanning electronmicroscopy (SEM), Energy Dispersive Spectrum Energy (EDS) and X-ray diffraction (XRD) studies. Finally, an attempt was made to employ statistical models for parameter optimization of self-healing characteristics in terms of compressive strength, sorptivity, RCPT and UPV by design and analysis of experiments. Evaluation of results to determine self-healing efficiency indicated that a significant amount of self-healing was achieved by all three selected bacteria, out of which Sporosarcina pasteurii and Bacillus subtilis subsp. spizizenii found to be promising choices. Both zeolite and pumice turned out to be effective protective vehicles. Statistical modelling of the experiment proved to be the ideal choice for modelling self-healing characteristics.
Highlights
This chapter provides an introduction to the self-healing mechanism by describing the characteristics of self-healing behavior and the basic underlying principles of self-healing mechanism
Increase in ultrasonic pulse velocity (UPV) values shows the healing efficiency. It can be seen from the graph that for the control, nutrients + pumice and nutrients + zeolite specimens, increase in UPV values are negligible compared to that treated with selected bacterial species
The increments in UPV were found to be 100m/s for the control, 137m/s for unprotected bacteria, 218 m/s for S. pasteurii + zeolite and 194m/s for B. subtilis + zeolite after 1 month of healing
Summary
We provide an introduction to the self-healing mechanism by describing the characteristics of self-healing behavior and the basic underlying principles of self-healing mechanism. This chapter illustrates parameter optimization in modelling self-healing characteristics in terms of compressive strength, sorptivity, Rapid Chloride Permeability (RCP) and Ultrasonic Pulse Velocity (UPV) evolution of bacteria incorporated normal and fibre reinforced mortars by statistical design and analysis of experimental results. Various permutations and combinations in terms of the bacterial concentration and amount of minerals substrates to be added into the matrix were carried out in this study This was performed in order to determine the optimum quantity of healing agent addition that gave the best result in inducing self-healing
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