Self-healing in cementitious composite containing bacteria and protective polymers at various temperatures
Autonomous sealing of cracks in concrete through bacteria-induced calcification has become a topic of great concern in the last two decades. This paper is focused on two main issues of the so-called bio-based self-healing concrete, i.e. protection of the bacterial spores embedded in the cementitious matrix and behavior of the material at low temperatures. The second aspect is particularly important as the impact of the conditions corresponding to real outside environment was rarely investigated before. An investigation of the influence of temperatures below the freezing point is a unique extension of the current state of the art. In the current study, as a form of protection, superabsorbent polymers (SAP) powder and 16 % polyvinyl alcohol (PVA) water solution are applied. The performed mechanical tests showed pronounced negative impact of the PVA addition on both tensile and compressive strength (a decrease of 56 % and 79 %, respectively), while the SAP negatively affected only the compressive strength (a drop of 30 %). In our study, the composite containing SAP reached even slightly higher tensile strength compared to the control (around 7 % increase). The healing action was observed on cracked cementitious composites beams at ideal (i.e. room) temperature, low temperature (10 °C), and after exposure to freeze cycles (–5 to 0 °C). After 28-day immersion in water at the ideal temperature, the series containing SAP and bacterial spores (BAC_SAP) showed the most pronounced healing – the value of the average maximum healed crack width (Δwmax) reached 219 μm. In the case of preliminary freeze cycling, the BAC_SAP also reached the highest values. At low temperatures, the positive impact of SAP seems to be inhibited as Δwmax is the highest in the control series. In all of the applied conditions, insufficient crack-sealing was detectable in the samples containing PVA. Thus, the SAP proved to be applicable for the protection of bacterial spores at ideal temperatures; however, more research concerning its mechanism in cementitious composite at lower temperatures is needed.