Study of a New Healing Precursor Derived from Waste Streams For Bacterial Self- Healing Concrete

Abstract

The introduction of autonomous and stimulated autogenous self - healing of concrete cracks has been a wonderful technological breakthrough for our built infrastructure. By reducing manual dependence on repair and maintenance activities on concrete public structures, the application of self-healing can potentially save millions in public economy. However, despite the existence of a large body of research on the domain, the judgement to choose one out of several potential strategies to effectively heal a crack is still met with heavy contestation. Currently, the approach to biologically heal a crack by promoting bacterial precipitation of Calcium Carbonate crystals, is deemed the most environment friendly of all. Research on this has proved that this approach is indeed successful in closing cracks up to at least 0.4mm. However, the bacteria responsible for the precipitation is dependent on the constituent precursor and the nutrients of the healing agent. The bacterial precursor that has been successfully applied so far in OPC cementitious composites is often based on lactic acid derivatives, that involve substantial costs in its production process. Recent studies have also demonstrated some incompatibility of the same precursor on low pH environments, such as that characterised by the addition of supplementary cementitious materials like blast furnace slag. For instance, a higher dosage of the lactic acid based precursors lead to negative effects in strength in blast furnace slag cements. In the Netherlands, CEMIII/B (slag cements) finds reason- ably larger market share than OPC cements. As such, the incompatibility of lactic acid based bacterial self-healing agents presents a discouraging scenario.

Polyhydroxyalkanoates or PHA extracted from waste streams, have been suggested to be a low cost biodegradable polymer that can effectively replace high cost polymers such as PLA (poly lactic acid). It is also established in recent literature, that PHAs can be metabolically converted by bacterial species to form Calcium Carbonate. Besides, unlike the PLAs, these are hypothesized to be applicable in higher dosages in even low pH environments. Taking these into consideration, the current study delves into the potentials of this possible new alternative for bacterial precursor. Scientific questions and objectives based on the probable effects of the PHA on functional properties, healing efficiency, durability, sustainability and economy, were explored. It was found through a number of experimental and analytical data, that the new healing agent demonstrates ample promise to be used as an effective healing precursor for the bacterial self-healing of cement based applications. This holds true in both OPC and Slag rich cement types. With this, numerous novel possibilities are now open for further research into the large - scale application of PHA based self-healing.