Micro and macro-structural properties of waste tyre rubber fibre-reinforced bacterial self-healing mortar

Abstract

Incorporating waste originated fibre in cementitious mixes facilitate safe waste disposal and leads to environment-friendly construction practices. The use of waste originated fibre sometimes degrades cementitious mixes’ properties due to weak fundamental properties of waste originated fibre. In the present study, waste tyre rubber (WTR) fibre was used to prepare fibre-reinforced self-compacting mortar (SCM) up to 2% volume fraction. To improve the efficacy of WTR fibre-reinforced SCM, calcite precipitating bacteria Escherichia Coli was introduced to the mix by i) direct addition with the mixing water and ii) the use of WTR fibre as bacteria carrier. The effectiveness of two different modes of the bacteria incorporation was evaluated by performing the air content, density, flow spread, and flow time test as fresh state properties. The microstructural characterisation, self-healing ability, compressive strength, flexural strength, indirect tensile strength, porosity, and water absorption tests were conducted as hardened state properties. Results indicated that untreated WTR fibre improved the flow of SCM, whereas bacteria immobilised fibre hindered particle movements of the fresh SCM. Microstructural characterisation revealed loose and non-uniform bacterial calcite precipitation over untreated WTR fibre while incorporating WTR fibre as bacteria carrier showed properly adhered calcite precipitation. Compared to the untreated WTR fiber-reinforced SCM, bacteria immobilised WTR fiber-reinforced SCM exhibited the highest mechanical and durability properties. This study compares two modes of incorporating the bacteria, which indicated that the use of WTR fibre as a bacteria carrier improved the properties of fibre-reinforced SCM.