Self-Healing and Mechanical Properties of Bioinspired Recycled Coarse Aggregate Concrete

Abstract

Due to strength, endurance, and affordability in comparison to other building materials, concrete is the most often utilized engineering material in the construction industry. By minimizing the need to create new aggregate quarries and the quantity of construction debris that is disposed of in landfills, the use of RCA in concrete protects the environment. However, one of the main weaknesses of concrete is the development and propagation of cracks under tensile stress, especially in RCA concrete. The strength and durability of concrete are influenced by the characteristics of RCA, including its specific gravity, absorption, and level of contamination. Micro-level cracks, poor ITZ, and low quality of adhering mortar in RCA degrade durability and led to the development of macro-level cracks creating structural integrity and capacity decrease issues. Repair/maintenance of such cracks is required to preserve their serviceability, which is typically costly, laborious, and ecologically unfriendly. Controlling the development and spread of smaller cracks in RCA concrete and improving RCA quality is crucial for long-lasting and excellent structural concrete. Therefore, crack healing can help in the mitigation of RCA quality, microstructure, crack formation and propagation, and improvement of ITZ in RCA concrete. Synthesizing organic compounds from the microorganisms and precursor ingredients added during the mixing phase as bio-inspired self-healing cementitious composites can improve the quality of RCA and repair cracks. This research compares several techniques for improving the performance and evaluating the effect of immobilizer and its size on RCA concrete with a novel strain Bacillus Pumilus. By using a combination of techniques and various nano and macro carriers, including direct incorporation into the mix, immobilization in RCA, sand, and with IONPs, bacteria have been incorporated into concrete. The crack healing abilities of the resultant concrete mixtures, as well as mechanical properties, microstructure, and phase configuration, were investigated. The results indicated satisfactory precipitation of healing component in bacterial mixtures incorporated with Bacillus Pumilus. Bacteria immobilized via IONPs were more productive and efficient in pre-cracked samples at 3 and 7 days, whereas bacteria immobilized in recycled aggregates were more efficient in pre-cracked samples at 28 days. Trends for compressive strength and split tensile strength of all mixes indicated that adding the bacterium "Bacillus Pumilus" led to a substantial improvement in RCA concrete.