Nondestructive Monitoring of Bacterial Intrinsic Self-Healing in Cementitious Structures Using Ultrasonic Wave Propagation

Microbial induced calcium carbonate precipitation (MICCP) has applications in improving the quality of cementitious constructions by enhancing its compressive strength, reducing porosity, and increasing durability against environmental degradation. In this study, an attempt has been made to develop an in situ, online, and nondestructive ultrasonic monitoring tool to capture bacterial self-healing in cementitious materials using cheaper source of bacterial nutrition medium. Samples casted and cured in corn steep liquor (CSL) and nutrient broth (NB) demonstrated higher ultrasonic pulse transmitted signals at successive days of curing relative to water cured control (C) specimens. The rise in ultrasonic signal due to bacterial admixing and curing is due to calcite precipitation in bacterial admixed and cured specimens. The compressive strength of CSL specimens was 8.8%, 11.4%, and 11.1% higher, while in NB specimens was 13.5%, 14.6%, and 12.7% higher as compared to water casted and cured specimens at 7, 14, and 28 days, respectively. The water absorption in bacterial treated specimens was significantly reduced due to the filling of pores in the mortar matrix and a reduced sorptivity coefficient of 0.0027 and 0.0022 was observed in CSL and NB specimens respectively as compared to 0.0197 of water casted and cured C specimens. This suggests successful calcite precipitation in bacterial treated mortar specimens and ultrasonic pulse transmission monitoring technique can successfully pick up bacterial intrinsic healing and can serve as in situ and nondestructive monitoring technique in civil engineering applications. Bacterial intrinsic self-healing in cementitious materials is an inherent process and this paper highlights the successful implementation of nondestructive and in situ ultrasonic wave monitoring tool to pick the same. Commonly used nondestructive testing (NDT) techniques like ultrasonic pulse velocity (UPV), acoustic emission monitoring can capture crack initiation in cementitious structures but not its intrinsic healing. In present research, ultrasonic wave monitoring has been used to capture bacterial microstructural development in the initial curing period in MICCP. This innovative NDT technology would go a long way in developing an in situ ultrasonic monitoring technique to pick up efficacy of MICCP in concrete structures for on-site applications.