# Enhancement of Bacterial Survival and Self-Healing Performance in Mortars After Exposure to Negative Temperature Using Alumina Hollow Spheres as Bacterial Carriers

## TL;DR

Researchers used alumina hollow spheres to protect bacteria in cement, improving survival and self-healing in cold temperatures.

## Contribution

Acid-etched alumina hollow spheres are introduced as bacterial carriers to enhance survival and self-healing in cold environments.

## Key findings

- Alumina hollow spheres improved mortar mechanical properties and reduced thermal conductivity.
- Aluminum hydroxide flocs formed during metabolism enhanced crack healing by binding calcium carbonate.
- Bacteria encapsulated in alumina spheres showed improved survival in negative temperature environments.

## Abstract

Negative temperature environments inhibit bacterial survival in cementitious materials and reduce the self-healing ability of bacteria. To address this challenge, acid-etched alumina hollow spheres are proposed as carriers to encapsulate microorganisms in cementitious materials. The effects of these carriers on the mechanical properties, thermal conductivity, self-healing properties, and self-healing products of specimens after exposure to −20 °C were investigated. Finally, the self-healing mechanism was examined and analyzed. The results demonstrated the effectiveness of the acid-etched hollow microbeads as bacterial carriers. The addition of the alumina hollow spheres participating in the cement hydration reaction enhanced the mechanical properties of the mortar and reduced its thermal conductivity, which supported bacterial survival in the negative temperature environment. Although negative temperature environments may reduce bacterial populations, the hydrolysis of aluminum ions in the alumina hollow spheres during bacterial metabolism resulted in the precipitation of aluminum hydroxide flocs. These flocs adsorbed free calcium carbonate in the pores, converting it into effective calcium carbonate with cementing properties, thus enhancing the crack healing capability of the examined specimens. This microbe-based self-healing strategy, utilizing alumina hollow spheres as bacterial carriers, is anticipated to provide an effective solution for achieving efficient crack self-healing in mortars that is resistant to the detrimental effects of negative temperature conditions.