Biological Self-Healing of Cement Paste and Mortar by Non-Ureolytic Bacteria Encapsulated in Alginate Hydrogel Capsules

Abstract

Crack formation in concrete is one of the main reasons for concrete degradation. Calcium alginate capsules containing biological self-healing agents for cementitious materials were studied for the self-healing of cement paste and mortars through in vitro characterizations such as healing agent survivability and retention, material stability, and biomineralization, followed by in situ self-healing observation in pre-cracked cement paste and mortar specimens. Our results showed that bacterial spores fully survived the encapsulation process and would not leach out during cement mixing. Encapsulated bacteria precipitated CaCO3 when exposed to water, oxygen, and calcium under alkaline conditions by releasing CO32− ions into the cement environment. Capsule rupture is not required for the initiation of the healing process, but exposure to the right conditions are. After 56 days of wet–dry cycles, the capsules resulted in flexural strength regain as high as 39.6% for the cement mortar and 32.5% for the cement paste specimens. Full crack closure was observed at 28 days for cement mortars with the healing agents. The self-healing system acted as a biological CO32− pump that can keep the bio-agents retained, protected, and active for up to 56 days of wet-dry incubation. This promising self-healing strategy requires further research and optimization.

A review on the potential of filamentous fungi for microbial self-healing of concrete

“…Autogenous selfhealing can be enhanced by incorporating fibres, adding mineral admixtures, using curing agents or dispersing water-absorbing polymers, however, it never allows the healing of cracks with a width larger than 0.2 mm [4,9,13,14], necessitating the use of self-healing agents, such as microorganisms. Emergent research in biocementation aims at substituting cement with more sustainable microbially induced calcite precipitation (MICP) [15,16], thereby strengthening the concrete and enhancing the durability of concrete by leading to self-healing of larger-sized cracks [2,5,11,[16][17][18][19][20][21][22][23]. The process of biocementation is based on the precipitation of CaCO 3 on sand grains [24].…”

“…+ is known to be an environmental pollutant and poses a health risk for animals and humans [2]. Therefore, the use of non-ureolytic bacteria, which is based on the metabolic conversion of an organic calcium source through bacterial respiration leading to CO 2 production and calcium carbonate precipitation [29], is a more environment-friendly approach.…”

“…The direct addition of bacterial spores and nutrients to the concrete mix has been shown to result in a decreased intrinsic compressive strength of the material and in a loss of viability of the spores [2]. The reduced cell's functionality is related to the mechanical forces during the mixing process, a decrease in matrix pore diameter due to cement hydration and to the harsh alkaline environment [2,21,41].…”

“…Although concrete is one of the most widely used construction materials, used in 80% of the construction cases [1,2], the related durability issues cannot be neglected. Due to its shrinkage during hardening, its low tensile strength and brittle behaviour, concrete typically suffers from crack formation.…”

Albumin Microspheres as “Trans-Ferry-Beads” for Easy Cell Passaging in Cell Culture Technology

“…Hydrogels have become an important class of material in diverse fields of applications such as bulk absorber materials [ 1 , 2 ], cosmetics [ 3 ], and even building industries [ 4 ]. Especially hydrogels making use of the advantageous intrinsic properties of biopolymers such as proteins and nucleic acids with their defined sequence lengths (also referred to as ‘precision polymers’) have been shown to possess advanced properties over synthetic polymers for life science-related applications, including biochemistry, cell biology and the field of medical applications [ 5 , 6 , 7 , 8 , 9 ].…”