International Conference on Cement-Based Materials Tailored for a Sustainable Future, İstanbul, Turkey, 27 - 29 May 2021, pp.302-310
Recent studies focused on development of self-sensing and self-healing
concrete to replace the cost and labour intensive maintenance
strategies. For the former, use of microbial healing agents that induce
calcite precipitation in the crack is a popular approach. So far,
ureolytic axenic cultures were mostly proposed as healing agents. Yet,
non-axenic cultures, biogranules in particular, may be advantageous by
their enhanced performance and resilience. This study presents the
compatibility of nitrate reducing biogranules with the mortar matrix and
the self-healing performance of corresponding bacteria-based specimen.
In-house produced biogranules were incorporated into
mortar mix at dosages varying between 0.35% to 4.30% w/w cement (0.25%
to 3.00% of bacteria w/w cement). Due to their self-encapsulated
structure, biogranules were added into the mortar mix without using any
additional protective carrier. A representative specimen containing
1.40% biogranules was also tested for self-healing under alternating a
week-long wet/humid treatment for a crack width range of 50 to 600 μm.
Considering fresh and hardened mortar properties, the tolerable
biogranule content was determined as 3.60% w/w cement. Due to its
optimized design mix, the novel microbial self-healing mortar appeared
to be 30% stronger than the plain mortar.
Upon alternating wet/humid treatment for 4 weeks, cracks up to a 400 μm
crack width were effectively healed. Overall, non-axenic biogranules
appear to supersede the axenic cultures in development of self-healing
bioconcrete by their self-protected structure, compatibility with matrix
and enhanced performance under spraying or intermittent wetting
conditions, which pave the way for development of cost-efficient
self-healing bioconcrete for a broader range of applications.