Abstract
Biogenic self-healing cementitious materials target on the closure of micro-cracks with precipitated inorganic minerals originating from bacterial metabolic activity. Dormant bacterial spores and organic mineral compounds often constitute a biogenic healing agent. The current paper focuses on the investigation of the most appropriate organic carbon source to be used as component of a biogenic healing agent. It is of great importance to use an appropriate organic source, since it will firstly ensure an optimal bacterial performance in terms of metabolic activity, while it should secondly affect the least the properties of the cementitious matrix. The selection is made among three different organic compounds, namely calcium lactate, calcium acetate and sodium gluconate. The methodology that was used for the research was based on continuous and non-continuous oxygen consumption measurements of washed bacterial cultures and on compressive strength tests on mortar cubes. The oxygen consumption investigation revealed a preference for calcium lactate and acetate, but an indifferent behaviour for sodium gluconate. The compressive strength on mortar cubes with different amounts of either calcium lactate or acetate (up to 2.24% per cement weight) was not or it was positively affected when the compounds were dissolved in the mixing water. In fact, for calcium lactate the increase in compressive strength reached 8%, while for calcium acetate the maximum strength increase was 13.4%.
Highlights
Cracking is an unavoidable characteristic of concrete that originates from its brittle nature, and it is a sign that the tensile strength has been locally exceeded
Isolates Pre-Grown on Acetate Iso-06 pre-grown in acetate exhibited a very significant increase in oxygen consumption rate for respiring on calcium lactate (CaL)
Isolates Pre-Grown on Gluconate Iso-10 pre-grown in gluconate, was the only cell suspension that exhibited positive relative respiration values for respiring on CaL or on calcium acetate (CaA)
Summary
Cracking is an unavoidable characteristic of concrete that originates from its brittle nature, and it is a sign that the tensile strength has been locally exceeded. Micro-cracks do not necessarily put in danger the integrity of the structure, yet, they can impair its durability (Weiss, 1999; Schlangen and Joseph, 2009). The concrete that is able to repair itself; i.e., self-healing concrete, is an approach that has been adapted the last two decades in order to address this problem (de Rooij et al, 2013). The technology targets on the closure of micro-cracks by the release of the healing agent that pre-exists in the bulk concrete. Active bacteria can deposit calcium carbonate (CaCO3) and other inorganic minerals, seal the open cracks and, sustain the integrity of the structure by closing the road to harmful substances
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