Self-protected nitrate reducing culture for intrinsic repair of concrete cracks

Abstract

Attentive monitoring and regular repair of concrete cracks are necessary to avoid further durability problems. As an alternative to current maintenance methods, intrinsic repair systems which enable self-healing of cracks have been investigated. Exploiting microbial induced CaCO3 precipitation (MICP) using (protected) axenic cultures is one of the proposed methods. Yet, only a few of the suggested healing agents were economically feasible for in situ application. This study presents a NO3− reducing self-protected enrichment culture as a self-healing additive for concrete. Concrete admixtures Ca(NO3)2 and Ca(HCOO)2 were used as nutrients. The enrichment culture, grown as granules (0.5–2 mm) consisting of 70% biomass and 30% inorganic salts were added into mortar without any additional protection. Upon 28 days curing, mortar specimens were subjected to direct tensile load and multiple cracks (0.1–0.6 mm) were achieved. Cracked specimens were immersed in water for 28 days and effective crack closure up to 0.5 mm crack width was achieved through calcite precipitation. Microbial activity during crack healing was monitored through weekly NOx analysis which revealed that 92 ± 2% of the available NO3− was consumed. Another set of specimens were cracked after 6 months curing, thus the effect of curing time on healing efficiency was investigated, and mineral formation at the inner crack surfaces was observed, resulting in 70% less capillary water absorption compared to healed control specimens. In conclusion, enriched mixed denitrifying cultures structured in self-protecting granules are very promising strategies to enhance microbial self-healing.

Validation of Self‐Healing Properties of Construction Materials through Nondestructive and Minimal Invasive Testing

“…When bacteria are used to heal cracks in cementitious materials, the crystal growth and crack width reduction can be monitored in time by using microscopic analysis . Also when crystalline admixtures, expansive agents, autogenous healing, promoted and stimulated autogenous healing with SAPs, microcapsules with bacteria and other healing agents, the combination of bacteria and SAPs, and sodium‐silicate saturated lightweight aggregates are studied, microscopic analysis can be used.…”

“…In this way, the healing products can be studied in time and as a function of the location. Bacterial precipitation can be studied qualitatively and quantitatively using the SEM technique . Based on counting of bacteria, conclusions may be drawn on their viability and ability to precipitate.…”

“…This gives information about the constitutional elements of the material studied, i.e., the formed healing crystals. If a small powder sample can be extracted, X‐ray diffraction and/or Fourier transform infrared spectroscopy (FTIR) is also an option to study the formed healing products in autogenous healing and bacterial healing, as well as attenuated total reflectance (ATR) FTIR . XRD measures the angles and intensities of diffracted incident X‐ray beams to determine the molecular structure of a crystal.…”

Microbial biotechnology approaches to mitigating the deterioration of construction and heritage materials

“…Degradation of natural or synthetic carbon compounds Carbonatogenesis in self-healing concrete (Jonkers, 2011;Dhami et al, 2013) Removal of organic matter from frescoes (Ranalli et al, 2005 been criticized in terms of the safety and the possible undesired reactivation of dormant cells on the substrate (Rodriguez-Navarro et al, 2003). In the same way, the combination of microorganisms with specific delivery matrixes that provide conditions for the desired metabolism has been evaluated in the case of treatment of stonework and sulfate reduction (Cappitelli et al, 2007) or for the delivery in self-healing materials (Ersan et al, 2015). In summary, a better understanding of the complex link between microbial metabolism and biogeochemical cycling has had surprising consequences in our current take of microbial activity and its relationship to construction and heritage materials.…”

Self‐Healing of Cracks in Concrete Using Bacillus Strains Encapsulated in Sodium Alginate Beads

“…The Bacillus strains are widely used in self‐healing or self‐repairing purposes for concrete cracks . Theses strains are easily extractable from an organic soils or wastes.…”