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

View Article: PubMed Central

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.

No MeSH data available.


Evolution of the available NOx-N in the bulk solutions during the 28 days incubation of the 28 days old specimens and the pH of the solution (A) mass of the available NOx-N (B) the pH change [N: Nutrients – 2% Ca(HCOO)2 + 3% Ca(NO3)2; n = 3, error bars represent the standard deviation].
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Figure 5: Evolution of the available NOx-N in the bulk solutions during the 28 days incubation of the 28 days old specimens and the pH of the solution (A) mass of the available NOx-N (B) the pH change [N: Nutrients – 2% Ca(HCOO)2 + 3% Ca(NO3)2; n = 3, error bars represent the standard deviation].

Mentions: One of the components of microbial self-healing concrete is the nutrients that initiate and maintain the bacterial activity. Therefore, availability of the nutrients for the bacteria is important. The results of the abiotic control are representative for the NOx-N passed from mortar to the solution, thus indicates the nutrient availability (Figure 5A). Based on the results, 14% of the NO3-N in a mortar specimen became available for microbial use (See Supplementary Material for calculations). Additionally, one can confirm the bacterial activity by the evolution of the abundance of nitrate or formate in solution. Weekly measurements of the NOx-N revealed that 92 ± 2% of the available NO3-N was consumed by the ACDC culture during the crack closure process (Figure 5A). Bacterial activity ( reduction rate) significantly improved after pH decreased below 10 (Figures 5A,B).


Self-protected nitrate reducing culture for intrinsic repair of concrete cracks
Evolution of the available NOx-N in the bulk solutions during the 28 days incubation of the 28 days old specimens and the pH of the solution (A) mass of the available NOx-N (B) the pH change [N: Nutrients – 2% Ca(HCOO)2 + 3% Ca(NO3)2; n = 3, error bars represent the standard deviation].
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4631954&req=5

Figure 5: Evolution of the available NOx-N in the bulk solutions during the 28 days incubation of the 28 days old specimens and the pH of the solution (A) mass of the available NOx-N (B) the pH change [N: Nutrients – 2% Ca(HCOO)2 + 3% Ca(NO3)2; n = 3, error bars represent the standard deviation].
Mentions: One of the components of microbial self-healing concrete is the nutrients that initiate and maintain the bacterial activity. Therefore, availability of the nutrients for the bacteria is important. The results of the abiotic control are representative for the NOx-N passed from mortar to the solution, thus indicates the nutrient availability (Figure 5A). Based on the results, 14% of the NO3-N in a mortar specimen became available for microbial use (See Supplementary Material for calculations). Additionally, one can confirm the bacterial activity by the evolution of the abundance of nitrate or formate in solution. Weekly measurements of the NOx-N revealed that 92 ± 2% of the available NO3-N was consumed by the ACDC culture during the crack closure process (Figure 5A). Bacterial activity ( reduction rate) significantly improved after pH decreased below 10 (Figures 5A,B).

View Article: PubMed Central

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.

No MeSH data available.