Microbial-induced calcium carbonate precipitation is a promising technology for self-healing concrete due to its capability to seal microcracks.The main goal of this study was to evaluate the effects of adding hydroge...Microbial-induced calcium carbonate precipitation is a promising technology for self-healing concrete due to its capability to seal microcracks.The main goal of this study was to evaluate the effects of adding hydrogelencapsulated bacteria on the compressive strength and the self-healing efficiency of concrete.To achieve this objective,12 sets of mortar samples were prepared,including three different mineral precursors(magnesium acetate,calcium lactate,and sodium lactate),at two concentrations(67.76 and 75.00 mM/L),and under two different biological conditions(with and without bacteria).In addition,a set of plain mortar samples was prepared to serve as a control.For each sample set,three mortar cubes and three beams were prepared and subjected to compression and flexural strength tests.From the compression tests,it was found that the sample containing calcium lactate along with yeast extract and bacteria displayed the best results.As for the flexural tests,once cracked,the beams were subjected to 28 d of wet/dry cycles(16 h of water immersion and 8 h of drying),where the bottom crack width was monitored(at 0,3,7,14,28 d of wet/dry cycles).Once the sample with the highest healing efficiency was identified(the one containing calcium lactate and hydrogel-encapsulated bacteria),the study was scaled up to concrete specimens.Two sets of concrete cylinders(consisting of three control samples and three samples with bacteria along with calcium lactate)were tested under compression in order to evaluate the effect of the bacteria-precursor combination on the concrete mechanical properties.The samples that yielded the greatest compressive strength were the ones containing calcium lactate and bacteria,displaying an improvement of 17%as compared to the control specimen.Furthermore,a flexural strength recovery analysis was performed on the concrete specimens revealing that the control showed better flexural strength recovery than the bacteriacontaining variant(41.5%vs.26.1%)after 28 d of wet/dry cycles.A healing efficiency analysis was also performed on the cracked samples,revealing that the control displayed the best results.These results are due to the fact that the control specimen showed a narrower crack width in comparison to the bacteria-containing samples.展开更多
Background: The silica leaching attribute of some of the mystifying bacteria present in the cluster of hot springs (temperatures range 35°C - 80°C) at Bakreshwar (West Bengal, India, 23°52'...Background: The silica leaching attribute of some of the mystifying bacteria present in the cluster of hot springs (temperatures range 35°C - 80°C) at Bakreshwar (West Bengal, India, 23°52'48"N;87°22'40") has provided some significant advancements in construction technology when incorporated to the concrete/mortar specimens. The present investigation was designed to isolate other novel bacterial strains from 65°C hot spring that could have similar or better performance in construction technology. Methods: Soil sample collected from the 65°C hot spring was inoculated to the culture vials (incubated at 65°C) containing a specific synthetic growth medium (pH 8.0) to grow the bacterial population anaerobically by degassing the medium with CO<sub>2</sub> gas. Subsequent serial dilution techniques were employed to isolate pure culture of a specific bacterial strain. 16S rRNA gene sequence and phylogenetic analysis was carried out to identify the novelty of the isolated bacterial strain. The isolated bacteria were incorporated to the cement sand mixture at various cell concentrations to evaluate the efficacy of the strain in construction technology. Results: The work revealed the presence of a novel bacterial strain (BKH3;GenBank Accession No.: KP 890928) within the same hot spring consortium whose 16S rRNA gene sequence data showed 96% identity with Citrobacter freundii bacterial species. The newly isolated bacteria when incorporated at different cell concentration to the cement/cement-sand mixture were found to possess the similar compressive strength increment property, the cracks repairing ability and the water ingression resistivity. It also reduced the permeability of sulphate ions to the cementitious matrix reflecting the increment of durability of the incorporated material. Conclusions: The enhancement of compressive strength and durability of the as prepared bio-concrete material by using the isolated bacterial strain (BKH3) was due to the silica leaching activity of the bioremediase like protein secreted by the bacterium. This may open up another vista of utilization of hot spring bacterium for beneficial purposes in construction technology.展开更多
基金The financial support of the Transportation Consortium of SouthCentral States(Tran-SET)is greatly appreciated(Tran-SET Project 20CLSU05 Grant Number 69A3551747106).
文摘Microbial-induced calcium carbonate precipitation is a promising technology for self-healing concrete due to its capability to seal microcracks.The main goal of this study was to evaluate the effects of adding hydrogelencapsulated bacteria on the compressive strength and the self-healing efficiency of concrete.To achieve this objective,12 sets of mortar samples were prepared,including three different mineral precursors(magnesium acetate,calcium lactate,and sodium lactate),at two concentrations(67.76 and 75.00 mM/L),and under two different biological conditions(with and without bacteria).In addition,a set of plain mortar samples was prepared to serve as a control.For each sample set,three mortar cubes and three beams were prepared and subjected to compression and flexural strength tests.From the compression tests,it was found that the sample containing calcium lactate along with yeast extract and bacteria displayed the best results.As for the flexural tests,once cracked,the beams were subjected to 28 d of wet/dry cycles(16 h of water immersion and 8 h of drying),where the bottom crack width was monitored(at 0,3,7,14,28 d of wet/dry cycles).Once the sample with the highest healing efficiency was identified(the one containing calcium lactate and hydrogel-encapsulated bacteria),the study was scaled up to concrete specimens.Two sets of concrete cylinders(consisting of three control samples and three samples with bacteria along with calcium lactate)were tested under compression in order to evaluate the effect of the bacteria-precursor combination on the concrete mechanical properties.The samples that yielded the greatest compressive strength were the ones containing calcium lactate and bacteria,displaying an improvement of 17%as compared to the control specimen.Furthermore,a flexural strength recovery analysis was performed on the concrete specimens revealing that the control showed better flexural strength recovery than the bacteriacontaining variant(41.5%vs.26.1%)after 28 d of wet/dry cycles.A healing efficiency analysis was also performed on the cracked samples,revealing that the control displayed the best results.These results are due to the fact that the control specimen showed a narrower crack width in comparison to the bacteria-containing samples.
文摘Background: The silica leaching attribute of some of the mystifying bacteria present in the cluster of hot springs (temperatures range 35°C - 80°C) at Bakreshwar (West Bengal, India, 23°52'48"N;87°22'40") has provided some significant advancements in construction technology when incorporated to the concrete/mortar specimens. The present investigation was designed to isolate other novel bacterial strains from 65°C hot spring that could have similar or better performance in construction technology. Methods: Soil sample collected from the 65°C hot spring was inoculated to the culture vials (incubated at 65°C) containing a specific synthetic growth medium (pH 8.0) to grow the bacterial population anaerobically by degassing the medium with CO<sub>2</sub> gas. Subsequent serial dilution techniques were employed to isolate pure culture of a specific bacterial strain. 16S rRNA gene sequence and phylogenetic analysis was carried out to identify the novelty of the isolated bacterial strain. The isolated bacteria were incorporated to the cement sand mixture at various cell concentrations to evaluate the efficacy of the strain in construction technology. Results: The work revealed the presence of a novel bacterial strain (BKH3;GenBank Accession No.: KP 890928) within the same hot spring consortium whose 16S rRNA gene sequence data showed 96% identity with Citrobacter freundii bacterial species. The newly isolated bacteria when incorporated at different cell concentration to the cement/cement-sand mixture were found to possess the similar compressive strength increment property, the cracks repairing ability and the water ingression resistivity. It also reduced the permeability of sulphate ions to the cementitious matrix reflecting the increment of durability of the incorporated material. Conclusions: The enhancement of compressive strength and durability of the as prepared bio-concrete material by using the isolated bacterial strain (BKH3) was due to the silica leaching activity of the bioremediase like protein secreted by the bacterium. This may open up another vista of utilization of hot spring bacterium for beneficial purposes in construction technology.
