Shweta Goyal

Corrosion Prevention of Reinforced Concrete with Microbial Calcite Precipitation

The corrosion of steel and reinforcing bar in concrete structures is one the most common reasons for civil infrastructure failures, especially for structures located in coastal and marine environments. Microbially induced calcite precipitation (MICP) on concrete or mortar is an important area of research to enhance the durability of construction materials. The effectiveness of MICP in reducing reinforcement corrosion is investigated in this article. Reinforced concrete (RC) specimens were treated with the bacterial strain Bacillus sp. CT-5, isolated from the cement sample, and subjected to accelerated corrosion. The results showed that bacterial-treated RC specimens reduced the corrosion rate four times more than the control specimens. A considerable reduction in mass loss and increase in pullout strength is observed with MICP-treated specimens. Corn steep liquor, an industrial pollutant, was used as a nutrient source to grow the bacterial cells for MICP in cementitious structures. This is a step toward the development of microbial concrete that provides a greener and more ecofriendly option.

Microbial healing of cracks in concrete: a review

Concrete is the most widely used construction material of the world and maintaining concrete structures from premature deterioration is proving to be a great challenge. Early age formation of micro-cracking in concrete structure severely affects the serviceability leading to high cost of maintenance. Apart from conventional methods of repairing cracks with sealants or treating the concrete with adhesive chemicals to prevent the cracks from widening, a microbial crack-healing approach has shown promising results. The unique feature of the microbial system is that it enables self-healing of concrete. The effectiveness of microbially induced calcium carbonate precipitation (MICCP) in improving durability of cementitious building materials, restoration of stone monuments and soil bioclogging is discussed. Main emphasis has been laid on the potential of bacteria-based crack repair in concrete structure and the applications of different bacterial treatments to self-healing cracks. Furthermore, recommendations to employ the MICCP technology at commercial scale and reduction in the cost of application are provided in this review.

Corn steep liquor as a nutritional source for biocementation and its impact on concrete structural properties

Microbial-induced carbonate precipitation (MICP) has a potential to improve the durability properties and remediate cracks in concrete. In the present study, the main emphasis is placed upon replacing the expensive laboratory nutrient broth (NB) with corn steep liquor (CSL), an industrial by-product, as an alternate nutrient medium during biocementation. The influence of organic nutrients (carbon and nitrogen content) of CSL and NB on the chemical and structural properties of concrete structures is studied. It has been observed that cement-setting properties were unaffected by CSL organic content, while NB medium influenced it. Carbon and nitrogen content in concrete structures was significantly lower in CSL-treated specimens than in NB-treated specimens. Decreased permeability and increased compressive strength were reported when NB is replaced with CSL in bacteria-treated specimens. The present study results suggest that CSL can be used as a replacement growth medium for MICP technology at commercial scale.

Influence of single and dual particle reinforcements on the corrosion behavior of aluminum alloy based composites

This article presents the results of a study on the corrosion characteristics of the single and dual particle reinforced aluminum alloy 6063 based composites. The reinforcements of silicon carbide and zircon sand were utilized to fabricate the composites by stir casting technique. The influence of reinforcement and their weight percentage on the hardness variations was investigated. The electrochemical tests in sodium chloride solution were conducted to study the corrosion performance of reinforced composites and base alloy. From the corrosion analysis, it was observed that the single particle reinforcement offered better solution on enhancing the corrosion resistance of base aluminum alloy in comparison with dual particle reinforced composites. In the single particle reinforced composites, addition of zircon sand exhibited increased corrosion resistance, when compared to silicon carbide reinforced composites. The governing mechanism behind increased corrosion resistance was found to be the absence of galvanic coupling between the elemental compounds and the corrosive media at particle–matrix interface. The scanning electron microscopy of composites was performed to analyze corrosion mechanism and correlated well with the corrosion behavior.

Performance evaluation of accelerated corrosion techniques using electrochemical measurements and acoustic emission parameters

One of the major causes for deterioration of reinforced concrete (RC) structures is corrosion of steel reinforcement and subsequent cracking of concrete. The natural corrosion process is usually slow and takes a long time to initiate. Hence to enable corrosion and health monitoring of RC elements, the specimens are usually subjected to accelerated corrosion. This push for speed becomes a cause for problems such as difference in electrochemistry at the surface of steel rebar in concrete due to difference in various accelerated corrosion techniques as identified by some of the researchers in literature. The present experimental work investigates the effectiveness of three different accelerated corrosion techniques namely alternate drying - wetting process, admixed chloride diffusion method and impressed current technique based on electrochemical and acoustic emission measurements. From the research it was found that alternate drying - wetting process and impressed current technique are more suitable than admixed chloride diffusion method. Further, there was no prominenteffect of specific accelerated corrosion technique on AEmeasurements, indicating the suitability of this technique for structural health monitoring of RC structures under corrosion distress.