Date of Award

31-8-2024

Document Type

Thesis

School

School of Civil Engineering

Programme

Ph.D.-Doctoral of Philosophy

First Advisor

A.Sumathi

Keywords

Bacteria, Isolation and Identification, Strength, Durability, Crack Healing

Abstract

Concrete is the most broadly utilized construction material due to its availability and cost. It is more susceptible to cracks, allowing chemical substances and water to enter and deteriorate the materials over time, as well as affecting the durability properties of structures. In recent years, the use of bacteria and natural fibers in concrete has not only reduced cracks but also enhanced its strength and durability.

Microbial-induced carbonate precipitation (MICP) is highly acceptable in concrete to improve rheological and crack repair properties. In the current research isolated five bacteria from various locations and subjected to basic tests such as urease enzyme activity, CaCO3 production, and pH growth. The bacteria Bacillus paramycoides was isolated from concrete efflorescence and showed good results in basic tests. It was used in concrete with hybrid combinations of coir, flax, and jute, and the results were studied. The bacteria (self-healing agent) was added to natural fiber reinforced concrete using direct addition (DA) and immobilization (IM) techniques.

Compared to control and DA, IM rendered improved values in strength, durability and crack healing properties. The strength results of IM specimens showed improved compressive strength by 25.95%, compressive strength regain by 61.45%, split tensile strength by 45.65%, flexural strength by 28% and impact strength by 444.92%.

The IM samples under durability tests, showed 85.41% reduction in sorptivity, 2% strength loss in chloride exposures, and 2% strength loss in sulphate exposure. The average rate of crack healing (internal and external) for pre-cracked cube samples (crack range - 0.3 to 1.2 mm) after 28 days of full-wet curing, wet-dry curing, normal soil curing, and marine soil curing was 87.85%, 96.18%, 79.86%, and 49.66%, respectively. The corrosion level of reinforced steel bars under chloride curing was assessed, using gravimetric analysis.

At 270 days, the corrosion level of embedded bars from bacterial samples (DA and IM) showed a range of 0.07–0.23%. The microstructure study was carried using Scanning electron microscopy (SEM), X-ray diffractometers (XRD), and Energy dispersive spectroscopy (EDS). It was concluded that the presence of aragonite, calcite and vaterite (polymorphs of CaCO3) in bacterial samples is due to the biological activity of Bacillus paramycoides with a natural fiber-reinforced cementitious system.

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