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Cracks in concrete are inevitable and are one of the inherent weaknesses of concrete. Water and other salts seep through these cracks, cor...

BACTERIA BASED SELF HEALING CONCRETE

Cracks in concrete are inevitable and are one of the inherent weaknesses of
concrete. Water and other salts seep through these cracks, corrosion initiates,
and thus reduces the life of concrete. So there was a need to develop an inherent
biomaterial, a self-repairing material which can remediate the cracks and
fissures in concrete. Bacterial concrete is a material, which can successfully
remediate cracks in concrete. This technique is highly desirable because the
mineral precipitation induced as a result of microbial activities is pollution free
and natural. As the cell wall of bacteria is anionic, metal accumulation (calcite)
on the surface of the wall is substantial, thus the entire cell becomes crystalline
and they eventually plug the pores and cracks in concrete. This paper discusses
the plugging of artificially cracked cement mortar using Bacillus Pasteurii and
Sporosarcina bacteria combined with sand as a filling material in artificially
made cuts in cement mortar which was cured in urea and CaCl2 medium. The
effect on the compressive strength and stiffness of the cement mortar cubes due
to the mixing of bacteria is also discussed in this paper. It was found that use of
bacteria improves the stiffness and compressive strength of concrete. Scanning
electron microscope (SEM) is used to document the role of bacteria in
microbiologically induced mineral precipitation. Rod like impressions were
found on the face of calcite crystals indicating the presence of bacteria in those
places. Energy- dispersive X-ray (EDX) spectra of the microbial precipitation
On the surface of the crack indicated the abundance of calcium and the
precipitation was inferred to be calcite (CaCO3)


2. INTRODUCTION

Concrete which forms major component in the construction Industry as it is cheap,
easily available and convenient to cast. But drawback of these materials is it is
weak in tension so, it cracks under sustained loading and due to aggressive
environmental agents which ultimately reduce the life of the structure which are
built using these materials. This process of damage occurs in the early life of
the building structure and also during its life time. Synthetic materials like
epoxies are used for remediation. But, they are not compatible, costly, reduce
aesthetic appearance and need constant maintenance. Therefore bacterial induced
Calcium Carbonate (Calcite) precipitation has been proposed as an alternative
and environment friendly crack remediation and hence improvement of strength
of building materials. the concept was first introduced by Ramakrishna. Journal
publication on self-healing concrete over the last A novel technique is adopted
in re-mediating cracks and fissures in concrete by utilizing Microbiologically
Induced Calcite or Calcium Carbonate (CaCO3) Precipitation (MICP) is a
technique that comes under a broader category of science called bio-
mineralization. MICP is highly desirable because the Calcite precipitation
induced as a result of microbial activities is pollution free and natural. The
technique can be used to improve the compressive strength and stiffness of
cracked concrete specimens. Research leading to microbial Calcium Carbonate
precipitation and its ability to heal cracks of construction materials has led to
many applications like crack remediation of concrete, sand consolidation,
applications.so it can be define as “The process can occur inside or outside the
microbial cell or even some distance away within the concrete. Often bacterial
activities simply trigger a change in solution chemistry that leads to over
saturation and mineral precipitation. Use of these Bio mineralogy concepts in
concrete leads to potential invention of new material called ―Bacterial Concrete”
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