User:TahsinRPI/sandbox

Self-Mending Biocement

Synthesis and Fabrication

• concrete prepared through the addition of bacteria with the capacity for precipitation of calcium carbonate (MICP), and aids in sealing the cracks that appear in it
• protection of cells through addition of nutrient sources and different materials e.g., polyurethane, sol-gel ceramics
• Sporosarcina pasteurii immobilized on polyurethane which increases compressive strength

Properties

• 3 Constraints
  • Microorganisms capable of Microbially Induced Calcium carbonate Precipitation (MICP), nutrients and calcium ions which form cementitious materials

• Self-healing features dye to MICP and improvement of mechanical and durability properties
• Waste Concrete Aggregates(WCA) are used to prevent corrosion and can also be recycled
  • Different methods such crushing and grinding can be used to form WCA's

• Permeability of cement also increased compared to normal cement
• Some microorganisms such as Pesudomonas aeruginosa are pathogenic however and unsafe for humans

Potential Uses

• Sidewalk and and pavement building
• Biological building construction
• Different Current Uses
  • spray bars
  • hoses
  • injection and extraction wells
  • drip lines
  • and high-powered pumps

• Can be used to create cement, mortar, and concrete

Self-Mending Biocement

Definition

Advancements in optimizing methods to use microorganisms to facilitate carbonate precipitation are rapidly developing. Biocement specifically is a material that is most well known for its self-healing properties due to microscopic organisms such as bacteria and fungi that are used along with calcium carbonate(CaCO3) in the formation process of the material.

Synthesis and Fabrication

Microscopic organisms are the key component in the formation of bioconcrete as they provide the nucleation site for CaCO{sub|3} to precipitate on the surface. Microorganisms such as Sporosarcina pasteurii are useful in these fabrications as they create alkaline environments where high is pH and dissolved inorganic carbon(DIC) count are both high. These factors are essential for micro biologically induced calcite precipitation(MICP) which is the main mechanism in which bioconcrete is formed. Other organisms that can be used to induce this process are photosynthetic microorganisms such as microalgae and cyanobacteria, or sulphate reducing bacteria(SRB) such as Desulfovibrio desulfuricans. The nucleation of calcium carbonate is dependent on four major factors: 1. Calcium concentration, 2. DIC concentration, 3. pH level, and 4. availability of nucleation sites. As long as calcium ion concentration is high enough, the microorganisms previously described can create such an environment through processes such as ureolysis.

Biocement application in bee nesting. Figure (a) shows a virtual diagram of the biocement brick and housing area for bees. Figure (b) shows the cross section of the design and the holes the bees can nest in. Figure (c) shows the prototype of the bee block made of biocement..

Properties

Biocement is able to "self-heal" due to bacteria, calcium lactate, nitrogen, and phosphorus components that are mixed into the material. These components have the ability to remain active in biocement for up to 200 years. Biocement like any other concrete can crack due to external forces and stresses. Unlike normal concrete however, the microorganisms in biocement can germinate when introduced to water. Rain can supply this water which is an environment that biocement would find itself in. Once introduced to water, the bacteria will activate and feed on the calcium lactate that was part of the mixture. This feeding process also consumes oxygen which converts the originally water soluble calcium lactate into insoluble limestone. This limestone then solidifies on surface it is lying on, which in this case is the cracked area, thereby sealing the crack up.

Oxygen is one of the main elements that cause corrosion in materials such as metals. When biocement is used in steel reinforced concrete structures, the microorganisms consume the oxygen thereby increasing corrosion resistance.This property also allows for water resistance as it actually induces healing, and reducing overall corrosion. Water concrete aggregates are what are used to prevent corrosion and these also have the ability to be recycled. There are different methods to form these such as through crushing or grinding of the biocement.

The permeability of biocement is also higher compared to normal cement. This is due to the higher porosity of biocement and this can leader to larger crack propagation when exposed to strong enough forces. The fact that biocement is now roughly 20% composed of a self healing agent also decreases its mechanical strength. The mechanical strength of bioconcrete is about 25% weaker than normal concrete, making its compressive strength significantly lower. There are also some organisms such as Pesudomonas aeruginosa that are effective in creating biocement but are unsafe to be near humans so these must be avoided.

Uses

Biocement is currently used in applications such as in sidewalks and pavements in buildings. There are ideas of biological building constructions as well. The uses of biocement are still not widespread because there is currently not a feasible method of mass producing biocement to such a high extent. There is also much more definitive testing that needs to be done to confidently use biocement in such large scale applications where mechanical strength can not be compromised. The cost of biocement is also twice as much as normal concrete. Different uses in smaller applications however include spray bars, hoses, drop lines, and bee nesting. Biocement is still in its developmental stages however its potential proves promising for its future uses.