I want some powerpoints about biological concrete.

ppt presentation on bio concrete

Bio-Concrete A Promising Technology of Future

Cracks in 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. Concrete structures usually show some self-healing capacity, i.e. the ability to heal or seal freshly formed micro-cracks. This property is mainly due to the presence of non-hydrated excess cement particles in the materials matrix, which undergo delayed or secondary hydration upon reaction with water. Scientists have developed a new type of self-healing concrete in which bacteria mediate the production of minerals which rapidly seal freshly formed cracks, a process that concomitantly decreases concrete permeability, and thus better protects embedded steel reinforcement from corrosion. 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 negatively charged, 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. It was found that use of bacteria improves the stiffness and compressive strength of concrete. Initial results show that the addition of specific organic mineral precursor compounds plus spore-forming alkaliphilic bacteria as self-healing agents produces up to 100-µm sized calcite particles which can potentially seal micro- to even larger-sized cracks.Further development of this bio-concrete with significantly increased self-healing capacities could represent a new type of durable cement.

Crack-penetrating water would not only dissolve calcite (CaCO3) particles present in the mortar matrix, but would also react together with atmospheric carbon-dioxide and also with not fully hydrated lime constituents such as calcium oxide and calcium hydroxide. Although concrete with a high self-healing (crack healing) potential is wanted, the addition of healing agents such as bacteria and/or (organic) chemical compounds to the paste may result in unwanted decrease of strength properties. A 10% compressive strength loss due to incorporation of bacteria (B. pseudofirmus) was observed. However, such a loss in strength may be acceptable when this is compensated for by a substantial increase in the materials self (crack)-healing capacity. A lowered permeability due to healing of cracks would result in a decreased ingress rate of aggressive chemicals, which could lead to premature matrix degradation or corrosion of embedded steel reinforcement. Self-healing with the aid of incorporated bacteria could thus result in a better healing (sealing of larger cracks) compared to healing of non-amended pastes. The capacity of this autogenous chemical self-healing mechanism is directly related to the amount of non- (fully) hydrated cement particles present in the material matrix. The crack width that can be self-healed in such high strength concrete appears to be limited.

From an economical and environmental point of view, however, such a cement particle-based chemical self-healing system is not preferred due to the high costs of cement andthe high amount of CO2 that is released during its production. A two-component self-healing system based on bacterial mineral production as proposed in the study would for the latter two reasons be preferential, and moreover, the size of bacterially produced minerals suggests that larger cracks could potentially be healed. The mechanism of bacterially induced self-healing is based on the metabolic conversion of suitable organic compounds to calcite, e.g. represented by the bio-conversion of calcium-formate with portlandite present in the paste matrix.

In several studies, bacteria were also applied for durability improvement or concrete repair. In conclusion we can state that the investigated bacterially based two-component system seems a promising- and definitely more sustainable, alternative to high strength pastes which are characterized by high cement content. However, the self-healing capacity (crack-sealing and concomitant permeability reduction) remains to be quantified in future studies.