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Fracking (also known as hydraulic fracturing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of bedrock formations by a pressurized liquid. The process involves the high-pressure injection of "fracking fluid" (primarily water, containing sand or other proppants suspended with the aid of thickening agents) into a wellbore to create cracks in the deep-rock formations through which natural gas, petroleum, and brine will flow more freely. When the hydraulic pressure is removed from the well, small grains of hydraulic fracturing proppants (either sand or aluminium oxide) hold the fractures open.[1]
matlab 2014a crack key 35
Most mineral vein systems are a result of repeated natural fracturing during periods of relatively high pore fluid pressure. The effect of high pore fluid pressure on the formation process of mineral vein systems is particularly evident in "crack-seal" veins, where the vein material is part of a series of discrete fracturing events, and extra vein material is deposited on each occasion.[37] One example of long-term repeated natural fracturing is in the effects of seismic activity. Stress levels rise and fall episodically, and earthquakes can cause large volumes of connate water to be expelled from fluid-filled fractures. This process is referred to as "seismic pumping".[38]
Minor intrusions in the upper part of the crust, such as dikes, propagate in the form of fluid-filled cracks. In such cases, the fluid is magma. In sedimentary rocks with a significant water content, fluid at fracture tip will be steam.[39]
Self-healing concrete can be illustrated as concrete, which has the capability of repairing itself back to the original state. It is a green technology that embeds self-activating bacteria into concrete and fixes its cracks. Since the material used for this technique can be grown in the laboratory, it does not pose a risk to natural resources. Hence, this method can be an effective technology for the improvement of the strength of concrete [9].
Bacterial impacts on the crack and self-healing treatment offer cleaner, more sustainable, longer-lasting material and reduce the cost of repairing the cracks in long term. By reducing absorption, permeability, and diffusion as the key mechanisms for carrying concrete, the durability of concrete can be increased [10]. Several studies have documented the effect of bio-based healing agents on the permeability and water absorption of concrete. Cracks in concrete structures can be reduced by the presence of bacteria as can be seen from previous literature as described later. Sarker et al. [11] used E. coli bacterial strain on concrete mix and suggested from the mortar test that it enhances concrete strength and the cement quantity can be reduced by using microbes without compromising the strength.
Safiuddin et al. [12] studied the effect of mixing Bacillus subtilis and Escherichia coli on the time required for crack the mitigation and mechanical properties of concrete by mixing them with a percentage by weight of cement. The result shows that 3% Bacillus subtilis is the optimum dosage for self-healing of concrete, whereas Escherichia coli mixed at the dose of 3% by weight of cement can increase the strength up to 60%.
The microbes serve as a nucleation site, assisting in the formation of calcite that can gradually seal cracks and pores throughout concrete, improving its durability. This microbiologically induced calcite precipitation (MICP) is the product of a complicated sequence of biological processes. This process leads to the formation of CaCO3 crystal form, which expands and develops as the bacteria produce calcium lactate nutrition. The crystal formation grows until the entire void is filled. Hence, this natural and biochemical method increases the sustainability of concrete.
Nevertheless, based on the past studies as summarized earlier, the current study presents the crushing of concrete with the results obtained from UPV and water absorption test including SEM analysis for E. coli microbial culture ratio mixed with water in comparison with normal water. In direct application method of bacteria, bacterial spores and calcium lactate are added into concrete directly when mixing of cement is completed. The utilization of these microorganisms and calcium lactate does not change the typical properties of cement. At the point when water interacts with these microscopic organisms, they develop and feed on calcium lactate and deliver limestone. Consequently, the cracks are fixed. But in the case of an encapsulation method, bacterial spores are added with encapsulated nutrients in a concrete matrix. Hence, direct application method is chosen for this study for its easiness in use.
This study uses Escherichia coli (E. coli) bacteria that feed on carbon dioxide instead of traditional feed like sugar and other organic matter. E. coli is a well-known bacterium which has many other uses in the real world like synthesizing useful chemicals such as insulin, creating synthetic forms of human growth hormone. This bacterium can intrude into concrete cracks and can remain dormant for many years even at high temperatures. It is a nontoxic bacterium that reproduces quickly by splitting method, according to research. Therefore, one of the advantages of this bacterium is its easy culture within a short time. Plain water with a pH value of 7 and zero turbidity was used for the study. Sylhet sand with an absorption capacity of 2.78% and specific gravity of 2.51 is used as fine aggregates, whereas locally available stones with a specific gravity of 2.74 and absorption capacity of 2.33% are used as coarse aggregates. 2ff7e9595c