# Bio-Influenced Self-Healing Mechanism in Concrete and Its Testing: A Review
## 3 Results and Discussion
### Scale Level: Macro, Micro and Nano  
In order to establish the efficiency of the bacteria to repair the crack in hardened concrete, structure tests can be carried out at macro, micro and nano scale levels. These include the following tests: Macrostructure; microstructure; nanostructure. The self-healing efficiency of the bacteria in concrete can be evaluated based on the following tests and standard methods, as presented in Table 1.  
The macroscopic scale (\(10^{0}\)) is the length scale on which objects or phenomena are large enough to be visible with the naked eye without optical magnifying instruments [29]. The microscopic scale (\(10^{-6}\)) is the scale of an objects smaller than those that can be seen by the naked eye which would require the use of a microscope to view them clearly. The nanoscale (\(10^{-9}\)) refers to the scale length of an object with a range of 1-100 nanometers [30].  
The macrostructure test is a procedure wherein the material is evaluated macro-structurally for the quality and consistency of the properties using low or no magnification. The properties under this test are as follows: mechanical and permeability. For the mechanical tests, it includes the following: compressive; flexural; split tensile; ultrasonic pulse velocity; stiffness and toughness tests--while, for permeability, it includes the following: water permeability; chloride penetration; sorptivity; gas permeability tests.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Scale Level** & **Test** & **Standard Methods** \\ \hline \multirow{4}{*}{Macro} & Mechanical Properties(Flexural, Compressive, Split & ASTM C39, C1585-13, ASTM \\  & Tensile, Stiffness and Ultrasonic Pulse Velocity Test) & C1202, RILEM 25 PEM (II-6), \\  & and Permeability (Chloride Penetration/Permeability, & JSCE-G571-2003, RILEM \\  & Porosity, Gas Permeability) & CEMBUREU \\ \hline Micro & SEM, FESEM, XRD, EDS & ASTM E986-97, D3906-03, E1508 \\ \hline Nano & Nano-structure measurement & ASTM E2546-07 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Macro, Micro and Nano Structure Tests.  
Figure 5: Topic mixtures generated through MATLAB.  
A microstructure test is a procedure wherein the material is examined through the aid of a microscope or any instruments capable of revealing the morphology and fine structure of a material. It includes the following tests: X-ray diffraction (XRD); Scanning Electron Microscope (SEM); Energy dispersive spectroscopy (EDS); Field Emission Scanning Electron Microscope (FESEM).  
The third scale level is the nanostructure test. For this test, properties are evaluated at the nano-scale, which can provide an insight into the behavior of the individual atoms present in the material. This requires powerful scientific instruments that can capture the nanostructure of a material, which is smaller than a micron and larger that an atom.  
Concrete is a very complex multiscale material whose behavior at the engineering scale is strongly influenced by the heterogeneous character of its internal material structure [31]. Thus, a multiscale approach is necessary in order to establish the significant role of a bacteria with respect to the cracks in concrete. Multiscale modeling (MM) is defined as the field of solving physical problems that have important features at multiple scales, particularly multiple spatial or temporal scales [32]. According to [PERSON] et al. [33], there are generally two categories of multiscale modeling strategies or approaches. For the concurrent multiscale method, a combined model is established by linking the several computational methods together [34]. For the sequential multiscale method, a series of hierarchical computational methods are linked in some methods, such as the homogenization method [35].