# The Efficiency of Calcium Oxide on Microbial Self-Healing Activity in Alkali-Activated Slag (AAS)
## 2 Experimental Program
### The Assessment Technique
#### 2.3.2 Durability Property Testing  
The durability properties, including water absorption, porosity, chloride attack resistance, and surface electrical resistivity, were evaluated to check the effectiveness of bacteria in precipitating calcite crystals in the AAS specimens' pores. Specimens adopted for durability testing are cylindrical discs of 100 mm diameter and 50 mm thickness. Water absorption and porosity tests were performed according to ASTM C-642 [33]. All observations were taken in triplicate.  
To assess the AAS mixtures, the Rapid Chloride Permeability Test (RCPT) was carried out on 28-day-old specimens following the specifications of ASTM C1202 [34] and AASHTO T277 [35]. The first specimens were placed in a vacuum desiccator. The vacuum pump was operated until the pressure reached less than 6650 Pa and was maintained for 3 h. After that, the funnel was filled with de-aerated water. Specimens were preserved underwater in an RCPT cell (without allowing air access) for 182 h. The rapid chloride permeability test started by applying a potential of 60 V across a circular disc of 100 mm diameter \(\times\) 50 mm depth. The edges of all specimens were epoxy-coated. One end of the sample was immersed in sodium chloride (3% NaCl). The other side was placed in sodium. hydroxide (0.3 M). A direct current was applied across the two sides, as highlighted in Figure 3a. The current passing through the specimen was recorded at a time interval of one minute for six hours, and the total charge in Coulombs was automatically computed. Based on the total charges passed, the chloride resistance was classified.  
Surface electrical resistivity was determined by applying the four probe Wenner electrodes, as shown in Figure 3b. The electrical resistivity test was adopted by using the nondestructive \"respond concrete resistivity meter\". The Wenner electrodes were localized in an equal-spaced straight line. The external electrodes emitted an alternating current (AC) into the specimen, while the inner ones determined the electric potential produced. The specimens should have a 100% saturated surface and be dry during the testing for reliable electrical resistivity measurements. The resistivity was determined in kiloMs-centimeters (k\(\Omega\)-cm). As per AASHTO T358-15 [36], the surface resistivity could give a good indication of chloride ion penetration. Three cylindrical specimens with a 100 mm diameter and 200 mm length for each mix are recommended by AASTO T358-15 [36].  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Mix ID** & **Slag** & **NaOH** & **Na2 SiO3** & **H2O** & **Na2O\%** & **Ms** & **L/B** & **Bacteria** & **CaO** \\  & **kg/m3** & **kg/m3** & **kg/m3** & **kg/m3** & **Ratio** & **Ratio** & **Cells/mL** & **kg/m3** \\ \hline C & 387.40 & 60.45 & 82.81 & 81.61 & 8\% & 0.8 & 0.38 & - & - \\ C5 & 387.40 & 60.45 & 82.81 & 81.61 & 8\% & 0.8 & 0.38 & \(10^{5}\) & - \\ Ca-5 & 359.60 & 60.45 & 82.81 & 81.61 & 8\% & 0.8 & 0.38 & \(10^{5}\) & 27.80 (7\%) \\ \hline \hline \end{tabular}
\end{table}
Table 5: AAS mixes proportions.