# Durability of Mortars with Partial Cement Replacement by Recycled Brick Powder
## 2 Experimental Plan
### Methods
The specimens were laterally sealed with epoxy paint and vacuum-saturated with calcium hydroxide before being placed in a test cell, ensuring that one exposed face was in contact with a 2-molar chloride solution, while the other face was in contact with a 0.3-molar sodium hydroxide solution. Chloride diffusion through the specimen was accelerated by applying a potential difference, with its value and duration defined by the standard based on an initial calibration measurement. At the end of the test, the specimens were split by indirect tensile failure, and their internal faces were sprayed with a 0.1 N silver nitrate solution. This colouration technique allowed for the determination of the chloride penetration depth (x\({}_{d}\)) in millimetres and the calculation of the chloride migration diffusion coefficient (D\({}_{\text{nssm}}\), \(\times 10^{-12}\) m\({}^{2}\)/s) according to the equation specified in the test standard (Equation (3)) [80]. This equation also considers the applied voltage (U, in volts), the test duration (t, in hours), the average test temperature (T, in Celsius), and the specimen thickness (L, in mm). For all the mortar samples tested, cylindrical specimens with a thickness of 50 mm were employed. A constant potential difference of 30 V was applied throughout the test, which was conducted over a period of 24 h. The temperature in the testing room was maintained at a constant level of 23 \(\pm\) 2 \({}^{\circ}\)C to ensure consistency in the test conditions. As previously mentioned, the average depth of chloride penetration for each specimen was determined at the end of the test using a colorimetric method with silver nitrate (0.1 N), which allowed for a clear visual demarcation of the chloride penetration depth. \[D_{nssm}=\frac{0.0239\cdot(273\ +\ T)\cdot L}{(U-2)\cdot t}\cdot\left(x_{d}-0.02 38\cdot\sqrt{\frac{(273\ +\ T)\cdot L\cdot x_{d}}{U-2}}\right) \tag{3}\]
* Electrical resistivity Lastly, electrical resistivity was studied as it reflects the material's ability to transport electric charges, which is crucial for the ohmic control of reinforcement corrosion processes, one of the primary causes of durability loss in reinforced concrete structures [81]. To determine this parameter, the procedure outlined in European Standard UNE-EN 12390-19:2023 was followed [82]. The test was conducted on three 40 \(\times\) 40 \(\times\) 160 mm prismatic specimens, which, at 90 days of age, were vacuum-saturated with demineralised water. After 24 h under these conditions, the specimens were removed from the solution and surface-dried. Using a conductivity metre (Crison GLP 32), the electrical conductivity of the material was measured, which is the inverse of its electrical resistance. The measurement was recorded for three minutes until a stable signal was achieved, and this final value was considered for each specimen. At the end of the test, each specimen was re-immersed to maintain saturation conditions, and weekly measurements were taken over one month to monitor the evolution of this property. The result of each test and mix was expressed as the arithmetic mean of the recorded values. * Electrical conductivity and pH  
One method for assessing the pozzolanic reactivity of recycled brick powder (RBP) is to measure the electrical conductivity and pH of lime-pozzolan aqueous suspensions over a seven-day period [83]. When lime is introduced into water, Ca(OH)\({}_{2}\) dissociates into Ca\({}^{2+}\) and OH\({}^{-}\) ions. The addition of a siliceous material to a saturated lime suspension can lead to system undersaturation. If the silica in RBP can react with the ions in the solution, insoluble reaction products will form and precipitate. Consequently, as the ion concentration decreases, the electrical conductivity will also decrease. Similarly, a reduction in OH\({}^{-}\) concentration will result in a lower pH.