The apparatus set-up consisted of two polymethylemethacrylate (PMMA)
blocks 600 200 to which a recess that accommodated a concrete core 100 mm in
diameter. Brass shims 0.0200 thick to which a 20 mesh brass screen was soldered
were placed inside the recess. Reservoirs for sodium chloride and sodium hydroxide
solutions were drilled in each PMMA block. A brass wire was connected from the
shims to a terminal and a voltmeter attached to a 60 V power supply by a banana
clip. The concrete core was placed in between the two blocks with the unsealed
concrete surfaces touching the brass mesh held in place by the brass shims. One
side of the cell was filled with 3% sodium chloride solution and was connected to
the negative terminal of the power supply while the other side of the cell was filled
with 0.3 N sodium hydroxide solution and connected with the positive terminal of
the power supply. The power supply was set at a constant 60 V supplied to the electrolyte,
and the initial reading was recorded. The current passing through the cell
was recorded every 15 min for 6 h. The voltage was monitored to check that the
power supply was working properly. Temperature was also monitored in case of
overheating of the solutions. The final result was obtained from the area under
the graph of current (in amperes) against time (in seconds) using the following
formula:
Charge passedðCoulombÞ ¼ CurrentðamperesÞ TimeðsecondsÞ: