After 7 days curing, two cylindrical samples with 100 mm in
diameter and 100 mm in height were coated with epoxy resin
around the cylindrical surface to allow chloride ion to diffuse into
sample in one direction. After that, they were immersed in 3% NaCl
solution. The GC samples ware then splitted and spayed with 0.1 N
AgNO3 solution. The white color of AgCl indicated the chloride
penetration depth (Otsuki et al., 1993). These depths were
measured and the reported results were the average of 10 measurements
of two samples.