The TCLP test is the method prescribed by the US EPA guidelines to
determine if the solid waste is hazardous (Townsend, 1998). The TCLP
tests were assessed on 100% RAP, RAP + 20%FA blend, and
RAP + 20%FA geopolymer at the NaOH/Na2SiO3 ratios of 100:0 and
50:50 for different types of heavy metal. Napia et al. (2012) studied
the leaching of heavy metals from solidified waste and indicated that
the leachability reduced when sample age increased. Thus, in this
study the early 7 days cured samples were crushed to smaller particles
of b9.5 mm for the leachate tests. The crushed sample was extracted
using an acetic acid solution (pH=4) in a volumewith a solid to liquid
ratio of 1:20. The mixturewas agitated for 18 h in the extraction vessels,
whichwere rotated in an end-over-end manner at 30 rpm. The leachate
was then filtered through a 0.45-μm membrane filter to remove
suspended solids and divided into two portions. One portion was used
for a pH measurement, and the other was used for the determination
of the metals present in the leachate by Inductively Coupled Plasma –
Optical Emission Spectrometry (ICP-OES). The average values from
each extraction were obtained by testing in triplicate samples to ensure
the data consistency (Asavapisit et al., 2005).