2.4. Testing of specimens
Setting times of geopolymer pastes were tested in accordance
with ASTM C191-08 [33]. The test was conducted at a temperature
of 21–23 C. The paste was prepared by mixing the binders and the
alkaline solutions manually in a bowl and tested for setting time
using a Vicat apparatus.
The workability of fresh geopolymer concrete mixtures was
tested by slump test [34]. Flow of fresh geopolymer mortars was
measured in accordance with ASTM C1437-07 [35]. Slump and
flow tests were conducted immediately after mixing.
Compressive strength test was conducted at 3, 7, 28, 56 and
90 days. Cylinder specimens of concrete and cube specimens of
mortar were tested at a loading rate of 0.33 MPa/s with a Controls
MCC8 machine.
To observe the microstructure of the geopolymer products a
scanning electron microscope (SEM) (Zeiss EVO 40XVP) was utilised.
Elemental composition was observed with energy dispersive
X-ray spectrometer (EDX, Oxford Instruments) fitted with SEM.
The sample was cast and stored in a controlled temperature of
20–23 C and relative humidity 65 ± 10%. After 28 days, the sectioned
surface of the geopolymer paste specimen was carboncoated
prior to microstructural imaging.
For XRD analysis, randomly oriented powder specimens were
prepared by grinding small portions of the dried specimens in a
ring mill for 30 s (dry milling) and then packed into a sample
holder. XRD patterns from the samples were measured using a Bruker-
AXS D8 Advance Diffractometer with copper radiation and a
LynxEye position sensitive detector. The data were collected for
2h values of 7–90 with a nominal step size of 0.015 and a collection
time of 0.7 s per step.