| dc.description.abstract | Geopolymerization process utilizing kaolin as aluminosilicate source was performed.
The goal of this study was to investigate the effect of NaOH concentration, S/L ratio,
Na2SiO3/NaOH ratio, curing temperature and time as well as mechanical treatment of
kaolin on kaolin geopolymers. The results showed that 8M of NaOH concentration, S/L
ratio of 1.00, Na2SiO3/NaOH ratio of 0.32 and curing conditions at 60°C for 72 hours
were the optimum mixing conditions for kaolin geopolymers synthesis. In order to
increase the reactivity of kaolin towards geopolymerization reaction, mechanical
treatment of kaolin was conducted through milling process. The optimum milling time
of kaolin was 5 hours. Mechanical treatment of kaolin has successfully decreased the
particle size and increased the surface area of kaolin particles, producing mechanicaltreated
kaolin geopolymers with better compressive strength (9.58 MPa) compared to
kaolin geopolymer synthesized with untreated kaolin (5.94 MPa). Bulk density
measurement showed that kaolin geopolymers were lightweight (< 1870 kg/m3). During
the geopolymers synthesis, workability must be taking into consideration since it
affected significantly the strength development of kaolin geopolymers. Microstructural
analysis (SEM) revealed that kaolin geopolymers only undergo low dissolution as
shown by the presence of large amounts of unreacted kaolin particles in the
microstructure of kaolin geopolymers. However, the formation of homogeneous
geopolymer gel was observed at longer day of testing. Besides, elemental composition
analysis (EDX) results supports the continuous development of geopolymer structure as
indicated by the increased Na/Al and Si/Al ratios by the day of testing. Zeolites peaks
appeared in kaolin geopolymers after the geopolymerization reaction as determined by
phase analysis (XRD). The amorphous geopolymer and crystalline zeolite phases
contributed to the strength of geopolymers. Even so, these crystalline zeolites peaks
gradually decreased in intensity at longer day of testing and were found degraded the
compressive strength of geopolymers. Functional group identification (FTIR) shows the
formation of more geopolymer bonding in kaolin geopolymers at longer testing day. On
the other hand, based on compressive strength results, the optimum oxide molar ratios
of SiO2/Al2O3, Na2O/SiO2, H2O/Na2O and Na2O/Al2O3 for kaolin geopolymers
synthesis were concluded at 3.28, 0.28, 14.61 and 0.92, respectively. In general, kaolin
has low reactivity and it required more time for dissolution in alkaline activator solution
and hence the formation of geopolymer structure. The slow rate of geopolymerization
reaction led to a slow strength development of geopolymers. As a conclusion, this study
provides a better understanding of the properties (compressive strength, workability and
bulk density) and characteristic (microstructure, phases and functional groups) of kaolin
geopolymers. Thus, for future research, it is suggested to increase the reactivity of
kaolin towards geopolymerization reaction in order to improve the mechanical strength. | en_US |
