C.Y. Heah

Kaolin-based geopolymers with various NaOH concentrations

Kaolin geopolymers were produced by the alkali-activation of kaolin with an activator solution (a mixture of NaOH and sodium silicate solutions). The NaOH solution was prepared at a concentration of 6–14 mol/L and was mixed with the sodium silicate solution at a Na2SiO3/NaOH mass ratio of 0.24 to prepare an activator solution. The kaolin-to-activator solution mass ratio used was 0.80. This paper aimed to analyze the effect of NaOH concentration on the compressive strength of kaolin geopolymers at 80°C for 1, 2, and 3 d. Kaolin geopolymers were stable in water, and strength results showed that the kaolin binder had adequate compressive strength with 12 mol/L of NaOH concentration. When the NaOH concentration increased, the SiO2/Na2O decreased. The increased Na2O content enhanced the dissolution of kaolin as shown in X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. However, excess in this content was not beneficial for the strength development of kaolin geopolymers. In addition, there was the formation of more geopolymeric gel in 12 mol/L samples. The XRD pattern of the samples showed a higher amorphous content and a more geopolymer bonding existed as proved by FTIR analysis.

Influence of Solidification Process on Calcined Kaolin Geopolymeric Powder

This paper aims at investigating the influence of solidification condition on the processing of calcined kaolin geopolymeric powder. This is a new process developed using the geopolymerization process. Geopolymer slurry was prepared from calcined kaolin and activating solution (mixture of NaOH and Na2SiO3). This slurry was allowed to solidify in oven and then crushed and grounded to fixed particle size. Compressive testing and SEM analysis were performed in this study. The results showed that the solidification condition at 80 °C for 4 hours was the best to synthesize the geopolymeric powder where this solidification condition results in geopolymeric powder which can produce higher strength resulted geopolymer paste. The microstructure showed more intervening gel phase which indicates that the geopolymerization process continued to react after the addition of water to the calcined kaolin geopolymeric powder.

Curing Behavior on kaolin-based geopolymers

This paper aims at investigating the influence of curing process on kaolin-based geopolymers. Kaolin-based geopolymers were prepared by the alkali-activation of kaolin with alkali activating solution (mixture of NaOH and Na2SiO3 solutions). The compressive testing, XRD and FTIR analysis were performed. The compressive strength results showed that curing at 60°C for 3 day achieves better strength. XRD analysis revealed that the entire geopolymer sample reduced in intensities and became amorphous at longer age while FTIR analysis indicated the presence of geopolymer bondings. Both analyses showed the presence of large amount of un-reacted remained in the system were the reason of the low compressive strength obtained.

Strength and Microstructural Properties of Mechanically-Activated Kaolin Geopolymers

Kaolin geopolymers exhibit low strength properties due to its plate-like nature which contribute to smaller surface area for geopolymerization reactions. Layered kaolin structure only allows very little, if any, substitution of other elements. Therefore, mechanical activation is an alternative way to break the kaolin structure to become finer to change the morphological features to smoother surface, and to cause edge distortion to the kaolin particles. Rounded particles also can be produced using this technique. This mechanically-activated kaolin was used to produce mechanically-activated kaolin geopolymers in this study. From the results, compressive strength increased as mechanical activation time increased and the compressive strength increased with the ageing day. The SEM micrograph showed that the mechanically-activated kaolin geopolymers have denser structure which complies with the compressive strength measured.

Chemical composition and strength of dolomite geopolymer composites

The chemical composition of dolomite and the compressive strength of dolomite geopolymer composites were studied. The both composites prepared with mechanical mixer manufactured by with rotor speed of 350 rpm and curing in the oven for 24 hours at 80˚C. XRF analysis showThe dolomite raw materials contain fewer amounts of Si and Al but high Ca in its composition. Dolomite geopolymer composites with 20M of NaOH shows greater and optimum compressive strength compared to dolomite geopolymer with other NaOH molarity. This indicated better interaction of dolomite raw material and alkaline activator need high molarity of NaOH in order to increase the reactivity of dolomite.

Effect of Poly(Methyl Methacrylate) (PMMA) on Tensile Properties and Spectroscopy Infrared (FTIR) Characteristics of LDPE/WHF Composites

In this work, the effect of PMMA in low density polyethylene/water hyacinth fibers composites were prepared and characterized in terms of tensile properties and FTIR characteristics. Water hyacinth fibers (WHF) were incorporated into the LDPE matrix with different fiber loading. LDPE/WHF and LDPE/WHFPMMA composites were prepared with Z-blade mixer at 180 °C with rotor speed of 50 rpm. The PMMA modified WHF increased the tensile strength and Young’s modulus while reduced the elongation at break of LDPE/WHFPMMA composites in comparison with LDPE/WHF composites. The absorption peak at 1736.28 cm-1 indicated the presence of ester carbonyl group (C=O) in LDPE/WHFPMMA composites.

Effect of curing regimes on metakaolin geopolymer pastes produced from geopolymer powder

The properties of metakaolin geopolymer paste are affected by the alkali concentration, the initial raw materials, solidification process, and amount of mixing water as well as the curing conditions. This study aimed to investigate the effect of curing temperature (room temperature, 40°C, 60°C, 80°C and 100°C) and curing time (6h, 12h, 24h, 48h and 72h) on the geopolymer pastes produced from geopolymer powder. The results showed that curing at room temperature was unfeasible. Heat was required for the geopolymerization process, where strength increased as the curing temperature was increased. Moderate elevated curing temperature favored the strength development of geopolymer pastes in comparison with those treated with extreme elevated curing temperature. When geopolymer paste was subjected to extreme elevated curing temperature, shorter curing time should be used to avoid deterioration in strength gain. Similarly, longer curing time was recommended for moderate elevated curing temperature. The microstructure of geopolymer paste cured at moderate curing temperature showed obvious densification of structure. In contrast, the structure formed was weak and less compact at very high elevated curing temperature.