Meta-halloysite to improve compactness in iron-rich laterite-based alkali activated materials

In this paper, the results of the experimental investigation were used to understand the effect of fine meta-halloysite on the reactivity, mechanical and microstructural properties of laterite-based geopolymers. Laterite was replaced by 0, 20, 30 and 50 wt% of meta-halloysite in order to improve the physico-chemical performance. Meta-halloysite was prepared by calcination of natural halloysite at 600 °C. The moduli (molar ratio SiO2/Na2O) of the activating solutions were 1.04, 0.92, and 0.75 with H2O/Na2O = 9.78, 10.45 and 12.04, respectively. The results indicated that calcined laterite has a high specific surface area (43.00 ± 0.12 m2/g), notwithstanding a high average particle size (d50 = 45.20 μm) compared to meta-halloysite with a smaller average particle size (d50 = 8.40 μm) and a specific surface (29.80 ± 0.16 m2/g). The compressive strength of geopolymers increased upon the addition of meta-halloysite from 12 MPa to 45 MPa at 28 days. While the setting time and water absorption decrease with increase in the of meta-halloysite content as well as with increase in Si/Al, Si/Fe, Al/Fe and Na/Al molar ratios used in the synthesis of geopolymers. The use of fine meta-halloysite resulted in better efficiency and improved mechanical performance of synthesized products

Mechanical Performance, Phase Evolution and Microstructure of Natural Feldspathic Solid Solutions Consolidated Via Alkali Activation: Effect of NaOH Concentration

Five different alkali activators were prepared by mixing sodium hydroxide with molar concentrations of 8, 10, 12, 14 and 16 M and sodium silicate, Na2SiO3 in volume ratio 1:1. The obtained alkaline activators were used for producing metakaolin/feldspathic rock-based geopolymer composites. These geopolymer composites were obtained by mixing different solid precursors of natural solid solutions (trachyte, pegmatite and granite) in the range of 70 to 85 wt% with metakaolin and adding each alkaline solution at a liquid/solid mass ratio of 0.37. The pastes were cured at room temperature for 28 days before testing. The influence of NaOH concentration on structural modifications was investigated using Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD). Water absorption for open porosity, Environment Scanning Electron Microscope (ESEM) and compression tests were adopted to observe the morphology and mechanical properties. The results indicate that the NaOH concentration of 12 M was optimum for solid solution of trachyte with 98–106 MPa due to content of higher amorphous phases compared to solid solutions of pegmatite (94–105 MPa) or granite (101–108 MPa) where the better results were achieved at 10 M