This paper presents an investigation on the effect of ground granulated blast furnace slag on the geopolymerization of low reactive volcanic ash. Volcanic ash was blended up to 50 wt% with slag at 10% intervals. The fresh geopolymer samples were cured at 25 and 60 °C for 3, 7 and 28 days. XRD, FTIR, TG and SEM were used for phases analysis.The results outlined that only 10 wt% of slag was enough to reduce the initial setting time of the geopolymer from more than 7 days to couple of hours (6.7 hours). At 25 °C, the 28 days compressive strength increased with the addition of slag in the system until an optimum value of about 85 MPA. This strength development was suggested to arise from a synergetic formation of C-A-S-H /N-A-S-H gel. At 60 °C, curing for periods longer than 7 days was not beneficial for strength development. These results are of interest for the valorization of low reactive volcanic ashes in the development of structural geopolymers, with related environmental and socioeconomic benefits.

A kaolin deposit from Mankon (northwest Cameroon) was prospected and studied for potential applications in ceramics. Six samples were investigated with X-ray diffraction (XRD), infrared (IR) spectroscopy and scanning electron microscopy (SEM) to determine the mineralogical composition and with X-ray fluorescence (XRF) to determine the chemical composition and properties for ceramic applications. The main minerals in the clays are kaolinite/halloysite and anatase associated with alunite, illite, gibbsite and maghemite. The kaolin samples have abundant organic matter (4–10%) and low absorption of methylene blue (0.2–2.5 meq/100 g), while SiO2 (33.28–56.31%) and Al2O3 (19.26–35.87%) are major oxides. The particle-size distribution derived from sieving and the hydrometer method indicates that 12–38% of the samples are in the <2 μm clay fraction. The clays have low to moderate plasticity (7–21%). One sample with K-feldspar and plagioclase displays the necessary properties for red ceramic products. SEM confirmed the occurence of halloysite in sample M9. The high kaolinite/halloysite content (64–97%), associated with low Fe2O3 content (0.5–1.4%) demonstrates that five samples are suitable raw materials for white firing industrial kaolin.