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Tchakoute H.K.,University of Yaounde I | Tchakoute H.K.,Leibniz University of Hanover | Ruscher C.H.,Leibniz University of Hanover | Kong S.,University of Yaounde I | And 3 more authors.
Journal of Sol-Gel Science and Technology | Year: 2016

Abstract: Three sodium waterglass (NWG) such as commercial NWG (S1), NWG from pure rice husk ash (S2) and NWG from raw rice husk ash (S3) were applied for producing geopolymer cements using metakaolin (MK) as aluminosilicate source. Geopolymers (Geo1, Geo2 and Geo3) were prepared using each NWG with the molar ratios SiO2/Na2O and H2O/Na2O kept constant at 1.5 and 12, respectively. It could be observed that the water absorption of Geo1, Geo2 and Geo3 is 7, 9 and 13.2 % and the mass loss is 15.8, 14.7 and 12.4 %, respectively. Their compressive strength at 20 days (37.5/34.3/29.6 MPa) and 28 days (43.3/40.3/33.2 MPa) increases with increasing the aging and decreases in the course Geo1/Geo2/Geo3. Their average pore radius (6/8/20 nm) and cumulative pore volumes (155/205/245 mm3/g) increase in the course Geo1/Geo2/Geo3. It is discussed that the presence of phosphate known as corrosion inhibitors in raw rice husk ash hinders the dissolution of SiO2. It entails the formation of NaH2PO4 in S3 which reduces the soluble Si atoms. Therefore, less amount of metakaolin could be dissolved leaving thus a higher amount of unreacted metakaolin particles in Geo3. The reacted volumes and compositions of the geopolymers are different in the three cases, too. A content of approximately 20, 25 and 35 % of unreacted metakaolin was proved for Geo1, Geo2 and Geo3, respectively. Graphical Abstract: [Figure not available: see fulltext.] © 2016 Springer Science+Business Media New York Source


Tchakoute H.K.,University of Yaounde I | Tchakoute H.K.,Leibniz University of Hanover | Ruscher C.H.,Leibniz University of Hanover | Kong S.,University of Yaounde I | And 3 more authors.
Construction and Building Materials | Year: 2016

Rice husk and waste glass from sources in Cameroon were used for producing sodium waterglass (NWG) solution denoted S1 and S2 respectively as alternative activators to prepare metakaolin-based geopolymer binder. Metakaolin-based geopolymer binders (G1, G2) were obtained using freshly prepared NWG with a mass ratio NWG/MK = 0.83. The IR spectra of S1, S2 using ATR and KBr methods show the presence of SiQ0, SiQ1, SiQ2 units, and S1 contained also SiQ3 and SiQ4 units. The mechanical testing, environmental scanning electron microscopy, mercury intrusion porosimetry, X-ray diffractometry, infrared spectroscopy, amount of binders and thermogravimetric analysis are investigated to study the properties of the geopolymer binders. The results show that the compressive strength values of geopolymer G2 (22.9, 27.6, 32.6, 36 and 39.7 MPa) are higher than that of G1 (17.7, 19.1, 21.2, 29.9 and 32.8 MPa) at 7, 14, 21, 28 and 56 days respectively. The microstructure of G2 is more compact with fewer unreacted metakaolin particles. It can be concluded that sodium waterglass from waste glass and rice husk ash are suitable alternative activators for the production of metakaolin-based geopolymers. In addition, they constitute a better ecological choice when compared to commercial sodium silicate from melting process. © 2016 Elsevier Ltd. All rights reserved. Source


Ndjigui P.-D.,University of Yaounde I | Mbey J.A.,University of Yaounde I | Nzeukou A.N.,Local Materials Promotion Authority
Journal of Building Engineering | Year: 2016

Four clay samples (Nt12, Nt11, Ab12 and Ab11) from the Ngog-Lituba alluvial deposits (Southern Cameroon) were investigated for their possible ceramic applications. X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal and physico-mechanical analyses were used to assess the phase evolution and microstructure of the specimens fired between 850 and 1250 °C. The red color of the products at 850-1050 °C and the dark red at 1150-1250 °C are ascribed to the hematite formation and the disappearance of the organic matter. Mullite and glassy phase increase the mechanical strength and reduce the water absorption. Nt12 sample has the highest flexural strength and is suggested for porcelainized stoneware due to its low water absorption (0.51 vol%) around 1250 °C. According to the European Norm EN176, Ab11 and Ab12 samples (with respective water absorption of 1.32 and 2.38 vol%) are promising for the production of red-stoneware products, meanwhile Nt11, with water absorption of 4.48 wt%, is suitable for single fired bodies (earthenware). © 2015 Elsevier Ltd. All rights reserved. Source


Ndjigui P.-D.,University of Yaounde I | Ebah Abeng S.A.,University of Yaounde I | Ekomane E.,University of Yaounde I | Nzeukou A.N.,Local Materials Promotion Authority | And 2 more authors.
Journal of African Earth Sciences | Year: 2015

Mineralogical and geochemical investigations have been done on the hydromorphic clays (pseudogley soils and recent alluvial clastic sediments) in the Sanaga Maritime region (Southern Cameroon). Pseudogley soils are developed on gneisses from the Yaoundé Group. They have a dark brown to greyish brown color, with silty clay texture. Their mineral assemblage is made up of kaolinite, goethite, quartz, smectite, rutile, muscovite-illite and feldspars. The alluvial clastic sediments are characterized by variable colors (purple yellow, greenish, dark brown and purple brown) and sandy clay to clay texture. The mineral assemblage of alluvial clays is similar to that of pseudogley soils. SEM observations confirm the presence of kaolinite, smectite, quartz and muscovite-illite. Infrared data show that kaolinite is more orderly in pseudogley than in the alluvial clastic sediments. The Ngog-Lituba gneisses have moderate contents in SiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O and several trace elements including REE. High element depletion is noticed in the pseudogley soils except Cr, V, Zr, Pb and REE. However, the alluvial clays are marked by a strong mobilization of LILE (Na, K, Ba, Rb and Sr) and REE, relative to the parent rock and pseudogley soils. The chondrite-normalized REE patterns are homogenous and parallel with Ce-anomalies. The (La/Yb)N shows that the REE fractionation increase from the parent rock to the alluvial clastic sediments. The mineralogical and geochemical features show that the clastic river sediments are derived from the erosion of the neighboring pseudogley materials before hydraulic sorting. © 2015 Elsevier Ltd. Source


Obonyo E.A.,University of Florida | Kamseu E.,Local Materials Promotion Authority | Kamseu E.,University of Modena and Reggio Emilia | Lemougna P.N.,Local Materials Promotion Authority | And 3 more authors.
Sustainability (Switzerland) | Year: 2014

Two iron-rich clayey materials (L1 and L2, with the main difference being the level of iron accumulation) have been studied for their suitability as solid precursors for inorganic polymer composites. L1, with the lower iron content, was calcined at 700°C for 4 h and used as replacement, in the range of 15-35 wt%, for both raw laterites in the formulations of geopolymeric composites. The different mixtures were activated with a highly concentrated alkaline solution containing sodium hydroxide and sodium silicate. River sand with semi-crystalline structure was added to form semi-dry pastes which were pressed to appropriate shape. X-ray diffraction, Infrared spectroscopy, Scanning Electron Microscopy and Mercury Intrusion Porosimetry results demonstrated the effectiveness of the calcined fraction of L1 to act as nucleation sites and extend the geopolymerization to the matrix composites. A highly compact matrix with low porosity and good stability in water, together with a strength comparable to that of standard concretes was obtained allowing for conclusions to be made on the quality of laterites as promising solid precursor for sustainable, environmentally-friendly, and cost-efficient structural materials. © 2014 by the authors. Source

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