Uphie C. Melo

Uphie C. Melo
Local Materials Promotion Authority of Cameroon

PhD Engineering Metallurgy

About

92
Publications
36,503
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2,640
Citations
Citations since 2017
28 Research Items
2143 Citations
20172018201920202021202220230100200300400500
20172018201920202021202220230100200300400500
20172018201920202021202220230100200300400500
20172018201920202021202220230100200300400500

Publications

Publications (92)
Article
Full-text available
In the present study, the performances of the end products prepared using calcined iron-rich laterite at 600 °C (LAT600) with different alkaline solution (AS) to calcined laterite (AS/LAT600) mass ratio (0.45-0.65) were investigated. The effect of AS/LAT600 mass ratio on microstructural and mechanical properties of consolidated geopolymer samples,...
Article
Laterite soils are one of the promising aluminosilicate materials that can be utilized as precursors in the synthesis of geopolymers. However, it is critical to understand how the composition of the laterites and the type of activator influence the corresponding performance of geopolymer composites. Hence, this study was undertaken to evaluate the...
Article
Full-text available
The present study deals with the use of locally prepared rice husk ash (RHA)-based sodium silicate for alkaline activation of laterites (uncalcined (LNW) and calcined (LCA)). RHA-based activator (SSR) was prepared by adding as-collected RHA to 6 M NaOH at a solid/liquid mass ratio of 0.56. The various proportions of metakaolin (MK) and basalt powde...
Article
Concrete structures built in granite-based aggregate develop and proliferate contour-like cracks as they aged. Such cracks are often associated to alkali-aggregate reactions (AAR). Though, in most cases, the alkali-silica reaction (ASR) involving these aggregates has shown to be non-destructive to concretes, their contents of iron-contained mineral...
Article
Full-text available
The type of aluminosilicate precursor used in the synthesis of geopolymer binders plays a huge role in the resulting performance. Thus, it is critical to understand the properties of precursors and how they influence the corresponding performance of geopolymer binders. In this study, metakaolin and meta halloysite are used as the aluminosilicate pr...
Article
An experimental investigation was carried out to investigate the feasibility of using calcined iron-rich aluminosilicate (i.e. laterite soil) as a precursor for making alkali-activated mortars (AAMs). Laterite soil was calcined at a temperature of 600°C and activated with an alkali solution in order to produce the AAMs. The developed AAMs were cure...
Article
This paper presents the results of experimental evaluation of curing conditions on the microstructure and performance of geopolymer binders developed from iron-rich laterite soils. Two calcined iron-rich laterites namely LB600 and LY600 were used as solid precursors in the preparation of geopolymer binders. The geopolymer samples were cured at 20,...
Article
Full-text available
Two calcined clays (halloysite and kaolinite clays at 700 °C) were used as solid precursors for geopolymer synthesis. This study compares the physicochemical properties of the both resulting geopolymer series heated at 200, 400, 600 and 800 °C. The end specimens were characterized using Optical Dilatometer, XRD, FTIR, MIP and SEM analyses. Results...
Article
This project aims to study the effect of ripe powdered banana peel (BP) on properties of calcined halloysite based geopolymer activated with alkaline silicate solution. Ripe powdered banana peel (BP) obtained after drying and milling banana peels was mixed with calcined halloysite (MH) at the rate of 0, 5, 10, 15 and 20 wt% by weight of binder. Set...
Article
In this work, two different laterites (iron contents of 13.07 and 49.34 wt%, respectively, for lateritic clay, LAC, and iron-rich laterite, LAI) were selected and calcined at 600 °C. The obtained calcined laterites, namely LAI600 and LAC600, were separately mixed with an alkaline solution (silicate modulus of 1.35) or an acidic solution (phosphoric...
Article
The present project deals with the production of alkali activated concretes based on volcanic and calcined laterite under different curing temperatures (28-80°C). A fraction of 0-40% calcined laterite was added to improve the reactive phase content and the resulting mixtures were labelled GL0, GL20 and GL40. The raw materials and hardened products...
Article
In this paper, four samples of meta-halloysite from widely available Cameroon halloysite clay calcined at 600, 650, 700 and 750 °C, respectively, and the resultant geopolymer binders were systematically characterized. Isothermal conduction calorimetry (ICC) was used to measure the reaction kinetics of meta-halloysite geopolymers at room temperature...
Article
Limestone was used to modify the fluxing action of two potash feldspars (a pure potash feldspar and a soda-potash feldspar) labeled P and C, respectively, in the formulation of porcelain stoneware based on Cameroonian raw materials. The effect of limestone addition (0–10 mass%) was investigated in the range of sintering temperature between 1125 and...
Article
Full-text available
Microporous porcelain formulations are successfully carried out through sintering processing. During the thermal treatment of ceramic products, it was found that the addition of kyanite together with ϕ- and γ-Al2O3 allowed to enhance interconnected pores network with micrometric size from 0.1 to 9 µm in a semi-vitrifed composite. Between 1200 and 1...
Article
To improve the thermal stability of porous geopolymers, metabauxite and metatalc were used as partial replacement of metakaolin. The results of optical microscopy, Scanning Electron Microscopy (SEM), thermal sintering, mercury intrusion porosimetry (MIP) and hot disk investigations, were used to establish the effective stability of the porous compo...
Conference Paper
This study valorizes the laterites widely available in Cameroon in the production of geomaterials for sustainable buildings through an acid consolidation process. Laterites LAI600 and LAC600 were consolidated using fulvic and phosphoric acids. The different samples are kept at 20 and 40°C and then mechanically tested (7 and 28 days). Steaming at 40...
Article
The objective of the present work is to study the effect of RHA on the performance of fresh and hardened metakaolin geopolymer pastes with focus on tensile strength and microstructure. The metakaolin was partially substituted by 12.5–50% RHA in the solid mixes and reacted with 10 M sodium hydroxide solution at ambient conditions of 20 ± 3 °C and 70...
Article
Volcanic ashes are pyroclastic materials commonly found in many regions of the world. Many deposits of volcanic ashes are unexploited, despite their potential interest for several engineering applications. The mineralogy and chemical composition of volcanic ashes depend on the type of magma from which they originate. The two common pyroclastic mate...
Article
This paper studies the alkali activation of iron-rich aluminosilicates (laterites). Three activating alkaline solutions were prepared from sodium hydroxide solution (8, 10 and 12 M) with sodium silicate (Na2SiO3) in order to obtain the sodium silicate solutions with moduli of SiO2/Na2O equal to 0.75, 0.92 and 1.04; H2O/Na2O = 9.78, 10.45 and 12.04....
Article
Cameroonian Balengou clay has been characterized as precursor for inorganic polymer (geopolymer) binder. The lowest possible calcination temperature for this halloysite type clay was found to be 600 °C to convert it into meta-halloysite (MH), which is reactive enough for geopolymerization. This implies an energy saving compared to the 800 °C, previ...
Article
The objective of this study is to develop low cost, eco-friendly and sustainable building materials by applying the technology of mineral polymerization (geopolymerization) process on naturally abundant iron-rich aluminosilicate (laterite) materials. Iron-rich aluminosilicates based-geopolymer composites containing 10 to 40 wt% of rice husk ash (RH...
Article
Full-text available
Using Fe-containing silica-alumina materials as heterogeneous catalyst for Fenton-like degradation of organic pollutants has attracted a lot of attention during the last decades. In this work the catalytic activity of an iron-rich natural silica-alumina material (namely volcanic ash) for the abatement of Rhodamine 6G (Rh6G) has been evaluated. The...
Article
Full-text available
The crystal structure, the unit cell parameters and the extent of mullitization were determined, using the Rietveld method, for range of mullite matrix formulations in which kyanite is used as particles reinforcement. The results combined with the mechanical properties and microstructure indicated the effectiveness of the kyanite particles to enhan...
Article
This paper reports the development of inorganic polymers from laterite, for a potential use at least as non-load bearing building materials. The effect of blending laterite with Ground Granulated Blast Furnace Slag (GGBS) and calcite (CaCO 3) was investigated. Laterite was substituted by calcite at 2 to 20% in mass and by GGBS at 5 to 50% in mass....
Article
Clay based ceramic composite materials with hydraulic permeability were elaborated using sawdust as porogent agent. Their mechanical, morphological, microstructural and pore network properties were investigated. Mixtures in various ratios of two kaolinite clay minerals, Ba (highly plastic) and Va (sand-rich) constitute the five ceramic matrixes stu...
Article
Rice husk ash (RHA), a by-product from the rice industry, was used as principal source of amorphous silica for the production of sodium silicate solution (MR ∼ 3) used for the replacement of standard commercial sodium silicate in the mix-design of metakaolin based geopolymer composites. Three initial concentrations of NaOH were considered (8, 10 an...
Article
Full-text available
Fine particles of kyanite were used as reinforcement in mullite matrix composite. Mix of metakaolin and meta-alumina (calcined bauxite) received different fraction of fine kyanite particles: 37.5, 42.5 and 50 mass%. The objectives were to improve the crystallization of kaolin-based mullite matrix reducing the amorphous content and the grain growth....
Article
An overview of advances in geopolymers formed by the alkaline activation of aluminosilicates is presented with their technological and commercial potentials. The potentiality to valorize a wide range of synthetic and natural aluminosilicate minerals or industrial aluminosilicate byproducts using geopolymerization is highlighted. Factors affecting t...
Article
Full-text available
hirty clay samples collected from three hills in Koutaba (west Cameroon) werecharacterized in order to evaluate their potential use as raw materials for ceramics. After preliminarymineralogical identification by X-ray diffraction, three representative samples from the three differenthills, referred to hereafter as K1M, K2M and K3M, were selected fo...
Conference Paper
Inorganic Polymer Cement paste was used as cleaner binder for the design of lightweight matrices as insulating envelopes and panels in building and construction industries. Sponge like structure with a homogeneously distributed pore network, reduction of the density and important decrease of the thermal conductivity permitted to classify the geopol...
Article
Full-text available
This article summarizes the different local construction materials observed in two regions of Ca-meroon (Adamawa and NorthWest). These raw materials were mapped and evaluated using various methods of investigation (spatial distribution, estimation of reserves, development of a database compatible with geo-referenced maps). The results obtained show...
Article
Full-text available
Thirty clay samples collected from three hills in Koutaba (west Cameroon) were characterized in order to evaluate their potential use as raw materials for ceramics. After preliminary mineralogical identification by X-ray diffraction, three representative samples from the three different hills, referred to hereafter as K1M, K2M and K3M, were selecte...
Article
Two K2O-MgO-Al2O3-SiO2 based geopolymer gels with bulk chemical composition corresponding to cordierite (Co) and 1:1 mullite-cordierite (MuCo) were successfully transformed to crystalline bonds in high temperature service of cold-setting made refractory concretes. Kyanite aggregates changed the flexural strength of the gels from11 to 28 MPa due to...
Article
Inorganic polymer cement paste was used as cleaner binder for the design of lightweight matrices as insulating envelopes and panels in building and construction industries. Sponge-like structure with a homogeneously distributed pore network, low density and low thermal conductivity permitted to classify the geopolymer-wood fiber composites promisin...
Article
Full-text available
L'industrie de la récupération et du recyclage des matériaux ferromagnétiques a pris une grande importance dans le monde à cause des intérêts environnemental, énergétique et écologique qu'elle présente par rapport à l'industrie de l'élaboration de ces matériaux à partir du minerai. Dans le cas du Cameroun, la production des déchets ferromagnétiques...
Article
Full-text available
Three types of bauxites containing aluminum hydroxide of 58.1% gibbsite and 19.3% boehmite for BX3, 95.5% of gibbsite for BX55 and 84.5% of gibbsite for BX8 were used with lime at 95% of CaO through solid state sintering in one stage to prepare a refractory clinker at 1550 °C. The powder obtained after grinding the clinker showed in the XRD curves...
Article
Rice hush (R) and volcanic (P) ashes, two recycled natural wastes were used for their high amorphous silica to improve the homogeneity and structure composition of inorganic polymer pastes before the expansion with aluminum powder. The fine powders were found to be appropriate in enhancing the geopolymerization and expansion conducting to lightweig...
Article
Two castable refractory concretes were made respectively from samples of high alumina calcined bauxite and calcium dialuminate (CaO·2Al2O3) refractory cement. Each castable refractory concrete was made up of 8% wt refractory cement and w/c=0.40 and then stabilized at 105 °C for 48 h. The refractory concretes were characterized by determination of Y...
Article
Full-text available
Prospection and characterization studies carried out in the Bamessing area (Nord-West region of Cameroon) has revealed the presence of heterogeneous clayey materials along the lower slopes of Sabga Hill (1240-1320 m altitude) and the upper limits of Ndop plain (approximately 1200 m altitude). Clayey materials identified are dark-grey (on the hill),...
Article
Full-text available
Fine needles of mullite grains were obtained successfully in a compact and low porous matrix using solid state sintering. We treated high-grade kaolin and sand-rich kaolin at 750 °C to amorphous metakaolins, and bauxite at 1,000 °C to metastable alumina. By designing a stochiometric composition of mullite, each amorphous metakaolin was added to met...
Article
Full-text available
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 degrees C for 4 h and used as replacement, in the range of 15-35 wt%, for both raw laterites in t...
Article
The present study investigates the suitability of alkali activation of a lateritic soil for building applications. Lateritic soil was found to contain kaolinite, associated with quartz and hematite minerals. Both the processing temperatures and the amount of NaOH used were found to influence the development of compressive strength which was in the...
Article
The sintering behavior and mechanical properties of four alluvial clays sampled from the Sanaga River (sampling sites: Nanga-Eboko, Mbandjock, Batschenga, and Ebebda), central region of Cameroon were investigated. Specimens were shaped by cold pressing and fired between 850 and 1100 °C. X-ray diffraction, energy-dispersive X-ray spectroscopy, and s...
Article
Full-text available
Well crystallizedmatricesofCaO � 2Al2O3 were successfullysinteredusingthreebauxites(BX3,BX55andBX8)containingrespectively 80.2; 89.4and91.1wt%ofAl2O3 and theappropriateamountsoflime.XRDdataonthesolidstatesinteredsamplesat1550 1C showcrystalline CaO � 2Al2O3 as themajorphase.TheXRDpatternoftheclinkermadewithBX3showedrelativelylowintensitiesofCaO � 2...
Article
The influence of chemical and mineralogical composition on alkali activation of four natural volcanic ashes was investigated. NaOH was used as the sole alkaline activator. The reactivity of the systems was studied with Differential Scanning Calorimetry. The X-ray spectra of reacted materials showed a mixture of amorphous and crystalline phases. The...
Article
Investigations correlating the pore size distribution-cumulative pore volume to the microstructure are used to compare the efficiency of two solid solutions of pegmatite and nepheline syenite as fluxing agents for the design of porcelainized stoneware. Particularly the fusibility of the two solid solutions was modified by adjusting the CaO content...
Article
Semi-vitreous bodies, with flexural strength of ~78 MPa and water absorption of ~0.4 % for the optimal maturated specimens, were successfully prepared with solid solutions of pegmatite and nepheline syenite, respectively, for the full dense (P) and relatively porous composition (G). Despite the similarity on the bulk chemical composition of the two...
Article
Alluvial clays from four localities along the Sanaga River (Center Cameroon) were studied by physico-chemical, mineralogical and technological characterization in order to assess their suitability as ceramic raw materials. The chemical compositions indicated that SiO2 (65-70%) and Al2O3 (12-15%) are major elements while Fe2O3 is less (4-7%). Kaolin...
Article
Clayey deposits of Nanga-Eboko (central Cameroon) were studied to assess their potential as building materials. Characterization was performed using XRD, FTIR, XRF, DTA/DTG and firing testing. Clays appear as discontinuous pockets with the same textural characteristics in three villages located on both sides of the Sanaga River. The average thickne...
Article
The behavior of the iron present in two volcanic ashes was investigated during geopolymer synthesis using sodium hydroxide as the sole alkali activator. XRD, SEM, and room-temperature Fe-57 Mossbauer spectroscopy were used to monitor the behavior of the iron during the synthesis reaction. Geopolymers with very good compressive strengths were formed...
Article
The influence of the activating solution composition on the stability and thermo-mechanical properties of geopolymers made from a Cameroonian volcanic ash is investigated. NaOH, KOH solutions and silicate solutions with low modulus were tested. The samples are cured at 90°C and the mechanical strength increases up to 21days. With NaOH the strength...
Article
The effects of bulk composition and microstructure on strengthening mechanisms and fracture resistance were investigated for metakaolin based geopolymers. Crack initiation and propagation under mechanical and environmental stresses were correlated to pore size distribution and bulk composition. Based on IR spectra and porosity analysis, it was obse...
Article
Full-text available
The cartography and characterization of an alluvial clay deposit from Ebebda (Central region of Cameroon) were carried out in order to assess its suitability for the production of fired clay bricks. The clayey area investigated is ~ 50,000 m 2 with an average thickness of the exploitable layer of 2.2 m, suggesting a deposit of about ~2.2 × 10 5 ton...
Article
Full-text available
In the present study, physico-chemical investigations have been carried out on the possibility of using Cameroonian volcanic or clay pozzolans as raw material for geopolymer or pozzolanic binder. The research had made some suggestive results and conclusions. Powders of less than 100 μm of five sampled pozzolans from volcanic or clay origins have be...
Article
Indurated lateritic blocks (yellow-brown and red) were collected from two deposits in Yaounde, Cameroon for investigation as structural building and construction materials. Dimensioned blocks were characterized using XRD, DTA/TGA, mechanical compression, water absorption and porosity tests, and examination by optical and electron microscope. Water...
Article
Full-text available
The Compressed Earth Blocks (CEB) are environmentally –friendly and lowcost energy materials for sustainable building applications in many Cameroonians regions. Therefore studies were carried out in 22 exploited lateritic soil quarries, 10 in Douala and 12 in Yaounde, Cameroon. The objective of this study was carry out an inventory of the various b...
Article
The volcanic ash occurring as an abundant and readily accessible natural resource in the Central African country of Cameroon was used to synthesize aluminosilicate geopolymers using sodium hydroxide as the sole alkaline activator. Both the curing conditions and the Na2O/SiO2 molar ratio were found to influence the development of compressive strengt...
Article
Full-text available
Lateritic soils are formed in the tropics through weathering processes that favor the formation of iron, aluminum, manganese and titanium oxides. These processes break down silicate minerals into clay minerals such as kaolinite and illite. Iron and aluminum oxides are prominent in lateritic soils, and with the seasonal fluctuation of the water tabl...
Article
Full-text available
Because of concerns over the construction industry‘s heavy use of cement and the general dissatisfaction with the performance of building envelopes with respect to durability, there is a growing demand for a novel class of ―green‖ binders. Geopolymer binders have re-emerged as binders that can be used as a replacement for Portland cement given thei...
Article
Kaolinite-corundum (derived from bauxite) associations were assessed as candidate matrices in the field of porous ceramics composites. Particles of corundum were expected to behave as non reactive second phase, deflecting the matrix cracks and increasing the toughness. Porosity and densification were monitored by developing coarse grains (67 wt.% o...
Article
To improve long-term hydraulic properties of binders from RHA and lime, 25–75% MK was added to RHA. Binders were formulated and properties were compared to that containing RHA or MK as only pozzolans. The lime–pozzolan ratio was 1:3. The properties tested after 7, 28 and 56days were: absolute density and fineness of the binders, initial setting tim...
Article
Two metakaolins from Al-rich and Si-rich kaolinitic clays were used to design polysialate matrices with different Si/Al and NaK/Al ratios. The aim was to investigate the influence of oligomers formed during dissolution and hydrolysis on the polycondensation and transformation to hard and stable matrices. Products of geopolymerization of the differe...
Article
Full-text available
This paper presents the results of the experimental studies of the microstructural and phase evolution of three samples of bauxite (BX3, BX5 and BX8) from Haleo-Danielle (Minim-Martap, Cameroon) fired between 1000°C and 1600°C. Correlation was drawn between phase evolution and densification (porosity, water absorption, bulk density) with the aim to...
Article
Full-text available
In the paper, the lime-barium and lime-zinc glazes used in Southern and Eastern Africa Mineral Center (SEAMIC) ce-ramic unit in Tanzania were investigated for the production of high temperature raw glazes in Cameroon. The base Seger formula used was 0.3KNaO, 0.3CaO, 0.4ZnO or BaO; xAl 2 O 3 and ySiO 2 . Different Al 2 O 3 /SiO 2 formula ratios for...
Article
Full-text available
Three bauxite samples (BX3, BX5 and BX8) of high alumina content from the region of Haleo-Danielle, Minim-Martap in Cameroon were characterized thermally at temperatures between 1000 degrees C and 1600 degrees C with the objective to study their suitability for dense refractory materials The water absorption, porosity, linear shrinkage, flexural st...
Article
In the present study, percentage of slaked lime (20–30%) in binder with metakaolin, water–binder ratio (0.8–1.0), sand–binder ratio (1–3) and sodium hydroxide (NaOH)–binder ratio (0.02–0.04) were factors varied to investigate properties of fresh or hardened mortars. Sodium hydroxide was used as a chemical activator in the slaked lime–metakaolin bin...
Article
Crystals of the pyroxene group (diopside, augite and enstatite, hedenbergite), series of crystals with the general formula (Mgx Fe1–x )2SiO4 having various geometry, identified as spinel (and olivine), and plagioclase crystals from anorthite to anorthoclase that grow together in mass having thin parallel groves embedded in a complex matrix together...
Article
In this study, a pozzolanic binder containing lime and a common thermally activated kaolinitic clay, at 750 °C, was formulated. The chemical, mineralogical and pozzolanic properties of raw materials were determined. The percentage of lime in the binder varies between 20% and 30%. The binder was used as a stabilizer in compressed lateritic soil in w...
Article
Volcanic ash powders from Etna (Italy) and Cameroon were used as the principal source of aluminosilicate to produce geopolymers with the potential for making building products. The volcanic ash was ball milled and reacted with concentrated alkaline solutions for polymerisation and subsequent curing at 75-400 °C for 12-48 h. It was found that the ge...
Article
The effect of alkali-silica glassy matrixes (AGM), as replacement for feldspar, on the microstructure, physical properties and mechanical strength of conventional porcelain has been studied. AGM with chemical composition similar to feldspars has been prepared to introduce alkali-ions (Na+ and K+) in porcelain compositions. It has been found that th...