Thermal behaviour of metakaolin–bauxite blends geopolymer: microstructure and mechanical properties

This paper investigates the use of bauxite widely available in northern Cameroon as an additive in the optimization of some properties of metakaolin-based geopolymer. To do this, several geopolymer mixtures were prepared by substituting metakaolin (MK) by bauxite (BA) (from 0 to 50%) and partially kept at room temperature (28 °C), while others were sintered at 200, 800 and 1200 °C. The raw materials and resulting products were characterized using X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), densification parameters, mechanical properties as well as microstructural morphologies. The results revealed that the setting time of the geopolymer pastes increased with the bauxite content due to its low dissolution in alkaline medium at room temperature. The mechanical strength of samples decreased from 35.20 to 11.10 MPa at room temperature. At 1200 °C, the higher strengths (50, 98 and 70 MPa) were achieved in MKBA10, MKBA20 and MKBA30, respectively. These samples also exhibited dense and compact microstructure partially due to packing particles effect and the nature of bauxite known as refractory material. Thermal shrinkage and relatively high mass losses reflected the decomposition of chemical compounds within the system. Thus, the synthesized materials heated at 1200 °C could be used as a potential candidate for refractory applications

Offshore Stratigraphic Architecture of the Miocene to Actual Deposits in the Southern Margin of Rio-Del-Rey (South Cameroon)

The study of the geometric deposits in a basin allows the reconstitution of its tectonic and eustatic history. The Rio-del Rey basin, upon which this study is being carried out, constitutes one of the two Cameroon margin basins located North of the Cameroon volcanic line. To study the stratigraphic architecture of the Miocene deposits consists in characterizing the deposits geometry by discriminating the controlling factors. This study is based on data, made up of 13 seismic lines and 07 wells and then on various methods related on seismostratigraphy and diagraphies. The obtained lithologies in the study area constituted essentially of sandy and clayey deposits from Paleocene to Recent. They are grouped differently in to Akata, Agbada and Benin Formations, and the Isongo Member. These deposits are set up in marines (bathyal and neritic), deltaics, turbiditic cones slope and fluvial channels environments. Three second-orders sequences were identified (S1, S2 and S3), they are made up of deposits presenting variable geometries along the basin. They are prograding, aggrading, in domes and synclinal. The disposition of the deposits was influenced by tectonic structures such as folds and faults. The isochronal map allows understand the sedimentary flow impact on topographic evolution of the basin in the upper- Miocene. It turns out that, deposits of this basin present various geometric tectonics control (subsidence and uplift) that constitute a major influential factor, being marked by the presence of synclines (gravity tectonics), domes (argilocinesis) and syn-sedimentary faults. The fall in marine level eustatism gives rise to progradations, whereas, a rise in marine level is responsible for retrogradations and aggradations. Thus, the sedimentary flow exerts a secondary control. It is related to the above two major factors

Comparative Study of Mortars Made with Sands of Different Geological Origin

The present work is a comparative study of sand mortars from various geological origins to highlight their influence on mortar qualities. Five different sands and the cement CEM II/B–P 42.5R were used to produce mortars with similar water/cement ratios (W/C). These are the “Sanaga” sand from the Sanaga River, the “Wouri” sand from the Wouri River, the Nyambaka basalt sand, the Meiganga granite sand, and the Leboudi gneiss sand. The physical, chemical, and mineralogical features of these sands were used to characterize and classify them. They were then used to formulate mortars, which were analyzed and compared. According to the results of the mortar setting time tests, the initial setting time ranges from 195 minutes for Sanaga sand mortar (MS04) to 210 minutes for gneiss sand mortar (MGN03), passing Wouri sand mortar (MW05) with 200 minutes, basalt sand mortar (MB01) with 198 minutes, and granite sand mortar (MGR02) with 196 minutes. The final setting time ranged from 496 minutes (MGR02) to 510 minutes (MGN03), with an average of 300 minutes added to the initial setting time. The flexural strength tests of the mortars reveal that crushed sands outperform alluvial sands. They range from 1.64 to 2.18 MPa after 2 days, 3 to 3.90 MPa after 7 days, and 7 to 14.84 MPa after 28 days. The results of the compressive strength tests show that quarry sand mortars have greater average compressive strengths than alluvial sand mortars, with basalt sand providing the greatest performance. These strengths range from 6.35 to 10.83 MPa after 2 days, 7.55 to 18.96 MPa after 7 days, and 22.81 to 34.58 MPa after 28 days, with the MB01 being the best sand. These findings reveal that the geological origin of sands, which specifies certain of their physicochemical and mineralogical attributes, has an impact on the properties of mortars. This impact is also influenced by granulometry and organic matter concentration

Tectono-stratigraphic evolution and architecture of the Miocene Rio del Rey basin (Cameroon margin, Gulf of Guinea)

International audiencehe Rio Del Rey basin located in the Gulf of Guinea is one of the two basins lining the Cameroonian coast. It evolved since the Cenozoic in a tectono-magmatic and seismic complex setting. During the Miocene, this evolution was controlled by tectonics, relative sea level changes, basin filling and mantle dynamics. Two deposit megasequences of second order, MS1 and MS2, were pointed out. MS1 (lower Miocene), aggradational and corresponding to the Isongo turbidites deposited during a period of relative sea level drop registered two sequences of third order differentiated by the degree of channel incision: S1a (Aquitanian-Burdigalian), hardly incised and S1b (Serravallian), moderately incised. A double extension along N-S (Burdigalian) and NE-SW (Serravallian) directions responsible for a set of horsts and grabens, high subsidence and depocentres trending NW-SE affected these sequences. MS2 (middle to upper Miocene), progradational and corresponding to deltaic alternations deposited during a period of creation of available space were controlled by the tilting, wrenching, a second stretching phase and low sedimentary filling. MS2 recorded three cycles of 3rd order: S2a (lower Tortonian), S2b (upper Tortonian) and S2c (Messinian) differentiated by their morphology in ramp for S2a and S2b and slope for S2c. The formation of grabens and horsts and the tilting of the margin coincide with the high activity of the Cameroon volcanic line interpreted as a result of deep mantle dynamics affecting the inner Congo craton lithosphere. This architecture, which differs from those of the other basins of the Gulf of Guinea, partly explains the low oil production of this basin