Room-temperature alkaline activation of feldspathic solid solutions: Development of high strength geopolymers

Amorphous fraction, grains defects and the incongruent dissolution of solid solutions (pegmatite, trachyte, and granite) were used to design high strength geopolymer composites with crystalline content in the range of ∼70–85%. The geochemical history of the natural solid solutions affects the dissolution and polycondensation/geopolymerization. These solid solutions were altered with 15, 20, 25 and 30% of metakaolin and activated with alkaline solution. Experimental results (phase evolution, three-point flexural strength, microstructure, mercury intrusion porosimetry and water absorption) indicated that polycondensation/polymerization is enhanced in trachyte, granite and pegmatite based specimens, compared to sand, due to the increase in N-A-S-H secondary phases. The amorphous/crystalline ratio of the solid precursors were used to understand the role of dissolved and undissolved fraction into the strength development of geopolymer composites. It was concluded that high strength geopolymer composites of chemico-mechanical equilibrium can be achieved with solid solutions having reduced fraction of pores volume and pore-size

Innovative porous ceramic matrices from inorganic polymer composites (IPCs): Microstructure and mechanical properties

The thermal performance of pegmatite-based geopolymer composites is investigated. Dense and compact matrix was prepared replacing metakaolin with pegmatite in the range of 70\u201385 wt% and activate with sodium hydroxide/sodium silicate solution in 1:1 vol ratio. The products of geopolymerization, cured at room temperature for 28 days, were heated at 100, 200, 400, 600, 800, 900, 1000 and 1100 \ub0C with 2 h soaking time. The high values of flexural strength (46\u201351 MPa) were observed at 1000 \ub0C as the consequences of low porosity (173 mm3/g) and water absorption (4.50\u20135.62%). The increase of the vitrification at 1100 \ub0C enhanced the liquid phase and develop porosities responsible for reduction of strength. The mechanical properties, microstructural evolution and pore size distribution were found to be influenced by the amount of fine powder of pegmatite (solid solution)

Mechanical Properties and Microstructure of a Metakaolin-Based Inorganic Polymer Mortar Reinforced with Quartz Sand

The synthesis, mechanical behaviour, and microstructure of metakaolin-based geopolymer mortar reinforced with quartz sand are presented in this investigation. Fine sand (quartz sand) aggregate were added in different proportions of 50, 60, 70 or 80 wt.% to prepare the fresh metakaolin-based geopolymer paste. The geopolymer mortar was achieved by a mixture of geopolymer paste and river sand in the ratio 2:5 by mass. The mixture of sodium hydroxide solution (10 M) and sodium silicate solution (Na2SiO3) in a volume ratio of 2:3 was used as an alkaline activator. All the specimens were cured at room temperature and tested after 28 days of curing. The investigations on microstructure and physical properties indicated a significant reduction of the open pores and interconnection of micro and meso cracks in the structure network with increase in the amount of quartz sand. As a consequence, the samples show a good mechanical strength principally with the addition of 60 wt.% of quartz sand to binder with values of 8 and 66 MPa for flexural strength and compressive strength, respectively

Severity of acne and quality of life of patients treated at Cameroonian hospitals (sub-Saharan Africa)

Background: The aim of this study was to assess the severity of acne and the impact on the quality of life (QoL) of patients undergoing anti-acne treatment. Methods: This was a cross-sectional study conducted from January to April 2017 at three hospitals in Yaoundé. Patients suffering from acne and under treatment were consecutively included. Clinical severity and QoL were assessed with the ECLA and CADI scales, respectively. Data was analyzed with SPSS 23.0. We employed the ANOVA test and linear regression to search for associations between variables. The significance level was at 5%. Results: We recruited 113 patients, predominantly female (83%), with a mean age of 26.0 ± 6.4 years. Mild-to-moderate forms were predominant (74%). The mean ECLA score was 10.1 ± 4.6, with a majority of the participants 74.3% (84/113) having mild-to-moderate acne, while 25.7% (29/113) had severe acne. The majority of the patients found the treatment expensive (69%). Therapeutic education had been conducted in 46.9% of the patients, and 60.2% of them reported a relapse during treatment. An impairment in QoL was found in 99% of the patients. The mean global QoL score was 6.3 ± 3.4. The impairment in QoL was positively correlated with clinical severity (r = 0.40; p = 0.003). Conclusion: The study revealed a predominance of mild-to-moderate forms of acne, an alteration in the QoL of almost all patients studied, and a positive correlation between the clinical severity of acne and the impairment in QoL. Key words: Acne; Clinical severity; Quality of life; Treatment; Cameroon; Sub-Saharan Africa</jats:p