In Mozambique, the task of providing infrastructural facilities for the rapidly growing population is enormous. Although the country has unique characteristics that present opportunities for timber construction to thrive, concrete continues to be one of the most used materials in modern construction. However, the concrete industry has a considerable impact on the environment due to production and the raw material consumed. Among the constituents of concrete, sand has been the one in which its exploitation causes the most damage to the environment. An alternative to solve this problem would be the use of fine sandy loam aggregate in the production of concrete. Thus, this research presents the study of the technical feasibility of using fine sandy loam aggregate in the production of concrete. The main study variables were the consistency and mechanical strength of concrete compression. For the production of concrete, two types of gravel of ¾ were used, sandy loam soil, sandy soil and Portland cement. Specimens were manufactured for 4 different mixes, with a reference mix containing cement, sand, gravel and water. To evaluate the performance of the mixes, tests of mechanical resistance to compression were carried out at 7, 14, 21 and 28 days of age. After determining the main physical and mechanical characteristics, promising results were obtained for the mixtures with 25% and 50% substitution, where the axial compressive strength test reached 26.3 MPa and 27 MPa, above the reference mixture of 25.6 MPa. The 100% mix of alternative soil reached an average strength of 25.2 MPa. This same mixture, although having low mechanical strength, has greater consistency, with a slump of ±10 cm. Keywords: concrete, cement, environment, fine aggregate, mechanical strength. DOI: 10.7176/CMR/14-1-02 Publication date: January 31 st 2022
Old Corrugated Container (OCC) is one of the most potential raw material for paper and paperboard manufacture but it has some disadvantage of a continued decrease in the quality of the fiber during the recycling process. It’s caused by decreasing of carboxyl groups when the fibers undergo drying, resulting in decreased ability for swelling, thereby reducing the ability of the bond between the fiber and the fiber strength. Modification of waste paper using laccase enzyme may increase the fiber content of the carboxyl group of waste paper, therefore will increase paper strength. Experiments carried out with the addition of laccase in various dosage paper stock originating from OCC by 5% pulp consistency. 80 g/m Laboratory sheets, was made from stock, then analyzed by tensile index, burst index, wet tensile index, the content of carboxyl groups and SEM analysis. The experimental results showed addition of 50 U/g laccase at OCC giving optimum value for physical properties. Keywords : OCC, laccase, Physical properties, Carboxyl groups, SEM. DOI: 10.7176/CMR/13-3-04 Publication date: November 30 th 2021
In this study, CFs were coated electrochemically with three different monomers (An, EDOT or Py) in different condition such as electrolyte (BA, H 2 S0 4 or NaClO 4 ), solvent (H 2 O as inorganic medium or ACN as organic medium), in presence of foreign material (EBC) and coating method (constant potential and cyclic voltammetry as controlled potential). Obtained CFs were compared with regard to electrical and capacitive and morphological features. In CPE the current flown in system was changed in certain values for each monomer in presence of EBC. But this changing was more for Py than that for the other. In CV experiments, the oxidation potential was increased for PAn and PEDOT when it was decreased for Py. Imax values were changed for each polymer and conditions. According to Randles-Sevcik equation, the electrocoating redox processes in BA-H 2 O were not controlled by diffusion under this conditions. But, all the redox processes carried out in NaClO 4 -ACN electrolyte solution were controlled by diffusion for each polymer coated CFs. In presence of EBC it could be concluded that redox process was controlled by diffusion in BA-H 2 O for PAn and in NaClO 4 -ACN for PEDOT. In presence of 1.8 % EBC. The C DL value was decreased to 4 µF from 6 µF; to 0.7 µF from 1.5 µF; to 1 µF from 3 µF in BA-H 2 O for Pan, PEDOT and PPy respectively. But, it was increased to 11.5 µF from 10.4 µF in NaClO 4 -ACN for PEDOT. Phase angle was in the same trend. The texture coatings were more compact in the presence of EBC in electrolyte solution than that of the absence of EBC for PPy coated CF. The relationship of between the radius of coating and the C DL of the coated CF was proportional. Thus, it may be concluded that the C DL and radius of coating were affected with the presence of different material/compound in electrolyte solution. Keywords: PAn, PEDOT, PPy, presence of EBC, comparison, impedance, texture coating. DOI: 10.7176/CMR/13-3-05 Publication date: November 30 th 2021
Hexavalent chromium ion removal by adsorption using rice husk ash and silica prepared from rice husks obtained locally from rice mill as biosorbents was evaluated as low cost wastewater treatment in this study. Batch equilibrium isotherm experiments were performed as well as effect of dosage and initial chromate solution pH to determine the potentials of the sorbent to remove hexavalent chromate ion from synthetic fed wastewater. Equilibrium isotherm experimental data isotherms were tested with isotherm models (Langmuir, Freundlich and Tempkin models), being best represented by the Langmuir model. Optimum conditions were: dosage = 0.5 g / 200 ml at room temperature and pH o > 6. The equilibrium between adsorbate in the solution and on the adsorbent surface was practically achieved in 2 h. The monolayer sorption capacity was 67.45 mg/g for rice husk silica and 55.98 mg/g for rice husk ash. Estimation of energy of the sorption process revealed chemisorption as the prevailing means of interaction between the adsorbents and adsorbates moieties. The abundance and affordable (cheap) cost of rice husks justifies its use as a precursor in the preparation of rice husk ash and silica as effective adsorbents for chromium removal from industrial effluents. Keywords :Hexavalent chromium, Biosorption, Isotherm, Rice husk ash, Rice husk silica DOI: 10.7176/CMR/13-1-02 Publication date: January 31 st 2021
Novel array arcs- fin heat sink 7×2 with 6×2 multi air jet impingement are presented in this paper by using numerical simulation. Temperature distribution of jets diameter of 5mm and arcs- fin heat sink with variety shapes at constant radius of 45mm are evaluated. Reynolds number ranges from 7000 – 11000. The study has been done at constant Z/d= 6 and constant heat flux =8333.33 W/m 2 . The best shapes of fins has an effective role in improving the rate of heat transfer .In this paper, the design concerned in arcs ships to construct fin geometry. Four concave arcs constricted the shape of fins heat sink for model A. This model has been changed to construct models (B-C-D-E) by reflect two concave arc from it to be convex arc. All five models at the same radius. The five configurations were comparative between each other and the best model comparative with flat plate heat sink. It is observed that model D of heat sink showed best temperature dissipation than the others. The results of this paper can help to select heat sink that meets a design's thermal, Power, packaging and cost requirements (specialized in arcs fins) with array of impingement jet, which is a popular used in cooling electronic devices.
