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Volume 10, Number 4, December 2021

An experimental study was undertaken to evaluate the performance of recycled polypropylene fiber (RPF) in concrete. The RPF materials were recycled from woven bags and used in concrete at various volume fractions corresponding to 0.1%, 0.2%, and 0.3%. Two different classes of strength, corresponding to normal and high strength concrete, were investigated. Fiber was used as substitution of coarse aggregate in concrete. The dosage of fiber was used at relatively lower dosages to avoid altering fluidity and to limit the reduction in coarse aggregate content. On the other hand, a commercial polypropylene fiber (PPF) was used at equivalent dosages than RPF for comparisons purposes. Test results indicated that optimized RPF volumes can secure comparable mechanical performance than those obtained with commercial PPF. On the other hand, the use of both fiber types resulted in lower compressive strength (10 to 20%), higher flexural strength (up to 27%), and lower elastic modulus (by 16%). Furthermore, the use of RPF type reduced the drying shrinkage (6 to 10%) of normal and high strength concrete types and increased the permeable pore void of both concrete types.

Key Words
compressive strength; elastic modulus; flexural strength; high strength concrete; permeable pore void; recycled polypropylene fiber; shrinkage

(1) Ahmed Touahri, Taieb Branci:
Civil Engineering Department, University Hassiba BenBouali of Chlef, Algeria;
(2) Ammar Yahia:
Civil Engineering Department, University of Sherbrooke, Canada, J1K 2R1;
(3) Karim Ezziane:
Geomaterials Laboratory, University Hassiba BenBouali of Chlef, Algeria.

Graphene has attracted enormous interest to researchers because of its remarkable electrical, mechanical, and optical properties. Chemical vapor deposition (CVD) method was used to synthesize the graphene. The methanol (CH3OH) was used to investigate the cleaning, doping and defective effect in the graphene surface. The samples were characterized by X-ray diffraction patterns (XRD), field emission scanning electron microscope (FESEM) images, Xray photoelectron spectroscopy (XPS) measurements, and Raman spectroscopy. XRD indicates the introduction of oxygen in graphene layer. FESEM images of samples suggest the sheet like morphology. XPS measurements confirm the existence of large number of oxygen containing functional groups (C=O, COOH, and CO) and C-C in the graphene surface. The Raman spectra confirm the n-doping and cleaning effects on graphene surface through the red shifts of G and 2D peaks. Furthermore, the optical images were used to observe the residues in graphene. The residues are obtained due to adsorption of CH3OH in graphene surface. Therefore, this work provides a simple and effective approach to investigate the cleaning, doping and defective effects on the surface of graphene using CH3OH solvent that can be applied in tunable electronic devices and gas sensor.

Key Words
defective effects; graphene; methanol; n-doping

(1) Krishna Bahadur Rai:
Department of Physics, Patan Multiple Campus, Tribhuvan University, Nepal;
(2) Ishwor Bahadur Khadka:
Department of Physics, Sungkyunkwan University, Suwon 16419, Republic of Korea;
(3) Agni Raj Koirala:
Korea Center for Artificial Photosynthesis, Department of Chemistry, Sogang University, Seoul 121-742, Republic of Korea;
(4) Schindra Kumar Ray:
Department of Environment and Energy, Sejong University, Seoul 143-747, Republic of Korea.

In this paper, a simple refined shear deformation theory which eliminates the use of a shear correction factor was presented for free vibration analysis of FG sandwich plates composed of FG porous face sheets and an isotropic homogeneous core. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. Material properties of FGM layers are assumed to vary continuously across the plate thickness according to either power-law function in terms of the volume fractions of the constituents. The face layers are considered to be FG porous across each face thickness while the core is made of a ceramic homogeneous layer. Four models of porosity distribution are proposed. Governing equations and boundary conditions are derived from Hamilton's principle. Analytical solutions were obtained for free vibration analysis of square sandwich plates with FG porous layers under various boundary conditions. Numerical results are presented to show the effect of the porosity volume fraction, type of porosity distribution model, side to thickness ratio, lay-up scheme, and boundary conditions on the free vibration of FG sandwich plates. The validity of the present theory is investigated by comparing some of the present results with other published results.

Key Words
free vibration; functionally graded materials; porosity; power-law function; sandwich plates

(1) Mohamed Saad, Lazreg Hadji:
Department of Mechanical Engineering, University of Tiaret, BP 78 Zaaroura, 14000 Tiaret, Algeria;
(2) Mohamed Saad:
Laboratory of Industrial Technology, Department of Mechanical Engineering, University of Tiaret, Algeria;
(3) Lazreg Hadji:
Laboratory of Geomatics and Sustainable Development, Ibn Khaldoun University of Tiaret, Algeria;
(4) Abdelouahed Tounsi:
Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria;
(5) Abdelouahed Tounsi:
YFL (Yonsei Frontier Lab), Yonsei University, Seoul, Korea;
(6) Abdelouahed Tounsi:
Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia.

The aim of this study was to investigate the effect of water/cement (w/c) ratio on the flexural behavior of reinforced concrete (RC) beams which contain polypropylene waste coarse aggregates (PWCA) coated with sands subjected to concentrated monotonic load. The process involved the experimental manufacturing of three RC beams with sand-coated PWCA concrete using 0.30, 0.35, and 0.36 w/c ratios at a width of 80 mm, a height of 160 mm, and a length of 1600 mm. The flexural performance, including load-deflection relationship, flexural strength, ductility index, stiffness, as well as toughness was investigated and discussed. Moreover, the analytical approach was verified using the Response-2000 program by comparing the analytical and experimental results. The sand-coated PWCA RC beams were discovered to have the ability to sustain the loads applied effectively by producing a flexural performance which is considered acceptable and reasonable. In addition, the variations in the w/c ratio were observed to have effects on the parameters of the beams investigated. Finally, the ultimate loads recorded for these beams confirmed their acceptability in the analytical investigation.

Key Words
beams; flexural performance; polypropylene coarse aggregate; water/cement ratio

(1) Gandjar Pamudji, Yanuar Haryanto:
Department of Civil Engineering, Faculty of Engineering, Jenderal Soedirman University, Jln. Mayjen. Sungkono KM 5, Blater, Purbalingga, 53371, Indonesia;
(2) Yanuar Haryanto, Hsuan-Teh Hu, Laurencius Nugroho:
Department of Civil Engineering, College of Engineering, National Cheng Kung University, No. 1 University Road, Tainan, 701, Taiwan (R.O.C.);
(3) Hsuan-Teh Hu:
Department of Civil and Disaster Prevention Engineering, College of Engineering and Science, National United University, No. 2, Lien Da, Nan Shih Li, Miaoli, 36063, Taiwan (R.O.C.);
(4) Farida Asriani:
Department of Electrical Engineering, Faculty of Engineering, Jenderal Soedirman University, Jln. Mayjen. Sungkono KM 5, Blater, Purbalingga, 53371, Indonesia.

This research shows the development of a composite material with an alumina matrix reinforced with different percentages of titanium (0.0%, 0.5%, 1%, 2% y 3%) with the intention of analyzing their mechanical and biocompatible properties for its possible application as a biomaterial. Alumina was synthesized using the reaction bonding aluminum oxide (RBAO) methodology. The powders resulting from the milling process had a size distribution ranging from nanometers to 2 microns. By means of X-ray diffraction and differential thermal analysis, it was determined that aluminum oxidizes in both solid and liquid states. It was also found that the alumina formation reaction is complete at 900°C. Using scanning electron microscopy, it was determined that the microstructure has fine grain sizes and homogeneous morphology. Likewise, the elastic modulus and fracture toughness of the composites obtained were determined, results indicate that these properties are higher than the properties of cortical bone. In addition, bioactivity was promoted using the biomimetic method. The results obtained demonstrate that the resulting composite can be used as a biomaterial.

Key Words
Al2O3/Ti composite; bioactivity; biomaterial; bone implants; RBAO process

(1) Ruth P. Alvarez-Carrizal, José A Rodríguez-García, Sergio J. Esparza-Vázquez, Enrique Rocha-Rangel:
Research Department, Universidad Polit&3233;cnica de Victoria, Av. Nuevas Tecnologías 5902, Ciudad Victoria, Tamaulipas, 87138, México;
(2) Dora A. Cortés-Hernández:
Cinvestav-Saltillo, Avenida Industria Metalurgica1062, Parque Industrial Saltillo-Ramos Arizpe, Ramos Arizpe, Coahuila, 25900, México.

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