Key Engineering Materials Vol. 913

Abstract: Sandy soil formations are widespread around the globe, particularly in the Arabian Peninsula. The Sandy formations were created as a result of long-term geological activities including but not limited to alluvial and wind deposition. Since the alluvial deposits contain fine soils, the clay layers are often intercepted in the foundation supporting strata. The geotechnical foundation design based on field and lab investigations usually relies on the average response of the layered strata and can satisfy both shear and settlement criteria. However, the enduring sustainability of the heavily loaded foundations is required to be investigated in detail. In this study FEM based numerical investigations have been carried out on a thin raft foundation resting on granular soil, with a soft clay layer in the influence zone. The COMSOL Multi-physics platform has been used for the analysis. The study cases are planned based on the thickness of the clay layer and building load. The analysis results predict the risk involved in the sustainability of rafts in terms of the settlement. The field engineers and designers are recommended to consider the risk and plan accordingly

Abstract: Pavement materials have developed significantly through many stages until they have reached what they are now. Despite the fact that there are many samples found in Oman which are not used or neglected, there are lots of natural samples can be depleted because of its huge use like the natural materials. Basically, the frequent’ use has a negative impact on nature. Accordingly, this study is going to shed lights on some considered samples that exist but are not used called waste products under some justifications and tests of particular samples classified as coarse-grained soil (coastal material, waste brick construction, desert sand) through some methodologies: Grain Sieve Analysis, Atterberg Limit Test, Clay Content Test, Proctor Compaction Test, and California Bearing Ratio test. The mechanical properties of these samples are tested to evaluate their efficiency and effectiveness in the paving layers. The most important parameter used in the evaluation process is the CBR and the sieve analysis. As a final result, it turns out that most of the samples are not complied with Oman's specifications for subbase and base use but some materials like Khour Al-Hamam can be modified using additive materials to be suitable.

Abstract: This paper presents the comparison between sediment and natural subgrade material for road construction to check its stability to improve soil properties. Two samples were investigated which are sediment and subgrade construction material which were taken from Wilayat A’seeb, Oman. Sediment was collected from Alkhoud dam, Muscat, and subgrade construction material was collected from Al Mubilah construction site, Muscat. Elemental analyses and mechanical tests were conducted to achieve the purpose of the study. According to the AASHTO classification, the result of the sediment samples shows that it was silty and clayey gravel A-2-4 and clayey sands or sandy clay mixtures according to USCS classification. Also, investigations on the subgrade construction material show that it was silty and clayey gravel and sand A-2-7 according to AASHTO classification and well-graded sands, gravelly sands according to USCS. The result of grain size distribution curves shows that subgrade soil is applicable to be used but sediment is not applicable as pavement construction and. The maximum dry density (MDD) and optimum moisture content (OMC) of the sediment sample are 1.422 g/cm³ and 20.3% respectively. Also, the maximum dry density (MDD) and optimum moisture content (OMC) of the subgrade construction material are 1.634 g/cm³ and 15.5 % respectively. As compared between the two materials, it found that the result of maximum CBR value of subgrade material was 16.13% and the maximum CBR value of sediment material was 16.07% and that means both materials are very close in strength and sediment has the power to be used in road construction with some improvement. According to the experimental results, it shows that the investigated sediment and natural subgrade soil are suitable to be used in the subgrade layer because it is corresponding to the range of Omani standards but it is not suitable to be used as subbase and base layers. Other standards might be compatible with the results to be effective use in subbase and base layers.

Abstract: This study investigates the use of wadi sediments as a potential source for the core of rock-fill dams. The current practice utilizes clay and silty materials for the core of the rock-fill dam. In Oman, clay is not abundantly available, so there is a need to propose a local alternative material as a potential source for the core of the rock-fill dam. Dredged sediment is believed to have properties like clay but is a waste material deposited in reservoirs. The samples of wadi sediments were grouped from the reservoir of Wadi Jizzi Dam, located a few kilometers away from the city of Sohar. A detailed laboratory-testing program investigates the physical characteristics, grain size distribution, liquid and plastic limits, specific gravity, compaction, hydraulic conductivity (permeability), swelling potential, and unconfined compressive strength. All the tests were performed following the British Standard. The pure dredged sediment has a hydraulic conductivity of 7.11x10^-6 cm/s, which is comparable to the requirements of the core of the dam. To improve the other properties of the dredged sediment, it is mixed in different proportions with dune sand collected from the Al-Sharqia Desert of Oman. The test results suggest that a mixture ratio of 50% of sediment to the dune sand gives optimal strength, durability, and permeability. On the other hand, for the comparison purposes, bentonite was mixed with sand by various percentage. The microscopic investigation and X-ray diffraction (XRD) analysis tests on dredged sediments suggest that the material can be utilized without causing any environmental concerns. The outcomes of this study is expected to assist the practitioners in achieving cost-effectiveness and sustainability in the design.

Abstract: The Casimiro Ulloa Hospital is a confined masonry structure more than 60 years old that does not satisfy the requirements of the Peruvian seismic code E.030 and it is located at high seismic zone. Therefore, this hospital is susceptible to collapse and becomes an essential deficient structure. Therefore, the present study is based on a comparative analysis between reinforced concrete wall and CFRP sheets through the nonlinear Push Over method in order to obtain which is the best reinforcement in structural capacity. The reinforcement with eight L-shaped concrete walls of 15 cm thick located at the corners of the structure, increased the strength of the hospital by 115% in longitudinal direction (Axis X) and 108% in transversal direction (Axis Y), and also increased the ductility by 3% and 117% in the directions respectively. The other reinforcement was carried out with CFRP sheets and anchors. The sheets were designed with a width of 9 inches and were placed in an X-shape in the masonry load-bearing walls and the anchors were implemented in the corners of the laminate walls in order to ensure adequate load transfer between the sheets and the surface. This reinforcement increased the strength of the structure by 345% in axis X and 150% in axis Y and increased the ductility by 59% in longitudinal direction and 331% in transversal direction.

Abstract: The study investigates the reduction in masonry walls' strength with different opening sizes and aspect ratios using simplified micro modeling. Calibration of the numerical wall model was done by following an existing wall model from the literature. Springs (COMBIN39) were used to model the compression and shear strength of mortar, whereas contact elements (CONTA178) were used to model the bond between mortar and bricks. The load was provided in two phases; first, the gravity load was applied in the vertical direction to compress the wall then the lateral load was applied. Five walls with an opening size 0%, 1.85%, 3.66%, 10.91%, and 16.5% of the total wall area have been modeled in this study. The analysis results showed that up to an opening area of 4% masonry wall showed approximately 50% reduction in strength and stiffness. Beyond 4% opening size, strength and stiffness drop almost linearly. Such modeling can save cost, time, and know beforehand the type of failure of a masonry wall to avoid life loss.

Abstract: The influence of SLM process parameters (i.e. laser power, scanning speed, and hatch spacing) on the microstructure and mechanical properties of 3D printed 18Ni-300 maraging steel was investigated. In experiments on 3D printed scan tracks, better fusion of powder material was achieved in parameter configurations with higher linear energy density (i.e. LED ≥ 375.00 J m^-1). A higher LED indicates that more laser energy is transferred to the powder material, resulting in complete melting of the powder and the creation of a microstructure with less defects. In experiments on fully built samples, higher relative density was achieved when the hatch spacing was increased or the scanning speed was decreased. Fully built samples produced using parameter configuration B-2 (300 W, 700 mm s^-1, 0.10 mm) have higher relative density and ultimate tensile strength as compared to the other parameter configurations.

Abstract: The study of the effects of cooling conditions on mechanical properties and wear performance by coating AISI S45C steel with Chrome Nickel Amorphous wire arc spray showed that the average surface hardness of specimens under different cooling conditions such as SCCW, SCCO, SCCS and SCCNT was 601.6 HV, while the surface hardness of HAZ of SCCS and SCCW specimens decreased to 80-90 HV. The tensile test revealed that the average ultimate tensile strength of coated specimens was 706 MPa which was slightly higher than that of uncoated specimens. This result is consistent with Tukey’s one-way ANOVA method, which found a significant difference in tensile strength values at 0.05 and 0.01 levels. For wear resistance, coated specimens showed higher wear resistance compared to uncoated specimens. Overall, the results of this study showed that wire arc spray coating could increase the strength and stress and decrease %elongation of the specimens. Therefore, this technique is suitable for maintenance work to increase the strength of steel in the industry.

Abstract: Aluminum alloys are of particular interest in the design of lightweight structures in different applications. Accordingly, welding aluminum alloys (AA) is a critical issue; for example, welding defects could arise during the traditional welding of aluminum alloys. This paper investigates the effects of welding using a robotic arm on the mechanical properties of 6061-T6 Aluminum alloy, as plates joined by Metal Inert Gas (MIG) welding. The tensile behavior and mechanical properties were investigated using tensile testing, hardness testing, and impact testing. The tensile behavior of AA-6061-T6 un-welded and welded specimens showed a decrease in the tensile strength of the welded specimens due to the fusion of the welded zone and the partially melted zone (PMZ). The hardness test showed an increase in the hardness values away from the welded zone, attributed to voids and defects in the welded and HAZ zones. In addition, the impact behavior showed that the maximum impact is in the base metal zone, and the minimum is in the HAZ. Scanning electron microscopy was used to investigate the welded and un-welded Aluminum microstructures. The mechanical properties of AA 6061-T6 Aluminum alloy were sensitive to the novel welding process.

Abstract: Recent research attempts have shown that graphene as a lubricant nanoadditive provides excellent tribological behaviour in mechanical applications due to its outstanding properties represented in its self-lubricating nature. In this work, a set of deep groove ball bearings lubricated using lithium-based grease mixed with different contents of reduced graphene oxide (rGO) were tested through a specially designed test rig under different loading conditions. The rGO additions were varied to include 0.5, 1, 2, 3.5, and 5 wt.%. The consumed power is introduced for the first time as a measure of lubrication efficiency. The results demonstrate that the addition of rGO reduces the consumed power required to drive the rotor under the applied test load. The most considerable power saving is obtained after adding 2wt.% rGO to grease, which has reduced the consumed power down to about one-fourth of that consumed using grease only. Also, the vibration levels were measured and analysed for each lubrication and loading condition.