Trang: 395-410 Can Xuan Khanh, Le Xuan Ba, Nguyen Truong An, Trinh Quang Hung, Nguyen Trung ThanhTóm tắtBoosting machining quality is a prominent solution to save production costs for burnishing operations. In this work, a machining condition-based optimization has been performed to decrease surface roughness (SR) and enhance Vickers hardness (VH) of the minimum quantity lubrication-assisted burnishing operation (MQLABO). The burnishing factors are the spindle speed (S), depth of penetration (D), and the air pressure (P). The burnishing trails of the hardened material labeled 40X have been conducted on a milling machine. The adaptive neuro-based-fuzzy inference system (ANFIS) was used to construct the correlations between the process inputs and MQLABO responses. The non-dominated sorting genetic algorithm-II (NSGA-II) is utilized to determine the optimal parameters. The scientific outcomes revealed that the optimal values of the S, D, and P are 800 RPM, 0.09 mm, and 4.0 Bar, respectively. The SR is decreased by 53.8%, while the VH is enhanced by 3.1%, respectively, as coBarred to the initial values.
Trang: 411-422 Thuy Anh Nguyen, Hai Bang LyTóm tắtA Gaussian process regression (GPR) model for predicting the bond strength of FRP-to-concrete is proposed in this study. Published single-lap shear test specimens are used to predict the bond strength of externally bonded FRP systems adhered to concrete prisms. A database of 150 experimental results collected from published works is used for the training and testing phases of the proposed GPR model, containing 6 input parameters (width of concrete prism, concrete compressive strength, FRP thickness, FRP width, FRP length, and FRP modulus of elasticity). The output parameter of the prediction problem is bond strength. Three statistical indicators, namely the coefficient of determination, root mean square error (RMSE), and mean absolute error (MAE) are used to evaluate the performance of the proposed GPR model over 500 simulations. The results of this study indicate that the GPR provides an efficient alternative method for predicting the bond strength of FRP-to-concrete when compared to experimental results.
A vision-based excavator productivity analysis in Vietnam
Trang: 423-436 Vu Quang Huy, Nguyen Hoang TungTóm tắtThe process of determining the working parameters of reverse bucket excavators is mainly consulted through the Ministry of Construction norm. However, in the era of industrialization and modernization, machine and equipment are increasingly modern and innovative, making the determination of excavator productivity or parameters through the regulations in the old norms unsuitable. Furthermore, updating the norms through data collected in the field take tremendous amount of time and procedures as it is labor intensive. Therefore, this paper proposes a vision-based analysis in calculating excavator productivity using image processing applications and coding language to automatically determine the excavator productivity and bring results on the basis of analysing big data collected from validated construction sites. To be specific, this paper introduces a new method in calculating the excavator productivity by extracting crucial coefficients from hundred images of the excavators using an open-source software, then compare with the traditional method to identify and analyse the importance of this new method and the practical use it might bring to the construction industry.
Trang: 437-451 Pham Xuan Dung, Hoang Huong Giang, Nguyen Thi Van HaTóm tắtStudying on transportation e-marketplaces (TEMs) has today received much concern because developing TEMs helps enterprises and their customers reduce operation costs and improve supply chain efficiency. This study evaluates the adoption of TEMs in Vietnam based on the demand side’s perspective, including the viewpoint of shippers and the Transport Service Providers (TSPs). While shippers and TSPs around the world are facing various issues related to transportation and logistics process in the competitive market, TEMs is a potential solution which can offer response to those challenges such as transaction cost reduction, better transport capability, inefficiency diminishment, … In Vietnam, TEMs is still a new concept with the limitation of usage, so that the number of researches on this topic is scarce. This study followed the quantitative research method via SPSS technique of data analysis to provide a brief view of TEMs adoption in Vietnam. These insights can make contribution to both research and practice in the future.
Trang: 452-467 Vu Thi An NinhTóm tắtInvestigation on the influence of beam theory and partial foundation support on natural frequencies play an important role in design of structures. In this paper, fundamental frequencies of a bidirectional functionally graded sandwich (BFGSW) beam partially supported by an elastic foundation are evaluated using various beam theories. The core of the sandwich beam is homogeneous while its two face sheets are made from three distinct materials with material properties varying in both the length and thickness directions by power gradation laws. The finite element method is employed to derive equation of motion and to compute the frequencies of the beam. The effects of the material gradation, the foundation parameters and the span to height ratio on the frequencies are studied in detail and highlighted. The difference of the frequencies obtained by different beam theories is also examined and discussed. The numerical results of the paper are useful in designing BFGSW beams with desired fundamantal frequencies.
Application of self-produced artificial sand in the production of green mortar
Trang: 468-476 Huynh Trong Phuoc, Lam Tri Khang, Pham Trong Binh, Phan Huy PhuongTóm tắtDue to the large disposal of locally industrial wastes and the shortage of natural resources, turning industrial by-products into green artificial materials has been attracting many researchers in the world. Following this trend, this study evaluated the potential application of self-produced artificial sand (AS) in the production of green mortar. The AS was produced by the alkali-activated method using a mixture of 36.4% fly ash, 36.4% slag, 3.5% 10M NaOH solution, 11% Na2SiO3 solution, and 12.7% water. The mortar mixtures were designed based on the densified mixture design algorithm with the incorporation of the AS as the substitution of natural sand (NS) by 0 – 100 wt.% (interval of 20%). The engineering properties of the mortar samples in both fresh and hardened states were evaluated through the tests of workability, compressive strength (CS), water absorption (WA), and shrinkage/ expansion. The experimental results showed that the mortar sample incorporating 20% of AS to replace NS performed superior engineering properties in comparison to other samples. Further increasing the AS content generally caused a negative impact on the mortar’s performance. Increasing AS content beyond 20% systematically decreased the CS while both WA and expansion were increased noticeably. However, the properties of the green mortar produced for this study satisfied all of the requirements of the official Vietnamese standards. Thus, the research results further confirmed a great potential in producing green mortar using AS to either partially or fully replacement of NS. In addition, the use of AS greatly contributes to not only saving natural resources but also limiting the negative effects on the environment due to the exploitation and use of naturally sourced materials.
An experimental study on production of high strength non-shrink grout containing fly ash
Trang: 477-485 Dang Thuy ChiTóm tắtCement-based grouts are widely used thanks to its outstanding features such as high workability, non-separation, non-bleeding, easy to fulfill small gaps with complex shapes. This paper descrcibes the first phase of a series of laboratory experiments that examined the ability of production of self - levelling mortar at the University of Transport and Communications. The Portland cement-based grout incorporated superplasticizer, fly ash, fine aggregate, water along with expansion agent to match as closed as possible the given high strength non-shrink grout. The experimental study focused on the performance of non-shrink grouts regarding the flowability, expansion and bleeding, strengths and drying shrinkage of the test grout mixtures. The high range water reducer (HRWR) at dosage of 1% by weight of cement was used as a flowability modifying chemical admixture to prevent water segregation and leads to an increase in compressive strength. The parameter tests consist of water-cement ratios, and fixed dosages of superplasticizer and expansive agent. To examine the flowability of grout mortars, the flow cone test was applied. The flow cone test result indicated that there were three proportional of grouts that can meet the requirement of fluidity. The compressive strength of specimens was tested according to ASTM C349-14. It was concluded that the compositions of grouts at a water-cement ratio of from 0.29 to 0.33 have compressive strengths greater than 60 MPa. The tested specimens using the expansive agent with the dosage recommended by the manufacturer meet the non-shrinkage requirement of a grout. The experimental results have demonstrated the ability of production of high strength non-shrink grouts.
Trang: 486-497 Huu Manh Tong, Anh Duong Do, Ngoc Anh Nguyen, Trung Duc Nguyen, Binh Minh Nguyen, Thi Huong Mai, Minh Hieu NguyenTóm tắtIn response to little known about the use of face masks for public transport passengers in developing countries, this study investigates the prevalence of using masks and using masks correctly together with influential factors. Using 570-passenger data collected on the whole bus network from 7 September to 3 October 2020 in Hanoi, the authors found that 100% of users wore masks; however, about 11% failed to wear masks correctly. As regards factors, passengers who are old, rarely ride by bus, take heavy luggage, travel with other(s) were more likely to use masks incorrectly. Having a health issue encouraged the correct use of masks. Attitudes towards the COVID-19 were significant factors. The higher levels of agreement with the acute danger of COVID-19 and the risk of infection from the public were involved in the higher likelihood of the correct mask wearing. Notably, over time with no community transmission of the coronavirus, the likelihood of incorrect use of masks was more inclined to increase. To address the wrong utilization of masks on buses, the role of ticket conductors in reminding and asking users using masks incorrectly should be enhanced. Additionally, authorities should issue messages and implement campaigns to encourage citizens to wear in public spaces on a regular basis, particularly when the adherence reduces over the time without community transmission of COVID-19. Although not covering all aspects representing the incorrect mask wearing, this study is one the first research on the incorrect use of masks, thus extending the literature on how public transport users respond the effects of COVID-19.
Trang: 498-509 Doan Dinh Thien Vuong, Nguyen Thanh Hung, Nguyen Dinh HungTóm tắtCorrosion of the steel reinforcement bars reduces the area of the steel bar and the bond stress between the steel bars and around concrete that decreases the capacity of concrete structures. In this study, the bond stress between steel bar with a diameter of 12mm and concrete was examined with the effect of different corrosion levels and different concrete grades. A steel bar was inserted in a concrete block with a size of 20×20×20cm. The compressive strength of concrete was 25.6MPa, 35.1MPa, and 44.1MPa. These specimens were soaked into solution NaCl 3.5% to accelerate the corrosion process with different corrosion levels in the length of 60mm. The pull-out test was conducted. Results showed that the bond strength of the corroded steel bar was higher than that predicted from CEB-FIP. Slip displacement and the range of slip displacement at the bond strength were reduced when the concrete compressive strength was increased. The rate of bond stress degradation occurred faster with the increment of the corrosion level when the concrete compressive strength was increased.
