Engineering Journal (Faculty of Engineering, Chulalongkorn University, Bangkok)
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Verifying the Reliability of Impressed Current Method to Simulate Natural Corrosion in Reinforced Concrete
Get PDFIn order to accelerate the corrosion of steel reinforcement in the reinforced concrete structures for laboratory research, the impressed current method has been used widely regardless of the appropriacy of this method on the various aims of the studies relating to the deterioration of the reinforced concrete structures. The aim of this study is to characterize the influence of the impressed current method on the steel-concrete interface in the reinforced concrete to verify the reliability of this method on simulating the natural corrosion. The mill-scale of the steel reinforcement and the steel-concrete interfacial region were investigated using SEM-EDS. The results indicate that impressed current can induce the non-uniform and localized corrosion on the steel reinforcement. The corrosion products formed were likely to the natural corrosion induced by chloride environments. However, the oxidization of OH- at anode can inhibit the precipitation of corrosion products at steel-concrete interfacial region and then slowing down the formation of crack in concrete. This positively leads to an overestimation of load capacity of corroded structure and raises doubt on utilizing this technique to simulate the corrosion behavior
Thermomechanical Performance of the Offset Crankshaft Heat Engine Driven by TiNiCu Shape Memory Alloys
Get PDFGeothermal hot springs are among the alternative clean energy sources to the fossil fuels for mitigating the current global warming crisis. However, the accessible geothermal water at the surface was mostly at low temperature, which impairs the practicality of harvesting these energy. Shape memory alloys (SMAs), which deform through the increased temperature, were adapted into the rotating mechanism as the actuators with the aims to convert the low-temperature heat into the mechanical work. This study utilized the helical spring-shaped TiNiCu SMAs as the actuators for the offset crankshaft heat engine. Performance of this engine was evaluated using rope brake dynamometer, by which the rotational speed, torque, and power were measured at the water temperature from 55-85°C. The results show that the engine performance increased with increasing water temperature and was dependent on the crankshaft arrangement. The offset angle of 30° was found to be optimal in this study with maximum torque of more than 5.8 N∙m and maximum power of 3.9 W at 15.7 rpm when operating at water temperature of 85°C. This study shows that the heat engine driven by TiNiCu SMAs could harvest low-temperature energy from the geothermal hot springs with the maximum observable efficiency of around 1.4%
Effect of Implant Diameter and Cortical Bone Thickness on Biomechanical Performance of Short Dental Implant-Supported Distal Cantilever: A Finite Element Study
Get PDFThe present study aimed to assess the effect of implant diameter and cortical bone thickness on the biomechanical performance of short dental implant-supported distal cantilever placed in posterior atrophic maxilla by finite element method. There were 6 stimulating models in this study, which consisted of a bone block and short dental implant of 7 mm in length, 3 differences of diameter (5.0, 5.5, and 6.0 mm) and 2 variations of cortical bone thickness (thickness of 0.5 and 1.0 mm). All models were applied with 200 N of force with 30° inclination to lingual direction. Von Mises stress and strains were used to evaluate the biomechanical performance of the short dental implant and surrounding bone. Results showed that increasing of implant diameter led to decrease in stress level on neck of dental implants and strains in surrounding cortical bone. However, the implant diameter equal or smaller than 5.0 mm should not be used due to high stress level with could be a cause of implant failure. In addition, clinicians should be aware of placing implant with inadequate bone stock which lead to surrounding bone resorption
Effects of In-bed Stoichiometric and Flue Gas Recirculation on Combustion and Environmental Performances of a Swirling Fluidized-bed Combustor
Get PDFThis work studied the firing of ground nut/peanut shells in a twin-cyclonic fluidized-bed combustor at the maximum combustor loading (~22.5 kg/h) in the flue gas recirculation (FGR) mode. During the experimental tests, excess air (EA) was fixed at about 60%, while the in-bed stoichiometric ratio (Sb) and FGR ranged from 1.0–1.2 and from 10–25%, respectively. The experimental results showed that nitrogen oxide (NOx) emissions significantly decreased when FGR increased; however, the opposite tendency was found for carbon monoxide (CO) emission. Meanwhile, FGR showed strong effects on both combustion and emission performances, the impacts of Sb were quite low. The FGR of ~10-18% and Sb from 1.0-1.2 appear to be optimum operating conditions for firing ground nut/peanut shells to ensure the lowering of major emissions under the limitations of Thailand’s emission standards, with high combustor efficiency at 99%
Extraction of Gallic Acid from Chromolaena sp. Using Ultrasound-assisted Extraction
Get PDFChromolaena sp. is believed to have phytochemical components namely alkaloids, flavonoids, flavone, essential oils, phenolics, saponins, tannins and terpenoids. In this study, ultrasound-assisted extraction (UAE) procedure was performed to extract the gallic acid from Chromolaena sp. UAE is known to be an environmentally green extraction method. This study was carried out with two different parameters which are sonication time and duty cycle. Phytochemical screening result showed the presence of phenolic compound when the dark-green colour of solution was observed. The best operating parameters to maximise the yield were as follows: sonication time of 80 minutes with yield of 3.006 mg/mL and duty cycle of 90% with yield of 3.764 mg/mL. The FT-IR result shows that presence of O-H and alkene group in the extraction samples. From the results, it can be concluded that UAE is an effective method to extract gallic acid from Chromolaena sp. The implication in this study was reducing the extraction time for the production of herbs medicine from natural resource
Time-Dependent Model for Evaluating Corrosion Potential and Electrical Resistivity of Reinforced Concrete
Get PDFThe main work presented in this paper is to propose prediction models for estimating electrical resistivity of concrete and corrosion potential of steel in reinforced concrete. The prediction models for electrical resistivity of concrete (r) and corrosion potential of steel (Ecorr) incorporated hydration degree (αHyd (t)), pozzolanic reaction degree (αPoz (t)), porosity (PCap (t)) and chloride content ([CL-]). Predicted results were verified with results of experimental measurement. An experimental program was run for 1 year with various concrete mix proportions. According to the results, corrosion resistance of concrete increased with time as the degree of hydration increased. Further, the introduction of fly ash offered a good corrosion resistance, which also increased with time. Lastly, the existence of chloride ions in the concrete weakened passive film on steel surface, by the fact that its presence eased the movement of ions in the concrete and increased the risk of corrosion
Towards a Successful Extension of Time (EoT) Claim: A Consensus View of Construction Professionals via a Modified Delphi Method
Get PDFUndeniably, the claim document provides an opportunity for the claimants to defend and fight for their rights. Hence, it should be prepared in a well-organized, professional and convincing manner to facilitate the assessor in assessing the claim. However, it is not an easy task as a good claim not only requires fact and evidences but also demands other important elements that complement each other. Despite the many studies that have been carried out with regard to improving the management of contract claims, yet very little research has been conducted to address the issue in relation to the extension of time (EoT) claim, specifically as to what constitutes a good EoT claim and the possible measures that can be taken by industry players towards the successful settlement of an EoT claim. This paper reports on a Delphi study focusing on identifying the success elements for EoT claim specifically in the Malaysian construction industry. Two rounds of a modified Delphi surveys were conducted and consensus was obtained from twelve experts. The Delphi survey has successfully elicit experts’ consensus on the elements that perceived to be the most important element in producing a quality EoT claim that may lead to a speedy, successful and amicable settlement of such claim. Findings from this study is expected to provide an aid in assisting the claimants in the preparation of claims through the identification of the success elements for EoT claims that will then lead towards achieving harmonious claim settlement
Performance Evaluation of Construction Companies in Malaysia with Entropy-VIKOR Model
Get PDFConstruction industry is an important industry that has an enormous impact on the country’s economic development. Nowadays, the government strives to encourage the construction industry to develop the advanced and modern infrastructure that related to health, transport, education, and housing. As a result, the Malaysian construction sector companies’ financial performance is studied in this paper based on the crucial financial ratios. This paper aims to assess and compare the Malaysian construction sector companies’ financial performance based on Entropy-VIKOR model. In this paper, the listed construction companies in Malaysia are investigated. The findings of this paper demonstrate that ZECON, DKLS, GADANG, TRIPLC, and MELATI are ranked as the top five construction companies based on the proposed model. The importance of this paper is to assess the construction companies’ financial performance as well as identify the weights of the financial ratios in assessing the Malaysian construction sector companies’ financial performance with the proposed Entropy-VIKOR model
Stress Analysis of Rib-to-Deck Joints in Orthotropic Steel Deck Based on Nominal and Effective Notch Stress Approaches
Get PDFThis paper presents the stress analysis of the rib-to-deck (RD) joint in an orthotropic steel deck. Finite element models were developed to evaluate the effects of the wheel load location and weld penetration ratio on the nominal and effective notch stresses at the RD joint. The critical wheel load locations for fatigue-sensitive locations of the RD joint were investigated comprehensively. The potential locations of fatigue crack initiation were evaluated for weld penetration ratios ranging from 0% to 100% at different transverse locations of single- and double-wheel loads. The analytical results indicated that the critical location of fatigue crack initiation was influenced by the weld penetration ratio and transverse wheel load location. An increase in the weld penetration ratio decreased the root notch stress and significantly increased the potential for toe-deck cracking, as the wheel loads were applied at the RD joint and close to the adjacent rib. The nominal stress approach was used to identify the fatigue crack type accurately only for relatively high weld penetration ratios, with the wheel loads applied at the RD joint and over the rib. For the condition of 100% weld penetration ratio with the loads applied at the joint, the fatigue life corresponding to the effective notch stress approach ranged from 66% to 73% of the fatigue life obtained using the nominal stress approach
Computational Framework for the Determination of Duration and Revenue Sharing Rates in PPP Concession Renewal: A Monte Carlo and Risk Premium Approach
Get PDFPublic Private Partnership (PPP) has been extensively used as an innovative and integrated form of project delivery, especially for large-scale infrastructure projects. When a PPP concession is about to expire, the PPP law may require a study to compare benefits and risks as part of the decision to renew or end the contract. The study, based on expected value analysis, will be used by the contracting authority for negotiating with the incumbent over terms such as contract duration and revenue sharing rate. However, a major flaw of expected value analysis is the inability to provide a possible risk profile of the contracting agency or concessionaire. Accordingly, this paper presents a computational framework for determination of the contract duration and the revenue sharing rate using Monte Carlo simulation and a risk premium approach. The proposed framework can be used to depict the risk profile of the concessionaire under different contract durations and revenue sharing rates. To illustrate how the proposed model can be applied in practice, a PPP toll road project is adopted as the case study. The results of the study suggest that the revenue sharing rate is the key to the negotiation of the contract to be renewed. The proposed method may be used by governments for negotiation with an incumbent concessionaire or to achieve a fair price when a competitive retendering process is considered