- Volume:18 Issue: 6, 2020
- تاریخ انتشار: 1399/02/03
- تعداد عناوین: 8
Effect of Locally Sourced Pozzolan on Corrosion Resistance of Steel in Reinforced Concrete BeamsPages 619-630
Corrosion of the reinforcing steel in concrete continues to be a major cause of damage to reinforced concrete (RC) structures. Eight reinforced concrete beams with dimensions of 100 mm by 150 mm in cross-section and 1000 mm in length were divided into two groups. For each group, locally sourced fly ash was used to partially replace the ordinary Portland cement in the proportions of 0% (control samples), 10%, 20% and 40% by weight. The reinforcing steel bars were weighed and then, after casting and curing, were subjected to accelerated corrosion by employing an anodic impressed voltage at 10 V DC (Group 1) and 20 V DC (Group 2) for 377 h (16 days). The beams were then flexurally tested and the reinforcing steel bars were removed, cleaned and re-weighed to determine the extent of corrosion. The results demonstrate that the Vietnamese-sourced fly ash significantly increases the corrosion resistance of the reinforcing steel with higher fly ash replacement providing better corrosion resistance. The flexural strength of the pre-corroded reinforced concrete beams with partial cement replacement by fly ash is increased by up to 16% for Group 1 and 120% for Group 2. The fly ash was also found to increase the ductility of the pre-corroded reinforced concrete beams.
Consideration of Both Latent Variables and Taste Variation in Modeling Destination Choice for Student’s Non-mandatory ActivitiesPages 631-640
Extensive studies have been conducted on urban travel behavior, but rarely have addressed the travel behavior of special trip generators such as dormitory students. One of the most important student travel activities is non-mandatory (shopping or recreation) ones. The purpose of this study is to investigate the influence of the factors (both tangible and intangible) on the destination choice of such activities for future policy-making in line with appropriate distribution of demand in the city. Therefore, a questionnaire was designed and distributed among the students residing in Imam Khomeini International University dormitories. The results showed that taking individual perception in addition to their taste variation into account would enhance the ρ2(0) index of the mixed hybrid logit model by 0.175 than the standard logit model (with no latent variable and no consideration of taste variations). Furthermore, it was found that increasing the distance to a zone and the absence of direct accessibility to a particular zone via public transportation (buses or taxies) reduced the utility of traveling to that zone. Moreover, the presence of the central business district (CBD) of city in a particular zone and increasing the individuals’ perceived attractiveness of a zone (as the latent variable) increased the utility of traveling to that zone. The results of the mean marginal effect of “Attractiveness” variable show that the probability of five investigated zones increases by 12.2–49.3%. Therefore, this study concludes that both tangible and intangible factors are needed to better understand students' destination choice behavior for using in future policy-making.
Impact of Weaving Segment Configuration Designs on Drivers’ Acute Driving Stress: A Case Study on Houston Freeway Weaving SegmentsPages 641-653
Weaving turbulence on freeways significantly increases the demand for complex driving maneuvers, leading to high driver stress. This study explored the impact of freeway weaving segment configuration designs on drivers’ stress attributed to complex vehicle maneuvers in dynamic traffic. An on-road driving test was conducted to measure healthy, young drivers’ heart rate variability, a biomarker of driving stress, while they performed various freeway weaving maneuvers under different traffic conditions. Statistical analyses were conducted to identify specific weaving maneuvers that triggered high- and medium-level driver stress. The probability distributions of the heart rate variability were estimated and the probabilities of high- and medium driving-stress were determined. Results indicate that intense demand of vehicle maneuvers significantly increases drivers’ stress, especially in the driving scenarios, where two-lane changes were required and the base length of weaving segments were shorter than 400 m or longer than 700 m under medium traffic, or the non-weaving segments were under medium traffic. The baseline driver stress probability is 3.34%. This grew dramatically to more than 60% under the driving scenarios. The results of the study concluded that two-sided weaving segment type, the shorter base length of weaving segments, and medium traffic, are the determinants for a higher likelihood of the driving stress.
Experimental Study of Shear-Deficient RC Beam Wrapped with GFRPPages 655-664
In this study, two types of shear-deficient beams having different stirrup spacing (150 mm c/c and 300 mm c/c) were used. The performances of shear-deficient beam strengthened with externally and internally wrapped GFRP were tested under three-point bending monotonic loading. The load-carrying capacity of GFRP-wrapped beam was found to be significantly increased in comparison to the unstrengthened (control) beam and was the highest in both externally and internally bonded shear-deficient beams, i.e., 39.60% and 45.3%, respectively. Significant increment was also observed in flexural ductility, energy absorption and inelastic performance of the strengthened beams. The performance of the externally GFRP-wrapped RC beam (GFRP–epoxy-bonded RC beam) was better than that of the internally wrapped beam. However, because of the low economy index, internal wrapping is more suitable as a strengthening technique than external wrapping.
Utilization of a New Locally Isolated Bacterial Strain for Promoting Mechanical Properties of MortarPages 665-671
Conventional reparation and maintenance method of mortars and buildings have adverse side effects on their surrounding environmental and aesthetic value. This study reported the impact of a locally isolated bacterium, Bacillus sp. strain SKC on the parameters affecting the properties of mortar. The abiotic control and bacteria-modified mortars were investigated to determine the differences in their properties. The compressive strength of the bacteria-modified mortar was successfully enhanced which was twofold higher than that of the abiotic control mortar, thus increasing the density. Calcium carbonate crystal deposition on bacteria-modified mortar reduced the porosity and permeability. The bacterial deposition of calcium carbonate was confirmed by SEM images and XRD analysis.
Response Characteristics of a Steel Fiber-Reinforced Porosity-Free Concrete Beam Under an Impact LoadPages 673-684
The utilization of ultra-high-strength concrete offers a weight reduction of concrete structures and improvements in disaster protection performance. Recently, porosity-free concrete (PFC) having the world’s highest compressive strength of 400 MPa has been developed, and its basic mechanical properties were determined; however, its impact-resistant capacity is yet to be examined. In this study, investigation of the impact resistance behavior of PFC is performed using a weight dropping impact test on a fiber-reinforced PFC beam. Steel fiber-reinforced PFC is used for preventing brittle failure, and the full plastic moment of the PFC beam cross-section is determined based on material test results. Also, the estimation of maximum response deflection is attempted by a simple plastic analysis. It was demonstrated that the response deflection could be reduced by 30–50% by increasing the steel fiber mixing rate in the PFC beam from 1 to 2%. The proposed estimation method revealed that the response deflection of the PFC beam could be estimated with an accuracy of approximately 80% considering the calculated full plastic moment when the plastic hinge is clearly formed. In the future, to establish a design procedure for the impact-resistant capacity of protective structures from steel fiber-reinforced PFC, it is necessary to conduct experimental and numerical research focusing on ultimate strength, including statistical processing.
The Effect of Soluble Mineral Salts in Ceramic Brick MasonryPages 685-699
This work discusses the effects of soluble mineral salts on ceramic brick masonry walls at Petrolina, Pernambuco, Brazil, located 780 km from the ocean. To understand this phenomenon, a mapping of the pathologies originating from the effects of soluble mineral salts in Petrolina was carried out and wells were implemented to monitor the underground water supply in five points considered to be where the most frequent occurrence of the phenomenon takes place. Samples of soil, groundwater, bricks affected by the phenomenon and the level of chloride in the atmosphere of these localities were collected and analysed in the laboratory in order to characterize their properties. The results obtained indicate that the building pathological manifestations present in ceramic block walls, located in the study areas, are strongly correlated with the high content of soluble salts observed in the soil and groundwater samples collected than by the amount of chloride content in the atmosphere soluble salt levels. Clay sands are a type of soil more prone to underground water runoff and, because of this feature, provide a more favourable environment for rising moisture that transports soluble mineral salts to the masonry walls accelerating their degradation process.
Development of Innovative Integrated Last Planner System (ILPS)Pages 701-715
Last planner system (LPS) has been recognized as one of the most formidable tools for implementing lean construction (LC) and improving construction productivity. The past 25 years have witnessed the sequential development of LPS but still, the construction industry is unable to utilize its full potentials. It was reported that users of LPS were only able to achieve 70% of their weekly assignments with much potential to perform better. Considering it is a complete lean construction tool, LPS is mostly implemented in isolation, thereby exposing many areas that are overlooked and poorly managed. In this study, an effort has been made in developing strategies to overcome LPS implementation challenges by integrating LPS with other available lean tools and techniques. A systematic literature review is carried out, followed by a conceptual development of findings and theories into a robust integrated LPS implementation model. Thirteen (13) major shortcomings in implementing LPS and sixteen (16) lean tools to overcome these shortcomings are identified. Presently, LPS is managed as a single entity. However, due to its vast diversity, all of its stages should be managed independently. In this study, lean tools are integrated within LPS stages to develop the innovative integrated last planner system (ILPS), allowing the management of LPS stages independently. Additionally, a guideline for sequential amalgamation of LPS with the lean tools at different stages is presented to smoothen the ILPS implementation process. The ILPS will facilitate the construction industry in utilizing LPS to its fullest potential. This newly developed ILPS will help the lean practitioners in increasing construction productivity and reducing cost and time.