International Journal of Civil Engineering
Volume:19 Issue: 3, Mar 2021
- تاریخ انتشار: 1399/12/09
- تعداد عناوین: 8
Mechanical Properties of Aggregates for Roadbase Partially Replaced with Reclaimed Asphalt ShinglesPages 233-243
The objective of this research is to evaluate the potential to partially replace the natural aggregates used for roadbase with reclaimed asphalt shingles (RAS). Three percentages of replacement were evaluated, namely 10, 20, and 30%. A control mix without RAS was tested for comparison. The physical properties of the mixtures, including particle size distribution, soundness, and abrasion were measured and compared with local material specifications. Additional laboratory testing to determine the compatibility (ability to achieve compaction), bearing strength, permeability, and shear strength were conducted. Overall, the mixtures would still meet the requirements for particle size distribution, soundness, and abrasion. The mixtures with RAS had a lower dry unit weight and higher optimum moisture content than the control. However, the addition of RAS to the natural aggregates could result in an exponential decrease in its bearing strength. RAS also reduced the permeability of the material. A replacement of 10% natural aggregates with RAS resulted in a 50% reduction in the California Bearing Ratio and an approximate reduction of 80% in the coefficient of permeability. Results from large-scale direct shear also show an increment in the cohesion and a decrease in the internal friction angle with the addition of RAS. A replacement of 10% natural aggregates with RAS resulted in a 20 kPa increase in cohesion, whereas the control material was cohesionless, and a reduction of 20% in the internal friction angle. Overall, it was concluded that replacements of natural aggregates with more than 10% RAS are not recommended for materials similar to those used in this study.
Structural Behavior of Strengthened Concrete-Encased Steel Beams with Web OpeningsPages 245-263
Concrete-encased steel beams (CESB) have become one of the fundamental composite members utilized in recent years. The research aims to investigate the effect of strengthening CESB with and without openings. Eleven simply supported fully CESB beams with and without web opening under static loading using a four-point loading system were studied. Two main stages were considered; studying the effect of the presence of web opening (located in the shear zone), and the effect of applying three different strengthening materials on the flexure or the shear zone of the beams on the behavior of the CESB. Carbon fiber-reinforced polymer wraps, glass fiber-reinforced polymer wraps, and steel plates were used as externally bonded reinforcement strengthening materials. The obtained experimental results were the mode of failure, the crack pattern, load–deflection curve at mid-span, load–strain curves at different locations, first crack load, serviceability load, ultimate load, energy absorption, and ductility ratio. A Finite-Element Analysis (FEA) is performed using ANSYS release 19.0 program to simulate the 11 tested specimens. Test outcomes showed that the ultimate load and its corresponding deflection decreased by about 58.28% and 80.17%, respectively, due to the effect of the web opening. Furthermore, shear strengthening of CESB with web opening located in the shear zone is more effective than the flexural strengthening using the three different strengthening materials. Also, using a steel plate is extra effective than using carbon fiber wraps or glass fiber wraps on the performance of the tested beams. Based on the FEA, high compatibility between both FE and experimental results is achieved.
Identification of Pavement Model Parameters in the Area of Discontinuous Surface Deformation Based on FWD TestsPages 265-282
Determination of the parameters of the pavement model in the linear discontinuous surface deformation (LDSD) area is presented in the article. The values are based on back calculations which involve results obtained from the elastic half-space model and the elastic—perfectly plastic model implemented in the finite element code compared with the results of the pavement deflection measured with Falling Weight Deflectometer (FWD). Based on the results of the calculations which have been matched to the results of the in situ measurements, the obtained values of the parameters of the pavement model within LDSD zone and outside it, were analysed. The results of pavement tests indicate at least a threefold increase in pavement deflections in the discontinuous deformation zone compared to deflections in the sections not affected by LDSD. The results of in situ tests and computational analysis presented in the paper allow their use in pavement reinforcement design in the area of anticipated LDSD.
Behavior of Plastic-steel Fiber Reinforced Lightweight Aggregate Concrete Columns Subjected to Concentric Axial LoadingPages 283-300
This paper presents the findings of an experimental study on the behavior of plastic-steel fiber (PSF) reinforced lightweight aggregate concrete (LWC) columns under axial compression loading. The experimental variables were concrete compressive strength, main reinforcement percentage, and PSF volumetric ratio. The behavior of the PSF reinforced LWC columns was evaluated in terms of the failure mode, load-bearing capacity, steel reinforcement strain, and ductility. The results showed that the addition of PSFs not only prevented premature spalling of the concrete cover but also strengthened the bond between the LWC and the steel bar. Compared with that of the control specimen, the ductility of the fiber-reinforced columns improved significantly. In addition to the experimental program, a numerical investigation based on nonlinear finite element (FE) analysis was performed using ANSYS 10.0. The experimental and numerical results were compared and found to be in satisfactory agreement. Furthermore, an analytical model developed in a previous study was used to predict the load-bearing capacities of the PSF reinforced LWC columns. The compressive strength of concrete, the spacing, and yield strength of transverse reinforcement were considered in the analytical models, and the analytical predictions were in agreement with the experimental results.
Investigation of Uncertainties in Nonlinear Seismic Analysis of the Reinforced Concrete Shear WallsPages 301-318
In this study, the use of the displacement-based fibre element (DBFE) method for modelling the nonlinear seismic response of reinforced concrete shear wall structures with a variation of damping ratios and types of structural damping is evaluated. The experimental seismic responses of the CAMUS I and NEES-UCSD shear wall structures are compared with nonlinear time-history analysis results obtained using the DBFE method. Comparisons are made in terms of the absolute maximum values of the top displacement, the base shear force, the base bending moment values and minimum differences between overlaps of top displacement time-history graphs. The Hilber-Hughes-Taylor-α integration method is selected for the dynamic solution algorithm. Recommendations are made for appropriate damping ratios for stiffness-proportional, mass-proportional, and Rayleigh damping to be used for the structural damping of nonlinear seismic analyses of the shear walls. The minimum difference between experimental and numerical analysis results is obtained less than 11% using Rayleigh damping. Additionally, the optimal number of fibre elements is researched with regard to the ratio of the mean length of the fibre elements to the longitudinal length of the shear wall. When the ratio is smaller than 3%, the differences between experimental and numerical analysis results for both shear walls are less than 2% at the optimal damping ratios.
The Major Causes of Construction Delays Identified Using the Delphi Technique: Perspectives of Contractors and Consultants in ThailandPages 319-338
At present, in the Bangkok Metropolitan Area of Thailand, numerous construction projects are in process or have recently been brought to completion. In pursuing this work, contractors regularly face construction delay problems, many of which are likely to have been avoidable. The research objective is to survey and prioritize the factors leading to construction delays from the perspective of both the consultants and the contractors. Data were collected via a survey instrument and the Delphi technique was used as the research methodology. To identify the factors that lead to construction delays relevant to the study context, a panel of experts comprising 18 construction public company leaders and 17 project engineers and 17 project consultants, 1 from each of the largest construction contractor and consultant companies in Thailand, and 20 academics in the field of construction were invited to share their opinions. Eventually, 13 factors leading to construction delays were identified from the data collected from the expert panel. A questionnaire was generated using a Likert scale with a range of 1–5 based on the factors suggested by the experts’ opinions. A total of 17 respondents from the contractor companies and 17 respondents from the consultant companies responded to the questionnaire. The numeric value of the responses was computed using the Delphi technique. The responses reached constancy at the second round of data collection. According to the statistical analysis, a Shortage of qualified labor was the most important factor leading to construction delays, according to both the contractors’ and the consultants’ perspectives with a mean value of 4.65 and 4.53, respectively. Change orders made by owners were the second most important factor according to both the contractors and the consultants with a mean value of 4.24 and 4.28, respectively. In addition, insufficient financial liquidity on the part of the contractor ranked as the third most important reason according to both the contractors and the consultants with a mean value of 4.18 and 4.12, respectively. The outcomes are applicable to the causes of construction delay in the Bangkok Metropolitan Area of Thailand, but may not be applicable to other settings. A review of the literature suggests significant differences in relation to such matters as the regulatory environment, societal practices and expectations, economic considerations, the environment, technology, and religion across settings may have an impact on what causes construction delays.
Investigating the Effects of Mixing Time and Mixing Speed on Rheological Properties, Workability, and Mechanical Properties of Self-Consolidating ConcretesPages 339-355
The mixing process performs a critical role in the concrete microstructure, which defines the final product’s quality. Optimizing mixing time and mixing speed during the mixing process can reduce the unit price and energy consumption without impacting product quality. Furthermore, the energy consumption to manufacture self-consolidating concretes (SCC) is more than that of conventional concretes due to their compositions and structures. Due to the fact that rheological and mechanical properties assess the performance of concrete, the effects of mixing energy on the mentioned properties of self-consolidating concretes are taken into consideration simultaneously in the current investigation. Accordingly, different mixtures contained polysaccharide-based viscosity modifying agent and limestone powder are made under different mixing speeds and mixing times. Drawing on the results of mixing time, the optimum time for mixing is 8 min in this study in order to improve the workability and to provide ideal levels of rheological features such as minimum yield stresses (static and dynamic). In the aspect of mixing speed, double increasing from 20 to 40 rpm rises the slump flow by 5%. Besides, accelerating mixing speed increases dynamic yield stress by 37% for 11 min mixed mixtures, which is more than that of other mixing times mixtures’ dynamic yield stress increment. In the aspect of mechanical properties, mixing time increment increases the concrete’s compressive strength. Nevertheless, other mechanical characteristic criteria do not significantly depend on mixing energy.
Experimental Investigation into the Impact of Compaction Energy Level on Thickness of Flexible PavementPages 357-368
As a means of gaining a better understanding of the impact of compaction energy levels on the thickness of flexible pavements, this study investigated samples that were 50% thicker than the standard Marshall specimen sizes. The gradations for those longer (thicker) specimens were based on the binder course gradations as specified by the Republic of Turkey’s General Directorate of Highways. To obtain reliable assessments of the thicker specimens, we compared our test results with those of a control group consisting of standard Marshall Briquettes prepared using the same materials. All specimens were compacted with 10 different compaction energy levels that were increased by fives, starting from 50 blows and ending at 95 blows. After determining their lengths, volumes and specific gravities, a special marble cutter was used to split the thick specimens into two equal parts. Those two identical specimens were identified as the "thin specimens". Subsequently, the Marshall stability test and the indirect tensile test were applied both to the standard Marshall specimen group and the thick and the thin specimen groups. The test results showed that asphalt specimens of 47 and 95 mm in height were optimally compacted after being subjected to 65 and 70 blows.