International Journal of Civil Engineering
Volume:16 Issue: 2, Feb 2018

Corrosion of reinforcing steel bars is the leading cause of deterioration in concrete. In this paper, corrosion process of rebars is controlled using montmorillonite nano-clay particles which are partially substituted as cement in the mix designs. Mechanical and physical properties of the mixtures are measured, and steel reinforced concrete specimens are exposed to chloride solution for 6 months. Passing electric current through the reinforcement is measured under constant voltage, and potential differences between the steel bars and the concrete surfaces are measured every week. Results show that Montmorillonite particles remarkably reduce the compressive strength and increase the water absorption, but they can postpone initiating of rebars corrosion and decrease the corrosion rate. Negatively charged surface of nano-clay particles repulse OH− and Cl− ions and as a result the formation of iron rusts is delayed and the corrosion process is declined. Consequently, neither the compressive strength nor the water absorption is suitable as a criterion to accept a reinforced concrete under chloride attacks.

In fires, reinforced concrete (RC) columns in the subway stations were seriously threatened by high-temperature gas fumes. In this paper, an axial compressive simulation test that involved eight RC columns was undertaken to investigate the effect of high-temperature gas fume on RC columns. Two of them were control specimens with different cross sections. The others were exposed to high-temperature gas fumes. The specimens were heated to 300, 400, and 500 °C. The effects of high-temperature degree on ultimate load capacity and failure mode were investigated. As the applied load was increased, the crack gradually spread to the unheated area. Meanwhile, the initial stiffness and energy dissipation capacity were also summarized. The test results show that the ultimate load capacity and initial stiffness of RC columns decreased sharply with the increase in temperature. Compared to unexposed RC columns with circle cross section, the ultimate load capacity of specimens exposed to high temperature decreased by 47.9, 56.0 and 67.9%. The initial stiffness of RC columns with circle cross section exposed to 500 °C was 13 times lower than those of unexposed RC columns. The energy ductility of RC columns increased with the flue gas temperature. Furthermore, an analytical model was established to predict the residual axial load-carrying capacity of RC columns. It was demonstrated that the analytical model is correct and the predicted results are consistent with experimental results.

In the recent years, compound channels received more attention in hydraulic engineering for their role in estimating and calculating the hydraulic parameters of natural rivers. Usually, for determination of the hydraulic parameters of compound channels, physical models are used which have cost and time assumption. According to the wide usage of numerical modeling in hydraulic engineering, this paper aims to evaluate the accuracy of numerical models in compound channels by simulating the hydraulic parameters in nine different types of compound channels and to compare them with experimental data. These simulations can show the interaction between velocity and vorticity and other hydraulic parameters by using contours and graphs along the channel length which help to have more and better understanding about their changes. Numerical simulations were performed using the renormalization-group turbulence model and volume-of-fluid free surface model for determining the level of fluid. Values of convergence ratio and the grid convergence index were calculated for evaluating the extrapolated values from numerical modeling and the sensitivity of the model solution to the numerical discretization, respectively, which indicates a proper validation of grid spacing and refinement selection for optimizing the calculation process. The comparison between numerical and experimental results shows a good agreement. The extracted numerical results show that by changing the floodplain width and depth, the water surface level changes 4–20% and 5–34%, respectively. Moreover, the numerical results show an increment of 20 and 145% in Froude and Weber numbers in floodplains, respectively, because of increment of velocity in floodplain.

In this paper, total ten geometrically similar self-compacting concrete (SSC) specimens were tested, under static and cyclic loading. These consisting a set of one control SCC and four strengthened SSC specimens of different percentages of fiber for static loading and similarly another set for cyclic loading. Research work is aimed on developing hybrid fiber reinforced self-compacting concrete, and experiments were carried out to observe the optimum dosage and influence of hybrid fiber on self-compacting concrete beam specimens in static and cyclic loading. This study focused on load carrying capacity, energy dissipation, and the initial stiffness improvement of hybrid fiber reinforced self-compacting concrete beams with respect to control self-compacting concrete beam specimen under both static and cyclic loading. It can be concluded that incorporation of hybrid fiber with optimum dosage in concrete improved the ductility of concrete and failure was more ductile and gradual compared with control specimens.

The objective of this research was to investigate the engineering properties and mix design of geopolymer mortar made using fly ash, natural zeolite and ground granulated blast furnace slag as source material and combination of sodium hydroxide and sodium silicate as alkaline activator. To study the effect of sodium hydroxide concentration on compressive strength, three different sodium hydroxide solutions (8, 10 and 12 M) were used. The ratio of sodium silicate/sodium hydroxide was varied from 1.0, 2.0 to 3.0. The test results demonstrate that the compressive strength of developed geopolymer mortar increases with increase in the concentration of sodium hydroxide solution and sodium silicate content in the activator. The average maximum compressive strength was obtained when the sodium hydroxide concentration was 12 M and sodium silicate content was 3.0. At higher alkali content, the water absorption is less due to lower void spaces. The utilization of industrial waste materials such as fly ash, ground granulated blast furnace slag and natural pozzolans such as zeolite would lead to significant economic and environmental benefits in geopolymer production.

International joint ventures (IJVs) are both advantageous and challenging due to differing technical abilities, economic and political environments, and cultural and legal frameworks. This study identifies the external risks particularly political, economic, legal, social and environmental in IJVs carrying out construction projects in Pakistan. It further analyzes the impact of these risks on the project success criteria of time, cost and quality. Data are collected using questionnaire-based survey and with the help of factor analysis, 16 critical external risks are identified. The top most critical risks are fluctuation in exchange rate, weather systems, political instability and delay in approval. Analytical Hierarchy Process is applied to prioritize critical external risks discretely for project success criteria. As a result, time is found to be the most influenced project criterion by the critical external risks, followed by cost and quality. The results are of importance for local practitioners in the form of recommendations for better management of IJV risks. Future research can benefit from incorporation of more dimensions of project success.

In the present study, the effect of carbon black (CB) as an additive on resistance of bitumen to delay or prevent rutting and low temperature cracking was investigated. For this purpose, different amounts of CB (0, 5, 10, and 15 wt%) were added into bitumen with PG 58-28. Conventional tests (penetration, softening point, Fraass breaking point, ductility, and kinematic viscosity) and Superpave binder tests (rotational viscosity, dynamic shear rheometer, and bending beam rheometer test) were carried out to determine the physical and rheological properties of pure and modified bitumens. In addition, high and low temperature performance grades of pure and modified bitumens were identified according to Superpave binder specification. The results indicated that the addition of CB increased the stiffness and resistance of bitumen to rutting at high temperatures and resistance to thermal cracking at low temperatures of bitumen. Finally, the bitumen becomes more elastic and less susceptible to temperature changes.

This paper analyses the occurrence of temporary speed restrictions in railway infrastructure associated with railway track geometry degradation. A negative binomial regression model is put forward to estimate the expected number of temporary speed restrictions, controlling for the main quality indicators of railway track geometry degradation and for the maintenance and renewal actions/decisions. The prediction of temporary speed restrictions provides a quantitative way to support the assessment of unavailability costs to railway users. A case study on the Lisbon–Oporto Portuguese line is explored, comparing three statistical models: the Poisson, the ‘over-dispersed’ Poisson and the proposed negative binomial regression. Main findings suggest that the main quality indicators for railway track geometry degradation are statistically significant variables, apart from the maintenance and renewal actions. Finally, a discussion on the impacts of the unavailability costs associated with temporary speed restrictions is also provided in a regulated railway context.

This paper presents the performance of a new prestressed composite lining applied in shield tunnels for water conveyance. The Yellow River Crossing Tunnel of the Middle Route Project of the South-to-North Water Division Project is adopted in this study as a case, and a three-dimensional finite element model is established to analyse the stress distribution and deformation feature of the prestressed composite lining when the tunnel is under the assembly condition, the tension condition and the water-filled condition. The finite element model is verified by comparing with the results of the full-scaled simulation experiment. The calculation and analysis results reveal that further open of the segmental joint gaps can be limited and full circumferential compression of the secondary lining can be realized when the tunnel is under the water-filled condition, which are conducive to long-term operation of the prestressed composite lining. The membrane has a significant effect on preventing stresses from being transmitted between the segmental lining and the secondary lining. The numerical calculations are verified by the results of the full-scaled simulation experiment, and the three-dimensional numerical model combined with the analysis method used can simulate the structural characteristics and the bearing mechanism of the prestressed composite lining.

Young’s modulus values are needed to conduct any computer simulation of structure behavior. The purpose of this survey is to estimate Young’s modulus of both rubberized mortar and concrete using two-phase composite models. To this effect, results of some previous experimental researches have been used as platform, and then, two-phase composite models were applied. It has been noticed that not all two-phase theoretical models can be directly used for predicting Young’s modulus of rubberized mortar or concrete, because they are composites with soft particles. In terms of Young’s modulus of matrix (mortar or concrete) and scrap tire rubber and their volume fraction, De Larrard and Le Roy model seems in close concordance with experimental Young’s modulus of both rubberized mortar and concrete.