97 publications from this institution
Corrosion is a long-term process resulting in the deterioration of the reinforced concrete (RC) structures. Most of the structural problems observed under the impact of either earthquakes or service loads might occur due to corrosion. Therefore, prediction of the remaining service life of a corroding RC structure plays an important role to prevent serious premature damage. In this study, a corroded, 25-year-old high school building which has been demolished at an earlier time was analyzed as a function of corrosion rate. Bond-slip relationships were taken into account in nonlinear analyses as a function of corrosion rate for different time periods (i.e., non-corroded (t: 0), existing (t: 25) and 50 years after construction); and they were used to ensure the effect of time-dependent slip rotation on the global structural behaviour by modifying the target post-yield stiffness of each structural member. Nonlinear push-over analyses were performed by defining the time-dependent plastic hinge properties as a consequence of corrosion effects. In order to define the performance levels of three different time periods, nonlinear incremental dynamic analyses (IDA) were performed for 20 earthquake ground motion records as a function of corrosion rate. Results showed that bond-slip relationship between concrete and steel is very important in evaluating the non-linear behaviour of corroded RC structures.
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In recent years, extensive research has focused on investigating rubberized concrete as a structural material due to its enhanced properties, including increased ductility, improved energy dissipation, and higher damping ratios. Additionally, rubberized concrete contributes to sustainable development by recycling non-biodegradable waste and reducing the use of natural aggregates in concrete mixtures. However, its performance in retrofitting existing structures remains unclear and requires thorough investigation before it can be widely implemented in construction activities. The main objective of this research is to evaluate the seismic performance of reinforced concrete buildings strengthened with rubberized concrete jackets under severe earthquake excitations. To achieve this, laboratory tests were conducted to assess the properties of high-performance, self-compacting rubberized concrete mixes with various rubber content levels. Additionally, finite element models of reinforced concrete retrofitted with these mixes were analyzed using nonlinear response history analysis to compare their performance against control models. The results of this experimental work indicate a significant reduction in the mechanical properties of rubberized concrete. However, there is a considerable improvement in the damping ratio, which enhances the energy dissipation capacity of the structures. This improvement contributes to an increase in damping energy and a reduction in hysteretic energy, suggesting that rubberized concrete jackets can enhance the seismic resilience of reinforced concrete buildings.
This paper aims to model the effect of density in 7, 14, 28 days on compressive strength of Ultra High Performance Concrete (UHPC) in same compaction and curing conditions by Design of Experiments (DOE) methodology using vary range of 5 variables: Silica fume (SF), Steel Fiber, Cement 42.5, Superplasticizer (SP), and water cemetiotious ratio (w/c).The results shows the significance effect of density on compressive strength of UHPC in different days, The models are valid for the mixes made with 1.0 sand, 0.15-0.30 silica fume amount, 0.70-1.30 cement amount, 0.10- 0.20 steel fiber, 0.04- 0.08 superplasticizer (all values are by sand by weight mass) and 0.18- 0.32 water cementitious ratio.
This paper investigates the suitability of copper tailings as a cement replacement material in mortars. The impact of copper tailings at 0%, 5%, 10% and 15% cement replacement level by mass on the rheology, mechanical and durability properties of mortars was evaluated. Results revealed higher yield stress and flow loss in mixtures incorporating copper tailings. High mortar compressive strength, flexural strength and abrasion resistance were determined at 5% cement replacement level. Furthermore, despite increased rate of water absorption, higher resistance to acid attack and chloride penetrations were also observed in samples containing copper tailings. These improved properties were more pronounced in samples containing pre-wetted tailings at 5% cement substitution level. The use of copper tailings in mortars could bring about significant environmental conservation and sustainability gains.
Over the last few years, many studies were performed to investigate rubberized concrete’s behavior as a sustainable alternative for conventional concrete by replacing natural aggregates with recycling old rubber tires. These studies have shown that the concrete's mechanical and durability properties are significantly reduced, while its ductility and damping ratio improved. Accordingly, using this material in RC structures could be a promising solution for improving their energy dissipation capabilities. Currently, the literature lacks a numerical study that can highlight the effectiveness of using high-strength rubberized concrete for retrofitting RC structures subject to earthquake loadings . Therefore, this research investigates the seismic performance of reinforced concrete buildings strengthened using different high-strength rubberized concrete mixtures under various ground motion excitations. As a part of the study, finite element models of reinforced concrete structure retrofitted with these concrete mixes will be analyzed using nonlinear response history analysis and compared against two different control models composed of a bare structure and a jacketed RC structure using the control concrete mixture. In general, using rubberized concrete jacketing improved the seismic performance of the bare structure significantly. Furthermore, utilizing high-strength rubberized concrete rather than the control one resulted in increasing the damping energy and slightly reducing the base shear forces of the structure.
Crusher dust is a fine material formed during the process of comminution of rock into crushed stone or crushed sand. This dust is composed by particles which pass 75 μm BS sieve. Effects of dust content in aggregate on properties of fresh and hardened concrete are not known very well. An experimental study was undertaken to find out the effects of various proportions of dust content on properties of fresh concrete and hardened concrete.
This study develops empirical models for the prediction of the bond strength of uncorroded and corroded reinforcement bars. The effects of hooked reinforcement on the bar’s development length when covered fully and partially are examined. An accelerated corrosion method is used to corrode the reinforcement bars embedded in concrete specimens. Pull-out tests are performed to investigate the ultimate bond strength of the concrete specimens. The effects of two different geometries of reinforcement bars are discussed by considering two different concrete strength levels and concrete cover depths. It is found that partly covered hooked reinforcement bars increase the radial stress on the concrete surface and reduce the bond strength. Increases in the bond strength due to the increased roughness of the steel bar caused by the confined corrosion products are less for hooked bars. The results reveal that the developed models show good relationships with the experimentally computed test results.
The evaluation of steel-fiber reinforced concrete using the maturity method was investigated in this study. There were four different volume fractions of fibers (0, 0.5, 1 and 1.5 by volume of concrete) and three different curing temperatures (8°C, 22°C and 32°C) considered. The compressive strength and flexural strength were tested at 1, 3, 7, 10, 14 and 28 days for all of the volume fractions of fibers and at the different curing temperatures. The results show that as the volume fraction of fiber increased from 0 to 1.5%, the compressive and flexural strengths increased by 14% and 35%, respectively, compared to plain concrete. The maturity method was used to predict the compressive and flexural strengths. Four different equations (linear hyperbolic, parabolic hyperbolic, logarithmic and exponential) were used to predict the compressive and flexural strengths. All of the predicted models have good correlations with the experimental results for both compressive and flexural strengths. Moreover, to predict the compressive and flexural strengths using the maturity method, the apparent activation energies were calculated.
A simple, economical, and practical drop-weight impact testing machine was developed to determine the impact resistance for high-strength fiber-reinforced concrete (HSFRC) composite. Impact and compression tests were carried out on concrete cylinders reinforced with three different aspect ratios of hooked-end steel fibers l/d (length/diameter): 60, 75, and 83 (30/0.50, 60/0.80, and 50/0.60 mm/mm), and four different percentages of steel fibers 0.5%, 1.0%, 1.5% and 2.0% by volume of concrete. For each aspect ratio and volume of fibers, complete stress–strain curves of HSFRC were generated in order to determine the total energy absorbed for each cylindrical specimen in compression. The addition of steel fibres to concrete has improved impact resistance and also the compression toughness. The test results showed that a logarithmic relation exists between compression toughness energy (E Ct) by means of the generated stress–stress curves from the compressive tests and the impact energy (EI) by means of the modified impact machine for HSFRC at different l/d ratio of 60, 75, and 83.
