Ahmed Gheni

Seismic Performance of Innovative Hollow-Core FRP–Concrete–Steel Bridge Columns

Abstract This paper presents the seismic behavior of hollow-core fiber-reinforced polymer–concrete–steel (HC-FCS) columns. The typical HC-FCS column consists of a concrete wall sandwiched between an outer fiber-reinforced polymer (FRP) tube and an inner steel tube. The inner steel and outer FRP tubes provide continuous confinement for the concrete shell; hence, the concrete shell achieves significantly higher strain, strength, and ductility than unconfined concrete in conventional columns. Three large-scale HC-FCS columns were investigated in this study. Each column had an outer diameter of 610 mm (24 in.) and a height-to-diameter ratio of 4.0. The steel tube was embedded into a reinforced concrete footing with an embedded length of 1.6–1.8 times the steel tube diameter, whereas the FRP tube only confined the concrete wall thickness and truncated at the top of the footing level. In general, the columns exhibited high lateral drift, reaching to 11.6%, and failed gradually as a result of concrete crushing a...

Seismic Behavior of Hollow-Core FRP-Concrete-Steel Bridge Columns

This paper presents the behavior of precast hollow-core fiber reinforced polymer (FRP)-concrete-steel tubular columns (HC-FCS) under combined axial and lateral loading. The HC-FCS column consisted of a concrete wall sandwiched between an outer FRP tube and an inner steel tube. Two large scale columns, RC-column and HC-FCS column were investigated during this study. The steel tube of the HC-FCS column was embedded into the footing while the FRP tube was stopped at the top of the footing level, i.e., the FRP tube provided confinement only. The hollow steel tube is the only reinforcement for shear and flexure inside the HC-FCS column. The FRP in HC-FCS ruptured at lateral drift of 15.2% while the RC-column displayed 10.9% lateral drift at failure. The RC-column failed due to rebar rupture and the moment capacity suddenly dropped more than 20% after that. However, the HC-FCS suffered gradual failure due to concrete crushing, steel local buckling and yielding, followed by FRP rupture.

Behavior of Hollow-Core FRP-Concrete-Steel Columns under Static Cyclic Flexural Loading

AbstractThis paper presents the seismic behavior of hollow-core fiber-reinforced polymer (FRP)-concrete-steel (HC-FCS) columns comparable with the conventional RC column. The typical HC-FCS column ...

Leaching Assessment of Eco-Friendly Rubberized Chip Seal Pavement

Companies in the United States need to mine billions of tons of raw natural aggregate each year. At the same time, billions of scrap tires are stockpiled every year. As a result, replacing the natural aggregate with recycled aggregate is beneficial to the construction industry and the environment. This paper is part of a comprehensive project that developed, and field implemented, a new eco-friendly rubberized chip seal where the mineral aggregate in chip seal is partially or totally replaced with crumb rubber made of recycled tires. This paper presents an extensive study of the environmental impact of using rubber aggregate in chip seal pavement in terms of leaching under different pH conditions, including simulated acid rain. The results are compared with those of conventional chip seal. Leaching from the constituents of chip seal, that is, rubber aggregate and emulsion, was investigated. Two types of rubber and two types of asphalt emulsions were studied. The leaching performance of rubberized chip seal was also investigated. This study revealed that the toxic heavy metals leached from the rubberized chip seal, for pH ranging from 4 to 10, were below that of the EPA drinking water standards. In addition, a significant reduction of heavy metal leaching was recorded when rubber was used with emulsion in the form of chip seal pavement under different pH conditions. Finally, the metal leaching in all types of samples (including rubber, asphalt emulsion, and chip seal) decreased with the increase in pH value.

Crumb Rubber as a Sustainable Aggregate in Chip Seal Pavement

The U.S. companies need to mine billions of tons of raw natural aggregates each year. In the same time, billions of scrap tires are going to landfills every year which makes the replacement of using natural aggregate with recycled and sustainable one is more beneficial to both industry and environment. This paper presents an extensive study on the performance of the chip seal pavement surfaces in terms of aggregate retention and performance. This study introduces a new eco-friendly chip seal by implementing the crumb rubber made of recycled tires as aggregates for such surface dressing. Twenty four specimens of chip seal were prepared and tested under three tests investigating the aggregate retention. The tests included the standard Vialit test, modified Vialit test, and sand patch test. Two types of emulsions, two types of binders, and three types of aggregates including the crumb rubber were examined in the tested specimens. This study revealed that the crumb rubbers from recycled tires would be used in the chip seal as aggregates but it is preferable to be used in conjunction with the conventional aggregates. The crumb rubber showed a remarkable performance in aggregate retention. This performance was mainly because of the low weight of the crumb rubber and its rough surface, which increased holding the crumb rubber into the asphalt emulsion or binder. In addition, crumb rubber as a partial or total replacement for the mineral aggregate was successfully implemented in the field using the traditional procedure and equipment.

Reduced zinc leaching from scrap tire during pavement applications

Large quantities of scrap tires have been generated and accumulated over the years. However, a significant amount of them are stocked due to the lack of environmentally-friendly methods for disposing of, or reusing them. Because tires contain approximately 1-2% zinc by weight, leaching of zinc from scrap tires could be an environmental concern. In this research, we investigated the leaching of zinc from tire particles that are used with asphalt for pavement applications. The effects of tire particle size and pH on zinc leaching were also examined. Our results indicated that asphalt treatment significantly reduced zinc leaching from tires, and that it was also reduced by increasing the tire particle size and pH. The leaching of zinc was quantified by using a speciation-based modeling approach. The model parameters, namely, the total leachable zinc mass and the adsorption constant, can be used to predict the leaching of zinc under different conditions. The reduction in zinc leaching from asphalt-treated tire particles was due to the physical blocking of the tire surface by the asphalt. Results also indicated that, while the leaching of zinc and other selected toxic elements from untreated tire particles using simulated acid rain was not significant compared to the drinking water regulations, asphalt treatment during the pavement application further improved the environmental performance of the tire particles.

Effect of Curing Temperatures on Zero-Cement Alkali-Activated Mortars

Three alkali-activated mortars (AAM), or what is called geopolymer, mix with different fly ashes sources were tested during the study. X-ray fluorescence was carried out on AAM samples to determine their chemical composition. Flowability and setting times of the AAMs were tested. Compressive strength was analyzed for five different temperatures of 30, 40, 55, 70, and 85 °C under five different time intervals of 4, 8, 16, 24, and 48 h. The compressive strength results indicate that the calcium content and ratio of silica to alumina played a pivotal role in the optimum curing conditions for each of AAMs.

Effect of Different Class C Fly Ash Compositions on the Properties of the Alkali-Activated Concrete

Class C fly ashes from two different coal-fired power plants were used to manufacture alkali-activated concrete. The workability and the compressive strength were studied in this paper. The workability was measured by the slump test. The compressive strengths at different ages of 1, 7, and 28 days were measured. Three different curing regimes including elevated heat curing at 70 °C, laboratory ambient curing at 23 ± 2 °C, and moist curing in the moisture room at 23 ± 2 °C were applied to identical mixtures to investigate the curing regime effects. Both types of fly ashes showed high slump of 212.5 and 225 mm. The results revealed that the compressive strength of the specimens that cured at the ambient or moist conditions increased with increasing the calcium content in the fly ash. However, the compressive strength of the specimens that were cured at 70 °C decreased when increasing the calcium content of the fly ash. The compressive strength of the concrete based on fly ash having higher calcium content at 28 days reached to 34.78, 36.62, and 51.46 MPa for oven-, ambient-, and moist-cured specimens, respectively. Furthermore, the compressive strength of the concrete based on fly ash having relatively lower calcium content at 28 days reached to 36.43, 30.79, and 47.45 MPa for oven-, ambient-, and moist-cured specimens, respectively.