Showing papers by "Mohamed A. ElGawady published in 2017"

Fresh properties and compressive strength of high calcium alkali activated fly ash mortar

Abstract: This paper reports the fresh properties and compressive strength of high calcium alkali-activated fly ash (AAFA) mortar. Two different sources of class C fly ash, with different chemical compositions were used to prepare alkali-activated mortar mixtures. Four different sodium silicate to sodium hydroxide (SS/SH) ratios of 0.5, 1.0, 1.5, and 2.5 were used as alkaline activators with a constant sodium hydroxide concentration of 10 M. Two curing regimes were also applied, oven curing at 70 °C for 24 h, and ambient curing at 23 ± 2 °C. The rest time, i.e., the time between casting the mortar cubes and starting the oven curing was 2 h. The results revealed that the setting time, and workability of mortar decreased with increasing the alkali to fly ash ratio, and decreasing the water to fly ash ratio. The optimum sodium silicate to sodium hydroxide ratio was 1.0, which showed the highest compressive strength and setting time. An increase of sodium silicate to sodium hydroxide ratio to 2.5 led to a significant reduction in the setting time, and workability of mortar. The 7-day compressive strength of the mortar approached 20.80 MPa for ambient cured regime and 41.10 for oven cured regime.

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...

Fresh Properties and Early Compressive Strength of Alkali-Activated High Calcium Fly Ash Paste

Abstract: This paper reports the influence of high calcium content in alkali-activated fly ash (AAFA) paste mixtures on the compressive strength, setting time, and workability. Class C fly ash was used to prepare alkali-activated paste mixtures. Four different sodium silicate to sodium hydroxide ratios of 2.5, 1.5, 1.0, and 0.5 were used as alkaline activators with a constant sodium hydroxide concentration of 10 M. Two curing regimes were also applied, oven curing at (70 °C) for 24 h, and ambient temperature at (23 ± 2 °C). The delay time between mixing and starting curing the specimens in the oven regime is 2 h. The compressive strength of the specimens was tested at 7 days for both curing regimes. The results showed that the fresh AAFA pastes had shorter setting time and lower workability with increasing the ratio of alkaline activators to fly ash ratio. However, the compressive strength of hardened AAFA was increased when the ratio of alkaline activators to fly ash ratio increased. A water to fly ash ratio of 0.3 with alkaline activators to fly ash ratio of 0.25, which displayed a balance between the fresh and hardened AAFA properties. The optimum sodium silicate to sodium hydroxide ratios were 1.0 for ambient curing and 1.5 for oven curing. The compressive strength of AAFA has reached up to 8 ksi after 7 days for ambient curing and 10 ksi for oven curing with initial setting time of approximately 180 min.

Durability of Polyester-Based GFRP Subjected to Hybrid Environmental and Mechanical Loads

Abstract: Fiber reinforced polymer (FRP), as a new alternative construction material compared to conventional materials like concrete and steel, has been introduced into civil infrastructure area for centuries and gained increasing interests by many researchers and contractors. FRP exbits several property advantages, such as high strength-to-mass ratio, ease of handling, and relatively high resistance to corrosion. However, one problem that hinders this material from wider acception in civil infrastructure application is the durability of FRP subjected to harsh complicated environmental conditions has not been fully investigated yet. This paper is aim to study the performance of the polyester-based glass fiber reinforced polymer (GFRP) subjected to combined cement alkaline solution, freeze-thaw cycles, wet-dry cycles, heating-cooling cycles, and sustained mechnical load. Concrete was poured into GFRP tube to make concrete-filled FRP tube (CFFT) cylinders, and the cylinders were put into environmental chamber with sustained axial load on. The concrete core of the CFFT cylinders was removed after 72-day’s conditioning, and the outer GFRP tube was cut into ring specimens to conduct hoop tensile tests. Test results indicated that the conditioned GFRP was slightly degraded in strength, but had significant decrease in strain. Sustained load had negligible effect on the strength of GFRP specimens, but did further deteriorate the strain of loaded specimens compared to unloaded specimens.

Hollow-Core FRP–Concrete–Steel Bridge Columns under Torsional Loading

Abstract: This paper presents the behavior of hollow-core fiber-reinforced polymer–concrete–steel (HC-FCS) columns under cyclic torsional loading combined with constant axial load. The HC-FCS consists of an outer fiber-reinforced polymer (FRP) tube and an inner steel tube, with a concrete shell sandwiched between the two tubes. The FRP tube was stopped at the surface of the footing, and provided confinement to the concrete shell from the outer direction. The steel tube was embedded into the footing to a length of 1.8 times the diameter of the steel tube. The longitudinal and transversal reinforcements of the column were provided by the steel tube only. A large-scale HC-FCS column with a diameter of 24 in. (610 mm) and applied load height of 96 in. (2438 mm) with an aspect ratio of four was investigated during this study. The study revealed that the torsional behavior of the HC-FCS column mainly depended on the stiffness of the steel tube and the interactions among the column components (concrete shell, steel tube, and FRP tube). A brief comparison of torsional behavior was made between the conventional reinforced concrete columns and the HC-FCS column. The comparison illustrated that both column types showed high initial stiffness under torsional loading. However, the HC-FCS column maintained the torsion strength until a high twist angle, while the conventional reinforced concrete column did not.

Nonlinear Analysis of Hollow-Core Composite Building Columns

Abstract: This paper numerically investigates the behavior of hollow-core fiber-reinforced polymerconcrete-steel (HC-FCS) building columns under combined axial compression and flexural loadings. The HC-FCS column for buildings consists of an outer circular fiber-reinforced polymer (FRP) tube, an inner square steel tube, and a concrete wall between them. A threedimensional numerical model has been developed using LS_DYNA software for modeling of large scale HC-FCS columns. The nonlinear FE models were designed and validated against experimental results gathered from HC-FCS columns tested under cyclic lateral loading. The FE results were in decent agreement with the experimental backbone curves. These models subsequently were used to conduct a parametric study investigating the effects of the concrete wall thickness, steel tube width-to-thickness (B/t) ratio, and local buckling instability on the behavior of the HC-FCS columns. The obtained local buckling stresses results from the FE models were compared with the values calculated from the empirical equations of the available design codes. Finally, an approximated expression based on the available empirical formulas and the FE model results has been proposed in this paper to calculate the local buckling stresses of

Crumb Rubber as a Sustainable Aggregate in Chip Seal Pavement

Abstract: 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.

Behavior of Concrete-Filled Hybrid Large Rupture Strain FRP Tubes Under Cyclic Axial Compression

Abstract: This paper experimentally investigates the behavior of concrete filled fiber reinforced polymer (FRP) cylinders under cyclic axial compression. The FRP used in this study were either Glass FRP or hybrid Large Rupture Strain (LRS-FRP) and conventional Glass FRP (GFRP). LRS-FRP are manufactured out of polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) obtained from recycled plastics. Hence, they are much cheaper and environment-friendly than conventional GFRP or carbon FRP (CFRP). LRS-FRP has high tensile rupture strain (usually greater than 5%) compared to 1-2% for GFRP and CFRP. This study presents the results of a total of 5 specimens having different confinement ratios to investigate the behavior of concrete filled LRS-FRP or hybrid LRS-FRP and GFRP tubes in terms of ductility, ultimate strain, and strength improvement. The results showed that using LRS-FRP significantly improved the ductility of the confined concrete. However, the improvement in strength was limited. The hybrid confinement improves both the ductility and strength.

Seismic Performance of Hollow-Core Composite Columns under Cyclic Loading

Abstract: This paper experimentally investigates the seismic behavior of a large-scale, hollow-core, fiber-reinforced, polymer-concrete-steel HC-FCS column under cyclic loading. The typical precast HC-FCS member consists of a concrete wall sandwiched between an outer fiber-reinforced polymer (FRP) tube and an inner steel tube. The FRP tube provides continuous confinement for the concrete wall, along the height of the column. The column is inserted into the footing and temporarily supported; then, the footing is cast in place around the column. The seismic performance of the precast HC-FCS columns was assessed and compared with previous experimental work. The compared column had the same geometric properties; but the steel tube was 25% thicker than the column that was tested in this study. This paper revealed that these HC-FCS column assemblies were deemed satisfactory by developing the whole performance of such columns and using that performance to provide excellent ductility with inelastic deformation capacity by alleviating the damage at high lateral drifts.