Moetaz M. El-Hawary

EFFECT OF FIRE ON FLEXURAL BEHAVIOUR OF RC BEAMS

Abstract The effect of fire on the flexural behaviour of rc beams is investigated. Four groups of rc beams were cast, exposed to fire at 650 °C for time durations of 0, 30, 60 and 120 min and then cooled by water. The concrete compressive strengths of the beams were determined nondestructively using a Schmidt hammer. The beams were tested in flexure by applying two transverse loads incrementally. Strains and deflections were measured at each load increment. Cracking loads, crack propagation and ultimate loads were recorded for each beam. A reduction of ultimate loads, increase in deflection, increase in both compressive and tensile strains and reduction in concrete compressive strength due to fire exposure were observed.

TEMPERATURE EFFECT ON THE MECHANICAL BEHAVIOR OF RESIN CONCRETE

Abstract The investigation of the mechanical behavior of resin concrete is becoming important, as the types of resins are increasing and the use of resin concrete is no longer limited to repair work. The structural use of resin concrete requires accurate design that can be achieved through the utilization of the Finite Element method which requires a complete constitutive model and full understanding of the mechanical behavior of resin concrete. The investigation of stress–strain relations under repeated loading for resin concrete cylinders, prepared using different types of resins and different ratios of resins to aggregate and subjected to different temperature stations was carried out. Three types of resins (two epoxy and one polyester) available in the market were used at three different percentages of resins, 9%, 12% and 15% by weight to cast the cylinders. The cylinders were then subjected to four different temperature stations of 20, 100, 150 and 200°C and then tested in compression using six cycles of loading and unloading to get the stress–strain relation for each case. Direct compressive strength, split tensile strength, toughness and modulus of elasticity were also evaluated.

Performance of epoxy-repaired concrete in a marine environment

The use of epoxy resins is becoming the most common method of concrete repair and rehabilitation. The performance of epoxy-repaired concrete in a marine environment has been investigated. Specimens were cast using two different types of cement, ordinary and sulphate-resistant Portland cement, damaged and then repaired using three different types of epoxy resins available in the Kuwaiti market. Specimens were then hung in the Arabian Gulf, in the tidal zone, so that they were subjected to cycles of wetting and drying for different time durations up to 18 months. The specimens were then tested in split and in slant shear to determine their tensile and bond strength. Results are compared with those of the control specimens, which were kept in a laboratory under controlled conditions.

Evaluation of bond strength of epoxy-coated bars in concrete exposed to marine environment

Abstract The bond strength characteristics of epoxy-coated bars were assessed using a series of pull-out tests on epoxy-coated bars embedded, axially, in concrete cylinders and subjected to marine environment. The specimens were divided in three groups. The first group of specimens were immersed in tanks full of seawater and kept at room temperature while the second group of specimens were put in seawater tanks and kept in open air at variable temperature. The third group of samples were hung in seawater in the tidal zone to capture the actual behavior. Specimens were exposed to the marine environment for time durations of up to 18 months. The effect of marine exposure conditions and duration on the bond strength of epoxy-coated bars in concrete and on the difference in bond strength between epoxy-coated and uncoated bars in concrete were investigated and assessed.

Effect of fire on shear behaviour of R.C. beams

Abstract In this research, the effect of fire exposure time and the concrete cover thickness on the behaviour of R.C. beams subjected to fire in shear zone and cooled by water is investigated. Eight reinforced concrete beams (180 × 20 × 12 cm) were investigated. The beams were divided into two groups. Group (1) consists of four beams with a cover thickness of 2 cm and group (2) consists of four beams with a cover thickness of 4 cm. Each group was subjected to a fire of 650 °C for different periods of time, i.e. 0, 30, 60, 120 min. The concrete compressive strength of the beams was determined nondestructively by using a Schmidt hammer the next day after exposure to fire. The beams were tested by applying two transverse loads incrementally. Strains and deformations were measured at each load increment. Cracking loads, crack propagation and ultimate loads were recorded for each beam. The behaviour of the beams exposed to fire in the shear zone is highly affected by the fire exposure time and the change of the cover thickness.

Bond shear modulus of reinforced concrete at high temperatures

The effect of fire and high temperature on the behavior and properties of concrete has drawn considerable attention. In this work an experimental program is used to determine the effect of high temperature on the interfacial bond shear modulus between concrete and reinforcement. Steel bars of different diameters were embedded in concrete cylinders for a depth less than that required for total development to assure failure by loss of bond. Specimens were then kept in an oven for different time durations and different temperatures. Specimens were then cooled by either keeping cylinders at room temperature or immersing them in water. The pull-out test was applied, and loads and displacements were recorded. Results from the pull-out test were then used along with an analytical model to calculate the bond shear modulus. The analytical model is based on the physical representation of the pull-out test, assuming linear elastic behavior of both steel and concrete.

Effect of sea water on epoxy-repaired concrete

Abstract Due to the Gulf War and the harsh environment in Kuwait, many concrete structures have been damaged and consequently repaired using epoxy resins. Some of these repaired buildings are close to the Gulf waterfront and were therefore exposed to sea water. The effect of sea water, at different temperatures, on the epoxy-repaired concrete has been investigated. Two different types of cement, ordinary and sulphate resistant, three different types of epoxy resins available in Kuwait, and different time durations of exposure to sea water at different temperature stations, were investigated. The effect of weather has also been studied, by keeping specimens immersed in tanks full of sea water in the open air for different time durations. Control specimens were also kept in sea water tanks which were put in an oven for different time durations and temperatures. Specimens were tested in compression, tension, flexure and shearbond. The results presented should help in understanding the expected behavior of epoxy-repaired concrete in Kuwait and other similar marine environments.

Strength and ductility of spirally reinforced rectangular concrete columns

Abstract This experimental study aims at investigating the effects of the inclusion of spiral reinforcement with or without steel fibers on the strength and ductility of rectangular column cross sections. The study included testing of 36 short column specimens with different spiral diameters, pitches of the spiral rebars and steel fiber contents as ductility enhancement measures. However, the other parameters were kept constant to observe clearly the effects of the parameters identified in this study. The results of this investigation indicated that the inclusion of spiral reinforcement in rectangular column sections may lead to an increase in its load carrying capacity (independent of the core diameter) and ductility especially in cases of spiral pitches within the ACI code limitations. It also indicated that the inclusion of steel fibers in spirally reinforced columns may lead to a significant improvement in its ductility.

Fire Resistance Testing of Concrete Beams Reinforced by GFRP Rebars

This article investigates experimental testing of fire resistance of concrete beams reinforced by GFRP rebars. Three beam specimens were used in the fire exposure testing with emphasis on their ability to sustain loads under fire exposure. One specimen was reinforced with ordinary steel rebars and the other two specimens were reinforced with GFRP rebars. The effect of concrete quality on fire resistance was examined. Sustained loads on beams specimens under fire exposure testing were 60% of the ultimate loads. Behavior of the beams up to failure was observed. Large reduction in fire resistance due to the use of GFRP rebars was observed. Language: en

On the mechanical properties of polymer Portland cement concrete

Abstract In this paper, epoxy which is the most common type of polymer used by civil engineers, and polyester, which is cheaper than most other types of polymers, were utilized to produce Polymer Portland Cement Concrete (PPCC). A rich concrete mix was designed and then five different ratios of cement (0, 20, 40, 60 and 100%) were replaced by either epoxy or polyester, rendering five different mixes for each type of polymer. Three types of samples were cast, compacted and then cured for 28 days. The three types of samples are standard beams of size 150×150×600 mm, standard cubes and standard cylinders. One third of the specimens were tested at room temperature, while the rest of the specimens were heated in an oven for 24 hours. Specimens were heated to two temperature stations of 80°C and 150°C. Samples received for flexure, compression, split tension, and direct shear tests, using a specially manufactured apparatus that was used before and found to be effective. The variations of compressive strength, split tensile strength, direct shear strength, and flexural strength with different variables such as temperature, percentage of polymer and type of polymer were determined and assessed.