Flexural behavior of Polyethylene terephthalate fiber reinforced concrete beams with layered distribution

Abstract

The study focused on casting concrete beams in two layers. Waste polyethylene terephthalate (WPET) fibers were added to concrete in three volumetric ratios (0%, 0.5%, and 1%) to change the properties of the layers. These fibers are rectangular shape with dimensions (50mm length, 4 mm width and 0.3mm thickness). There are nine cases (two beams for each case), three of which, the layers are differing only in location (top or bottom) but they are similar properties and four are differ in location and the percentage of fibers added within the layer, and the remaining two cases the layers are differ in location, percentage of fiber added, and thickness of the layers of the one beam. The thickness of the fibrous concrete layer is either quarter or half the height of the beam. All beams were tested up to failed, to know the effect of difference in layers on structural behavior of beams. The compressive strength, splitting tensile strength, and modulus of elasticity were examined for all types of concrete mixes. Beams dimensions are (1200) mm length, (150) mm width and (200) mm height with clear span (1000) mm. The beams were reinforced by ratio (ꝭ􀯠􀯜􀯡. < ꝭ < ꝭ 􀯠􀯔􀯫. ). The laboratory test results indicated that the addition of plastic fibers to the concrete led to a decrease in the workability and density of concrete at all added ratios, while the splitting tensile strength increased by about (11% and 5.3%) for the ratios (0.5% and 1%) respectively. The compressive strength and elastic modulus slightly increased around (2.7% and 5.5%) respectively, with the percentage of fiber 0.5% and decreasing by (9.9% and 4.5%), respectively, at content of the plastic fibers 1%. The layers beams with different properties showed better results in comparison with similar properties layers beams, where they are recorded higher ultimate load, ultimate deflection, toughness and ductility. Increasing the fibers ratio in the bottom layer of beams with different layers’ characteristics achieves an increase in the yield load of (5% and 15%) when the thickness of the fibrous concrete layer is a quarter and a half, respectively, in contrast to its increase (plastic fibers) in the upper layer, which led to a decrease in the yield load by 10%. Increasing the thickness of the fibrous concrete layer for the same percentage of fibers led to an increase in the ultimate load about (11.8 %, and 6.9%) for the ratios (0.5 %, and 1%), respectively. The best beam is consisting of a normal concrete layer at the top and a fibrous concrete layer at the bottom, its thickness is equal to half the height of the beam, and the percentage of fibers in it is 0.5%, its achieved increase of about (18.2%, 81.2%, 160%, 89%) for the ultimate load and the ultimate deflection, toughness and ductility index respectively. All beams were theoretically studied using numerical analysis (ANSYS software 2015). The results of the numerical study were very close to the results of the study in laboratory. The largest difference between the two studies experimental and theoretical was 8% in ultimate load. The best beam for experimental study was the best at theoretical study too.