Structural behavior of rubberized concrete containing synthetic fibers

Abdelaleem, Basem Hassan Abdelbaset (2019) Structural behavior of rubberized concrete containing synthetic fibers. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

This research program aims to investigate the combining effect of crumb rubber (CR) and synthetic/metal fibers (SFs/MFs) in the development of concrete suitable for structural applications subjected to monotonic and cyclic loading. The research also aims to overcome the challenge of optimizing the strength and stability of self-consolidating concrete (SCC) containing CR and SFs/MFs. Five comprehensive experimental studies were conducted on both small-scale and large-scale concrete samples to meet the research objectives. The first study aimed to develop and optimize a number of successful self-consolidating rubberized concrete (SCRC) and synthetic fiber SCRC (SFSCRC) mixtures with a maximized percentage of CR and minimized reduction in strength. The variables in this study included various supplementary cementing materials (SCMs) specifically metakaolin (MK), silica fume (SLF), fly ash (FA), and ground granulated blast-furnace slag (GGBS), different binder contents (500, 550, and 600 kg/m³), varying percentages of CR (0% to 30%), different types of SFs specifically micro-synthetic fibers (MISFs), and macro-synthetic fibers (MASFs), different lengths of SFs (19mm, 27mm, 38mm, 50mm, and 54mm), and different SFs volume fractions (0%, 0.2%, and 1%). The second and third studies evaluated the flexural and shear behavior of large-scale reinforced concrete beams made with SCRC, vibrated rubberized concrete (VRC), SFSCRC, and synthetic fiber VRC (SFVRC). The fourth study investigated the structural performance of rubberized beam-column joints reinforced with SFs/MFs under reverse cyclic loading. This study consisted of three stages: the first stage contained a total of six SCRC mixtures selected to cast six beam-column joints with varied percentages of CR (0-25%). The second stage included eight rubberized concrete mixtures with different coarse aggregate sizes and different MFs lengths and volumes selected to pour eight beam-column joints to be tested under cyclic loading. The third stage contained seven rubberized concrete beam-column joints reinforced with different types, lengths, and volumes of SFs to be tested under cyclic loading. The fifth study evaluated the cyclic behavior of engineering cementitious composite (ECC) beam-column joints made with different percentages of CR, different SCMs, and different sand types. In this study a total of eight beam-column joints were cast and tested under reverse cyclic loading. The main results drawn from the first study indicated that the addition of SFs reduced the fresh properties, which limited the maximum percentage of CR that could be used in SCRC mixtures to 20%, compared to a 30% maximum percentage of CR used in developing successful SCRC mixtures without SFs. However, using SFs in SCRC mixtures increased the impact resistance and appeared to alleviate the reduction in splitting tensile strength (STS) and flexural strength (FS) that resulted from adding CR. The main results of the flexural testing conducted in study 2 indicated that using MISFs slightly enhanced the deformability, flexural stiffness, ductility, energy absorption, first cracking moment, and bending moment capacity, while this enhancement significantly increased when MASFs were used. Combining high percentage of MASFs (1%) with high percentage of CR (30%) compensated for the reduction in the bending moment capacity that resulted from using high percentage of CR, and helped to develop semi-lightweight concrete beams. The inclusion of CR in study 3 negatively affected the ultimate shear load, post-diagonal cracking resistance, and first cracking moment of the tested beams while it improved the deformation capacity, self-weight, and cracking pattern. Combining CR with MISFs or MASFs, further improved the deformation capacity, self-weight, and narrowed the crack widths of the tested beams. The results of this study also indicated that the use of a relatively higher percentage of fibers (1% compared to 0.2%) in VRC beams significantly compensated for the reduction in shear strength resulting from a high CR percentage (30%). The results of the fourth study revealed that the optimum percentage of CR to be used in beam-column joint mixtures is 15%. Although using this percentage slightly reduced the load carrying capacity, it greatly enhanced the ductility, brittleness index, deformability, and energy dissipation. The results also revealed that using MISFs slightly improved the structural performance of beam-column joints, while using MASFs had a significant effect on enhancing the load carrying capacity, ductility, stiffness, and energy dissipation of tested joints. The main results of the fifth study reported that increasing the percentage of CR up to 15% significantly increased the deformability, cracking behavior, ductility, and energy dissipation of ECC joints, while the initial stiffness, first crack load, and ultimate load were decreased.

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