Flexural and Shear Behavior of Rubberized High Strength Reinforced Concrete Beams Strengthened with CFRP Ahmed S. Eisa, Ahmed Gab Allah, Ragab Shaker Mahmoud Department of Structural Engineering, Faculty of Engineering, Zagazig University, Zagazig, Egypt Email:ahmedeisa@zu.edu.eg, eng_ahmedgaballah2010@yahoo.com, Ragabshaker@yahoo.com Ahmed Ibrahim Department of Civil and Environmental Engineering, University of Idaho, Moscow, ID, 83843, USA Email:aibrahim@uidaho.edu Abstract—This study presents an experimental investigation of the flexural and shear behavior of strengthened high strength concrete (HSC) beams made with rubberized concrete. CFRP has been used in strengthening of all beams in shear and bending. The concrete mixtures have included a 15% of sand replaced with crumbed rubber with a size of 2 mm. Ten (10) simple span concrete beams have been prepared and tested to promote both flexure and shear failures. The tested beams were divided into two groups, where each group was divided into five beams. The first group was tested to fail in flexure and the second group in shear. Beams with crumbed rubber showed very good flexural and shear strength and all the strengthening techniques used were very effective in both flexure and shear. It was found that the most effective flexural and shear failure loads were increased by 51% and 64%, respectively. Overall, the results showed the feasibility of using rubberized beams in structural applications. Index Terms—crumb rubber, compressive strength, strengthening, flexural Strength, CFRP, ductility I. INTRODUCTION In the last 40 years, the compressive strength of cast- in-place concrete has been quite doubled, from 35 to 85 MPa. Strengths as high as 140 MPa are often achieved within the laboratory and on rare occasions in the field. Ultra-high strength concrete has been accomplished using reactive powder concrete with no coarse aggregates included. These advances have been made possible by two major developments: the introduction of high range water-reducing admixtures (HRWRA) and the utilization of nano-silica fume. Chemical admixtures allow the generation of workable concrete with very low water-to- cement ratios, and silica fume could produce cement paste with very low porosity. Nowadays, high strength concrete (HSC) is being used more and more frequently which offers smaller sections and thus result in more useable floor space compared to normal strength concrete (NSC). In addition, HSC has been used in joints between precast columns and beams for full development strength and for improving durability and service life. In addition, early strength development of HSC could accelerate construction schedules significantly. For example, a 105 MPa of HSC could gain a one-day compressive strength of 35 MPa compared to NSC which gains it in a month. Also, HSC exhibits excellent workability and ability to self-desiccate, thus reducing or eliminating moisture problems. Various research have investigated the replacement of fine and coarse aggregates by crumb rubber to produce rubberized concrete. Neil et al. [1], investigated the strength characteristics of rubberized concrete and examined the relationship between the size, percentage, and shape of rubber aggregate size and the strength measured. Rubberized concrete was found to possess acceptable workability, and a smaller unit weight compared to plain concrete. Overall, rubberized concrete showed greater ductility than normal concrete specimens. Toutanji et al. [2], investigated the effect of the replacement of mineral coarse aggregates by shredded rubber tire chips. All specimens were moist cured for 28 days at a temperature of 29 “C (850 F) and at a relative humidity in excess of 95%. A total of 50 cylindrical specimens were made (25 for compression and 25 for flexure). The study concluded that the failure of specimens containing rubber tire chips exhibited a ductile mode of failure compared to the control specimens. The incorporation of these rubber tire chips in concrete exhibited a reduction in compressive and flexural strengths. the reduction in compressive strength was approximately twice the reduction of the flexural strength. Similar conclusions were obtained by Zheng et al. [3], Raghvan et al. [4], and Khatib et al. [5]. The rehabilitation of infrastructures is not new, and various projects have been carried out around the world over the past two decades. Historically, steel has been the ordinary material used to strengthen concrete bridges and buildings. Bonded steel plates or stirrups have been applied externally to successfully repair concrete girders 98 International Journal of Structural and Civil Engineering Research Vol. 10, No. 3, August 2021 doi: 10.18178/ijscer.10.3.98-105 © 2021 Int. J. Struct. Civ. Eng. Res Manuscript received December 1, 2020; revised March 21, 2021; accepted May 8, 2021.