Effect of maximum coarse aggregate size upon shear strengthening of RC beams using NSM-CFRP strips

Abstract

Reinforced concrete (RC) is widely used because of its many desirable characteristics, such as high strength, fire resistance, and durability. However, structures that are made of concrete may need strengthening or repairing due to concrete deterioration, the harshness of the environment, steel corrosion, errors in design, and damage caused by earthquake load. The use of composite materials has recently become more popular for strengthening and repairing damaged concrete structures. It is also known that properties of the aggregates, such as shape, size, and surface texture, have important influences on the behavior of concrete. In fact, many studies have shown that changes in coarse aggregate will affect the concrete's strength and fracture properties. Towards this end, very little research has been carried out on the effect of maximum aggregate size (MAS) on the shear behavior of reinforced concrete beams. The impact of maximum coarse aggregate size on shear strengthening using the methods proposed in this study was not studied. This research is driven by both environmental and economic aspects where the use of large-size coarse aggregates provides a large volume and less void space compared to small-size aggregates. From an environmental perspective, such an approach will reduce the need for cement in concrete unit volume, hence reducing the pollution. The main purpose of this study is to examine the behavior of reinforced concrete beams under general loading and how this is affected by using different coarse aggregate sizes. This work’s main objective is to investigate the effect of maximum coarse aggregate size on the shear behavior of reinforced concrete beams and study the effectiveness of using the Near Surface Mounted (NSM) – Carbon Fiber Reinforced Polymer (CFRP) strips technique on the shear strengthening of the RC beams. The experimental variables of the study consist of different maximum coarse aggregate sizes (9.5 mm, 12.5 mm, 19 mm, and 25 mm), Carbon Fiber Reinforced Polymer (CFRP) strips spacing (75 mm and 150 mm), and concrete compressive strength (25 MPa and 40 MPa). Fourteen RC beams (150 mm × 200 mm × 1150 mm) were cast using six mixes of concrete to be prepared and tested. The experimental results showed that using maximum coarse aggregate size has a positive effect on ultimate shear strength, maximum deflections, toughness, and stiffness of strengthened RC beams. Using NSM-CFRP strips change the failure mode from pure shear for the control beams to shear-flexural failure for the strengthened beams, which is an ideal enhancement.