Nano-modified basalt fiber-reinforced cementitious composites for structural applications
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Date
2021-05
Authors
Bediwy, Ahmed
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Abstract
The use of fiber-reinforced concrete (FRC) has been proposed to develop high performance cementitious composites to strengthen and rehabilitate concrete infrastructure, particularly those in harsh environment. A pioneer research program is conducted to investigate; (1) the behaviour of basalt fiber reinforced cementitious composites (BFRCC) incorporating 40% slag, 6% nano-silica and reinforced with basalt fiber pellets (BP) under ambient and severe environmental conditions, and (2) the feasibility of implementing the BFRCC in large-scale structural elements. The program consists of three phases. Phase I is devoted to study the mechanical properties of the BFRCC on small-scale specimens, Phase II focuses on assessing the bond of GFRP bars embedded in such composite under ambient and harsh conditions to confirm its potential for structural applications. Phase III consists of two stages, experimental and analytical. The experimental stage involves the construction and testing of eleven simply supported deep beams under one-point loading. As for the analytical stage, it involves the assessment of current shear design models for FRP-FRC deep beams and the introduction of new models.
The results show that the nano-modified slag-based cementitious composites reinforced with 4.5% or 6.9% BP are suitable for new construction and rehabilitation applications vulnerable to freeze–thaw and wet-dry environments, as the presence of BP in the cementitious composites effectively discounted the rate of deterioration. Moreover, the partial replacement of cement with 40% of slag, in addition to 6% of nano silica, significantly increases the failure load, and the addition of BP is capable of retaining approximately 90% of the pullout capacity for specimens exposed to harsh conditions. Furthermore, the inclusion of BFRCC in the whole depth of the deep beams is an effective substitution to conventional transverse reinforcement in deep beams. However, from the direct cost perspective, adding the BP as a layer in the tie zone reduces costs and achieves an acceptable level of performance in terms of strength and ductility. The strut-and-tie models in most of the design codes, such as North American, European and Japanese, do not provide proper prediction of the capacity of deep beams. Therefore, a new model is proposed to account for the effect of incorporating different types of discrete fibers into the beam either as a layer in the tie zone or entirely over the whole depth
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Keywords
Basalt, Fiber, FRP, Deep beams, Concrete