The Impact Resistance of FRC Specimens with Steel Fibers and CFRPs

What is it about?

In this paper, the effects of macro-synthetic steel fibers and bidirectional carbon fiber-reinforced polymers (CFRPs) on the impact resistance of concrete specimens were studied. 54 concrete cylindrical specimens with different compressive strengths (20, 30, and 40 MPa) and with different fiber content ratios (0 %, 1 %, 1.5 %, and 2 %) were tested under impact loading. Half of these specimens were tested with the CFRP wrapping. The specimens were subjected to weight (46.7 and 66.8 kg) dropping at a height of 1.62 m. The process of weight dropping was continued until 30 % weight loss in the specimens was observed and the number of weight droppings related to this loss was recorded. Results indicated that the impact resistance of the concrete specimens (corresponding to the number of weight droppings) increased by using steel fibers or CFRP wrapping, separately. However, the results demonstrated that the specimens wrapped with the CFRP sheets had much further impact resistance than the FRCs without wrapping. Finally, the results showed that the greater the compressive strengths of the concrete, the better the impact resistance.

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Photo by Matthew Henry on Unsplash

Photo by Matthew Henry on Unsplash

Why is it important?

In this study, the effects of the steel fibers and CFRP wrapping on the axial impact behavior of concrete specimens were experimentally studied. The performance of CFRPs and steel fibers were in different scenarios were experimentally compared with each other. We specified the optimum ratios of steel fibers and rehabilitation methods to improve the impact behavior. During the last 80 years, building construction all over the world has been dominated by the use of concrete materials. Despite the clear advantages and necessity of concrete as a building material, its production and use cannot be considered environmentally friendly or sustainable. This is mainly because cement content and its current production process lead to vast CO2 emission . Hence, to be in line with global and local climate strategy, the material consumption of reinforced-concrete (RC) structures must be reduced while their strength, ductility, and impact resistance are maintained under extreme conditions as well as normal conditions. One of the most visible consequences of global warming is an increase in the intensity and frequency of extreme weather events. Such extreme events must be considered in newly built structures. Extreme conditions and their effects can cause substantial damage to civil infrastructure resulting in the worst case, for example, in structural collapse causing civilian casualties. These extreme effects are mostly connected to impact actions (loads) : • Extreme wind action is one of the environmental effects, that causes damage to both land-based and offshore structures. It is essential to highlight that climate change is leading to an increasing prevalence of extreme wind actions . • Severe impact action can arise from collisions or explosions. These actions have severe social and economic consequences. A few well-known and relevant Norwegian examples from the past few years can be mentioned in this context: Gas explosions on an oil platform or in a residential building – with subsequent casualties and structural damage. Although the serious consequences of impact effects are known, there are still many open questions in the calculation of the resistance of concrete structures against impact loads: Standards such as Eurocode 2 for the design of concrete structures mainly discuss the load side in detail, but not the resistance side. Moreover, the effects of novel materials such as different types of high-performance fiber-reinforced cementitious composites (HPFRCCs) have not been comprehensively studied. To improve the resistance of concrete structures, including against these extreme actions, technological developments commenced about 50-60 years ago, and substantial research is still conducted to investigate the effects of new materials, such as different types of concrete and different reinforcements . HPFRCCs are a combination of fiber-reinforced concrete (FRC) and high-performance concrete (HPC). FRC is an approach to improving the weak tensile properties of the concrete material. Its positive effects include increasing the ductility of concrete, increasing fatigue resistance and reducing cracking due to shrinkage . The most often used fibers are made of steel and polypropylene (PP). However, FRC applications have shortcomings due to fiber rupturing or sliding. To overcome these setbacks and improve the compressive strengths, durability, and workability of FRCs, HPFRCCs are introduced (by adding meta-kaolin, fly-ash, micro-silica, etc.). Meta-kaolin improves durability and micro-silica improves the strength of concrete.

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