The interfacial adhesion existing between steel and concrete is a critical determinant of the overall behaviour of reinforced concrete structures as a composite material. The efficient distribution of forces between steel and concrete is crucial to improve the structure's durability and effectiveness. The inadequate embedment length of reinforcement bars may lead to the development of flexural cracking in structural members, thereby diminishing the overall performance of the structure. The bond performance of concrete structures is subject to the influence of multiple factors, including but not limited to compressive strength, concrete cover, bar characteristics (such as diameter, embedment length, and deformation), and structural attributes (such as the presence of transverse reinforcement and the incorporation of fibre) [1–2]. ACI 408, as per the American Concrete Institute (ACI) in 2003, outlines four discrete assessments aimed at assessing the bond and gauging the impact of the diverse factors that contribute to it. The four tests include pull-out, beam end, beam anchorage, and beam splice. The pull-out test is a commonly employed method by scholars worldwide to evaluate the bond strength in concrete due to its ease of manufacture and execution. Sustainable construction has become increasingly prevalent within the building sector. Sustainability in concrete can be achieved in many methods, including the use of cement containing Supplementary Cementitious Materials (SCMs) such as FA, SF, metakaolin, Ground Granulated Blast Furnace Slag (GGBFS), lime sludge, and other additives [3–4].
De Almeida Filho et al. (2008) used pull-out and beam tests to examine the bond-slip behaviour of self-compacting concrete (SCC) and vibrated concrete (VC) and found that they behaved similarly. The study revealed that the compressive and bond strengths exhibited a slower rate of development in SCC compared to VC, suggesting that the filler employed positively impacted the bond strength. FA, which is a by-product of thermal power stations that burn coal, is the most widely accessible supplementary cementitious material globally. FA is a residual substance generated during the combustion of coal, predominantly sourced from coal-fired power stations, and collected at the uppermost part of boilers. The chemical composition of FA is used to classify it into three distinct categories, namely class N, F, and C [5–6]. Conventionally, the utilisation of FA in structural concrete as a substitute or ancillary component is confined to a range of 15–25% cement replacement. The investigation of the impact of a considerable quantity of FA on the strength evolution of concrete and the hydration properties of this substance is a subject of noteworthy scholarly inquiry. SF, also known as microsilica, is a by product of the production of silicon and ferrosilicon alloys in the metallurgical industry. It is a highly reactive pozzolan that is commonly used as a supplementary cementitious material in concrete [7–8]. In recent decades, the construction industry has placed greater emphasis on sustainability, significantly promoting the development of eco-friendly construction materials. To date, there have been two prominent approaches towards identifying sustainable remedies for construction materials. The first approach involves substituting non-renewable aggregates with recycled materials, while the second approach entails utilising SCMs (such as FA and blast furnace slag) to partially or entirely replace Portland cement. The implementation of these measures facilitates the achievement of cleaner production through the mitigation of emissions, air pollutants, and waste generated during the mining and manufacturing processes of materials. The substitution of Ordinary Portland Cement (OPC) with FA in concrete has gained widespread popularity in contemporary times. The construction industry has acknowledged the adverse environmental impacts of Ordinary Portland Cement (OPC) for a considerable period of time. The production of one metric tonne of Ordinary Portland Cement (OPC) results in the emission of 0.8 metric tonnes of carbon dioxide, which is a significant contributor to the phenomenon of global warming [9–10]. Azimi et al. (2018) investigated the effect of FA and SF on the bond strength between steel bars and concrete. The results showed that the addition of FA and SF significantly improved the bond strength between the steel bars and concrete [9]. Comprehensive research has been done on both the fresh and hardened properties of HVFAC, but very little research has been performed on the structural behaviour of HVFAC. The study conducted pull-out tests on samples containing varying proportions of FA as a replacement for Portland cement, specifically at levels of 10%, 20%, and 30%. The investigators arrived at the determination that the adhesive potency exhibited an enhancement upon escalation of FA content up to approximately 20% substitution of cement, beyond which a decline was observed [11–12].
A group of researchers from Montana State University conducted a set of pull-out experiments on samples, substituting Portland cement with 100% Class C FA. The experimental setup comprised of 13 millimetre bars that were incorporated into a concrete cylinder measuring 152 X 312 millimetres. The depth of embedment was altered within the range of 203 to 305 mm for all materials. The findings of this investigation revealed that the bond strength of high-volume FA concrete (HVFAC) was comparatively lower than that of conventional concrete. The study employed pull-out tests to evaluate the impact of a 50% substitution of cement with FA on the bond strength. The experimental samples were comprised of 150 mm concrete cubes with 20 mm bars embedded within them. The investigators documented that the bond strength of both HVFAC and CC specimens was indistinguishable. Using a pull-out test, it investigated the bond strength between concrete and reinforcing steel bars [13–14]. The results showed that the addition of SF significantly improved the bond strength between the concrete and steel bars.In a study the bond strength between concrete and a variety of materials, including steel bars and fibers, was investigated with the addition of FA and SF. The results showed that the addition of these materials improved the bond strength between concrete and the various materials. The study used a pull-out test to study the effect of FA and SF on the bond strength between concrete and steel reinforcement bars. The results showed that the bond strength was significantly improved with the addition of FA and SF.Itis investigated that the bond strength of concrete with various types of steel fibres and the addition of SF. The results showed that the bond strength was significantly improved with the addition of SF, and that the type of steel fibre also affected the bond strength [15–16].
Elchalakani et al. (2018) conducted a study on the bond strength between concrete and high-strength steel bars with the addition of SF. The results showed that the bond strength was significantly improved with the addition of SF, and that the use of high-strength steel bars resulted in higher bond strength. It investigated that the bond strength of concrete with the addition of SF and high-range water-reducing admixture. The results showed that the bond strength was significantly improved with the addition of SF, and that the combination with high-range water-reducing admixture resulted in the highest bond strength. It conducted a study on the bond strength of concrete with the addition of FA and SF and different types of fibers [17–18]. The results showed that the bond strength was significantly improved with the addition of FA and SF, and the type of fibers also affected the bond strength. In a study on the bond strength of concrete with the addition of FA and SF and different types of fibres using a pull-out test. The results showed that the bond strength was significantly improved with the addition of FA and SF, and that the type of fibers also affected the bond strength. It investigated the bond strength of concrete with the addition of FA and SF and different aggregates. The results showed that the bond strength was significantly improved with the addition of FA and SF, and that the type of aggregate also affected the bond strength. The studied on the bond strengths of concrete with the addition of FA and SF with different types of fibersand steel reinforcement bars. The results showed that the bond strength was significantly improved with the addition of FA and SF, and that the type of fibers and steel reinforcement bar also affected the bond strength. It investigated the bond strength of concrete with the addition of FA and SF and different types of super-plasticizers. The results showed that the bond strength was significantly improved with the addition of FA and SF, and that the type of super-plasticizer also affected the bond strength. Study conducted on the bond strength of concrete with the addition of FA and SF and different curing methods. The results showed that the bond strength was significantly improved with the addition of FA and SF, and that the curing method also affected the bond strength [19–20].