Advances in Technology Innovation, vol. 9, no. 2, 2024, pp. 143-155 English language proofreader: Chih-Wei Chang Influence of Surface Roughness on Durability of New-Old Concrete Interface Nurdeen Mohamed Altwair * , Younis Omran Yacoub, Abdualhamid Mohamed Alsharif, Lamen Saleh Sryh Department of Civil Engineering, El-Mergib University, Al-Khums, Libya Received 01 April 2024; received in revised form 29 April 2024; accepted 30 April 2024 DOI: https://doi.org/10.46604/aiti.2024.13533 Abstract The bond zone between old and new concrete is greatly affected by environmental factors. This study investigates the impact of surface roughness on durability using as-cast surface (CS), drilled holes surface (DS), and grooved surface (GS). After a 28-day water-curing, specimens undergo a 5% NaCl solution immersion for 30 and 60 days; exposure to temperatures of 200 ℃ and 500 ℃; and a water permeability test. Slant shear and splitting tensile tests assess durability. Results show that CS exhibits the greatest decrease in resistance to sodium chloride solution and temperature, while DS and GS show less pronounced effects. At 500 ℃, CS and DS specimens fail, whereas GS retains 50% and 75% of its shear and tensile strengths, respectively. GS has the lowest water permeability (7 × 10 -11 m/s), followed by DS (1.2 × 10 -10 ) and CS (1.5 × 10 -10 ). Overall, surface roughness enhances durability and mitigates environmental effects. Keywords: bonding strength, temperature, NaCl solution, permeability 1. Introduction Repairing and strengthening structures often involves adding new concrete to an existing concrete substrate. Typically, before applying the concrete, the surface of the substrate is intentionally made rough. Numerous methods are evidenced to enhance surface roughness, with one of them being the mechanical approach. Tools like scarifiers, grinders, or shot blasting machines are frequently adopted to create a surface by removing the layer of the existing substrate and exposing the aggregate [1]. This rough texture promotes bonding between the old concrete, enabling mechanical methods to be highly effective in enhancing bonding. The roughness of the existing substrate is particularly crucial in strengthening the bond between the new concrete [2]. A rough surface provides a contact area for the concrete to adhere to, resulting in improved bond strength. Additionally, it enables interlocking between both layers of concrete, further enhancing their bond strength. In other words, enhancing the roughness of the concrete substrate surface leads to improved interfacial bond strength, primarily attributed to increased interfacial shear friction and mechanical interlocking between the layers of concrete [3]. Previous research has examined techniques for creating surface roughness on concrete and improving bonding with newly applied concrete. The aforementioned methods were employed to roughen surfaces in real-world applications including utilizing a steel brush to prepare the surface, partially chipping the surface through holes, sandblasting the surface, and creating a textured surface [3-4]. The identification and characterization of bond qualities between old and new concrete have elicited considerable advances in structural engineering research in recent years. Nevertheless, the strength of the connection often serves as a critical area in repaired structures. Despite the progress herein, several ongoing concerns about the durability of bonding * Corresponding author. E-mail address: nmaltwair@elmergib.edu.ly