Thesis Abstract

Abstract
The bond resistance between concrete and steel reinforcement is a critical factor in the performance and durability of reinforced concrete structures. This research project aims to investigate the effect of environmental conditions on the bond between concrete and steel reinforcement. The environmental factors considered in this study include temperature variations, moisture levels, and exposure to aggressive agents such as chloride ions and carbonation. The bond between concrete and steel reinforcement is influenced by several mechanisms, including mechanical interlocking, adhesion, and chemical interactions. Changes in environmental conditions can significantly impact these mechanisms, leading to variations in bond strength. High temperatures can accelerate the hydration process of concrete, affecting the development of bond strength between the concrete and steel reinforcement. On the other hand, low temperatures can slow down the hydration process, potentially compromising the bond performance. Moisture levels in the concrete can also affect the bond between concrete and steel reinforcement. Excessive moisture can lead to a decrease in bond strength due to the formation of a weak interfacial transition zone. In contrast, low moisture levels can hinder the hydration process and reduce the development of bond strength. The presence of aggressive agents like chloride ions can cause corrosion of the steel reinforcement, further weakening the bond with concrete. Carbonation, another environmental factor, can reduce the alkalinity of concrete, leading to the depassivation of the steel reinforcement and promoting corrosion. This corrosion can deteriorate the bond between concrete and steel reinforcement, compromising the structural integrity of reinforced concrete elements. Understanding the impact of carbonation on bond resistance is crucial for assessing the long-term durability of reinforced concrete structures. Overall, this research project seeks to enhance the understanding of how environmental conditions influence the bond resistance between concrete and steel reinforcement. By investigating the effects of temperature, moisture, chloride ions, and carbonation on bond strength, this study aims to provide valuable insights for designing durable and resilient reinforced concrete structures. The findings of this research can contribute to the development of guidelines and recommendations for optimizing the bond performance in various environmental conditions, ultimately improving the longevity and sustainability of reinforced concrete infrastructure.

Thesis Overview

INTRODUCTION

1.1       BACKGROUND OF RESEARCH

Reinforced concrete design is based on the assumption that concrete and steel reinforcement combines to create a new, composite material. Generally, the concrete is designed to carry the compressive loads while the reinforcing bar is designed to carry the tensile loads. There must be bond between the reinforcing bar and the concrete if it is to carry the tensile load and maintain equilibrium. However, bond between concrete and reinforcing bar is been affected by corrosion, a leading cause of structural failure. Reinforcing bar corrosion is a major concern in the world of concrete structures. It develops high pressure within the concrete causing the cracking and spilling of the concrete cover and the exposure of the reinforcing bar to further corrosion activity.

The Bond clause of the BS 8110 –1:1997 code is simply based on the compressive strength of concrete, a factor that could be expected to increase useable bond capacity. All other factors known to affect bond were not taken into consideration. The ACI 318 (2002) code took various factors like concrete cover, diameter of bar, lap length, transverse reinforcement, spacing, transverse steel strength and the cylinder strength into consideration but the environment was not considered. The Eurocode EN 1992–1–1: 2004 (E) took various factors affecting bond into consideration including the environment and a factor of 0.7 of the normal bond strength was recommended in aggressive environment.

A developing country like Nigeria can adopt any code of practice but local specifications must be written to compliment the adopted code. The lifespan and failure of structures especially reinforced structures has been of great concern to professionals and researchers in and out of the construction industry and over time, there has been a list of other factors that supposedly reduces the lifespan of structures or even possible failures. The environments where the reinforced structures are built affect the bond between concrete and steel reinforcement which in turn accelerates the performance loss of reinforced structures especially when reinforced concrete structures are located in aggressive environments, where they are exposed to corrosive fumes, sea water spray, abrasive actions, adverse weather conditions etc. hence an attempt to study the effect of the environment on bond between concrete and steel is desirable and worthwhile.

Not much work has been done on the effect of the environment on bond between concrete and steel reinforcement. This investigation is an attempt to generate data that can be used in developing local specification on bond between concrete and steel reinforcement in aggressive environments like coastal and industrial, to be able to justify the use or otherwise of the recommended reduction factor of 0.7 in the Eurocode or to be able to recommend appropriate reduction factor in severe environments.

1.2       AIMS AND OBJECTIVES

The aim is to determine the effect of the environment on bond resistance between concrete and steel reinforcement. The objectives are to:

        i.           Generate data on bond between concrete and steel reinforcement exposed to different environments (Normal, Coastal and Industrial); and

      ii.           Compare the effect of each environment on the bond between the concrete and steel reinforcement.

1.3       SCOPE OF RESEARCH

Seventy-five (75) RILEM push-in specimens were cast. Twenty-five (25) specimens each were cast in the Normal, Coastal and Industrial environments, using 16mm high yield diameter bars in 160mm cube moulds. Three (3) control cubes were also cast to monitor the strength of concrete cast in each environment. All the materials used were exposed to the respective environment for fourteen (14) days. The RILEM specimens cast were cured in their respective environment for twenty-eight (28) days, and afterwards push-in tests were conducted to determine their bond resistances.

1.4       SIGNIFICANCE OF RESEARCH

The results of this present study would enhance the writing of local specifications for bond in different environments.