Durability Design of Concrete Structures

Phenomena, Modeling, and Practice

Kefei Li

• Publisher: Wiley
• Year: 2016
• Print ISBN:
  9781118910092
• Edition: 1
• eBook ISBN:
  9781118910122
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Comprehensive coverage of durability of concrete at both material and structural levels, with design related issues

• Links two active fields in materials science and structural engineering: the durability processes of concrete materials and design methods of concrete structures
• Facilitates communication between the two communities, helping to implement life-cycle concepts into future design methods of concrete structures
• Presents state-of-the-art information on the deterioration mechanism and performance evolution of structural concrete under environmental actions and the design methods for durability of concrete structures
• Provides efficient support and practical tools for life-cycle oriented structural design which has been widely recognized as a new generation of design philosophy for engineering structures
• The author has long experience working with the topic and the materials presented have been part of the author's current teaching course of Durability and Assessment of Engineering Structures for graduate students at Tsinghua University
• The design methods and approaches for durability of concrete structures are developed from newly finished high level research projects and have been employed as recommended provisions in design code including Chinese Code and Eurocode 2

Part One
Deterioration of Concrete Materials

1
Carbonation and Induced Steel Corrosion

This chapter treats the first important durability process of concrete materials and structures: the carbonation and the induced corrosion of steel bars in concrete. The carbonation of concrete originates from the reaction between the alkaline pore solution of concrete and the carbon dioxide (CO₂) gas migrating into the pores. The carbonation does not compromise the material properties but decreases the alkalinity of the pore solution, which has an adverse effect on the electrochemical stability of steel bars in concrete. The risk of steel corrosion can be substantially enhanced in a carbonated concrete. This chapter begins with the phenomena of concrete carbonation and its effect on the long‐term durability of concrete materials and structures. Then the detailed mechanisms are presented, according to the state of the art of knowledge, for concrete carbonation and the induced steel corrosion, together with a comprehensive analysis on the main influential factors for these processes. On the basis of the available knowledge, the modeling aspect is brought forth through mechanism‐based and empirical models for engineering use. Since the valid scope and the uncertainty are two fundamental aspects for model application, the critical analysis is given to the models presented and their application. Some basis for durability design against the carbonation and the induced corrosion is given at the end.

1.1 Phenomena and Observations

As concrete is exposed to the atmosphere, the CO₂ present in the atmosphere can migrate into the material through the pore structure and react with the cement hydrates such as portlandite (Ca(OH)₂ or CH) and the calcium silicate hydrates (C‐S‐H). These reactions are termed the “carbonation” of concrete materials. The direct consequence of carbonation is the consumption of CH, eventually C‐S‐H, and the decrease in pH value of the pore solution. Under a less alkaline environment, the electrochemical stability of the embedded steel bars in concrete can be destroyed, the steel can be depassivated and the electrochemical process of corrosion can occur. As the corrosion develops to a significant extent, the reaction products from corrosion accumulate at the concrete–steel interface and can fracture the concrete cover. Since all concrete structures are built and used in the envelope of the atmosphere, carbonation is a basic and fundamental process for the long‐term durability of concrete elements. Note that the detrimental aspect of carbonation resides mainly in the corrosion risk for the embedded steel bars and the carbonation itself is not found detrimental to concrete materials. Relevant studies show that the products of the carbonation reaction can notably reduce the porosity of hardened concrete, and the carbonation can also be used as a pretreatment technique for the recycled coarse aggregates to reduce the water sorptivity (Thiery et al., 2013).

Concrete carbonation has been well investigated with regard to both the reaction mechanism and the alteration of properties of material and structural elements. The mechanism of carbonation is to be detailed later, while the most severe deterioration of concrete elements by carbonation is usually due to the less compacted concrete, insufficient protection of steel bars from the concrete cover, and the favorable moisture conditions for steel corrosion. For residential buildings, most reinforced concrete (RC) elements, like slabs and walls, usually bear surface lining or protection la...

Table of contents

• Cover
• Title Page
• Table of Contents
• Preface
• Acknowledgments
• Part One: Deterioration of Concrete Materials
• Part Two: From Materials to Structures
• Part Three: Durability Design of Concrete Structures
• References
• Index
• End User License Agreement