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D7. |
Project
title: Stainless Steel Reinforcing
Bars as a Green Material With
governments all over the world now pouring money into infrastructural
development under the current financial crisis, there will be an increase in demand
for the use of steel reinforcing bars for construction projects. Stainless
steel is an environmentally friendly material. It is extremely durable
and is almost 100% recyclable. Deterioration
of carbon steel reinforcing bars in concrete structures is a worldwide
problem. The corrosion product (metal oxide) has a lower density than the
metal and this increase in volume causes cracking and subsequent spalling of the surrounding concrete. This often results
in premature failure of buildings and structures, and has even culminated in
accidents causing injury or death to people. In order to
minimize the need for costly repair or replacement of defective structures,
there is now a general shift of emphasis on life cycle costs for new
construction projects, as opposed to considering only the initial capital
costs. This approach helps to focus attention on total costs, including the
frequency and cost of future maintenance and replacement work. Many
analyses have shown that the use of stainless steel reinforcing bars may
reduce overall cost in the long run. Durability also leads to less
frequent demolition of structures with the associated benefit of minimizing
environmental pollution. Type 304 is
one of the most common materials used in stainless steel reinforcing
bars. In the vast majority of applications involving the use of this
steel, it is used in a metallurgical state called "solution
treated" condition and has a relatively low tensile strength and high
ductility compared with the carbon steels used in concrete reinforcing
bars. Manufacturers
of stainless steel reinforcing bars have tried to overcome this lack of
strength by producing high strength grades of stainless steel reinforcing
bars. Unlike the carbon steels, type 304 stainless steel cannot be
hardened by phase transformation such as the formation of martensite
by rapid cooling from a high heat treatment temperature. Consequently,
increase in strength is achieved by a series of hot and cold working
operations to vastly increase the dislocation density in the material.
For example, in one commercial type 304 stainless steel reinforcing bar, the
yield strength is increased from 250MPa to 650MPa with a reduction of
elongation from 50% to 30%. Relatively
little information is available on the properties of these high strength
stainless steels, e.g. their long term corrosion behaviour, notch tensile and
fatigue properties, and their behaviour in the presence of fire. This project
aims to enhance our present knowledge of these high strength stainless steels
and generate new information for the design of structures involving the use
of these steels. Supervisor/Associate
Supervisor: Prof Joseph K L Lai (apjoelai@cityu.edu.hk)/ Dr C H Shek (apchshek@cityu.edu.hk) Suitable for: M.Phil./Ph.D. |