Monday, June 20, 2016

"The conversation"

Read a wonderful article which appeared to me as a link in Bill Palmers Concrete Construction e-news letter today.   The article is written by 
Associate lecturer, UNSW Australia who has made an excellent summary of the fact that concrete is a vibrant active material and that hidden steel rebar is a "secretly active" degradation mechanism.   
He writes; "Steel is often perceived to be inert and resilient too. Terms such as “Iron Age” suggest an ancient durability, although Iron Age artefacts are comparatively rare precisely because they rust. If construction steel is visible, it can be maintained – for instance, when the Sydney Harbour Bridge is repeatedly painted and repainted.
However, when embedded in concrete, steel is hidden but secretly active. Moisture entering through thousands of tiny cracks creates an electrochemical reaction. One end of the rebar becomes an anode and the other a cathode, forming a “battery” that powers the transformation of iron into rust. Rust can expand the rebar up to four times its size, enlarging cracks and forcing the concrete to fracture apart in a process called spalling, more widely known as “concrete cancer”. "

Read the full article here:

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