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Q: Concrete cancer- what causes it ? ( Answered 4 out of 5 stars,   1 Comment )
Subject: Concrete cancer- what causes it ?
Category: Science > Chemistry
Asked by: poetic-ga
List Price: $5.00
Posted: 15 Jul 2002 02:55 PDT
Expires: 14 Aug 2002 02:55 PDT
Question ID: 39689
There is a theory that Alkali- agregate reaction causes metal
reinforcing to
rust in buildings and produce what is known as Concrete Cancer.
Is this a reasonable theory and if so, would the metal set in concrete
rust if it had been given a protective galvanizing coating before
leaving the factory.
Subject: Re: Concrete cancer- what causes it ?
Answered By: thx1138-ga on 15 Jul 2002 08:14 PDT
Rated:4 out of 5 stars
Hi poetic and thanks for the question.

It would seem that the Alkali- agregate reaction you mention in your
question did happen in concrete but is not related to the steel  ie.
the concrete cancer would happen anyway whether or not steel was
present in the structure.  The problem is the chemical reaction in the
concrete, and is known as an Alkali(being a substance within the
concrete) Silica (being a substance within the aggregate, sand) 
reaction.  One of the problems was that as the concrete began to
disintegrate, water could get into the cracks and start corroding the
steel inside.  However it would seem that this problem is now under
control and modern construction methods have started to reduce the
‘concrete cancer’ problem (see the link to B.S. 8110:Part 1:1985 site
The problems nowadays are with buildings that were constructed from
about the 1940īs – the 1980īs as the concrete cancer has taken effect
exposing the steel within to moisture and so they are beginning to
corrode due to the process of being exposed to the atmosphere.  Had
the steel within the structures been treated by painting or
galvanising then yes, the corrosion of the steel would be greatly
slowed down but the concrete cancer would have happened anyway (but of
course they didnīt know that when the structures were built)
Another problem that accelerated the problem was that in climates
where freezing conditions occur, water would collect in the cracks,
freeze (so expand) breaking off flakes of concrete, detereorating the
structure even more quickly.

To summarize:
Yes, the Alkali- agregate reaction can happen, but it is not related
to any steel that might be in the structure.  If the steel within a
structure that is suffering from concrete cancer has been treated then
it will protect the steel from exposure to the environment
(rusting/corrosion) but this will not have any effect on the concrete

Useful information:
“Alkali Silica reaction is the chemical result of the alkaline in the
cement and the silicon in the aggregate reacting with one another and
giving way to the concrete cracking open, in general, in a star
formation. When the concrete cancer appears this can then lead to
other problems, these being things like enabling water to penetrate
the concrete to a deeper level, which, especially in winter can cause
major problems as in freeze/thaw action causing the concrete to break
up even more. There are way to prevent this during the construction
stage which are set out in B.S. 8110:Part 1:1985, but there aren't an
methods as yet to prevent it in structures that have already been

B.S. 8110:Part 1:1985 (Guidlines mentioned above)
Structural Use of Concrete

“Without going into a detailed explanation, ASR occurs when the
strongly alkaline cement actually begins to dissolve susceptible sand
and rock within the concrete itself. The chemical reaction creates a
gel material, which in turn creates tremendous pressures in the pores
of the concrete surface. The amount of hydraulic pressure was
estimated in a 1953 study to be approximately 500 psi. A later study
more precisely determined the pressures to range from as low as 1700
kPa (250 psi), up to 10,300 kPa (1,500 psi). This activity helps to
explain the tremendous pressures witnessed under sheet goods and epoxy
floor systems. It also is a much more plausible and scientifically
responsible theory than the vapor pressure (up to a pressure of 6.9
kPa, 1.0 psi) and unsubstantiated "backpressure" theories. “

Thank you for the question and if this was the answer you were looking
for please do not hesitate to rate it, and if you have any doubts
regarding my answer just ask for a clarification and I will be happy
to help.


Search Strategy
"concrete cancer" study
poetic-ga rated this answer:4 out of 5 stars

Subject: Re: Concrete cancer- what causes it ?
From: hopsa-ga on 15 Jul 2002 06:01 PDT
As far as I remember (no references, though), concrete cancer is
caused by air bubbles in the concrete, which allows the iron to rust.

Without air bubbles, the iron should have no chance to rust.


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