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[GreenYes] Re: portland cement chemical analysis



Wayne,

Unfortunately, cement chemistry is a much more complex topic than one
would imagine! As a result, cement science and engineering remain an
active area of research. I found a very short overview at
http://matse1.mse.uiuc.edu/concrete/prin.html under "Hydration of
Portland Cement" that gives an idea of the chemical and microstructural
changes that occur when cement chemically reacts with water.

You could also check out the Portland Cement Association's (PCA)
website for technical information on cement and concrete:
http://www.cement.org/tech/index.asp.

If you're interested in broad background information, the text
"Concrete," 2nd edition by Mindess, Young and Darwin is a good place to
start. It's very readable.


Hydrated/cured cement products are chemically very different from
cement. Cement powder cannot be recovered from cured
mortar/grout/concrete, but these things can be ground up and used as
aggregate.

Use of recycled concrete aggregate (RCA) in new concrete products is a
common practice, although it's much more commonly used in road bases or
sub-bases than in pavements themselves. FHWA did a state survey on the
use of RCA: http://www.fhwa.dot.gov/pavement/recycling/rca.cfm.

There's some specific info on the use of RCA on the PCA's website:
http://www.cement.org/tech/cct_aggregates_recycled.asp.

One problem, maybe the biggest, is that RCA is more porous than natural
aggregates. This changes the mix design and the consistency of a fresh
concrete mix, and it affects shrinkage and creep of the finished
product. This can result in cracking. This can be controlled in
pavements by replacing only a percentage of total aggregate with RCA
(you can't use 100%), and the size of the aggregate is an important
variable.

Hope this helps.

Wayne Turner wrote:
> Greenyessers,
>
> Slightly off-topic but still recycling related:
>
> Does anyone know how the chemical composition/analysis of portland
> cement changes once it undergoes the setting process? I'm interested in
> this for the purposes of investigating the chemical properties of
> crushed/pulverized concrete from the C & D waste stream. As always,
> thanks in advance for any assistance.
>
>
>
>
> Wayne Turner
> Assistant Solid Waste Administrator
> Winston-Salem/Forsyth County Utilities
> phone: (336) 727 8418
> fax: (336) 727-8432
> email: waynet@no.address


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