OT - High-mix and low-mix concrete
 

I just finished a book describing the building
of Boulder Dam, and there's something I don't
understand. The book mentioned that two concrete
batch plants were made, one to product "low-mix"
concrete for the lower portions of the dam and
another to produce "high-mix" concrete for the
top.

The two plants were not run at the same time.
Any ideas as to why they needed two separate
plants and what the difference in the concrete
was?

OT - High-mix and low-mix concrete
 

This is somewhat speculation, and some bit of foggy memory so somebody that
really is up on this feel free to disabuse me.

From what I understand the engineers needed one monolithic block of concrete
when all was said and done so the lower portions were blended to cure real
slowly so the end result would be no seams. Also the lower part of the damn
is much thicker than the upper part but the concrete mixture had to be
adjusted to maintain a steady cure rate and the thinner sections having less
cross section had to be a hotter mix than the lower part because the heat
generated from the chemical reaction was disapated faster in the thinner
sections.

--
Roger Shoaf

If knowledge is power, and power corrupts, what does this say about the
Congress?


"Jim Stewart" wrote in message
...
I just finished a book describing the building
of Boulder Dam, and there's something I don't
understand. The book mentioned that two concrete
batch plants were made, one to product "low-mix"
concrete for the lower portions of the dam and
another to produce "high-mix" concrete for the
top.

The two plants were not run at the same time.
Any ideas as to why they needed two separate
plants and what the difference in the concrete
was?

OT - High-mix and low-mix concrete
 

Roger Shoaf wrote:

This is somewhat speculation, and some bit of foggy memory so somebody that
really is up on this feel free to disabuse me.

From what I understand the engineers needed one monolithic block of concrete
when all was said and done so the lower portions were blended to cure real
slowly so the end result would be no seams. Also the lower part of the damn
is much thicker than the upper part but the concrete mixture had to be
adjusted to maintain a steady cure rate and the thinner sections having less
cross section had to be a hotter mix than the lower part because the heat
generated from the chemical reaction was disapated faster in the thinner
sections.

--
Roger Shoaf

If knowledge is power, and power corrupts, what does this say about the
Congress?

"Jim Stewart" wrote in message
...
I just finished a book describing the building
of Boulder Dam, and there's something I don't
understand. The book mentioned that two concrete
batch plants were made, one to product "low-mix"
concrete for the lower portions of the dam and
another to produce "high-mix" concrete for the
top.

The two plants were not run at the same time.
Any ideas as to why they needed two separate
plants and what the difference in the concrete
was?


From a contemporary account:
"On the trestle-bridge mentioned above, was placed a fifty-ton traveling
crane with which to dump the concrete. The concrete was mixed in
two houses, one on either side of the river, by the world's largest and
most up-to-date mixing plants. It was carried from these plants to the
fifty-ton crane by a traveling chain of buckets.
The structure of the dam is honeycombed with thousands of pipes,
the purpose of which is to cool the concrete. As the concrete hardens
great heat is generated inside the structure, and it is said that it
would
take one hundred and fifty years for it to cool naturally, but by
passing
icy water through the pipes the engineers are able to reduce the
temperature to normal within a month."

Jim

*** Posted via a free Usenet account from http://www.teranews.com ***

OT - High-mix and low-mix concrete
 

I've read that the Three Gorges Dam on Yangtze River
uses over a dozen different concrete formulations
depending on the task and conditions.

Jim Stewart wrote:
I just finished a book describing the building
of Boulder Dam, and there's something I don't
understand. The book mentioned that two concrete
batch plants were made, one to product "low-mix"
concrete for the lower portions of the dam and
another to produce "high-mix" concrete for the
top.

The two plants were not run at the same time.
Any ideas as to why they needed two separate
plants and what the difference in the concrete
was?

OT - High-mix and low-mix concrete
 

I would suspect that the interior portions of the dam run lower strength
(less % of portland cement) mixes. Major sections of the dam are
mostly filler.

I did some reading years back, the "gravel" used for the dam was graded
with rocks up to 6" or so. Why not, the best concrete mixes use a
variety of aggregate sizes to produce the best 'fit' of small pieces
next to larger pieces.

Jim Stewart wrote:
I just finished a book describing the building
of Boulder Dam, and there's something I don't
understand. The book mentioned that two concrete
batch plants were made, one to product "low-mix"
concrete for the lower portions of the dam and
another to produce "high-mix" concrete for the
top.

The two plants were not run at the same time.
Any ideas as to why they needed two separate
plants and what the difference in the concrete
was?

OT - High-mix and low-mix concrete
 

Jim Stewart wrote:
I just finished a book describing the building
of Boulder Dam, and there's something I don't
understand. The book mentioned that two concrete
batch plants were made, one to product "low-mix"
concrete for the lower portions of the dam and
another to produce "high-mix" concrete for the
top.

The two plants were not run at the same time.
Any ideas as to why they needed two separate
plants and what the difference in the concrete
was?

My speculation:
Modern bath plants vary the cement content in each load in accordance
with the customer's order. The plants used in building that dam didn't
have the technology that we use today to vary cement content so easily,
and since there was plenty of demand (round the clock pouring), it made
sense to have two plants, each producing a diffent mix.

--
Gary Brady
Austin, TX
www.powdercoatoven.4t.com