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Re: FW: Low Concrete Quality

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Leonardo

I think for the results you are looking for a 10 to 15 % of silica fume would be an optimum proportion. You should remember Silica Fume is a fairly expensive material, so it should be weighed against cost/benefit ratio. That is, more silica fume might offset the cost economics.

By the way, i would suggest you to use silica fume in combination with fly ash. This has two advantages:

i) It will keep cost down.
ii) It will improve handling of silica fume, because as you know, due to its extreme fineness, silica fume is a very difficult materail to handle, both prior to & after mixing. Use of fly ash keeps this material favourably under control. More over research findings exhibit added benefit for this combination of use.

For further study you can refer to the following ACI COMMITTEE report:
ACI 234R-96: GUIDE TO THE USE OF SILICA FUME IN CONCRETE.

This can be found in PART-1  of ACI MANUAL OF CONCRETE PRACTICE.
Regards,

SYED FAIZ AHMAD; MENGG, Mem ASCE
SENIOR STRUCTURAL ENGINEER
SAUDI OGER LTD
RIYADH, SAUDI ARABIA.


From: Leonardo Zapata <Lzapata(--nospam--at)otepi.com.ve>
Reply-To: seaint(--nospam--at)seaint.org
To: seaint(--nospam--at)seaint.org
Subject: FW: Low Concrete Quality
Date: Tue, 19 Jun 2001 14:42:44 -0400

Thank you for your suggestions, and I take advantage to make another
question:

> How can we be sure about what percentage of Silica Fume should be used in
> order to achieve all these wonderful benefits? ACI mentions ranges up to
> 20 % but in this case contractor used between 8-10 %. Is it good enough?
> In addition to this, we met with the contractor and they accepted to give
> a warranty to the client for the life of the building (25 years) but we
> request some tests to support this document. A load test and a
> "petrography" were suggested. In this last test 2 core samples will be
> taken, one from a "bad" pedestal and one from a "good" location. These
> samples will be analyzed by an independent laboratory to identify and
> compare mix compositions (including Silica Fume %) and other properties
> (permeability, porosity, water absorption and Abrasion-Erosion
> resistance).
>
Thks again.


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