Return to index: [Subject] [Thread] [Date] [Author]

RE: Expansive Grout

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Juan,

I appreciate the update, and I understand your concern.  There is not much
research in this particular area, and there is no good way to do NDT or even
visual inspections of strand to detect hydrogen embrittlement.  The problem
is worse with bonded strand.  Unbonded strands erupt when they pop, and the
owner will call.

Again, I am not sure if you are using the grout in bonded PT or if you are
filling a cable stay.  In bonded PT, the strand would have direct contact
with the grout.  In a cable stay the strand would probably not have direct
contact with the grout.

In galvanized strand for telecommunications towers, they just look for any
pitting.  If it is pitted at all, it is replaced.  Granted, galvanizing hard
steels does exacerbate hydrogen embrittlement.

The 1978 PTI Post-Tensioned Box Girder Bridge Manual, and the 14th Edition
of AASHTO, Div II, Sect. 4.33.9.2.3(b) specifically mention aluminum powder
in the grout, and allow its use.  I don't know if they still do.  Perhaps
someone on the list can look it up in a 16th Edition AASHTO. 

I would suggest doing a search at: NCHRP, AASHTO, PTI, ACI, and NACE to see
if has ever been a problem.  If it hasn't been a problem in the past, and is
still allowed, you can rest easy.

Regards,
Harold Sprague

> -----Original Message-----
> From:	Juan C. Gray [SMTP:juangray(--nospam--at)col2.telecom.com.co]
> Sent:	Thursday, February 10, 2000 12:40 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Re: Expansive Grout
> 
> Harold:
> Intraplast Z is described as a "Expansive-plastifier" additive in the
> Sika catalogue. It is a gray powder with expansive agents. People from
> Sika have admitted privately that aluminum powder is used in it. When I
> told them about the undesirability of hydrogen as an expansive agent,
> they said they never have heard of any problems with the additive. Ben
> Gerwick in his book "Construction of prestressed concrete structures" ,
> page 167, recomends the use of nitrogen releasing admixtures; the guys
> at Sika told me they never heard about these, and asked me for a copy of
> the article. It would be great if we could have an official position on
> this from Sika.
> As for me , since this I started to use Sikament as a fluidifier, and a
> lot of prayer for the previously executed jobs.
> 
> Juan C. Gray
>