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RE: Construction Joint for massive Foundation Slab

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This may be a viable solution to your problem.
During the construction of the multi-dimensional test facility we placed
thermocouples at several locations within the ten foot deep concrete floor.
These thermocouples monitored the heat of hydration for about forty-five
days.   The highest  temperature recorded was approximately 160 F.   The
concrete mix contained superplasticizers and other proprietary compounds
from MASTER BUILDERS to achieve a 9 inch slump and 7500 psi 28-day strength.

I can fax the graphs to you if you want.


Best Regards,

Peter  De Vere
JSC, Houston, Texas
peter.p.devere1(--nospam--at)jsc.nasa.gov <mailto:Peter.p.devere1(--nospam--at)jsc.nasa.gov> 
281-483-2961

		-----Original Message-----
		From:	Kho Poh Teck [mailto:ptkho(--nospam--at)pc.jaring.my]
		Sent:	Tuesday, May 25, 1999 7:17 PM
		To:	seaint(--nospam--at)seaint.org
		Subject:	Re: Construction Joint for massive
Foundation Slab

		The main thrust of my question is not so much of the
measures to control the
		heat of hydration but the minimum period elapsed between the
peak temperature of
		concrete in a section of the work and removing the forms. By
doing so, I presume
		the concrete may be subjected to thermal shock. Think of it
as baking a cake.

		Spraying cold water on warm and young concrete in the
preparation of
		construction joint as you have mentioned is probably a wrong
practice though it
		is still commonly done. Also the cooling of the first pour
will cause thermal
		cracks on the young conrete of the second pour because of
the restraint at the
		construction joint.

		I have never investigated the formation of micro cracks in
the construction
		joint and its effects on the final tensile strength of the
hardened concrete.
		Comments please.

		Regards
		KHO pt
		CEng

		Harold Sprague wrote:

		> This is an interesting question.  I don't know a lot about
dam construction,
		> but an adjacent placement is cast after the forms are
stripped and the
		> surface is prepared by wet sand blasting and water
cleaning.  The heat of
		> hydration is more of an issue in controlling the thermal
gradient.
		>
		> You can control the heat of hydration by minimizing the
cement, lowering the
		> initial mix temperature, and using fly ash as a partial
cement replacement.
		>
		> A well graded aggregate mix and the use of as large a
maximum aggregate as
		> possible will also drop the amount of cement required and
help minimize
		> shrinkage.
		>
		> Harold Sprague
		> The Neenan Company
		>
		> -----Original Message-----
		> From: Kho Poh Teck [mailto:ptkho(--nospam--at)pc.jaring.my]
		> Sent: Friday, May 21, 1999 9:26 PM
		> To: 'seaint(--nospam--at)seaint.org'
		> Subject: Construction Joint for massive Foundation Slab
		>
		> Can anyone give some advice on the appropriate time lapse
prior to
		> casting a 2nd half pour of a massive foundation slab? Size
50m x 50m x
		> 3m. Is it acceptable to cast the adjoining piece at the
peak temperature
		> of hydration of the first slab provided adequate
reinforcement is
		> provided to prevent thermal cracks. Personally I don't
think the young
		> concrete is able give sufficient bond strength for making
tthe rebars
		> effective to limit the crack width. What is the normal
practice in Dam
		> construction?
		>
		> Regards
		> KHO Poh Teck
		> CEng
		>