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re:hot weather concrete

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Title: re:hot weather concrete

My two cents on high temps and concrete is use ice. In your wall the concrete is going to be using up water so fast that consolidation is going to be a problem, you will probably end up with pockets all over the place and the different loads may even leave a seam where they don't bond. The material coming out of the trucks will be so dry that your contractor is going to be screaming for water and the end product will not look very good, even if they know how to use a vibrator.  Strength of cylinder samples taken are probably going to pass your required strength, but the wall in reality will not be very good. (cylinder strength testing is just that, a minimum standard met in the job specs., longevity and durability values are not necessarily included in strength testing). On a slab it would be even worse, the top would dry out and give you cracking all over while the water below would be trapped, the contractor would have a terrible time screeding the slab and would probably be spraying water all over the place to allow them to finish the top. Might even look good until the top started coming off in a few weeks or months. Best bet is find some way to place the mud in the cool of the night, spray down the forms with a lot of water before placing the mud, and keep the sun off the area (especially rebar) also. I have an IBC special inspection card for reinforced concrete, as well as trying to learn what I can from the better contractors and suppliers, and have worked on a lot of summer time concrete jobs, and these are just factors that I have seen over and over. 

         ACI 305R "Hot Weather Concreting" recommends keeping concrete temperature as=
low as possible in hot weather, and provides a long list of detrimental=20
effects due to hot weather and hot concrete.  =20

I recall touring a nuclear power plant under construction west of Phoenix=20
several decades ago and being informed that 90% of the water in their mix wa=
s in=20
the form of ice.   I assume there were good reasons to do that.  =20

Ralph Hueston Kratz, S.E.
Richmond CA USA

In a message dated 2/27/08 4:41:21 PM, tiger(--nospam--at) writes:
> All,
>  I am hoping that someone on the listserver knows of literature that=20
> discusses the benefits of using crushed ice for concrete batching when sus=
> ambient temperatures for both placement and curing are in the range of 95=20=
to 100=20
> degrees F.
>  Let=E2=80=99s say I am placing concrete for two 8 inch precast walls (NOT=
> concrete) in ambient temps of 95 to 100 deg F.
>  I use one mix design, but in one batch I replace some of the water with=20
> crushed ice (no change in W/C ratio) resulting in the temp of the concrete=
> discharge being less than 90 deg F.=C2=A0 For the second batch I do not us=
e ice and=20
> so the concrete at discharge is 95 deg F or a bit above.=C2=A0 Both wall p=
> are shaded and moisture cured in exactly the same fashion at the same ambi=
> temperature of 95 to 100 deg F for 28 days.
>  My question is, will the 28 day strength of the two panels differ=20
> significantly?
>  =C2=A0
>  Based on literature I have been able to dig up, it would seem that there=20
> are two major problem areas with regard to placing concrete at these temps=
> First would be the placement itself, as the hot weather would tend to redu=
> workability and decrease set time.=C2=A0 It seems to me that the addition=20=
of ice=20
> would help in this area by lowering the concrete temp at discharge.
>  Second problem area is overall decrease in ultimate concrete strength.=
> Since the temp of the iced concrete would rise and match that of the unice=
> concrete within a few hours and stay at that level through almost all of t=
> curing time, it seems to me that there would likely NOT be a significant b=
> by adding ice in terms of 28 day concrete strength.
>  =C2=A0
>  I searched the listserver archives and didn=E2=80=99t come up with anythi=
ng on this=20
> topic.=C2=A0 I am trying to determine if it is necessary to use ice at all=
, since=20
> other methods such as the addition of plasticizers to ensure workability=20
> could be used to address the first problem area.=C2=A0 If, however, there=20=
is a=20
> noticeable effect on 28-day strength than keeping the ice requirement woul=
d be=20
> preferable.
>  =C2=A0
>  Thanks
>  =C2=A0
>  Terangue *Tiger* Gillham, PE
> GK2, Inc.
> tiger(--nospam--at) <mailto:tiger(--nospam--at)>
>  =C2=A0

Kent T Golding
New Prison Construction-Oregon Department of Corrections
Deer Ridge Correctional Institution
541-475-4433 ext. 5206
541-475-4300 fax

The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair