Need concrete advice

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mminter1973

mminter1973

Joined
Apr 1, 2006
Threads
46
Messages
439
Location
alabama
I am about to pour 150yds of concrete for my shop pad but i am worried about the cold weather. I talked to some local concrete guys and they said they add calcium to help it set up faster in cold weather. Is this OK for the strength and integrity or will it be cracking badly in 10 or 20 years?
 
I wouldnt use calcium. Most DOT or public projects I work on dont allow them. Use a non chloride accellerant like accel 80 at 2% and cover it with blankets as soon as you can. Blankets are the key dont rely on plastic get the insulated ones. Concrete makes its own heat dont let it get away. Ideally you want to maintain a temp above 60 degrees for 7 days but adding the accellerator will cut down on this.
 
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150 yds is a sizable pour, are you doing the work yourself? And how cold are we talkin about? I didn't know it could get cold in Alabama. Out here our concrete guys start with warm water and some even heat the aggregate itself to get the reaction going ASAP. Depends a lot on your definition of "cold" Are we talking below freezing?

I would also recommmend against the calcium, go with a modern admix like Jeff suggested. You wan't to keep the hydration process going as long as possible, don't let the heat or water escape from the slab for as long as you can.
 
I am hiring the work done, I just want to gather info before i make a rash decision. If i am going to "possibly" have problems because we added calcium i would just wait until spring. But if its no big deal and there are no side effects i would like to go ahead and get on with the project. It ranges between 40-50 in the daytime and 20-40 at night between dec-mar. Sometimes there is a warm spell though.
 
mminter1973 said:
I am hiring the work done, I just want to gather info before i make a rash decision. If i am going to "possibly" have problems because we added calcium i would just wait until spring. But if its no big deal and there are no side effects i would like to go ahead and get on with the project. It ranges between 40-50 in the daytime and 20-40 at night between dec-mar. Sometimes there is a warm spell though.
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Wow - I wish it were that cold around here in the winter time. I wouldn't worry about a barely freezing temperature if you can cover the entire slab, the concrete will make enough heat that I sure wouldn't worry about that. Especially if you pour on a vapor barrier, that moisture has to come out from the top it will slow down the cure as well, accelerator will make the finishers happy. I'm sure you have a relativley high humidity and that will help out too.
 
Make sure the ground is not frozen, use the non-chloride admix to help it set up a little quicker and cover it up well. The key is to prevent the water in the concrete from freezing. It will cure slower in cold weather, but it will still eventually gain it's design strength.

Just be thankful you're not working for the Army Corps of Engineers. They require that you keep the surface of the concrete at 55* for 4 days, per the ACI 306.1 publication. I'm dealing with this right now and I'm losing weeks on my schedule :bang:
 
Never put Calcium Chloride in a garage slab. It never really fully hydrates, and it re-crystalizes as the concrete cures, as it's not part of the bonding agent chemisty, it's just there to provide heat during the cure. The problem with this is when you pull the vehicle in after a rainy or snowy day, the water dripping off the car will re-hydrate the free calcium, which is corrosive. The fumes of the drying puddles will promote rusting on the bottom of the car. Once the water dries, the calcium re-crystalizes, and the process starts over again each time you bring it in from the rain.
 
Thanks guys after hearing what you all had to say and talking to the construction engineer where i work i think i will just wait until warm weather.
 
mminter1973 said:
I am hiring the work done, I just want to gather info before i make a rash decision. If i am going to "possibly" have problems because we added calcium i would just wait until spring. But if its no big deal and there are no side effects i would like to go ahead and get on with the project. It ranges between 40-50 in the daytime and 20-40 at night between dec-mar. Sometimes there is a warm spell though.
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You can successfully place concrete it in the cold weather conditions you describe. I agree with the avoiding calcium chloride admixtures. There are some other admixture choices including water reducers that will help, or just add more cement. A lower slump (less water) mix helps too. The initial temperature of the delivered concrete is important and can be adjusted.

Basically, you need to keep the concrete from freezing for the first 24 hours and then keep it at least 50 degrees. This isn't as hard as it might sound. The hydration process produces heat, especially during the first few days so you will likely only need to cover/insulate it. There are insulating blankets available or just use plastic sheets and straw. You can buy a couple inexpensive max/min thermometers and monitor the temperatures.

ACI 306 Cold Weather Concrete is your friend!

Good times!

:cheers:
 
Arya Ebrahimi said:
Just be thankful you're not working for the Army Corps of Engineers. They require that you keep the surface of the concrete at 55* for 4 days, per the ACI 306.1 publication. I'm dealing with this right now and I'm losing weeks on my schedule :bang:
Click to expand...

pismojim said:
ACI 306 Cold Weather Concrete is your friend!

Good times!

:cheers:
Click to expand...

Do you work for the COE?? :lol: ;p

ACI 306, while a great resource, is very frustrating to work with at times :bang: :D
 
Type iii

Consider Type III concrete. as opposed type I/II which it typical
and most likely what you are planning on using.

Type 3 Cures faster its a hotter cement. Its used here for paving
intersections that need to be driven in in less than 48hrs.

Its more money.. this I know. I am familiar with type 3 from the
cement side. I worked for 8 years at Cement Manufacuring Plant. So I know very little about the real world useage other than what I was told by my supervisors when asked the question. Whats it used for?

Anyway It wouldnt hurt to ask you contractor about avail. and practicality of using it. And if it would benefit your situation.

They use the heck out of it here. Seems all major traffic intersections are getting redone in concrete.
 
According to ACI 306, you can do one of three things to improve the cold weather characteristics of concrete and reduce the cure time.

1) Use a non-calcium accelerant
2) Add 100lbs/cy of portland to the mix design
3) Use Type III concrete
 
Wow this guy is going to be ACI certified by the end of this.:clap:

Its a simple slab, I didnt realize where he was from in the first post and I agree with the others...with those temps just cover the s**t up and be done with it. If evening temps drop to just below freezing youll be fine.

FWIW Id stay away from type 3 (dynamite) high early mixes unless you have a lot of experience with your dispatcher and faith that the truck wont get stuck in traffic or else youll be finishing your floor with a plate compactor. I could tell you some real good stories about high early mixes gone bad...it happens a lot even to professionals.

I wouldnt put off the project. You postpone weddings, building a new shop......never.:cheers:
 
Arya Ebrahimi said:
Do you work for the COE?? :lol: ;p

ACI 306, while a great resource, is very frustrating to work with at times :bang: :D
Click to expand...

Not the COE or USBR but a just as "bad" State agency, :D
25+ years Resident Engineer, building Dams, Power Plants, pumping plants, Large Diameter Pipelines, etc. Old school, over built, long life, low maintenance. ;)

Retired and now working for a very large engineering firm.

Last job, a $120M reservoir, had operational outage constraints that required working 7/24, including 1000's of CY of mid-winter concrete work that also included the USBR's "stone finish" (now that's a real PITA) for large conduits that carry 3100 CFS at 40 ft/s :eek:. The remote 3000+ ft high desert location, with snow, freezing wind and 100+ degree summers provided many challenges. In summer we used liquid nitrogen to cool concrete. :cool:
I love concrete. :rolleyes::lol::D
 
Guys i think i am going to go ahead and have my pad formed with footers dug and wire and rebar laid in and just be a weather watcher for the next few months to see if we catch a warm spell. If we dont then no big deal, Ill just wait till it finally does warm up. I will have WAY to much money invested in this concrete to end up not being satisfied.
 
Careful now, you don't wanna expose your bearing surfaces to too much moisture and lose your bearing capacity in the soil.

Footers are generally easy to pour in cooler weather 'cause they're in the ground and easy to cover. It's walls and slabs that are harder because they're much more exposed.

If you can get your footers in, then being a weather watcher may work out well for you(it's what I'm doing right now :) ).
 
Arya Ebrahimi said:
Careful now, you don't wanna expose your bearing surfaces to too much moisture and lose your bearing capacity in the soil.

Footers are generally easy to pour in cooler weather 'cause they're in the ground and easy to cover. It's walls and slabs that are harder because they're much more exposed.

If you can get your footers in, then being a weather watcher may work out well for you(it's what I'm doing right now :) ).
Click to expand...

Dang guys, i cant win for loosin'
 
concrete cracks in the best of weather. good info so far but I would reinforce slab properly (rebar) and use control joints often. Tool joints and even saw cut next day another 3/8''
 
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