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Heat of Hydration of Mass Concrete
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The attached document may be helpful. If nothing else, it will point you to a bunch of other documents. ACI 211.1 touches on this but probably doesn't get into enough detail to suit your purposes. I'd definitely recommend getting the supplier's input at some point prior to construction.
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The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
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Looks quite helpful thanks KootK. Into this subject because once did a mass pour on a raft slab, 17,300 sq.ft x 3 feet thick, 1 pour, 1 day. Had a materials testing company install 5 sets of thermo-couples and the temp peaked at 52 degrees C 4.5 days after pour. Covered the slab with insulated tarps in the middle of July. That turned a few heads. So familiar with the problems associated.
Current problem is a chunk of concrete about 2.5' wide at the top and about six feet wide at the bottom. Vertical front face 7' high, sloped back face. the total length is 1300 feet with expansion joints every 70 feet. It ended up developing shrinkage cracks about every 6 foot o.c. about 2 days after the pour. I'm doing a structural condition assessment/forensic investigation.
This is definitely a thermal expansion problem during curing, compounded by the fact that the previously mentioned piece was poured on top of a previously poured foundation, so restrained at the base. The codes and literature tell you that you will get cracking if the outside temp differs from the inside temp by 20 degrees C, European is 19 deg C.
I'll take a look at what you sent and see if can figure out how to predict the core temp given the myriad of other variable. Thanks again.
Current problem is a chunk of concrete about 2.5' wide at the top and about six feet wide at the bottom. Vertical front face 7' high, sloped back face. the total length is 1300 feet with expansion joints every 70 feet. It ended up developing shrinkage cracks about every 6 foot o.c. about 2 days after the pour. I'm doing a structural condition assessment/forensic investigation.
This is definitely a thermal expansion problem during curing, compounded by the fact that the previously mentioned piece was poured on top of a previously poured foundation, so restrained at the base. The codes and literature tell you that you will get cracking if the outside temp differs from the inside temp by 20 degrees C, European is 19 deg C.
I'll take a look at what you sent and see if can figure out how to predict the core temp given the myriad of other variable. Thanks again.
Temperature may have something to do with it, but base restraint will inevitably cause drying shrinkage cracking. How much horizontal reinforcement do you have. With 6' spacings between cracks, they should be narrow, so why are they a problem?
Get your hands on a copy of Ciria C660. Covers temperature rise/fall and differentials in a lot of depth
The 20 deg is a temperature differential value above which cracking will occur in thick members due to internal restraint. In your case you also have external restraint due to it being poured on old concrete; that sort of restraint can be pretty high and can require a lot of reinforcement near the base to control crack widths. In the external restraint case the temperature differential doesn't matter as much as the drop in temperature from the max to ambient temperature as well as shrinkage of the concrete (as hokie mentioned).
Also as hokie mentioned: what are your crack widths? Might not be a problem at all
The 20 deg is a temperature differential value above which cracking will occur in thick members due to internal restraint. In your case you also have external restraint due to it being poured on old concrete; that sort of restraint can be pretty high and can require a lot of reinforcement near the base to control crack widths. In the external restraint case the temperature differential doesn't matter as much as the drop in temperature from the max to ambient temperature as well as shrinkage of the concrete (as hokie mentioned).
Also as hokie mentioned: what are your crack widths? Might not be a problem at all
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