Concrete ASR/freeze-thaw question 1

[hlc105]

I am looking for some assistance with understanding ASR and freeze-thaw damage. I have concrete cores and petrographic analysis for the structure described below and I'm trying to make a recommendation for repair/replacement based on the results. I'm trying to determine the cause of the cracking in order to make a recommendation.

The structure is a concrete pier at a dam. The pier is roughly 10'Wx30'Lx35'H with non-airentrained concrete. 10' deep vertical core was taken along longitudinal centerline and about 3' from nose of pier. The core was reported as being "extensively fractured" and broken into 5 separate pieces. Petrographic analysis was done and distress was reported as being caused by a combination of ASR and freeze-thaw damage. In the photos of the cores I see both diagonal and horizontal cracking. Structure was built in early 1940's and is located in the northeast. The piers support a concrete deck and gantry cranes used for lifting gates.

I'm thinking the cracking deep within the structure is likely due to freeze-thaw and not the ASR as I have read that it is rare for alkali-aggregate reactions to be the cause of cracking. Am I off base here? Can the breaks in the core be caused by ASR? Any suggestions for repair methods I can research? My initial thought was remove and replace. Is it possible to pin the pier somehow? Someone at work suggested I look into a polymer wrap (because of the ASR) but I thought that was more of a surface repair and was concerned that it might add thickness to the pier (which could interfere with gate movement).

I appreciate any help.

 

[graybeach]

We had a similar situation at a dam with frequent water level fluctuations, and a very cold climate. The concrete in the wet/dry zone was delaminated and/or fractured in the 6" to 1 foot or so, and the petrographic analysis found no air entrainment and mild ASR. Outside of the wet/dry zone the concrete is in near perfect condition for its 60 year age. We repaired one location about 15 years ago by removing the unsound concrete, placing dowels and mesh, and shotcreting. The height of the repair extended over the entire wet/dry zone. Recently we made a few patch repairs in the shotcrete and repaired some other areas using the same shotcrete method as before. We pondered other methods like vacuum injection and steel cladding. We ended up settling for what we knew would work pretty well and would be compatible with our fluctuating water levels.

If you go this route, and your water level varies as well, be prepared for the area of unsound concrete to extend over the entire wet/dry zone.

 

[frv]

No offense, but you really shouldn't be offering to provide recommendations if you don't have experience in this sort of thing. It concerns me that you are seeking advice on interpreting results on an online forum. You really should leave this to a specialized forensic engineer.

 

[Ron]

hlc105...opposite from your thoughts, freeze-thaw does not typically occur deep within concrete structures (the concrete is a reasonable insulator and mass concrete does not typically freeze through its section). Freeze-thaw damage is a niggling, near surface issue where localized saturation can occur or the voids are sufficiently filled to cause damaging expansion upon freezing. It is usually a progressive depth damage consideration.

ASR; however, can be insidious and can do damage at any level in the concrete as long as the reactants are there. The speed of the reaction is generally influenced by water availability, but will ultimately occur even at low moisture contents in the concrete.

Without looking at the concrete samples and the particle sizes being affected by the ASR, I cannot make a true assessment, but I would be more inclined to look toward ASR for such described damage rather than freeze-thaw.

 

[shobroco]

I'm with Ron on this one. Not having seen the structure, the samples, or anything else, I wouldn't offer a guess on the cause of your problems, but freeze-thaw is usually a surface (or close to) phenomenon.

 

[hokie66]

Agree that freeze-thaw would not be the cause deep in the body of the pier. Is cracking visible at the concrete surface? Have you discounted the possibility that the core was damaged in the extraction process? I would be reluctant to attach any credence to an interpretation of a petrographic examination which said that freeze-thaw was the cause of deep seated cracking.

 

[dik]

I'm curious that ASR damage could have occurred so deep... a 10' core having 5 fracture planes seems extreme with not real 'popout' conditions at the surface... ASR is generally pretty obvious and usually surface.

Could the problem be thermal from the mass concrete? Were there thermocouples installed at the time? not likely common for 70 year old concrete. Were the 'fractures' caused by cold joints?

Just some thoughts... Dik