Strength Invesitgation of Extensively Heated Concrete

[pat2]

I am investigating a foundation of two large turbine generators. The concrete is about 40 years old, and it has been heated to 400 to 700 degrees Fahrenheit for most of its life. Spalling and cracking of the concrete in some areas has made the client concerned about the concrete strength. The foundation is not on grade, but is supported on an elevated slab with beams and columns for support.

We will be doing Windsor Probe tests as well as taking some cores to determine the concrete's present strength. I would also like to research the effects of high temperatures on reinforced concrete to help with the investigation and report write up.

Does anyone know an easily accessible, and thorough resource for the effects of temperature on reinforced concrete?

Any information would be appreciated.

Paul

 

[jheidt2543]

The American Society of Civil Engineers (ASCE) has a seminar program called "Structural Condition Assessment of Existing Structures". They make extensive use of various publications by the American Concrete Institute (ACI) regarding strength testing and non-distructive testing methods for all sorts of conditions, including heat damaged concrete. I would start with contacting these two organizations and check their latest publication lists. I'm sure you will find plenty of up to date information. By the way, the ASCE seminar is very good and covers concrete, masonry, steel and wood materials.

 

[Ron]

Paul,
The Portland Cement Association has extensive literature on heat affects on concrete. Much of it follows the fire resistance analysis of concrete, not necessarily consistent, long term exposure. Armand Gustaferro is the noted expert in this field.

I would suggest you check the depth of carbonation of the concrete from the cores you take. Remember, concrete is a fairly good insulator and the surface damage might not be indicative of the integrity of the concrete at depth. Petrographic examination of the cores, in addition to the check for depth of carbonation, will tell give you a good assessment of the matrix integrity.

The Windsor Probe should not be used as a definitive tool, but may be used as a discriminator of area changes.

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[Laser28]

The temperatures that you describe will generally have an effect only in the early ages of the concrete, and only while there is still moisture present in the concrete. The temperature will cause the concrete temperature to rise to the boiling point of the water in the concrete and eventually boil that off. SOme spalling will occur, as the result of steam pressure in larger voids in the concrete. In a fire, the next step is conversion of the aggregates, especially silicious aggregates but at a much more elevated temperature than what you have described. This process results in excessive spalling and carbonation of the concrete, which can be checked with a phenolpthalein solution.

I would expect that the spalling and cracking are related to temperature cycling in the early life of the structure, and that the concrete is not greatly compromised in terms of strength.