Age of concrete

[charliealphabravo]

It would be helpful if I could make a very approximate determination as to the age of a concrete sample that was recovered from a site. The sample is concrete laitance that overflowed a sidewalk form during construction and entered a cavity in an adjoining building where it cured and fell through a ceiling panel.

The concrete is still relatively green but this is a pretty subjective assessment. I am wondering if there might be a more objective test. I don't need a quantitative age, only a qualitative determination as to whether the sample is something like 6 months old (the recent construction) or more like 40 years old (the original construction).

As an alternative, perhaps some chemical composition analysis could determine if the concrete laitance was the same as the concrete in the newly poured sidewalk.

A long shot on the whole but thanks in advance for any opinions.

 

[ztengguy]

if it was original, wouldnt there be some place it would show that it 'broke off' and fell?

 

[charliealphabravo]

It spilled onto the bottom flange of an existing steel beam and then cured.

But that is a good point. There may be related concrete closer to the point of entry. The access to the beam pocket is pretty tight from the inside but a more intrusive examination might be the simplest solution.

 

[TXStructural]

A petrographer should be able to tell you whether it is months or years old.

 

[Ron]

As TxStructural noted, petrography is perhaps your best choice; however, that will be based on an observation of unreacted (unhydrated) cement particles.

If there is a lot of unreacted cement, then one could guess that the concrete is relatively new; however, I've seen concrete that was over a year old with unreacted cement particles.