Your Experience with Core Tests

[97EOs]

What is your experience with concrete core tests? What strengths do you usually find? And if it falls below requirements, do you replace the whole sections or do you retrofit it by the concept of confining the strain hence making it stronger?

I was having conversation with another engineer about this yesterday in a get together and he said it's dangerous to remove large sections of columns where core tests detect poor strength owing to the bars just bending if shoring is not perfect. Instead what is safer to do is to wrap it with retrofit to confine the strain hence increase the strength much like a cup holding sands and the sands having poor compressive strength. What is your actual experience on this?

 

[Ron]

I have done hundreds of core tests. In most instances, as long as the core strength reaches 85% of the design strength, the concrete is considered acceptable (for American standards...others might be different).

A decision to replace or remediate in place is based on lots of variables so there is no single answer to your question for that.

It is not that difficult to shore a column and remove defective concrete...much better than leaving it in place. Wraps can be good but might not be sufficient to solve an understrength problem...keep in mind that a wrap only combats lateral strain from compressive stress (Poisson's ratio), and actually does little else. If the compressive strength of the concrete is sufficiently low that failure occurs during loading, there is sufficient space between the wrap and the bars to allow buckling to occur...not good.