Different ways to test concrete in buildings

[reyzers]

Besides the following:

1. Rebound hammer
2. Ultrasonic Pulse Velocity Test
3. Core Sample

What are other ways to test for voids inside concrete? Would there be a direct X-ray test?

 

[Ron]

A rebound hammer is a poor way to detect voids in concrete. Coring is good, but limited to only the area of the core's circumference and depth.

Pulse velocity will detect relatively large areas of voids, but is not good for small sections of concrete as the velocity is too fast to differentiate between good and potentially bad areas.

Radiography will work for distinctly large voids, but is not so good for small discrete voids. Further it is expensive and requires a lot of safety controls.

The best method to prevent voids is to have a good mix design and place it properly so that appropriate consolidation is achieved.

 

[reyzers]

If you did coring test for instance 3 inches diameter by 6 inches depth sample. What do you usually use to replace the concrete that would ensure there is absolutely no gap in the replacement (100% binding to the concrete socket left)? Did you use tiny formworks over the 3 inches hole and maybe put in non-shrink grout? But the coring company said non-shrink grout is only used for vertical hole, and not for horizontal hole.

 

[Ron]

reyzers...perhaps you should describe your whole issue and condition so that we may better respond. You are giving bits and pieces....by the way, non-shrink grout can be used in any orientation, as long as there is no expansion pressure built up in the grout.

Usually if a core is taken in a structural member, it is taken in an area that has little or no structural impact, so the repair is simply to fill the hole.

 

[reyzers]

We bought a used building and simply want a random check on the concrete quality especially in critical areas like columns and beams. You stated that a core is taken in an area that has little or no structural impact. But the company said core samples are usually taken in middle of beams or columns (the purpose being to sample it). Why do you need to take sample in unrelated region if you want to test a particular portion?

 

[Ron]

I said nothing about an unrelated region. I said that samples would be taken in an area of little or no structural impact. As an example, if we take a 3" diam sample from the horizontal and vertical center of a 16" deep concrete beam, it has little or no structural impact (shear is zero and if symmetric, at the neutral axis for bending), yet it represents the concrete below it ( in tension) and the concrete above it (in compression) so that we may make reasonable inferences from the data.

The selection of sampling locations should be done be a competent structural engineer....not the coring guy.

 

[reyzers]

Thank you.