Questionable Concrete Strength
Questionable Concrete Strength
(OP)
Has anyone ever heard or seen the strength of a concrete pour going from 1450 psi at 28 days to over 4000 psi at one year? Seems like one value or the other is phony to me...
Mike McCann, PE, SE (WA)





RE: Questionable Concrete Strength
RE: Questionable Concrete Strength
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RE: Questionable Concrete Strength
RE: Questionable Concrete Strength
Mike McCann, PE, SE (WA)
RE: Questionable Concrete Strength
i hope it is something really dumb.... like 6" cylinder math used on 4" cylinders
RE: Questionable Concrete Strength
However, have you ever heard of all thread for holddowns being able to be backed out of a foundation wall with a socket wrench? To be able to do that to means little to no bond to the all thread to me. This is torsional shear, but is also related to tensile shear from seismic or wind. So... greatly reduced capacity for any holddowns that employed threaded rods.
Mike McCann, PE, SE (WA)
RE: Questionable Concrete Strength
RE: Questionable Concrete Strength
RE: Questionable Concrete Strength
Mike McCann, PE, SE (WA)
RE: Questionable Concrete Strength
RE: Questionable Concrete Strength
He happened to mention that they saw variations in fly ash cylinder tests. They attributed some of variations for early testing may have come from the slow rate of curing for fly ash concrete and the handling of "young" samples that were very fragile and easy to damage with minor errors, while cores taken from the same projects yielded much more reliable (less "scatter") and more predictable.
This anecdotal comment was based on using a common Type F (not C) fly ash and there was little GGBS in their 3 state area.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Questionable Concrete Strength
Mike McCann, PE, SE (WA)
RE: Questionable Concrete Strength
Other than concrete coring which is destructive, is there a non-destructive way to specifically test for aggregate distribution in a pour?
Mike McCann, PE, SE (WA)
RE: Questionable Concrete Strength
RE: Questionable Concrete Strength
The only NDT method I know of for segregation would be radiography.....expensive, time consuming, requires shut down of other work around it. Check with Olsen Engineering in Colorado....they have a few whizbang NDT devices that might pick up segregation.
RE: Questionable Concrete Strength
Mike McCann, PE, SE (WA)
RE: Questionable Concrete Strength
Mike McCann, PE, SE (WA)
RE: Questionable Concrete Strength
Just want to know, as UPV is to check uniformity of concrete cant it interpret segregation of concrete or radiography is only option?
As per Qatar Specs.
For upv
The use of data from nondestructive testing devices, such
as impact hammers or probes (ASTM C 805, ASTM C 803), ultrasonic equipment
(ASTM C 597), and pull-out devices (ASTM C 900) may be useful in determining the
uniformity and quality of the in-place shotcrete. These tests, however, may not provide
reliable values for compressive strength.
For radigraphy
Gamma rays and high energy X-rays, which illustrate by radiographs the concrete defects:
The testing shall be carried out in accordance with the requirements of BS 1881-205 or
equivalent.
RE: Questionable Concrete Strength
Conversely, if we are looking at voids or underconsolidation in the concrete, we might find that in one location we get 12000 fps and in another location we get 9000 fps. From that we can clearly conclude that there is some reason for such a large reduction in velocity, most likely related to the sound path having to bounce around the voids, thus creating a longer sound path and a lower observed velocity.
Pulse velocity and other ultrasonic methods are generally considered secondary methods of testing. They do not yield direct results, but must be correlated to direct results such as the compressive strength.
Radiography is a direct, visual method whereby the aggregate can actually be seen and its distribution identified.