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"1:2:4" Concrete Strength
3

"1:2:4" Concrete Strength

"1:2:4" Concrete Strength

(OP)
I am analyzing some existing structural damage an old condo building from 1938 where the original drawings specify all concrete to be 1:2:4. This building was also designed under the WSD design method.

If my memory serves me correctly, I believe 1:2:4 was very common for the time and would extrapolate to about 2000 to 2500 psi concrete today.

Can anyone verify that or shed further light on the issue? I do not have my older info from the City of Seattle with me right now.

Mike McCann, PE, SE (WA)


RE: "1:2:4" Concrete Strength

Not a direct answer to your question, but FEMA 356 (Seismic Rehab) states the following regarding historical concrete strengths by element type:



Does the structural damage warrant undertaking concrete cores to be more definitive of the compressive strength?

RE: "1:2:4" Concrete Strength

(OP)
It may.

Looks like the courtyard was spec'd for 2 feet of earth, but I measured 4 feet. => problem... Only an additional 230 psf of load... nosmiley

Mike McCann, PE, SE (WA)


RE: "1:2:4" Concrete Strength

If I remember correctly, 1:2:4 concrete ran 2500 psi for the higher slumps and up to 3500 psi for the low to medium slumps.
Just to keep everyone shaking their heads, My father & I used that proportion to place some in-fill slabs around the house in 1968, kept the slump low and had 4000 psi concrete.

RE: "1:2:4" Concrete Strength

it kind of makes a difference whether it is batched by weight or volume. and how wet is the sand and aggregate. A very small change in weight or volume of cement could make a very large difference in compressive strength, another reason why this sort of batching is just not used anymore.

RE: "1:2:4" Concrete Strength

Might be worth getting it tested if it will make a difference. That old concrete has alot of time to cure!

RE: "1:2:4" Concrete Strength

If you core you might get crazy strength numbers, last time we cored what was supposed to be 3000 psi concrete we got from 4500 to 6000 psi results, coring horizonatally which is supposed to be weaker. Could explain away the extra soil load

RE: "1:2:4" Concrete Strength

(OP)
BB:

I guess you are showing your age too, aye matey? peacelol

Thanks for the link. That is great!

Mike McCann, PE, SE (WA)


RE: "1:2:4" Concrete Strength

Mike,

You're quite welcome AND you're absolutely right - I was thinking the same thing today. I worked on two bridge projects recently - one was built in 1940; the other in 1941 - these were the earliest plans where I came across the names of people I worked with. roll1

RE: "1:2:4" Concrete Strength

I hate to put a damper on the "old concrete has had a long time to cure" party, but just for future reference, this might not always be the case. I've had a couple of projects lately with harsh environments or Aliki-Silica Reaction that have resulted in old concrete having degraded significantly over the years.

In general, I agree, but always through the veil of common sense and good judgement.

RE: "1:2:4" Concrete Strength

at least with modern cement, the rate of strength gain decreases over time and after somewhere between 90 days to a year, the rate slows to nearly zero strength gain. After some point the opposite trend begins and the concrete may begin to slowly lose strength. If you add in ASR or freeze-thaw or corrosion of steel reinforcement, the degradation with age can be significant.

RE: "1:2:4" Concrete Strength

Quote (Lomarandil)

I hate to put a damper on the "old concrete has had a long time to cure" party, but just for future reference, this might not always be the case. I've had a couple of projects lately with harsh environments or Aliki-Silica Reaction that have resulted in old concrete having degraded significantly over the years.

In general, I agree, but always through the veil of common sense and good judgement.

Party Pooper! Good to know. Most of my evidence is from contractors trying to cut old concrete or install Tapcons where they easily break. Never had any tested, however.

RE: "1:2:4" Concrete Strength

You can also run into cases where the building does meet specified design strength, that's a very fun conversation to have with the owner.

Unrelated but give me a couple weeks and I will have over 40 cores tested with the same specification, not it will help you.

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