Compressive Strength % of 28-day moist-cured Concrete Chart 4

Just so I have the story straight: Your concrete break machine was inoperable and you were unable to make cylinder breaks when they were actually due. Now that your concrete break machine has been restored to working order (and presumably calibrated) you have gotten caught up on the breaks and you want to back-calculate the 7 day and 28 day breaks from the numbers that you have. Seeing as how different mixes cure and gain strength at different rates, won’t you need a different chart for each supplier and mix?

How many days were you behind and how many tests are we talking about?

The machine is fully calibrated and such. I have about two weeks worth of test 7-day & 28-day.

This is the chart I'm looking for in excell.


Matt

There is no one chart like that for all concrete. As boffintech said, you will need a separate chart for each concrete mix that is represented by the cylinders that you have. You might be able to create a chart using other breaks on the same mix and the supplier may be able to suplement your data.

TWO WEEKS WORTH! OUCH!

If you try to publish data that was not actually collected at the time of the break, you are publishing fraudulent data. give the people paying for the tests data you got on day 11,23, or whatever.

Richard A. Cornelius, P.E.

I agree with disksewerrat - when you break the tests, you have to report the actual day (e.g., 21-day break, etc.). Then, in a letter report, you can provide the estimated 7-day/28-day strength(s) based on a rational and industry accepted trend. As GeoPaveTraffic states, you should have one for each class of concrete. The concrete supplier might have such specific charts that he has developed for his internal use if you are using commercial supplier. While not ideal, they may help. You are in a bit of a dilemma, but you must be up-front about it. When this has happened to us, we went to another lab and had them break the cylinders for us on the correct day. Might have cost you some money (or trade in kind later) but it would have been a better decision on your part, I believe.

Thanks for everyone's input. I thought the Percent/Age chart was a standard chart to be used when crush dates or not on 7-day/28-day. I don't understand how there can be a chart for each concrete mix. It's just a ratio chart, and is used to determine the strenght by adjusting your f'c value be the standard percent value.

Maybe I'm wrong, but I have used this chart in the past and I have seen other use it as well.
I guess we we'll just post the results for the actuall days ie. 35 days, 10, days ect.

Thanks again

Matt

While I am not familiar with the chart you have posted, I assume that it was a general chart prepared to show how concrete cures in average. However, depending on the amount of cement, flyash, admixtures, etc. in the concrete the actual shape of the curve will be different.

How would I create the chart with the data I have.

I have cement powder, admixtures, water. The chart doesn't seem to care about whats in the mix, its just based on Percent. ie. Usually your 7-day is 75% of your 28-day strenght. Isn't this chart a standard?

“Usually your 7-day is 75% of your 28-day strength. Isn't this chart a standard?”

The chart is not standard. Say a mix has a quantity of flyash substituted for cement. This mix might reach only 50% at 7 days and only 90% at 28 days.

Every mix cures and gains strength at different rates. Otherwise every 7 day break for every 3000 psi mix would be exactly the same.

We don't use flyash and our mix design is the same everyday. What kind of data would I need to have to create that chart?

Here are our results. We only spec 35MPa after 28-days.

Pour # kN Mpa Actual Day Crushed Required Day Crush
163A 328 40 8-Sep 14-Day 1-Sep 7-Day
164A 329 41 8-Sep 13-Day 2-Sep 7-Day
165A 331 41 8-Sep 10-Day 5-Sep 7-Day
166A 300 37 8-Sep 9-Day 6-Sep 7-Day
167A 305 38 8-Sep 8-Day 7-Sep 7-Day
168A 289 36 8-Sep 7-Day 8-Sep 7-Day

148B 325 40 8-Sep 35-Day 1-Sep 28-Day
148C 355 44 8-Sep 35-Day 1-Sep 28-Day
149B 357 44 8-Sep 34-Day 2-Sep 28-Day
149C 352 43 8-Sep 34-Day 2-Sep 28-Day

169A 296 37 12-Sep 10-Day 9-Sep 7-Day
150B 364 45 12-Sep 35-Day 5-Sep 28-Day
150C 360 44 12-Sep 35-Day 5-Sep 28-Day
151B 349 43 12-Sep 34-Day 6-Sep 28-Day
151C 351 43 12-Sep 34-Day 6-Sep 28-Day
152B 322 40 12-Sep 33-Day 7-Sep 28-Day
152C 319 39 12-Sep 33-Day 7-Sep 28-Day
153C 331 41 12-Sep 32-Day 8-Sep 28-Day
154B 357 44 12-Sep 31-Day 9-Sep 28-Day
154C 345 43 12-Sep 31-Day 9-Sep 28-Day

Well even your 7 day breaks appear to meet the 28 day requirement. Why not just report what you have?

I reported all the data and made notes about the actual crush date.

"Well even your 7 day breaks appear to meet the 28 day requirement. Why not just report what you have?"

My 7-days were more like 10-day crushes.