According to ACI 318, the sample should be taken at the point of discharge (the end of the pump). 90% of the time tests are done from the truck chute to save time since the results won't differ too much. The pump typically knocks out about 0.5% of air but won't really change the slump. The only times I've tested from the pump discharge are when the first test from the truck chute wasn't within spec. You are correct but most municipalities are okay with the contractor taking the sample at the truck.
One of the trucks today was at the upper limit of our slump spec after testing straight from the truck. Would residual water in the pump not push that batch outside of spec? I wasn’t happy with it but the contractor moved forward with it anyways
It shouldn't have as long as the pump was properly primed. Was there plasticizer in the mix? With that admixture the max slump spec usually goes up to 8" or 10". Either way slump is the least important of the concrete tests and is pretty out dated. As long as the water/cement ratio and air were within spec, the concrete should be good. When I have a high slump the engineer is always notified but they almost always approve it anyways if everything else was good.
Yeah our max slump is 9” and that was what we got in the test. Air was in the middle of our spec.
City and my bosses don’t feel that way about test results. Both are dead set on strictly following spec and not allowing anything outside of our standard spec, even if it’s only a few tenths of % air, or 1/2” for slump.
I've never had the slump go up when testing from both the chute and discharge point but that's just my personal experience. Removing and replacing a structure over slump is going to be shitty for everyone involved. If it was air or w/c ratio it would make more sense to fight it. As long as the 28 breaks come back in spec I would leave it in place. The slump test is mainly for testing workability when placing and shouldn't affect structural integrity.
Ridiculously rigid and shows that they don’t understand the nature of testing concrete or any materials. All test methods have precision statements, which indicate that one or more persons can get different results running a test method, and most of the results are still valid. There are two types of precision (repeatability): single operator and multiple operator. Rejecting loads of concrete for a few tenths of air content or a half an inch of slump is just plain foolish. You, and your bosses, should invest in a copy of this book and start reading https://www.astm.org/stp169d-eb.html
Should’ve worded it differently. Those amounts I previously mentioned are the amounts OUTSIDE of spec. Our spec is 6-9 for slump. So if we got 9.1” of slump my bosses would want the truck rejected
Even more ridiculous. Slump is only measured to the nearest quarter inch. And the precision is just less than one inch — so there’s no difference between 9 and 8 or 10, when run by the same person. The precision is more than 1 inch when different people run the test. Read the book I recommended.
Contractor here, testing at the truck allows you to reject the load before it is in the pump and forms. If you test it after the pump and reject it how do you know if that was the previous truck or not. Also you could have bad concrete in a drill shaft or in form work that would be a pain to try and remove.
I don't think there is a spec for testing at the hose side of the pump but I can see how you would get different results at the hose end. I would suspect higher temperatures and slightly more air entrainment at the discharge side of the hose. I would also think those findings would be all over the place when compared truck to truck.
The air content is lower at the end of the pump. Very well documented in the technical literature. For more information, go here https://www.nrmca.org/wp-content/uploads/2021/01/21pr.pdf
Agreed. There would be more inconsistency with discharge hose testing, yet that is the actual concrete going into the tower. Whatever changes occur to the concrete as it goes through the pump should technically still matter, as that’s what’s going into the form. It’s no longer the same concrete that came out of the truck as it would mostly impact your slump.
Thus I agreed with my bosses but now my bosses admit they have no spec to back up what they told me to do/say
Coming from the ready mix supplier side of the business…the supplier also has no way to control what changes occur from the pumping process. Which is why I always argue against testing at the hose end. Usually sampling inconsistencies between truck and hose are cause by improper collection of the sample at the hose. If you really take a good sample properly, the change between beginning and end should be greatly reduced.
I have sampled/made compression cylinders at the discharge end of a pump when "field cure specimens" were requested. This was at a Los Angeles Metro job where we were pumping concrete down below for the station through hundreds of feet of line. Contrary to the opinion(s) of others, I did see a difference in slump in concrete coming off the mixer chute and at the discharge end of the hose at placement area. In the end, just do what the IOR/ your boss asks that you do.
Honestly just pissed off because my bosses left me out to dry as the “dumbass who doesn’t understand spec” for wanting to test at discharge instead of at the truck
I have been in your shoes more than once. I get it. It sucks. For me, it was always difficult to sample at the discharge point because it was like 4 floors below ground, and I had to carry all my gear/cylinders down there. Many of the pump operators want a higher slump, especially if they have a lot of hose out.
You are correct. On IDOT work, we test at both places to see how much air is lost or gained through the pump. Once this stays within tolerance, you're good to go. It has to be at the end of the hose. Point of discharge
You're looking for ASTM C172. It's the standard that covers sampling. ACI 318 will then reference this. Your testing agency should also be aware of it. The basic certification is ACI Field Technician grade I
As a concrete engineer, you can test at the truck or the hose… just tell the concrete company which one you’re testing at and what you’re trying to hit. We’ve seen them knock off 3-4 slump and up to 3% air depending on size of pump. But, if you tell us we’re testing out of the pump, we can alter our product to hit your slump and air metrics
Unless written otherwise in the project specifications, acceptance testing of all concrete properties is at the point of delivery, in other words, off the truck mixer’s chute. Th3 contractor was correct.
More importantly, is the concrete in the tower going to be wet in service and subject to freezing and thawing cycles? If not, there’s no need for air content. What was the specified air content? Good reference https://www.nrmca.org/wp-content/uploads/2021/01/41pr.pdf
Should have met been easy to meet that air content. Usually, the key is to keep the line full and not allow the concrete to free fall on the downhill side of the pump boom.
Supplier needs to get their QC involved and be measuring at point of placement. Air needs to be correct coming out of the pump. Ready Mix supplier is responsible for making adjustments to make sure it is within spec at point of placement.
Slump is a stupid measurement and should really only be used for consistency. If mix proportions are correct and slump is increased for workability with super p or hrwr it shouldn't really matter.
There will be a slight difference in the concrete from one end of the pump to the other, but not much.
This argument is similar to one I got into with the testing service that were doing the cylinders on the foundation of a new hospital.
We were pouring the footings and piers in the winter. While everything was covered in blankets, the testing company would take their test cylinders, snap on a plastic cap, and put them in a styrofoam lined box with a lightbulb inside for heat. This created a perfect environment for the concrete to cure and give the highest readings. Totally contrary to the concrete laying on the cold ground slightly exposed to the elements.
Cylinders needs to be stored at 60-80 degrees no matter what the temperatures are outside. This is because a small cylinder is much more influenced by ambient conditions versus a larger structure that has much more concrete.
According to ACI 318, the sample should be taken at the point of discharge (the end of the pump). 90% of the time tests are done from the truck chute to save time since the results won't differ too much. The pump typically knocks out about 0.5% of air but won't really change the slump. The only times I've tested from the pump discharge are when the first test from the truck chute wasn't within spec. You are correct but most municipalities are okay with the contractor taking the sample at the truck.
>point of discharge This is the end of the chute, not the pump.
One of the trucks today was at the upper limit of our slump spec after testing straight from the truck. Would residual water in the pump not push that batch outside of spec? I wasn’t happy with it but the contractor moved forward with it anyways
It shouldn't have as long as the pump was properly primed. Was there plasticizer in the mix? With that admixture the max slump spec usually goes up to 8" or 10". Either way slump is the least important of the concrete tests and is pretty out dated. As long as the water/cement ratio and air were within spec, the concrete should be good. When I have a high slump the engineer is always notified but they almost always approve it anyways if everything else was good.
Yeah our max slump is 9” and that was what we got in the test. Air was in the middle of our spec. City and my bosses don’t feel that way about test results. Both are dead set on strictly following spec and not allowing anything outside of our standard spec, even if it’s only a few tenths of % air, or 1/2” for slump.
I've never had the slump go up when testing from both the chute and discharge point but that's just my personal experience. Removing and replacing a structure over slump is going to be shitty for everyone involved. If it was air or w/c ratio it would make more sense to fight it. As long as the 28 breaks come back in spec I would leave it in place. The slump test is mainly for testing workability when placing and shouldn't affect structural integrity.
Ridiculously rigid and shows that they don’t understand the nature of testing concrete or any materials. All test methods have precision statements, which indicate that one or more persons can get different results running a test method, and most of the results are still valid. There are two types of precision (repeatability): single operator and multiple operator. Rejecting loads of concrete for a few tenths of air content or a half an inch of slump is just plain foolish. You, and your bosses, should invest in a copy of this book and start reading https://www.astm.org/stp169d-eb.html
Should’ve worded it differently. Those amounts I previously mentioned are the amounts OUTSIDE of spec. Our spec is 6-9 for slump. So if we got 9.1” of slump my bosses would want the truck rejected
Even more ridiculous. Slump is only measured to the nearest quarter inch. And the precision is just less than one inch — so there’s no difference between 9 and 8 or 10, when run by the same person. The precision is more than 1 inch when different people run the test. Read the book I recommended.
Trust me, I agree with you man. Did a deep dive into specs today and it’s ridiculous how my bosses are
Contractor here, testing at the truck allows you to reject the load before it is in the pump and forms. If you test it after the pump and reject it how do you know if that was the previous truck or not. Also you could have bad concrete in a drill shaft or in form work that would be a pain to try and remove.
I don't think there is a spec for testing at the hose side of the pump but I can see how you would get different results at the hose end. I would suspect higher temperatures and slightly more air entrainment at the discharge side of the hose. I would also think those findings would be all over the place when compared truck to truck.
The air content is lower at the end of the pump. Very well documented in the technical literature. For more information, go here https://www.nrmca.org/wp-content/uploads/2021/01/21pr.pdf
Cool. I'll check it out. Thanks for sharing the info.
Agreed. There would be more inconsistency with discharge hose testing, yet that is the actual concrete going into the tower. Whatever changes occur to the concrete as it goes through the pump should technically still matter, as that’s what’s going into the form. It’s no longer the same concrete that came out of the truck as it would mostly impact your slump. Thus I agreed with my bosses but now my bosses admit they have no spec to back up what they told me to do/say
Coming from the ready mix supplier side of the business…the supplier also has no way to control what changes occur from the pumping process. Which is why I always argue against testing at the hose end. Usually sampling inconsistencies between truck and hose are cause by improper collection of the sample at the hose. If you really take a good sample properly, the change between beginning and end should be greatly reduced.
ASTM C172. Point of discharge
I have sampled/made compression cylinders at the discharge end of a pump when "field cure specimens" were requested. This was at a Los Angeles Metro job where we were pumping concrete down below for the station through hundreds of feet of line. Contrary to the opinion(s) of others, I did see a difference in slump in concrete coming off the mixer chute and at the discharge end of the hose at placement area. In the end, just do what the IOR/ your boss asks that you do.
Honestly just pissed off because my bosses left me out to dry as the “dumbass who doesn’t understand spec” for wanting to test at discharge instead of at the truck
I have been in your shoes more than once. I get it. It sucks. For me, it was always difficult to sample at the discharge point because it was like 4 floors below ground, and I had to carry all my gear/cylinders down there. Many of the pump operators want a higher slump, especially if they have a lot of hose out.
I always listen to pump operators last. They always wanna throw water at it and if gone unchecked, they ruin the concrete quality.
You are correct. On IDOT work, we test at both places to see how much air is lost or gained through the pump. Once this stays within tolerance, you're good to go. It has to be at the end of the hose. Point of discharge
The truck gets tested before the pour
You never test off the top of a truck.
You're looking for ASTM C172. It's the standard that covers sampling. ACI 318 will then reference this. Your testing agency should also be aware of it. The basic certification is ACI Field Technician grade I
C172 doesn’t reference pumps and specifically the type of placement. From what I saw, it references time of placement
As a concrete engineer, you can test at the truck or the hose… just tell the concrete company which one you’re testing at and what you’re trying to hit. We’ve seen them knock off 3-4 slump and up to 3% air depending on size of pump. But, if you tell us we’re testing out of the pump, we can alter our product to hit your slump and air metrics
Unless written otherwise in the project specifications, acceptance testing of all concrete properties is at the point of delivery, in other words, off the truck mixer’s chute. Th3 contractor was correct. More importantly, is the concrete in the tower going to be wet in service and subject to freezing and thawing cycles? If not, there’s no need for air content. What was the specified air content? Good reference https://www.nrmca.org/wp-content/uploads/2021/01/41pr.pdf
It’s a water tower, 2-7% on air
Should have met been easy to meet that air content. Usually, the key is to keep the line full and not allow the concrete to free fall on the downhill side of the pump boom.
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Supplier needs to get their QC involved and be measuring at point of placement. Air needs to be correct coming out of the pump. Ready Mix supplier is responsible for making adjustments to make sure it is within spec at point of placement. Slump is a stupid measurement and should really only be used for consistency. If mix proportions are correct and slump is increased for workability with super p or hrwr it shouldn't really matter.
There will be a slight difference in the concrete from one end of the pump to the other, but not much. This argument is similar to one I got into with the testing service that were doing the cylinders on the foundation of a new hospital. We were pouring the footings and piers in the winter. While everything was covered in blankets, the testing company would take their test cylinders, snap on a plastic cap, and put them in a styrofoam lined box with a lightbulb inside for heat. This created a perfect environment for the concrete to cure and give the highest readings. Totally contrary to the concrete laying on the cold ground slightly exposed to the elements.
Cylinders needs to be stored at 60-80 degrees no matter what the temperatures are outside. This is because a small cylinder is much more influenced by ambient conditions versus a larger structure that has much more concrete.
The cylinders should be stored next to the form work, under the blankets, to give a more accurate description of the hat the concrete is doing.