mix and delivery of concrete
mix and delivery of concrete
(OP)
Arrived site to observe concrete placement and help train a new concrete testing tech. Huge placement of 3yd3 today for a few piers.
The concrete was truck mixed and delivered in two 1 1/2yd3. High range water reducer was added at the site by the producer's QC tech. The producer's QC tech erred when adding the Super-P. The load being so small was way down at the bottom of the drum and he just dumped the Super-P in the at the top of drum. This simply got the inside of the drum moist with Super-P. To get the Super-P down to the load he (you guessed it) got the water hose a rinsed in down. This appeared to cause the mix to completely segregate.
Upon filling the oyster bucket with the mix, the water in the mix appeared to repel itself from the mix and immediately rise to the top. I have never seen anything like this.
The producer's QC insisted on a slump to which I said on what, that 6" of grey water on the surface there? I mean it was water, grey with no sand or rock. All aggregate has sunk directly to the bottom of the bucket.
The load was rejected. A few minutes later I asked the QC guy what the ETA was in the second truck to which he said the second 1 1/2 yd3 truck had been recalled so that they could add another 1 1/2 yd3 to that truck.
1) I looked in C-94 but could not find anything that precluded an already mixed truck from having more mix added to it. Is this practice restricted by an ASTM standard, by an ACI standard, or just by common sense.
2) I know the addition of water to the mix after the addition of SP is not allowed by spec but where does this restriction come from.
3) I thought I remembered that loads under 3 yd3 were not allowed. This particular job's spec book however did not list this restriction. I couldn't find this is C-94 either. Is it restricted by an ASTM or ACI code?
Thanks!
BTW, The second truck was rejected as well. This was the fist time I ever got a load rejected PRIOR to being mixed. How sweet is that! Also the placement was postponed until tomorrow just to make sure the plant didn't try to sleaze that bum load in on us. I mean they can't save it over night, right?
The concrete was truck mixed and delivered in two 1 1/2yd3. High range water reducer was added at the site by the producer's QC tech. The producer's QC tech erred when adding the Super-P. The load being so small was way down at the bottom of the drum and he just dumped the Super-P in the at the top of drum. This simply got the inside of the drum moist with Super-P. To get the Super-P down to the load he (you guessed it) got the water hose a rinsed in down. This appeared to cause the mix to completely segregate.
Upon filling the oyster bucket with the mix, the water in the mix appeared to repel itself from the mix and immediately rise to the top. I have never seen anything like this.
The producer's QC insisted on a slump to which I said on what, that 6" of grey water on the surface there? I mean it was water, grey with no sand or rock. All aggregate has sunk directly to the bottom of the bucket.
The load was rejected. A few minutes later I asked the QC guy what the ETA was in the second truck to which he said the second 1 1/2 yd3 truck had been recalled so that they could add another 1 1/2 yd3 to that truck.
1) I looked in C-94 but could not find anything that precluded an already mixed truck from having more mix added to it. Is this practice restricted by an ASTM standard, by an ACI standard, or just by common sense.
2) I know the addition of water to the mix after the addition of SP is not allowed by spec but where does this restriction come from.
3) I thought I remembered that loads under 3 yd3 were not allowed. This particular job's spec book however did not list this restriction. I couldn't find this is C-94 either. Is it restricted by an ASTM or ACI code?
Thanks!
BTW, The second truck was rejected as well. This was the fist time I ever got a load rejected PRIOR to being mixed. How sweet is that! Also the placement was postponed until tomorrow just to make sure the plant didn't try to sleaze that bum load in on us. I mean they can't save it over night, right?





RE: mix and delivery of concrete
RE: mix and delivery of concrete
An NCR?
The basis for rejection was that the mix could not be slumped due to extreme segregation. The producer is obligated to supply the mix at the specified slump for the specified time:
6.2 Concrete shall be available within the permissible range of slump for a period of 30 min starting either on arrival at the job site or after the initial slump adjustment permitted in 11.7, whichever is later.
Could have gotten them on the re-mixing because the first 1 1/2 yd3 would have been way over the 90 minute rule:
ASTM C-94 11.3 The mixing time shall be counted
from the time all the solid materials are in the drum.
ASTM C-94 11.7 Discharge of the concrete shall be completed within 1 1?2 h, or before the drum has revolved 300 revolutions, whichever comes first, after the introduction of the mixing water to the cement and aggregates or the introduction of the cement to the aggregates.
But they hadn't planned on telling us that the 3 yd3 load was really a 1/2 a load added to an old 1/2 a load. They were going to try to sleaze one by us. Their own QC guy spilled the beans.
I didn't reject the load; I only say that the mix appears out of spec and that XYZ Engineering recommends not placing out of spec concrete in the forms.
The contractor can decide for himself what to do but I have direct communication with the owner soooo....
RE: mix and delivery of concrete
RE: mix and delivery of concrete
RE: mix and delivery of concrete
RE: mix and delivery of concrete
RE: mix and delivery of concrete
There are 2 types of superplaticizers. One is the basic high-range water reducer which complies with either ASTM C 494 Type F or ASTM C1017 Type 1. The other has ingredients which causes retardation of the mix....and complies with either ASTM C 494 Type G or ASTM C 1017 Type II.
The Type F super-P has been around longer....and is meant to be added at the jobsite.
The Type G super-P is meant to be added at the batch plant. Can you imagine a ready mix truck with a full load of soupy platicized mix driving up a steep road on the way to the job?
don45640's recommendation is the way to do it. It is important that the individual adding the super-P be properly trained.