Concrete mix question
Discussion
Could any of the concrete experts please give there views on the following concrete issue? I received a batch of PAV2 specified as S3 (120) both stated on the delivery note, the mix was very stiff, having received the batch information from the supplier, the supplier admits it was mixed in error, insufficient water, with the following contents;
Sand 4770kg
Stone (4-20mm) 6450kg
GGBS 820kg
CEM1 1230kg
Water 676kg
AEA 3L
Would this be considered a minor defect or major defect in the supplied concrete?
Bit of background
Unfortunately this was the first ready mix I have had in over 5 years, so I was out of practice, after the first part of the poor less than 1m3, I stopped the driver as the mix to me appeared too stiff, he agreed it was stiffer than S3, I now realise that at this point I should of sent him away, learning for me, but not having any recent experience, and only limited previous experience, I was not confident to risk a charge for returning the load, this supplier had previously given me excellent service.
This slab didn't require the full strength of PAV2, I accepted the drivers offer to add water, the next metre or so was poured with around 50 litres added from memory, still very stiff, boot holes left near vertical sides, agreed to add the max available water total 150 litres, the remainder was better but still stiffer than the subsequent deliveries. I stated not to spec on the delivery note, and did not sign the customer adding water disclaimer. I lost too much time trying to place the first part of the load and ended up with a failed pour. With the site added water the W/C was virtually the same as the next delivery that was poured without issue (apart from the delivery note stating the wrong grade). The third delivery I sourced from another supplier and was a much more workable (they appear to have added a superplasticiser).
The supplier is stating they will not refund the defective load, as they state it is normal practice to add water on site and for them to supply concrete stiffer than specified, however the deliver note states they accept no responsibility for the quality of the concrete if any water is added by customer request. It was my understanding that you should not add water to ready mix, but a small amount is often added to modify within a slump class at customers risk, is my understanding correct? They also state that the addition of water on site brought the mix to spec so there is not issue, even the last part of the pour did not have the workability of the subsequent deliveries, is this due to the mix curing faster in the drier state for the hour between batching and the water being added?
Sand 4770kg
Stone (4-20mm) 6450kg
GGBS 820kg
CEM1 1230kg
Water 676kg
AEA 3L
Would this be considered a minor defect or major defect in the supplied concrete?
Bit of background
Unfortunately this was the first ready mix I have had in over 5 years, so I was out of practice, after the first part of the poor less than 1m3, I stopped the driver as the mix to me appeared too stiff, he agreed it was stiffer than S3, I now realise that at this point I should of sent him away, learning for me, but not having any recent experience, and only limited previous experience, I was not confident to risk a charge for returning the load, this supplier had previously given me excellent service.
This slab didn't require the full strength of PAV2, I accepted the drivers offer to add water, the next metre or so was poured with around 50 litres added from memory, still very stiff, boot holes left near vertical sides, agreed to add the max available water total 150 litres, the remainder was better but still stiffer than the subsequent deliveries. I stated not to spec on the delivery note, and did not sign the customer adding water disclaimer. I lost too much time trying to place the first part of the load and ended up with a failed pour. With the site added water the W/C was virtually the same as the next delivery that was poured without issue (apart from the delivery note stating the wrong grade). The third delivery I sourced from another supplier and was a much more workable (they appear to have added a superplasticiser).
The supplier is stating they will not refund the defective load, as they state it is normal practice to add water on site and for them to supply concrete stiffer than specified, however the deliver note states they accept no responsibility for the quality of the concrete if any water is added by customer request. It was my understanding that you should not add water to ready mix, but a small amount is often added to modify within a slump class at customers risk, is my understanding correct? They also state that the addition of water on site brought the mix to spec so there is not issue, even the last part of the pour did not have the workability of the subsequent deliveries, is this due to the mix curing faster in the drier state for the hour between batching and the water being added?
Can you give some more details please? Are the aggregate figures as batched or SSD (saturated surface dry) are they and the cement (CEM1, GGBS) individual weights or cumulative?
What was the moisture of the aggregate.
What was the size of the load?
What type of mixer was it.
Is the company QSRMC or BSI registered?
What part of the UK are you in?
What was the moisture of the aggregate.
What was the size of the load?
What type of mixer was it.
Is the company QSRMC or BSI registered?
What part of the UK are you in?
Edited by Drumroll on Saturday 9th September 20:11
Thanks for the reply, my understanding is that they are individual as batched weights.
The concern load 6m3
6.5m3 "good load"
According to the delivery note the cement is C111A
The mixer type was batched, then delivered in drum type truck. I do not know the moisture content of the aggregate, I only got the batching ticket due to the second load delivery note stating ST4 instead of PAV2 and needed some evidence it was what I ordered.
I have limited knowledge of concrete, so I am just trying to establish if I am being reasonable pursing the supplier for the cost of the first load, or if the problem is with me.
The concern load 6m3
6.5m3 "good load"
According to the delivery note the cement is C111A
The mixer type was batched, then delivered in drum type truck. I do not know the moisture content of the aggregate, I only got the batching ticket due to the second load delivery note stating ST4 instead of PAV2 and needed some evidence it was what I ordered.
I have limited knowledge of concrete, so I am just trying to establish if I am being reasonable pursing the supplier for the cost of the first load, or if the problem is with me.
So firstly I would say "if" the figures for the second load are correct they do tie in with the figures for the first load.
Regarding the first load the cement content come out at 340kg/m3 which is at the lower end of what I would expect for that mix, Minimum Cement content for that mix is 340kg/m3 with a maximum W/C (Water/cement) ratio of 0.45.
The "fines" percentage seems high to me as well.
If the moisture content of the sand is 6% (it is hand written on the ticket) the water cement ratio come out at 0.46. That is without the water added on site.
What does surprise me is the lack of a WRA (Water Reducing Admixture) in the mix. It could be part of the AEA (Air Entraining Admixture) but 3 litres for a whole load is a rather small amount.
As for the comments about mixing dry and adding water on site that is clearly wrong. It also is at odds with the statement no responsibility will be taken once water is added on site.
Water addition on site when you have hot days is not an exact science as you can't know how much water has been lost through evaporation. but regardless, if we take the figures "as batched" they have exceeded the Max W/C ratio.
I would suggest you "play dumb" and say you have been asked by (I am sure you can think of somebody) to provide a mix design certificate. Then we can have a look at the mix again.
Regarding the first load the cement content come out at 340kg/m3 which is at the lower end of what I would expect for that mix, Minimum Cement content for that mix is 340kg/m3 with a maximum W/C (Water/cement) ratio of 0.45.
The "fines" percentage seems high to me as well.
If the moisture content of the sand is 6% (it is hand written on the ticket) the water cement ratio come out at 0.46. That is without the water added on site.
What does surprise me is the lack of a WRA (Water Reducing Admixture) in the mix. It could be part of the AEA (Air Entraining Admixture) but 3 litres for a whole load is a rather small amount.
As for the comments about mixing dry and adding water on site that is clearly wrong. It also is at odds with the statement no responsibility will be taken once water is added on site.
Water addition on site when you have hot days is not an exact science as you can't know how much water has been lost through evaporation. but regardless, if we take the figures "as batched" they have exceeded the Max W/C ratio.
I would suggest you "play dumb" and say you have been asked by (I am sure you can think of somebody) to provide a mix design certificate. Then we can have a look at the mix again.
Thank you Drumroll, for taking the time to provide feedback, I had drafted a response this morning to the supplier, but I will hold on that and follow your advice.
The add mixtures listed on the delivery notes are slightly different between the 2 deliveries. The concern load states only AEA, the second load states AET + Master set 510 (retarder was agreed for that load)
The add mixtures listed on the delivery notes are slightly different between the 2 deliveries. The concern load states only AEA, the second load states AET + Master set 510 (retarder was agreed for that load)
The slump discrepancy may be partly due to the first lorry having a dry drum when loaded and the subsequent trucks having wet drums having already done a load.
Or the aggregate was dryer for the first load, batchers don't tend to want to leave their sheds once they're in their seat in my experience.
Unfortunately we can't now know if that was the case. Drumroll will have a better idea than me as to whether you have a chance of a refund, my feeling is that it will be difficult.
Or the aggregate was dryer for the first load, batchers don't tend to want to leave their sheds once they're in their seat in my experience.
Unfortunately we can't now know if that was the case. Drumroll will have a better idea than me as to whether you have a chance of a refund, my feeling is that it will be difficult.
Most of the concrete is for the drive, still got another 3-4 pours to do, most will be fairly light traffic, it will have to accommodate 32 tonne trucks and plant on occasions, it is also next to fairly significant tree roots which destroyed a lot of the original drive. Fortunately the failed slab is for the patio, so the strength is not required, I just kept the same spec for ease of ordering.
I am sure they will make it difficult for me to claim the first load refund, I just want to establish whether what I have received is normal for ready mix and therefore it is entirely my issue, or whether it was reasonable for me to have expected what I ordered. I believe that all the loads I received last week were first loads of the day.
From the initial information from Drumroll it appears there may be other issues with the mixes.
From the initial information from Drumroll it appears there may be other issues with the mixes.
Friend of mine was doing his first pour for the basement in his new house build. The mix coming out the first load (traditional cement mixer not Readymix) was dry as a bone to begin with, friend wisely decided to video it coming down the chute. Later during the pour a load of grey water came out. The slab didn’t cure right and failed every subsequent test. The cement works produced load certificates and refused responsibility.
Turns out the cement works wasn’t far away and the only mixing time they’d allowed for was while the mixer was in transit, but it wasn’t long enough. Still the supplier refused responsibility. It wasn’t until my friend showed them the video of dry aggregate coming out the machine that they finally admitted responsibility and paid to have the slab broken up and grabbed away.
I had issues with pumped readymix starting off too wet and causing the insulation to float. Again the supplier didn’t take responsibility but we managed to recover that situation - just - on the day and we only paid for the 6m3 we ordered not the 10m3 that eventually came down the pipes.
My experience is you’ll need to have very good evidence of their mistakes if you want to get a refund, because their first and second instinct is to refuse. If a pour feels wrong my builder’s in the habit of videoing it now.
Turns out the cement works wasn’t far away and the only mixing time they’d allowed for was while the mixer was in transit, but it wasn’t long enough. Still the supplier refused responsibility. It wasn’t until my friend showed them the video of dry aggregate coming out the machine that they finally admitted responsibility and paid to have the slab broken up and grabbed away.
I had issues with pumped readymix starting off too wet and causing the insulation to float. Again the supplier didn’t take responsibility but we managed to recover that situation - just - on the day and we only paid for the 6m3 we ordered not the 10m3 that eventually came down the pipes.
My experience is you’ll need to have very good evidence of their mistakes if you want to get a refund, because their first and second instinct is to refuse. If a pour feels wrong my builder’s in the habit of videoing it now.
Might be using the wrong terms (sorry) but a traditional cement mixer has it all mixed at depot and delivers a mixed load, but Readymix has a lorry with separate hoppers for aggregate, sand, cement and water and literally mixes it as it pours?
Edited by PhilboSE on Monday 11th September 08:50
PhilboSE said:
Might be using the wrong terms (sorry) but a traditional cement mixer has it all mixed at depot and delivers a mixed load, but Readymix has a lorry with separate hoppers for aggregate, sand, cement and water and literally mixes it as it pours?
I think that's called a volumetric mixer.PhilboSE said:
Ah ok. Down my way Readymix must be the local suppliers of the volumetric stuff as everyone uses it generically to describe that type.
Yes strange how different areas describe things. Readymix was/is actually a trademark of Readymix Concrete limited. (They had orange trucks, if anyone can remember) They were acquired by Cemex in 2005
Readymix became a generic name for drum mixer delivered concrete, in the same way Hoover became a generic term for vacuum Cleaners.
Volumatic mixers (carried in hoppers and mixed on site) is by comparison a relatively new concept.
I know I am a bit of an anorak when it comes to concrete.
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