Ready mixed concrete for bored pile
Ready mixed concrete for bored pile
(OP)
The contractor advise me that ready mixed concrete must be used for bored pile work.
Are there any reference standards to reject concrete mixing at site for bored pile work? Please comment.
Are there any reference standards to reject concrete mixing at site for bored pile work? Please comment.





RE: Ready mixed concrete for bored pile
For cast in place piles (assuming they are friction piles), there is not much of a technical issue. They are generally lightly loaded for concrete. Shrinkage is not normally an issue. Some areas require suplhate resistance due to the soils. Is there a particular reason for wanting to reject. If a slump test is taken prior to depositing the load and it is outside spec then you can have the contractor reject the load, but slump (reasonable) has little impact on pile construction.
You should also spec that the top 10' are mechanically vibrated to help consolidate the concrete against the soil.
Dik
RE: Ready mixed concrete for bored pile
Concrete for piles are never vibrated and slump is a very important parameter: it should be around 18 cm and should keep this value as long as it needs for concreting the complete pile
RE: Ready mixed concrete for bored pile
Dik
RE: Ready mixed concrete for bored pile
Now, say I am working in China - northwest. Nearest ready mix plant is 100km away or in Laos, which, to my knowledge has NO ready mix plants and doubtful of any vetting. Am I not able to pour concrete? Sure I can. I have used the portable 1/4 yd site mixers on many many bored piles, foundations, retaining walls, etc. They have been poured successfully. In fact, we watch the concrete being made on site in our supervising presence, we have control on the weights of the consitutents, we watch it being mixed and it is placed in the structure within minutes of mixing. Problems? No - other than for large pours, when you need several such mixers with no hiccups to prevent cold joints. We've had excellent concrete.
Not all jobs are in developed countries or inside large cities of the underdeveloped ones. Concrete can be made by portable mixers - but, you need to ensure good control on the consitutents and mixing. But wait, don't you need to do that too with ready mix plants? And, with ready mix plants and transit mixers, there is always the possibility of adding additional water 'on the way' or on arrival at the pour site. Doesn't happen with portable mixers - only problem with added water is when it is added during the mixing and you can observe that first hand - doubtful you do at a batch plant.
RE: Ready mixed concrete for bored pile
RE: Ready mixed concrete for bored pile
In France, it is mandatory to put , depending on the codes you are submitted, around 400 kg of cement per m3. This gives a concrete which does not need to be vibrated to get a good density and watertightness without any vibration.
With slumps of 18 to 20 cm ( obtained with plasticizers )maintained throughout the concreting session
RE: Ready mixed concrete for bored pile
I have seen minimum cement contents specified for 20 MPa concrete that forces the concrete (given the w/c ratio, etc) to end up with >30 MPa. Seems a waste of cement. Why don't they just do away with the 20 MPa and then specify 30 MPa?
Any take on it?
RE: Ready mixed concrete for bored pile
Dik
RE: Ready mixed concrete for bored pile
A, then use 400kg/m3; if type B, then use 375kg/m3." Of course, too, you will specify a different type (e.g., sulphate resistant) as needed.
RE: Ready mixed concrete for bored pile
RE: Ready mixed concrete for bored pile
It is also true that in our codes the type and quantity of cement can be influenced by the soil from an environmental point ( sulphates and so on )
RE: Ready mixed concrete for bored pile
RE: Ready mixed concrete for bored pile
Dik
RE: Ready mixed concrete for bored pile
We vibrated the concrete - but in shallow bored piles with sufficient shaft diameter, it was not uncommon to have workers down inside the cage in order to handle the elephant trunk. With respect to BigHarvey's experience, they are taking advantange of, I presume, plasticizers to increase the slump (workability) so that the final product is not much unlike self-consolidating concrete.
I don't think that vibrating the concrete really 'presses in' the concrete to the side wall - there just isn't enough energy being imparted to 'force the issue'. Still, to ensure that you do not have honeycombing with lower slump concretes, vibration is not a bad idea.
RE: Ready mixed concrete for bored pile
yes it is clear we are talking about different forms of construction. I am talking about bored piles for civil engineering structure in the order or 1.5m diameter and lengths 50-100m. In this case bentonite or polymer is used as excavation support, and I really do not see that it is practical to use vibrators at this depth and through the bentonite.
The concrete has a high slump so that the concrete is self compacting. The piles are of course tested and there is not a problem with uncompacted concrete.
RE: Ready mixed concrete for bored pile
RE: Ready mixed concrete for bored pile
RE: Ready mixed concrete for bored pile
you were maybe working with Thai Bauer - good company. I see that they are picking up work again in Thailand and we are also talking to them about work in Vietnam. The new airport link had a lot of bored piling rigs last time I had a drive past, Bauer, Pylon (previously Power P I think) Ital Thai Trevi.
RE: Ready mixed concrete for bored pile
RE: Ready mixed concrete for bored pile
RE: Ready mixed concrete for bored pile
the question about readymixed concrete is not phrased in a way which allows for a definite answer. The fact is that properly batched concrete is necessary, whether this is achieved by the contractor by using his own on-site batching plant or by using an off-site readymixed concrete supplier is his choice.
There is no spcific requirement for an additional 10% cement for a tremie concrete mix. Many large piling projects now use pumps and a mortar mix is used first, this mortar is of course discharged away from the pile.
Bentonite or polymer (or a mix of the two) will often be used as excavation support. Depending on the specification the pile may typically have to be completed within 12-24 hours of excavation. The actual time for placing the concrete will vary according to the size and depth of the pile, 100m+ is not unusual.