80 MPa Concrete. 1

[miningman]

I need some asistance in estimating the cost of 80 MPa concrete. This is not a typo, this is the specs on the drawings. I'd like an actual cost from Western Canada but would gladly accept a rule of thumb , "such as xxx% of the cost of 25 MPA"

No one Ive spoken to has experience with such a mix. They warn me that it would be very low slump. Is there a limit as to how much super P I can add to get something thats pumpable. I might need four hours retardation...... its going underground....is this feasible ??

If I install a slickline, say 500 metres, am I asking for major blockages with such a mix?? This line would be somewhere between vertical and 60 degrees.

All answers and comments appreciated

 

[Zambo]

80MPA is not so unusual these days. It is a special mix design where I expect you will need to do a number of trial mixes before you can get a reliable design mix. The following are some points to consider:

1. you need a very low water/cement ratio, so Super Plasticiser is required.
2. you should also consider using PFA with the OPC to lower the heat of hydration.
3. Silica fume probably needed.
4. you should place the concrete as cool as possible, this will need chilled water and probably crushed ice (but not too much as this increases the friction against the mixer)

I think (but this is new for me) that you will have trouble with the 4 hour retardation and the 500m pumping distance. Plus pumping over this distance will make it difficult to keep the concrete cool.

Just in case my advice is on the wrong track what sort of quantity of concrete are you placing and is it of large dimensions (I ask because with a large pour the heat of hydration of 80MPA concrete is a major concern)

 

[miningman]

Thanks Zambo, that doesnt contradict my gut feel. I handnt overlooked the heat of hydration / possible use of ice issue.... especially given that the ambient summer time temperature at the job site is 35 -40 degrees centigrade.

And just for clarification the slickline / retardation is an either / or situation. The placement location is`an underground mine, 500 metres below surface. Either I put in a slick line to drop the stuff by gravity and then pump say the last 200 metres horizontally underground or I need 4 hours retardatuion to allow time to truck the stuff down 4500 metres of underground ramp at 16% grade.

I anticipate one pour per week of about 50 cu metres, essentially as a slab 200 mm thick. If I can get it place, I'm sure I can deal with other issues.

 

[Zambo]

The fact that you are casting a slab 200mm thick is going to be an advantage to you, although you should still try to keep the temperature as low as possible there is some reduction in the risk of early age cracking due to the heat of hydration.

I will try to find a mix design tomorrow (it won't be suitable for your use, but you could use it to estimate a price) but for now I would say the concrete will be 2 x the price of 40MPA. Plus you have your placing method.

 

[hokie66]

Zambo has given you good advice, but your application is sufficiently "far out" that I would do a small trial first. You don't want to get started on a 50 m3 pour and find out it doesn't work.

 

[Zambo]

for price estimate only:

blended cement 450kg/m3 OPC blended with ggbs
silica fume 8% by weight of cement
Super-P about 10 litre
water 140kg/m3 w/c ratio about 0.30
coarse aggregate 780 kg/m3
fine aggregate 994 kg/m3

as hokie66 states you will neeed to carry out trial mixes, but as your original question was for a cost estimate just ask a ready mix concrete supplier to price the above. Note there are many different Super-P you will need to find one that suits your purposes and mix design (same for the blended cement).

 

[SirAl]

I would be tempted to discuss the application with a large international supplier such as LaFarge that have proprietary mixes such as Agillia(sp?) and other HPC products. It won't be cheap! I agree that a trial mix/mixes would be prudent.

 

[miningman]

Thanks Gentlemen, Ive already spoken to Lafarge who gave me a budget price of $450 per cu metre, which is only a bit higher than the $400 I had previuosly assumed.

It definitely seems Im going to have some placement issues but Ive got about 2500 cu metres to place so I should have the opportunity to get it right after a few trial and errors.