Recommended Compressive Strength of Dental or Rock Reconstruction Concrete

[BigH]

G'day Colleagues,

Some may think that this should be in the Concrete Forum, but I prefer to hear from geotechs on the issue - as I know y'all read both anyway.

If you were to specify a compressive strength for foundation dental concrete or concrete for rock reconstruction, what cylinder strengths would you propose? For my purpose, it is for foundation under a dam; however, some may have suggestions of different compressive strengths for different applications.

Please provide your thoughts - looking for a consensus or range from my expert colleagues!!

 

[EireChch]

BigH, you often pose these questions related to dam construction, which I have no experience or clue tbh!

Regardless - Ill post what I think is logical, and wait to be educated.

Question first, how deep does the dental concrete need to extend? Is this a surface that has been blasted and is a little uneven? If so it could likely be a concrete mix with typical workability parameters, slump etc.

If the concrete needs to travel to ensure that it is filling all voids in rock then a finer concrete would be required. This will have limitations on strength. From my experience in grouting, compressive strength of 30MPa is likely at the upper end.

If you have no constraints on concrete workability, then I would suggest a concrete strength that is above the rock strength, limited to 50MPa.

My thoughts, but maybe I am talking out my ass

 

[TigerGuy]

EireChch pretty much covers it.

How tall is the dam? Is this a retrofit project, or new construction? What are the strength characteristics of the native rock?

 

[BigH]

TigerGuy - Earth Dam height when finished - 335 m (1100 ft). Rock varies considerably - the geology here is very complex .. .

 

[cvg]

USBR indicates 3,000 psi for dental concrete and no requirements listed for slush grout or shotcrete.
it really depends on the application. for leveling, filling cracks to prevent erosion or seepage, to backfill holes, etc.

https://usbr.gov/tsc/techreferences/mands/geologyfieldmanual-vol2/Chapter21.pdf

 

[geotechguy1]

Probably irrelevant to a dam but for creating a level surface out of uneven rock cuts for footing foundations (apartment buildings) in calgary we just used 30 MPa concrete.

 

[GeoPaveTraffic]

I expect that the strength is not particuarly important. Think about the materials above, likely soil and crushed rock. I would say something like 3,000 psi is a good starting point. I would just make sure that durability is good and go with it.

Mike Lambert

 

[Milliontown]

I'm working on a spillway project and we will be using 3000psi dental concrete for our design. It will be overlaid by 5000 psi RC slabs