This might be a fanciful idea but I was thinking about building a 20'-30' high 10-15' diameter round tower using BlockBlock BuildRadius blocks. I'm a beginner and this isn't a super practical question so feel free to move on if you prefer more serious and productive discussions. As I've been puzzling through the design I realized that although the concrete and blocks won't be prohibitively expensive it would probably take 3 or 4 separate pours, with short loads of concrete every time. One pour to set the foundation and floor (probably no pump truck required), a second for the 0-10', a third for 10-20' and a fourth pour for the last 20-30' with a pump truck required and a day or two between each pour.

Is there any way to reduce the number of pours required for tall walls? I'm thinking that bracing will be easier with a circular structure, especially since window bucks will be narrow and can be spaced to avoid standing seams and the blocks will brace each other. Separate from bracing concerns, can you effectively pour and vibrate concrete into a 20-30' tall wall without creating voids or blowing out from static pressure?

Are there other examples of people building silo like structures with ICF?

You will probably need to do the pours in at least two lifts. A structural engineer could run some quick calcs if you know what bracing scheme you would use. Don't forget the rebar, that will need some work for the horizontal parts. How are you planning to side the the exterior?

Also consider building it with SCIPs. Can be done with a hand sprayer and lots of on-site mixed batches.

If I read your description correctly you are talking about stacking 30' of ICF then pouring it? I don't think you will be able to build this that way. The issue is the CC has to fall into the wall past rebar and crossties. This causes separation of aggregate and cement and entrains air that MUST be removed. Falling 8-10' is bad enough. The CC also would stick to the upper rebar effectively blocking the passage for subsequent pours leaving an increased possibility of voids beneath the blockages. I have also never seen a 30' consolidator nor someone with the arms and shoulders to pull it up and down a 30' wall, let alone placing 30' tied sticks of vertical rebar...

ICF is typically poured in stages. As you described slab and footings could be in one pour but this is not typical as the slab usually overrides the footing to touch the inside face of the wall to brace the inside of the wall, backfill braces the outside. But with some carefull formwork you could accomplish this in one pour, but you would have to mimmic the arc of the ICF block accurately as the block would have to be able to fit against it snugly. It is easier to pour the slab after the first wall is in place and poured. You also don't have to possibly damage the slab attaching your bracing/scaffolding.

After footing then you stack your block and horizontal rebar to the first floor height adding your braces and scaffold as you go, drop the vertical rebar and pour that first 10' in about 30" lifts(four passes around the circle wit the pump truck). 15' dia circle would be about 47' of wall. That pour would take about 2 hours if you really went slow. Pumper costs arond $150/hr in my area(YMMV) but usually has a 2-3 hour minimum, so $450 for the pumper plus CC. An 8" ICF wall 10' tall by 47' long would be about 11.5 yards of CC without openings, so about $1100 in CC or $1550 plus the labor for 2 hours to help you fill it(4 people?) Maybe $250? Or $1800 for each pour(less with openings)... lets say $7200 plus the cost of the block for a 30' tower 15' in diameter... That $7200 is of course a high as the CC cost would be reduced with the size of the openings and you would probably drop to 6" ICF for the second and third walls(25% less CC)...

Looking at it another way, if you are building most of this yourself, My CC guy once mentioned a cost of $10 per SF of wall area for a self build. So far mine has been pretty close to that including the footings and slab. 47' X 30' is 1410 SQ/FT or around 14,100 for the walls in this structure? With a very large YMMV added in

At any rate once you pour the first wall, then you remove the scaffolding, build the first floor system then start stacking the next wall and rebar, re-using the bracing/scaffolding but standing it on the floor system. You need the floor system to brace the wall and you need to give the CC in the first wall section time to cure properly to support the weight of the next section of wall. Tall narrow structures of course present some additional engineering challenges, so the details would have to be sorted out by the engineer...

I have done structures like this. I guess it depends on use as well. But Ronmar has it correct. Without knowing OA height it would be hard to say the exact number of pours. 20' is a long way from 30'. The jobs I did were stair towers, no floors. I poured the frost wall out of the truck. The next two pours were with a pump. I was 28' to truss bearing. 30' 8' OA. Product was 6" Fox radius blocks. No issues. GC had access to rounded scaffold planks they worked well to walk on. They could be made easy enough though. Good Luck.

This is a job for composite ICF. (Rastra, Techblock, Durisol.) I built half of a tower 23 feet tall (a radiused stairwell for a spiral staircase) using AAC blocks. In my case, I was filling 4 inch bore holes with two sticks of #5 rebar, along with three bond beams at first and second floor ceiling heights and at the apex. Rastra et all have a waffle style concrete but you can pour it every few courses if you want. Composite ICF can be cut with hand tools. Make a jig; get r done. I also built an open 4.5x4.5 chimney chase 23 feet tall for the mechanicals. All of them. I used bond beams to create four effective floors in that space.

We just finished one on a custom house at 38' from slab and 45' from ground. We poured it in 3 pours. 2 -12' pours with the floors and 18'6" on last pour. Bracing it was not super easy as it was a 5' radius (10' across inside), very congested but doable. Use a good mix and internal vibrate and you will be ok up to about 20'. Over that height you need to cut pour holes in to help segregation and access for the vibrator. You could use a good rebar shaker and get by with the right mix also. Build is posted on our Facebook page.