For me, I have found that a 26" spread is the sweet spot for SCC placement; the flow seems to be perfect, as well as not needing to foam-fill every gap in the formwork. In fact a hole up to 13/16" will spew out for a second where you have time to shove a small rock, rag or something similar to stop the leak. Typically you will foam large continuous gaps along the bottom of the forms where it seats on the footing, along the bulkheads if the reinforcing penetrates and laps out or unused tie holes. But as far as the smaller one's the paste will leak but if you're not pouring a pea-gravel SCC mix with a 30" spread, you don't have to spend a lot of time filling every quarter inch hole.
However the mud will flow, I have had success pouring core walls with the SCC traveling as far as 73', around and through connected double reinforced 10" wall's. Which were placed from the bottom up using a wall port, the mix was pea-gravel the spread was 26", total yardage was 145 CY; the truck spacing was 6 minute splits. We had the first three trucks on-site before we started placing; the important part of pouring from the bottom up is not waiting! You risk losing being able to use the port and the pour if the concrete sits and sets while waiting for concrete trucks to show up.
So if the only access is from the bottom up and its only 50 total yards, then its better to have all the trucks back to back and start placing once the last truck is batched to ensure a continuous pour. If it's going to be a 100+ yards then having a secondary port to be used as back up placed at a higher level on the wall, in case you have any problems you can go to the secondary port.
Typically when you hear the words "SCC" (self consolidating concrete) you think cost, leaks and formwork pressure. To only be used in areas with too much congestion so there is no way around it, slab to beam walls or simply as a last resort. I feel SCC is one of the greatest resources out there for concrete construction! Yes, cost and form pressures are concerns, but you have to look at the possible benefits; time savings, manpower and astethetics. All of which can save you time and money.
Why I love SCC?
What do you think about pouring core walls with heavy congested steel at 3:00 PM on a Friday? Typically you're thinking, "WOW we're going to be here all night!"
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