MASONRY RETAINING WALL - HOW LONG BEFORE BACKFILLING 2

[PT999]

I am designing a 3 ft high bar reinforced 8" masonry wall, with depth in the ground also 3 ft, all on a reinforced concrete footing.
How long should I allow for masonry curing before back filling? - I want to put this in notes. No cylinders or cubes will be taken to review reports.

 

[Agent666]

With no samples being taken I would say you can only rely on the nominal time to develop the specified strength of the grout fill. In this part of the world concrete strengths are based on 28 day strengths. We all know the time to develop the 28 day strength would be considerably faster than this as concrete suppliers have to be sure to hit the lower characteristic strength at this point in time. So most mixes develop a considerably higher strength over time.

In my experience usually within 2 weeks you hit the 28 day value, but it can vary a week either way depending on the mix design and environmental conditions. Only way to know for sure is to take some cylinders.

The concrete supplier may have historic data on the mix from testing within the batching plant which might offer some guidance with respect to the time.

Additionally I have seen some people specify for example that walls may be backfilled when 75% of the nominal strength of the grout is attained, over to the contractor as to how he determines this.

 

[oldestguy]

Since this is close to being a typical gravity retaining wall at only 3 feet high in front, it probably doesn't make any difference as to when you backfill. A typical gravity retaining wall has a thickness of 1/3 the height, and can be made out of material not significantly strong, such as rocks laid up without any grout. It's a judgement case and, to be more sure, just don't compact in back within 2 feet of the wall above outside grade elevation. Compacting early on up to outside grade elev. (front and back) will help in the curing process.

 

[JAE]

7 days preferred. 3 days minimum if they scream and holler and need to keep moving on the project.
But in neither case allow wheel or other loads above the wall closer than 5 feet.





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[msquared48]

At only three feet high, chances are that you have minimum steel in the wall and are nowhere near the moment capacity of the reinforcing with the backfill you mention. Three to four days should be fine here, but do keep the wheel loads and vibrating compactors away for 7 days minimum.

Mike McCann, PE, SE (WA)