Stronger wall

st1979

Which would be stronger as a retaining wall 6" solid blocks on there flat with usual amount of mortar or 9" cavity blocks with the centers filled with concrete and a rebar down the center.
I am imagining the cavity blocks would be faster to put up and less of them but would take a bit of time to fill the cavity but would be a better job all round. The job i am looking at doing is spec'd as blocks on there flat as being acceptable. Just taught the cavity would be better

kieranhr

It all depends on a whole range of factors, but what you're basically asking there is - what's stronger, mass concrete or reinforced concrete? And the answer is reinforced concrete of course.

sydthebeat

I wouldn't consider 'cavity filled' cavity block system as being any kind of an acceptable reinforced concrete wall. For one thing it would be incredible hard to fill the cavities after installation in one pour. You end up with haphazard skinny pillars of concrete in the cavities. 215 block on the flat would be better than the two suggestions in my opinion.

kieranhr

The skinny pillars of concrete have no structural purpose other than to form a shear key between the concrete block and the rebar. You could more or less achieve the same effect with threaded rebar and a plate bolted on tight at either end.

Also, you're right in that you won't be able to fill the cavities after the whole wall is built. It needs to be done as each course is laid.

I've specified this form of retaining wall construction several times in the past, properly designed and detailed of course, and they are all still standing.