Using broken concrete for rip-rap

[oldestguy]

I have a job where earlier work placed a 6 inch layer of concrete on a breakwater. The state guys that approve of work on these using state funds don't like it. They want it removed and ordinary riprap placed.

My plan is just to use jack hammers or hydraulic breakers on a back-hoe to reduce the concrete to pieces resembling rip-rap.

We may add some regular rock rip-rap and mix it in for getting a thicker layer.

Comments?

 

[blueoak]

I am familiar of breaking it down so the largest dimesion is no greater than 3 times any other for river bank protection. The biggest problem there has been when someone doesn't want rock they normally skip the filter/bedding requirements and you get scour under the concrete and it looks like the broken concrete was the problem.

On rivers there was some concern if you didn't break it, it floats really well and you may have to go downstream to clean up.

Is it appearance that is the problem? Could you color the concrete and add some rock of shapes to cover up the concrete to important locations? Or at least only "correct" the visible areas.

 

[oldestguy]

There is pretty good gradation from sand to cobble sized material in the basic breakwater body. However, no filter fabric on site and most areas behave fine.

This is on a lake crated by dams on the Mississippi where the only erosion action is occasional big waves in windy conditions, with a reach of a few miles. Wave height is a few feet max. At flood times this is overtopped and current is still quite slow.

The only real reason for this work is to fix up some areas that had a blacktop surfacing which broke up due to wave action. The concreted area held up well, but the funding for the work had the stipulation to remove the concrete.
We will add a mix of breaker run rock up to 18" armor rock on top of the broken up concrete, mostly hiding it.

 

[FarmallFan]

some hard learned advice ... if this project is in a river or lake make sure your permits will accomodate the change.
FarmallFan