RIP RAP, also known as REVETMENT STONE, SHOT ROCK, ROCK ARMOR or RUBBLE is larger, more massive stone which is used to stabilize slopes, protect shorelines, streambeds, bridge abutments, pilings, shoreline structures, and erosion control structures such as bridges and culverts protecting against scour and water or ice erosion. The stone must come from sound, durable ledges of limestone, dolomite and pass certain tests for abrasion and freeze-thaw.
The stone must also be crack and split resistant for at least 24 months of weather exposure. It is expected to last 50 years or longer without breaking down. The Army Corps of Engineers and each U.S. state have specific size range designations for Rip Rap. Sizes typically range from 30” maximum to 6” minimum diameter. Iowa, has defined 4 size classes:
- Class A: Stones range from 50 lbs to 400 lbs.
- Class B: Stones range from 25 lbs. to 600 lbs.
- Class C: Stones range from 50 lbs. to 450 lbs.
- Class D and E vary from 5lbs to 250 lbs.
Class D can be composed of lesser quality stone as it is used in temporary installations lasting not more than 3 to 5 years until vegetation is established.