Next step: compacting the new RCC to the same thickness as the previously placed material. Four passes with a 10-ton Ingersoll Rand DD-90; two with vibration, two without. Prairie Material uses ASTM’s D1557 modified Proctor test on both mix design and materials to determine optimum moisture and density.
Prairie Material of Bridgeview, Ill., delivers the mix – 400 pounds of cement and 125 pounds of fly ash with BASF Construction Chemicals’ Delvo hydration stabilizer – to a Blaw-Knox asphalt paver. The mixture reaches 6,000 to 10,000 psi at 28 days. “Materials producers are getting better and better at producing a mix that won’t fail,” says Public Works Director Matt Mann. The reason: They’re using a new type of equipment – ribbon mixers -- instead of pug mills.
Tim Dunne from materials consulting firm Rubino Engineering Inc. of Elgin, Ill., uses a Troxler 3430 surface moisture density gauge to test the pavement. He says “they’ve been getting better” than the required 98% density.
Feathered edges create a weak joint, so a wheel loader cuts a straight edge between one stretch of RCC and the next, ensures concrete on both sides of the joint is full thickness and properly compacted.
A public works crew uses asphalt paving equipment to rebuild residential streets using roller-compacted concrete (RCC), a process they’ve perfected over the last five years.
A crew member sprays a mixture of water and BASF’s Confilm along the edge to keep it moist until the adjacent lane can be placed.
Placement begins. The mixture is spread along the straight edge that was prepared earlier. Note that the RCC is placed about 2 inches thicker than the material from yesterday so that it can be compacted that amount to end up at the same elevation.