Dam near impossible
Aug 20, 2012
Have you ever hung your equipment from winches and needed to rappel to get a density measurement to meet a 97% minimum density specification? The joint venture team at ACA Moltz JV, comprising of ACA Products, Moltz Construction and Moltz Constructors met these challenges using asphalt containing Evotherm from Suncor Energy while repaving the Homestake Reservoir Dam. Located in Eagle County, Colorado, the dam was completed in 1968 and is currently undergoing a massive rehabilitation project. What sets this project apart from other dam rehabilitation projects is that the Homestake Dam is one of the few asphalt faced dams in the United States. The paving portion of the project will take two years to complete and requires milling and repaving the entire face of the dam. ACA Moltz JV, the CM/GC and paving contractor, chose Evotherm as anti-strip agent as well as a compaction aid to help establish density on this extremely unique project.
ACA Products produces the mix on site at a 160 ton portable batch-style asphalt plant. The mix contains PG76-28 asphalt from Suncor Energy and Evotherm warm mix asphalt technology. The high altitude of 10,260 ft about sea level and the slow nature of the unique paving process necessitates that the mix be produced between 355 and 375ºF. Even though the portable plant is on site, the loaded trucks drive approximately 10 minutes to the crest of the dam where specialized conveying and winching equipment transfers the mix into the paver on the dam's 35° sloping face. As you'd expect, this process is very time consuming and it takes 30-45 minutes to round trip each truck.
Here's the fun part….for placement the crew uses a Volvo ABG 7820B paver and for compaction they use two Bomag DW138 AD rollers. Cables attached to heavy duty portable winches at the top of the dam lower equipment down and up the face of the dam as lanes are paved vertically across the face. Irregular areas on the face of the dam demanded a lot of hand work. For these spots the crew used a skid steer or mini-excavator to place mix in the desired area and then compacted with a gas powered hand tampers and plate compactors.
Density readings from the first three days of paving ranged from 97-99.6% with only one reading of 96.8% below the 97% specification, including patching and hand placed areas. In order to take density measurements QC personnel had to rappel down the face of the dam with gauge in hand and find the specified locations.
Author: Ryan Bragg