Tough job conquered on I-35
Aug 29, 2011
I spent last night last week on the Angel Brothers (contractor) and Century Asphalt (supplier) project where they started using Evotherm as a compaction aid and for the second time they were able to bring the temperatures down.
The project has been a logistical nightmare. It is a mill and fill of an existing asphalt pavement on a bridge deck of I-35 in downtown San Antonio, Texas. The process includes milling the existing pavement applying a grade 4 chipseal and then putting in the overlay all between the hours of 8PM and 5AM. Any delays in opening the lanes costs them $$$$. There are plenty of freeway intersections and ramps the help to complicate the process. The mix is a Type D (similar to a 9.5mm mix) with PG64-22 and 16%RAP and 4%RAS. Oh, and one other interesting tidbit, the San Antonio district does not allow vibratory rollers to be used on their bridges! So, they are using vibratory rollers with the vibrators off.
When they started the job hot (330°F) without Evotherm they were struggling. Several roller passes were needed and they were barely achieving density. When they switched to Evotherm at hot mix temperatures they actually got too much density in the field and were able to back off to 5 passes and have consistently improved density by 2 to 2.5%.
The production was done in two, 300-ton runs with the second half of the first run at 260°F and all of the second run at 260°F. Seventy degree drop!! The mix was losing on average 0 to 10 degrees over its one hour haul. When it arrived it looked and worked great. There was no issues with hand work and only a slight amount of clumps that almost completely broke up through the paving process or under my boot. The rollers ran right behind the screed. Densities were 93.5 to 94's based on a Trans Tech that had been correlated with cores over previous nights.
When they switched from the left shoulder to the right shoulder there was approximately a one-hour delay with several trucks waiting through it. The mix behind the screed after the delay had lost another 10 degrees and was on average 240-250°F with at most a 10 degree thermal segregation. We kept the breakdown roller right up behind the screed and the mix was still hand workable with a slim to no amount of chunks. Towards the end of the night's run there was another 30 minute delay before the last ramp. The mix behind the screed there was 230-240°F. The hand work became a little more difficult, but was still doable.
Everyone seemed happy or were lying to me! Gabriel Alcala's comments from the QC lab were that the mix is fluffier and more workable in the lab when the Evotherm is present. In the field, Diego commented on the increases in density when using Evotherm and said he felt it was better yet when the temperatures came down. Rocky, the superintendent, was pleased as well and has heard good things from the counterparts in the company that work in the Houston area.
Author: John Christensen