NYS DOT came to realize that their deck design used on most bridges in the sixties to mid-seventies was flawed. Unfortunately, this was the divided highway era and there was a whole lot of bad bridge decks out there.
The problem was one inch of concrete cover over the top mat of rebar was not sufficient to keep salt from rusting the rebar causing the surface to spall.
To salvage these decks, the DOT came up with a method of removing the deteriorated concrete to a depth of one inch below the rebar and pour back with a latex modified mix or a high-density low slump concrete, while increasing the cover to two and a half inches above the rebar.
To accomplish this, the procedure was to mill to the top of the rebar, chip out the remaining around the bar with forty-pound busters. Pour concrete around the exposed rebar and then pour the final two inches over the whole deck. This needed some new advanced equipment.
The roto mill had just come to market, while CMI manufacturers built a unity based on a single lane trimmer. It was just too large for bridge deck work. Galion road grader built a mill head mounted to a slightly reinforced grader which seemed better suited for our purpose.
The first bridge out to bid was on Route 219 over Cattaraugus Creek. We were successful in the bid process, so now we had to figure it out.
The Galion Mill showed up on the job and started scarifying the whole surface at half an inch for a bonding surface for the overlay. To say everyone was disappointed in the outcome was an understatement. The machine could not hold any grade because of the bouncing on the tires and at the end of the first pass we picked up a paint can full of nuts and bolts that shook off the machine. This was not acceptable, and George went searching.
At the time Syracuse Supply was the CAT dealer and George called our salesman Jack Halsey. Jack told him he had heard of a new, yet to be released, CMI mill that was designed around this work.
The following Sunday Jack and George were in the CMI factory in Oklahoma checking out the new PR225 – four-foot roto mill. The CEO was there and when George asked about milling concrete the boss took it out to the yard and promptly started grinding on his driveway.
After seeing that, George signed the deal and had the machine on the job that week.
The low slump mix was spaced at ½”-¾” slump. This mix could not be dispensed in a normal redimix truck. This required, then known as Daffin, on site concrete mixers. They had bins for sand, stone, cement, and admix injection.
The material was metered onto a conveyor and dropped into a mixing chute which mixed and discharged simultaneously. The stiff mix was then dropped into power buggies and transported onto the deck and dumped. The concrete kept the same shape as the bucket off the buggy. At that time, the laborers knocked down the mix. Using
power buggies enabled the crew to get the load to the exact spot where needed to avoid trying to move any distance with shovels.
The next step was to strike off and finish with a Gomaco screed designed to handle low slump. It had two oscillating screeds with vibrators mounted every four feet to help compact the mix. The wet crew put the burlap down immediately behind the screed to keep what little water that was in the mix from evaporating.
This type of concrete placement was a whole new world for us, and the first season was a tremendous amount of trial and error.
As I look back, I’m looking at the cost of setting up this operation. As I recall, the two trucks, roto mill, and finisher totaled $500,000.
Add to that:
10 power buggies
Cement pig for charging yard
Calibrating mixer for each pour.
High amount of general labor cost.
In today’s dollars, the equipment alone would be in the $2.5 million range.
I would love to see Nick Osinski’s face if I told him we are setting up an operation to do work for the state that may be a “try it and see” deal, that would need $2.5 million to get going.
As it turns out, we had a tremendous amount of this work for thirteen years. At that time, the state changed to micro silica enhanced concrete produced by standard plants and delivery methods.
The four-foot mill grew old and was cannibalized and scrapped.
The Gomaco screed engine was installed in a Ferguson farm tractor and the rest was cut up for scrap. The mixers were removed from the trucks and ended up in the Caribbean Islands making redi mix. The trucks were converted to dump trucks and lived a long life with UCC.
