About five years ago, Pennsylvania infrastructure builder HRI Inc. bought two skid steer loader-mounted Mobile Mud Hog mixing stations in hopes of making life easier for crews grouting precast concrete bridge panels on a state DOT contract. It did. Able to mix more material at a single time, they filled and moved from joint to joint more quickly and easily while minimizing the wait time to mix a batch of material.
Little did the company know how fortuitous its investment would be. Four years later, a bigger Pennsylvania DOT (PennDOT) job came along as subcontractor to Pennsy Supply. Thinking this might be the time to buy or rent one, HRI shopped around for a volumetric mixer. Thanks to pandemic-induced global supply chain disruptions, none were to be found (at a reasonable price).
Instead, crews are using the mobile mixing stations to mix and place Rapid Set® Concrete Mix for partial-depth deck replacement on four bridges near the cities of Wilkes-Barre and Pittston on Route 309. Lanes are closed at 7 pm and reopened to traffic by 6 am daily Sunday through Thursday. Depending on the type of repair the state specified, crews jackhammer out the existing concrete to just below the first rebar mat or, if conditions warrant, the deck pan. They saturate surface-dry the exposed area and pour to the deck’s elevation. Another subcontractor later seals the patch with epoxy, an inexpensive way to increase repair durability.
PennDOT has allowed Rapid Set® Concrete Mix for at least two decades because, as CTS Engineering Sales Representative Mike Baker says, “they can’t have these bridges closed for a long time.” It’s a structural repair mix that reaches 3000 psi (20.7 MPa) compressive strength in an hour, so DOTs can minimize inconvenience to the driving public by quickly reopening repairs to traffic. A blend of Rapid Set® calcium sulfoaluminate (CSA) cement and aggregate that’s mixed, placed, and finished similarly to portland cement-based concrete repair material, Rapid Set® Concrete Mix is inherently more resistant to alkali-silica reaction (ASR), sulfate attack, shrinkage cracking, and freeze-thaw cycles. That’s another reason the state approved its use.
To save time, HRI first opens all patches. Then they zip from one patch to the next in their skid steer-mounted concrete mixer.
HRI does one more thing that increases productivity.
When working with a very-early-strength material like Rapid Set® Concrete Mix, anything you can do to save time between mixing and pouring gives your crew more time to optimize placement. Every night, HRI puts three 3,000-pound supersacks in a gravity bin mounted on a flatbed truck equipped with a vibrator pack and a water tank. At the jobsite, the vibrator pack ensures the mix flows smoothly and continuously from the gravity bin into the mobile mixer while a hose attached to the water tank feeds the mixer. Crew members don’t waste time and risk injury climbing onto equipment to keep production moving, so they’re ready and waiting to spread the mix when it’s delivered to the patch.
“I’d never seen a setup like that,” says HRI Project Manager Matt Degma. “Our operations manager, Brandon Culbertson, grew up on a farm and came up with that idea. It’s pretty slick.”
“Rapid Set® Concrete Mix usually comes in 60-pound bags,” CTS’ Baker says. “We were more than happy to help HRI reduce waste and streamline concrete production by custom-packaging the mix in 3,000-pound supersacks as they requested.”
Click here to watch a brief project overview.
