Fewer Joints in Big Slabs: Ductilcrete and Macro Synthetic Fibre

Why slabs have joints at all

Concrete shrinks as it dries. A slab that is held back by the ground under it can't shrink freely, so it cracks. Control joints, usually saw cuts made soon after finishing, are planned weak lines that tell the crack where to go. On a big warehouse floor that adds up to a lot of joints, and joints are where the maintenance lives: the edges chip under hard-wheeled traffic, they need to be filled, and they put a bump in every aisle.

That trade-off has pushed owners toward floors with fewer joints. There is more than one way to get there. Poppoff's project record shows two of them: the Ductilcrete slab system, and macro synthetic fibre in the mix combined with wider joint spacing.

Autozone, Pasco: 430,000 SF

On the Autozone Distribution Center in Pasco, Washington, finished in 2016, Poppoff placed a 430,000 SF Ductilcrete slab system. Their project write-up says it reduced the original amount of joints "by almost 5 miles in length," with joint spacing of 54' x 54'. That is five miles of joint edge that forklifts never cross and the owner never has to maintain.

The same project included 615,000 SF of 3D site paving. Joseph Lorson of Autozone wrote that the work "was completed on time, within budget and with high quality," and that Poppoff was "instrumental in assisting in design specs which allowed us to achieve substantial savings over bids." Notice where that saving came from: the design conversation, before anyone mobilized.

Fibre in the mix: Poppoff's own shop slab

Macro synthetic fibres are long, stiff plastic fibres mixed through the concrete. They are not a substitute for the engineered reinforcement a structural slab may call for, but they help hold cracks tight once they form, which is what lets a designer space joints farther apart. Whether a particular floor can use them is the structural engineer's decision.

Restraint is the enemy of a reduced-joint floor. The more the base grabs the slab as it shrinks, the more stress builds up in it. That is why the work under the slab gets as much attention as the concrete: a uniform, well-compacted base, and a low-friction layer where the designer calls for one. Mix design matters too, since a lower-shrinkage mix gives the slab less to fight. Joint spacing is the result of that whole system, not a number you pick off a table.

Poppoff tested the idea on its own property. The 2016 shop expansion in Moxee is a 125' x 100' slab addition with no saw cut control joints, using 7.5 lbs of Forta Fiber. Poppoff's project page says the slab "has performed flawlessly." A contractor who builds its own shop floor that way is putting its own money behind the method.

Baker Construction, Spokane Valley: 106,000 SF

Lucas Holmquist of Baker Construction & Development described a 106,000 SF concrete tilt-up building in the Spokane Valley for a client that wanted to reduce expansion joints. In his words, Matt Poppoff was recommended because of "his extensive experience with macro synthetic fibers in combination with increased expansion joint spacing," and his knowledge "was invaluable during the slab design." He also wrote that Baker was "pleasantly surprised that their pricing was competitive."

Poppoff's record includes more of the same system. Columbia Reach in Yakima is described on Poppoff's project page as "the first Ductilcrete slab in the valley," and the company lists two Ductilcrete warehouses among its Costco work.

What to settle before you spec a reduced-joint floor

• Who designs the slab, and has the engineer of record approved the joint spacing and the fibre or slab system?
• What loads and wheel types will run on the floor, and how do they interact with the joints that remain?
• How big are the pours, and can the pump and finishing crews place each one before it sets?
• What is the curing plan? Shrinkage is managed in the first days, and a thin curing plan undoes a good design.
• What cracking will the owner accept? Fewer joints is not the same as zero cracks, so agree up front on what a tolerable hairline looks like and how it will be repaired.

The common thread in every example above is that the decision got made early, between the owner, the designer and the concrete contractor. A reduced-joint floor is a design choice first and a pouring technique second. Poppoff Inc. has been working out of Moxee, Washington since 1977. If you are weighing a jointed floor against a reduced-joint one, call (509) 575-8353.