Why Ultra Early Entry Saws Work
Guest Author: George Shields

Since 1988, when Chiuminatta Concrete Concepts first introduced the Soff-Cut® saw, the Ultra Early Entry method of sawing control joints has become quite popular in the concrete industry. This is because the Ultra Early Entry sawing of control joints has proven to be very efficient in controlling random cracking on concrete slabs and pavements.

"Early entry" saws are able to cut control joints much sooner than conventional, water-cooled saws, without spalling or raveling the saw cut due to a patented anti-ravel skid plate and its lightweight construction. In addition, water is not needed to cool the cutting blade. Control joints can be sawn as soon as one can walk on the slab after finishing, usually within two hours. (See figure 1)

It is common industry practice to cut control joints as soon as possible for efficient crack control. Portland Cement Association publications state this well: "Timing of joint sawing is critical. To minimize tensile stresses and random cracking caused by restrained curling or cooling contraction, sawing should be done before concrete cools appreciably. Slabs are especially vulnerable to curling and contraction stresses within the first 6 to 18 hours after concrete placement, when tensile strength is very low."1 (See figure2)

When control joints are sawn soon after finishing the slab, depth requirements are less. With heavier, water-cooled conventional saws, the standard depths of cuts are normally 1/3 to 1/4 of the depth of the concrete (D/3 and D/4). So, with this formula, a six-inch thick slab would normally require a saw cut depth of 1.5 to 2 inches. With early entry sawing, contractors can control cracking in slabs up to 9 inches thick with only a 1-inch minimum depth2. Experience has proven that concrete paving up to 18 inches thick has had good crack control when contraction joints were sawn to only 1/5 to 1/6 of the thickness with early entry dry-cut saws3. Research has demonstrated that by sawing sooner, early entry saws are able to take advantage of greater changes in the concrete's temperature and surface moisture to initiate cracking with shallower control joints.4 (See figure 3)

The "early entry dry-cut" method is advantageous when a high percentage of slag cement is used in concrete, which retards early strength development and delays the cutting window. Random cracking in slag cement concrete may occur well before control joints can be sawn with conventional saws. The Slag Cement Association states, "One method to eliminate the guesswork in the timing of cutting joints in any concrete is using an early entry saw. This method allows a much larger window for saw cutting concrete before the development of uncontrolled shrinkage cracks."5

Soff-Cut is the first and only manufacturer of Ultra Early Entry concrete cutting saws. Because of its patented skid plate technology, Soff-Cut saws allow contractors to get on the concrete immediately after final set. No other saw manufacturer has been able to develop a saw to get on the slab that early.

The Soff-Cut Ultra Early Entry dry-cut method gives contractors another tool for the construction of high quality concrete slabs and pavements.

References

  1. James A. Farny, Concrete Floors on Ground, Portland Cement Association, Skokie, IL.
  2. Guide for Design and Construction of Concrete Parking Lots, ACI 330R-01.
  3. Early Cracking of Concrete Pavement-Causes and Repairs, TBO16.01P, American Concrete Paving Association, Skokie, IL.
  4. Zollinger, D., and others, "Sawcut Depth Considerations for Jointed Concrete Pavement Based on Fracture Mechanics Analysis," in Transportation Research Record 1449, TBR, National Research Council, Washington, D.C., 1994, pp 91-100.
  5. Saw Cutting Joints in Concrete, Slag Cement Association, www.slagcement.org/info-sheets/saw-cutting.htm

About the Author:
George Shields is an application specialist with Soff-Cut International, Inc. He has been involved in the construction industry for over 30 years, including tilt-up and cast-in-place concrete construction. George is a member of ACI International, Southern California and San Diego Chapters. He can be reached at 909-272-2330 or e-mail gshields@soffcut.com


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© 2004 L&M Construction Chemicals, Inc. | ConcreteNews Fall 2004.

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