Concrete Construction conducted a field test to learn more about shrinkage and curling in warehouse floors. A 60,000-square-foot warehouse floor in Bartlett, Ill., was divided into 5000- to 10,000-square-foot sections in mid-February 2009, each receiving a different mix design. Naturally, curling and movement changes varied in regard to the specific mix designs, as well as the ambient conditions, and each was monitored for the past two years. Our goal was to measure shrinkage, plot curling along joint lines, and moisture movement through the floor with different finishes during the curing cycle. See articles below.
 

Launch Slideshow

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    Exterior shot of the 60,000-square-foot warehouse that is home to the CC Field Test. The building is a warehouse development project owned by Scurto Cement, Gilberts, Ill., and a group of investors.

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    Prior to placing concrete, Scurto employees prepared the subgrade using skidsteers guided by a laser level, and rolling vibratory compactors. Proper subgrade compaction is essential to decrease void content within the soil.

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    Vapor barriers were placed over the subgrade prior to placing concrete. The vapor barriers also act as a slip sheet for all mixes, reducing the coefficient of friction but increasing early curling with less ultimate curling.

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    The HH Holmes Co. placed these maturity sensors in several locations. The sensors are placed in the middle of the concrete thickness and maturity readings can be taken over time.

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    The first of dozens of ready-mix trucks for each day provided the nine mixes for the 60,000-square-foot Field Test floor. The floor pour took place over three days.

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    Many concrete trucks were slump tested prior to being released for the pour. Of the 138 loads of concrete delivered to the jobsite by the ready-mix trucks, very few were rejected due to high water content.

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    Records were kept to monitor loads of concrete prior to placement. Note the time between loads 22 and 23, resulting in a cold joint in the floor.

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    Scurto employees back the next load of concrete into position. This particular mix included 700# of 1 1/2-inch aggregate, a nonchloride accelerator and a polycarboxylate superplasticizer.

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    Coordination among the ready-mix trucks and Scurto employees provided for a seamless floor pour. The concrete laser screed strikes off the freshly poured concrete to ensure a high FF level.

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    Scurto employees place even thickness concrete from the ready-mix truck to the floor.

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    Nearing the conclusion of the floor placement, space for the ready-mix trucks and the laser screed was limited.

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    Howard Kanare of the CTL Group is conducting crack testing in this specific section of the floor. This testing will provide relative humidity measurements for concrete with different surface finishes.

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    A Crack Comparator scale references the size of the broom finish marks.

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    This HDX 740 double trowel is a new product from Allen Engineering that was used for the first time by Scurto on the field test slab.

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    Scurto finishers paid close attention to construction joint details, using handheld edgers to consolidate concrete along the edges of the slabs.

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    The SEC Group provided laser scans of the concrete floor to measure floor surface elevations.

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    A screen shot of the laser scans.

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    Becky Kazmiersky from HH Holmes Testing Laboratories uses a D-Meter floor profiler to measure FF numbers.

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    Concrete sawed joints are 1/8-inch wide after they were cut. Over time, slab shrinkage and curling will cause them to increase in width. Curling will be the greatest where panel joints intersect.

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    Concrete sawed joints are 1/8-inch wide after they were cut. Over time slab shrinkage and curling will cause them to increase in width. Curling will be the greatest where panel joints intersect.

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    The floor is profiled with both a 3-D laser scanner and a D-Meter 30 days after placement. In the first 30 days of the Field Test, they were used to look for shrinkage and curling differences between mixes.

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    The 3-D laser scan shown here is of the entire 60,000-square-foot floor. The colors represent elevation differences adjusted for the original finish elevations of the floor. Blue is the base elevation, light blue colored areas are 1-8 -inch below base elevation (centers of panels have dropped in elevation), and dark blue represents locations where the elevation is higher than the baseline.

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    Photo: Sec Group

    A few weeks after the initial pour, laser scans of the floor were retaken and compared with scans taken the days of the initial pour.

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    To install relative humidity probes, 3/8-inch holes are drilled into the slab, cleaned, and vacuumed before the probes are installed. Relative humidity is being checked at depths of 1/2-, 1-, 2-, and 4-inch depths of the 6-inch-thick slab.

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    After the probes are inserted, they are wired to a control box, which sends the signals to a computer that takes a reading every 10 minutes and sends the information via the Web to Howard Kanare at CTL Group.

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    Probes mounted in the slab with wires going to the control box.

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    Besides measurements taken at the time of placement, and 30 days afterward, they also will be taken every six months for two years.

Launch Slideshow

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CC Field Test Scans

CC Field Test Scans

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    HR Green

    February 2009. 3D image taken just after the floor placement. This scan shows how well finishers placed and finished the concrete and is the bench mark that scans over the two years were compared to. Credit HR Green
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    HR Green

    April 2009. 3D image taken three months after the floor was cast there is evidence of curling throughout the floor. The dark blue colors at the corners of panels in Mix numbers 1 and 2 indicates the most curling. The light blue in the centers of panels shows small decreases in elevation as the edges lift of the ground. Credit: HR Green

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    March 2010
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    SEC Group

    August 2010. The medium blue color in the figure represents baseline elevation. Dark Blue represents a gain of 1/8 in. elevation and yellow green represents a decrease of 1/8 in. But the true elevation of the floor is essentially flat. The large control jointed area in the lower left side is where the 7 1/2 lbs. of macro fiber per yard of concrete was placed.

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    SEC Group

    September 2010. The medium blue color in the figure represents baseline elevation and yellow green represents a decrease of 1/8 in. But the true elevation of the floor is essentially flat. The large control jointed area in the lower left side is where the 7 1/2 lbs. of macro fiber per yard of concrete was placed.
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    HR Green

    January 2011. The 3D Scan shows the floor to be essentially flat. The indication of minimal curl at the upper right is probably due to the low angle of the scan at the greatest distance. Credit: HR Green.

 


Note: NCA (Nonchloride acclerator), Poly C (Polycarboxylate superplasticer), and Midrange H20 Reducer dosage is ounces per 100 weight of cement

 

CC Field Test Articles

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    Discovering the Unexpected

    Find out the results of CC's two-year warehouse floor study.

     
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    Unexpected Results

    One and a half years into the two-year curling field study on warehouse floors, the results have been unexpected.

     
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    One Year Later

    In February 2009, Concrete Construction magazine and Scurto Cement Construction Ltd., Gilberts, Ill., joined forces to conduct a field study focused on curling and shrinkage in warehouse floor slabs.

     
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    Curling and Shrinkage in Floors

    Six months ago Scurto Cement, Elgin, Ill., along with several companies that contributed products, constructed a warehouse in the Chicago area. As one of the nation's largest floor contractors, Scurto searches for ways to reduce long-term shrinkage and curling in its floors.

     
  • Warehouse Floor Field Test: Second Update

    This is the second in a series of articles about our warehouse floor field test. The purpose of the study is to find economical ways to reduce curling in warehouse floors and to study the rate of moisture loss in concrete after placement.

     
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    Researching Warehouse Floors

    The idea of initiating a field test to learn more about shrinkage and curling in warehouse floors is something that Concrete Construction magazine has considered for the past couple of years. So when Greg Scurto, president of Scurto Cement, Gilberts, Ill.

     
 

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