Drying shrinkage tends to happen in the middle of the concrete like the centerline of this parking garage ramp.
Crazing cracks, map cracks, alligator cracks or whatever you call them.
Have the audience come up with the answers.
Only .25 W/C is required for proper cement hydration. Everything above the red line is “Water of convenience”. Its just there to help the contractor get the concrete placed. Even at .40 W/C which is low, there is an extra cubic foot of water that leaves a cubic yard of concrete. That’s 1 cubic foot out of 27. It no surprise that the concrete cracks. The only surprise is that it doesn’t crack worse.
Typically 100’ of concrete will shrink 5/8”.
In a perfect world the subgrade were perfectly flat and there would be no friction, so it would just get 5/8” smaller and there would be no cracks. That isn’t going to happen
There is restraint from the subgrade, reinforcement, and surrounding concrete.
So here is what happens. The concrete gets a little smaller and we get cracks. The total is still 5/8”. This is why we put joints in concrete. We try to anticipate where the cracks will be. Usually we guess right, but sometimes we guess wrong.
This is one of our cement mills where we make Calcium SulfoAluminate Cement not Portland Cement. We use the same basic raw ingredients but different ratios. We burn at different temperatures and grind for longer and get a cement with very different properties.
This is the test equipment. Bars are 3” by 3” by 10”.
Full scale testing on strips 50’ by 6’. The red curve is Portland and .15% rebars. The blue curve is Komponent with the same amount of rebars. The green curve is System-K with K-Fiber and no steel. The System-K performs at least as well as SCC and rebar. The length to width ratio is over 8 to 1. ACI recommends 1.5 to 1 and a maximum of 2 to 1. These are now almost a year old and get continuous forklift traffic. The Portland strip has many cracks and the other strips have none.
Two slabs about the same size as a typical grocery store.
Traditionally with 15’ joint spacing 6270 linear feet of joints.
SCC ban have 150’ joint spacing so only 459 linear feet of joints. That saves over a mile of joints on this relatively small slab. That’s a mile of joints that don’t have to be sawcut, don’t have to be filled, and don’t have to be maintained for the life of the building.
The curl will always be worst at the corners because it curls from two directions. When there is a point load or impact load four corner cracking is common. This project wasn’t even completed yet. Notice the differential vertical movement as well.
These are quotes from the admixture literature. So at 1 year you have only half as many cracks.
Solutions for Crack-Free, Joint-Free & Maintenance-Free Floors
SOLUTIONS FLOORSfor Crack-Free, Joint-Free & Maintenance-Free By Matt Jabbari, M.S. Civil Engineer CTS Cement Manufacturing Corp. 800-929-3939 Ext. 173 www.ctscement.com
Matt Jabbari B.S. Civil Engineer University of Minnesota M.S. Eng. Management Northeastern University Design & Field Engineer Millstone III Nuclear Power Plant; Waterford, CT Research Engineer W.R. Grace & Company; Cambridge, MA Engineering Contractor, Public Works & Private Site Development Company; Santa Ana, CA Project Manager Consultant; P.W. City of La-Canada-Flintridge, CA Affiliations: ASCE, ACI, PTI, SEAOC, ICRI, and Public Works Greenbook Sub-Committee Member
Typical Industries Requiring Perfect Floors Pharmaceutical Companies Distribution Centers: Target, K-Mart, Costco Production & Manufacturing Facilities Parts & Inventory Warehouses Computer Production & Assembly Facilities Food Warehouse & Distribution Centers Beverage Production & Bottling Facilities Meat & Poultry Grinding/Packaging Facilities Anyone who wants to INCREASE PRODUCTION and DECREASE maintenance DOWN TIME!!!
SHRINKAGE ZONE CHART No Shrinkage / No Crack Zone Shrinkage / Crack ZoneAll panels were 50’ long by 6’ wide, 6” thick and had 7 days wet cure Traditional Portland Concrete with Rebar (#4 @ 24”oc) Type K Concrete with Rebar (#4 @ 24”oc) Type K Concrete with K-Fibers™ (aka: System-K™)
JOINTS OVERVIEW Types of joints and their purpose
PROBLEM: Number of Joints PORTLAND SLAB SLABTYPICAL SLABS 210’ by 240’ 50,400 ft2
PROBLEM: Number of Joints PORTLAND SLAB SLAB Portland Concrete Shrinkage-Compensating 6270 linear ft. of joints 210 linear ft. of jointsTYPICAL SLABS 210’ by 240’ 50,400 ft2
PROBLEM: Number of Joints PORTLAND SLAB SLAB Typical 1 day pour 25,200 square feet SAVES OVER A MILE OF JOINTS Portland Concrete Shrinkage-Compensating 6270 linear ft. of joints 210 linear ft. of jointsTYPICAL SLABS 210’ by 240’ 50,400 ft2
PROBLEM: Number of Joints PORTLAND SLAB SLAB Typical 1 day pour 25,200 square feet $12,000 $2,000 Portland Concrete Shrinkage-Compensating 6270 linear ft. of joints 210 linear ft. of jointsTYPICAL SLABS 210’ by 240’ 50,400 ft2
PROBLEM: Cracks & Joints Curling may occur at the intersections of all the joints
PROBLEM: Cracks & Joints PORTLAND SLAB SLAB Typical 1 day pour 25,200 square feet SAVES OVER A MILE OF JOINTS Portland Concrete Shrinkage-Compensating 6270 linear ft. of joints 210 linear ft. of jointsTYPICAL SLABS 210’ by 240’ 50,400 ft2
Shrinkage Reducing Admixtures but they should be called Shrinkage Delaying Admixtures .01 0Elongation (%) -.01 Shrinkage Reducing -.02 -.03 Control -.04 -.05 -.06 0 100 200 300 400 500 600 Time (days)