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  1. DaveFlax

    Microsilica vs Flyash

    The key ingredient in each prodcut is silicon dioxide, which reacts with the calcium hydroxide by-product of Portland cement hydration. Fly ash is about half the size of cement and is about 50% silicon dioxide. Silica fume is about 1% the size of cement and is 85% plus silicon dioxide; both its...
  2. DaveFlax

    Contraction joints in slab

    Per ACI 223, if you use Type K, shrinkage compensating concrete it is not necessary to put any control joints.
  3. DaveFlax

    Shrinkage in Concrete

    If you want concrete that does not shrink and crack, use Type K, shrinkage-compensating cement. It tries to expand a lot in the first 7 days, but most of the potential expansion is restrained by the reinforcement. This puts the reinforcement into tension and the concrete into compresssion which...
  4. DaveFlax

    cracks on slab-on-grade : need your input

    At least some of these cracks sound like they can be attributed to drying shrinkage. The solution to avoid them in the future would be to use Type K, shrinkage-compensating cement, because it expands rather than shrinks.
  5. DaveFlax

    Concrete spec. for Slab-on-grade

    The solution is simple and it has been around for decades. Type K, shrinkage-compensating concrete. It has little, if any, curl. It doesn't shrink so saw-cutting isn't required, cracks are almost non-existant, and construction joint spacings well over 100' are common.
  6. DaveFlax

    Concrete mix designs

    If non-curl is of primary importance in your mix 1, you may want to consider Type K, shrinkage-compensating cement. It eliminates sawcut joints as well.
  7. DaveFlax

    Industrial PT Slabs-on-ground

    If you are trying to maximize the panel size, which is usually a good thing to do for industrial slabs, you may want to consider Type K shrinkage compensating concrete. Type K works well in combinatioon with either post-tensioning or pre-stressing. Panel sizes hundreds of feet long are normal...
  8. DaveFlax

    Vertical Concrete Repair

    The most common way is to leave the first layer with a rough surface and let it set up only to the point that it will support the next layer without sagging. In some cases the first layer is allowed to harden for a day before the second layer, in which case a scrub coat of the material itself is...
  9. DaveFlax

    Vertical Concrete Repair

    Since epoxy bonding agents are so thin, the diferences in modulus and thermal characteristics do not normally cause any problems. Polymer modified cementitious products are fine as long as the modulus approximately matches concrete. You are right, placing 2 1/2" vertically is a challenge in...
  10. DaveFlax

    Vertical Concrete Repair

    As long as there is good surface preparation any structural CEMENTITIOUS repair material is good. I have found that CementAll from Rapid Set is among the best. While Sika does have products that will work well in this application, I would not recommend their epoxy or anyone else's epoxy. Epoxy...
  11. DaveFlax

    Raft Foundation Design

    Hollow areas caused by the curling at cracks and at the edges can be very detrimental, especially when the thickness is only 200mm. You may want to consider using shrinkage-compensating Type K cement to eliminate the curling problem.
  12. DaveFlax

    Control Joints for Monolithic Slab?

    I agree. 2 1/2 times thickness or 10' is the norm for Portland cement concrete. However, if you are looking for a way to increase the joint spacing, you should look into Type K cement, which doesn't shrink. With Type K concrete joint spacing can be 100' or more.
  13. DaveFlax

    Concrete Reinforcing Guidelines

    Definitely go with a structural engineer. One other suggestion would be to consider Type K shrinkage-compensating concrete. Since it expands, rather than shrinks, there will be few, if any cracks, to leak.
  14. DaveFlax

    Concrete with Static Electric Buildup

    I have been told that some concrete floors will have high static buildup and people will get shocks if they touch metal object while walking on them. I have been told that this high static buildup is due to the rebars and to aggregates with high iron contents. This does not make much sense to...
  15. DaveFlax

    Slab-on-grade Concrete

    As long as the job is in the US, the Type-K Cement is easy to get as long as there is some lead time. I have found that 4 weeks is more than sufficient. As to cost: Type-K cement does cost a lot more than portland cement. If all the savings from sawcutting, joint filling, etc are taken into...
  16. DaveFlax

    Slab-on-grade Concrete

    A newer refinement to type-K in the last couple years allows slabs to be placed without steel reinforcement. The only reinforcement at all are the little plastic fibers that are incorporated with the cement. The fibers are not there to keep the concrete from shrinking. The Type-K...
  17. DaveFlax

    Slab-on-grade Concrete

    You just described concrete made with Type-K Shrinkage-Compensating cement. Instead of shrinking, the concrete will actually expand. Spacing between joints of 150 feet and more without sawcuts and without cracks is common. Because the concrete expands rather than shrinks, it tries to curl up in...
  18. DaveFlax

    minimum reinforcement

    I apologize for my previous message. Your .2% is correct. ACI requires .0015 which is .15%. That's what I get for trying to type faster than I can think. Sorry. At least I got the information about Type-K and System-K correct.
  19. DaveFlax

    minimum reinforcement

    You mention .2% steel for crack control. I think you mean .02% steel. If you want to use steel, expansive (Type-K) concrete requires only .0015% steel per ACI 223. The steel in Type-K concrete is not there to prevent shrinkage. It is there to prevent to concrete from expanding too much. There is...
  20. DaveFlax

    Basketball Court Slab on Grade

    No amount of steel will help you. Your best choice would be to use Type-K cement, instead of Portland cement. Unlike Portland concrete that shrinks, Type-K concrete expands. Joint spacing of 100 feet and more is common.

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