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Concrete's Air Content

Producer solves air content variations in its exterior mixes.

 

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  • Skin burns from concrete

    Why will concrete severely burn the skin? Years ago I ended up with third degree burns on my legs, though prior to that I had concrete on my legs many times and never was burned. I know that there are several concrete burn cases a year at most hospitals, but it is still not a common occurrence in...

     

  • Nominal Weight of Standard Concrete

    What's the nominal weight of standard concrete?

     

  • R-Value of Concrete

    What is the R-value of a typical 8-inch-thick, cast-in-place, residential basement wall?

     
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Do you have questions that need expertise?

Ask editors Bill Palmer and Joe Nasvik by emailing cceditor@hanleywood.com.

 

Construction Methods

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    Rebar in Stem Wall

    Does the strength the p-t provides make it so that a horizontal bar is not needed at the top of the stem wall?

     
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    Demolition Options

    From CC’s LinkedIn discussion group comes this question: Does anyone have another option to remove mass concrete foundations without using an excavator and breaker?

     
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    Bulging Joint Fillers

    Under resilient floors, what is less likely to telegraph joints after moisture equilibration: semirigid epoxy or polyurea?

     
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Decorative

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Maintenance & Repair

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Mix Design & Materials

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Placing & Finishing

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    Expansion Joints

    Are expansion joints necessary?

     
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    Bulging Joint Fillers

    Under resilient floors, what is less likely to telegraph joints after moisture equilibration: semirigid epoxy or polyurea?

     

  • Pigment Effects on Concrete Properties

    Besides changing the color, does adding pigment to concrete have any other effects on its properties that a contractor should be aware of?

     
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Slab Problems

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    Expansion Joints

    Are expansion joints necessary?

     

  • Removing Burlap Stains

    For a concrete plaza surrounding a large sculpture, the engineer specified a wet cure. The contractor used burlap to keep the concrete wet while it cured, but the burlap left some ugly stains. Can you recommend a way for us to get rid of the stains?

     

  • Spalling in Parking Lots

    What causes spalling in concrete parking lots?

     
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Specifications & Testing

  • Floor Slab-on-grade Thickness

    Is the tolerance for the thickness of a floor-on-slab grade +3/8 inch and -1/4 inch?

     
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    Testing for Air in concrete

    Air content of concrete is usually tested with a pressure meter.

     

  • Too Much Air?

    The specifications for entrained-air content always include both minimum and maximum limits. I know that having too little entrained air reduces the concrete's resistance to freeze/thaw and deicer damage.

     
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Surface Issues

  • What's Hot?

    How do I know when to use hot weather concreteing techniques?

     

  • Fog Spraying and Concrete Strength

    If we fog spray flatwork to help prevent shrinkage cracking, is there any danger of increasing the water-cement ratio at the surface and reducing the strength of the concrete?

     

  • Concrete Expansion Joints

    Are joints in concrete meant to accommodate expansion or contraction? Someone told me that what I've always called expansion joints I should now call contraction joints. Does this mean that concrete doesn't expand? What are these joints actually supposed to do?

     
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Types of Concrete

  • Be careful with coatings on concrete with more than 20% fly ash.

    Fly Ash and Overlays

    Can concrete with high percentages of fly ash or slag create a problem when installing a polymer overlay?

     

  • Protecting Steel from Corrosion

    Does high fly ash concrete provide the same passivating protection as portland cement?

     

  • Popouts

    What causes popouts? Popouts on a concrete surface are from absorbant aggregates that freeze and expand.

     
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From the Archves

2000s

  • Biting the Dust

    The owner of a recently constructed manufacturing facility contacted us to help solve a problem with the concrete floor's surface.

     
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    Proper Prep Before Work Starts

    I'm relatively new to the concrete polishing business. My company has been involved in treating stone and tile floors for years, and recently began to polish more concrete surfaces. Recently, we were asked to bid on a project that featured a concrete floo

     
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    Using Stainless Steel Tie Wire With Standard Rebar

    Can stainless steel tie wire be used with standard rebar?

     
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1990s

  • Does Fogging Increase Water-Cement Ratio?

    When using a fog spray to prevent plastic shrinkage cracking during a concrete flatwork placement, aren't you taking a chance that the water-cement ratio at the surface will increase, reducing concrete quality?

     

  • Hydrophilic vs. Hydrophobic Polyurethane Grouts

    What's the difference between hydrophilic and hydrophobic polyurethane grouts? Whenever I ask anyone, they say that hydrophilic grouts "love water" and hydrophobic grouts "hate water," but this means nothing to me when I'm trying to select a grout for a certain application. When should each be used?

     

  • Effect of High Temperatures on Concrete

    I'm a distributor of concrete repair materials that are often used in steel manufacturing plants.

     
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1980s

  • Maximum Permitted Slump When Slump Isn't Specified

    We are bidding a concrete project on which slump doesn't seem to be specified. In the specifications there is reference to ACI 301, "Specifications for Structural Concrete for Buildings," and to ASTM C 143, Standard Test Method for Slump of Hydraulic Ceme

     

  • Painting Concrete in Bright Colors

    Where can we get a deeply colored paint for concrete, one that is highly saturated with primary color? We need it for a multiuse building 600 feet tall. The owner wants several bright colors, not the stains, pastels, and earth tones commonly used on concr

     

  • Protecting Concrete Exposed to Hydrofluoric Acid

    We re replacing concrete floors, pads, and pedestals damaged by hydrofluoric acid spills in an oil fuel processing plant. The acid is at ambient temperature and concentration varies from 10% to 60%. How do we protect the new concrete so it doesn't deterio

     
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1970s

  • Removing Acrylic Seal Coat From Tilt-Up Walls

    The finisher applied too much seal coat to some of the tilt-up panels for a post office building. Most of the panels with normal amounts of seal coat look fine, but where it has been applied thickly it has yellowed. It is reputed to be an acrylic. We have

     

  • Dry shakes good or bad?

    I am responding to your April 1979 special issue on concrete finishing. The author of the articles often referred to applying a dry shake when the concrete has started to set but before the water sheen has disappeared. I always thought that the dry shake was a bad concrete practice and highly...

     

  • Concreting on a slope

    In June 1965 you published an article "Concreting Inclined Planes" (page 205). We would appreciate additional information relating to concreting on inclined planes.

     
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1960s

  • Insulating concrete block

    I am using 8-inch, 3-core concrete blocks in the construction of residences and some stores. How can I avoid cold, damp walls (sweating walls)?

     

  • Shielding concrete

    I have a job requiring heavyweight shielding concrete. How do I get this type of concrete?

     

  • Surface Cracking

    We have been experiencing a considerable amount of surface cracking. How can this be prevented?

     
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1950s

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