Ron,
I'm aware that it is "possible" to have a flatness of 1/8 in. in 10 ft with a slope of 1/4 in. per foot. Other people who posted were confusing levelness and flatness, so I discussed that issue.
Mike illustrates my point perfectly. Proper form/screed setup is related primarily to...
Ron,
Sorry for the delay in responding to your response to my comment. We're in agreement that 3/8 in. in 32 in. is deplorable concrete construction if we're talking about the gap under a 32-inch-long straightedge for a floor that is supposed to be level and reasonably flat. A slope to drain of...
Ron,
1/8 in. in 10 ft is a common tolerance only because it was in use for many years when no one measured floors, and is now in use because some specifiers don't understand floor flatness. And it definitely is not "achievable without much difficulty," especially for residential construction. In...
With respect, Hokie66 and Ron, you know not of what you speak. Have you read ASTM C 94, which allows one addition of water at the jobsite? Have you tried to pump or finish concrete with very little water added at the plant, but enough superplasticizer to still produce the specified slump? The...
The same question was asked and answered in the October 2003 issue of Concrete International magazine. If you're an ACI member you can access it at www.concrete.org. Click on "Bookstore and Publications," then on "Concrete International." On the CI site click on "Archives," then on "Back Issues"...
If you're an ACI member, you can get a free download of the article on this subject by Tarr and Nussbaum (Oct. 2002). They recommend using plate bearing test data (ASTM D 1196) on the insulation because estimating the subgrade modulus for the material based on compressive strength data from ASTM...
The concrete producer may have been referring to equilibrium density as opposed to fresh density. If the fresh density was 120 pcf, the equilbrium density could be expected to fall between 116 and 112 pcf as a result of natural drying (not oven drying). The 4 to 8 pcf difference depends...
The public discussion period for the next revision of ACI 318 (ACI 318-08), “Building Code Requirements for Structural Concrete,” begins on July 1, 2007 and ends August 15, 2007. You can view the proposed revisions by going to www.concrete.org and clicking on a link for ACI 318-08 that will...
If the reinforcement is continuous through the joint, random cracking is likely regardless of the shrinkage characteristics of the concrete.
The following excerpt is from Section 3.2.4 of ACI 302.1R-04,"Guide for Concrete Floor and Slab Construction:"
"Reinforcing bars or welded wire...
Be careful in using old rules of thumb for this. When combining Grade 50 steel with LRFD design, the depth of the steel framing flexural members can be reduced enough to cause more deflection than expected. There's a good article that describes the phenomena at...
Go to www.concreteconstructiononline.com. Enter "clean" and "rebar" as search terms. The article, "How Clean Must Rebar Be?" was in the June 1998 issue of Concrete Construction magazine. Bondbreakers, form relase agents, cement splatter, and some other contaminants were placed on rebar before...
Will the slab receive a moisture-sensitive floor covering? If so, ACI 302.1R-96 recommends placing the concrete directly on the vapor retarder. An experienced floor designer recommends keeping the #4 bars 1-in. below the top surface. You may still get some curling, but it's easier (and usually...
Slickline is metal pipe through which concrete is pumped. It's used to differentiate pipe from rubber hose that's used at the discharge end of large-diameter pumplines or from rubber hose that's used for the entire line of small-line pumps.
The ASTM Manual of Aggregate and Concrete Testing is a helpful reference on this subject. It's included at the end of Vol. 04.02 of the Annual Book of ASTM Standards. For 3000-4000 psi concretes, conical fractures are typical and expected. Variation from a conical fracture may indicate a...
