rc63,

How can rebar fail in weight? Unless nominal area of steel doesn't meet spec, then it must somehow relate to the density of the steel.

What kinds of variations from nominal are we talking about here? How common is this problem?

More information, please!

Jeff

ASTM states;
Shall be at least 94 % of the applicable weight (nominal weight), this means the bar can be 6% light, with no max on the heavy side.  If a bar fails on weight we normally take two more retest and if one of those fails (over 6% light) we fail the heat of steel.  The diameter of the finish roll in the mill is three feet. Which means you can take a three foot section of rebar cut it into 3 one foot test bars and each bar would weigh a little different…may be 5.8 light, 6.1 light, and 6.1 light. Which would normally fail the rebar?  But we are now taking a three foot section weighting it and dividing it by three, which gives you 6% light and the bar passes. It does not happen that often, a couple of times a year, but astm states nominal weight per foot, does astm mean every foot of bar should be no more than 6% light, or can you average?

Is there something in the referred documents for the rebar that points to a sampling procedure?

I am on several ASTM committees and the testing procedures are usually linked to a sampling.

My activities are in the concrete products area, and we usually have requirements on the sample size, location, sampling method so the compliance with the material stanadrd can be applied to the test results. With concrete, there are also time limitations.

Does your testing procedure specify a sample size? Obviously a difference in length has an effect on the averages. It certainly specifies the type of measuring equipment and the accuracy.

The fact that there is no over weight requirement is interesting. Also, relating a sampling standard to a manufacturing precess is somwhat unusual since manufacturing methods are different in different countries and can be modified.

I would suggest looking deeper into the referred sampling, preparation and testing procedures before trying to apply the results to a product specification. ASTM is usually very detailed, especially for common building materials.

Dick

I don't have this spec handy, but I was looking at a pipe spec and it clearly says that for sizes below a cut off you weigh a bundle and divide by total footage.  Above hte cutoff you weigh a single piece and divide by length.  I would presume that the rebar specs are worded in a similar way.

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ASTM A615, paragraph 11 'Permissible Variation in Weight [Mass]' doesn't mention cutting bars into pieces for weighing. One presumes the ASTM committee meant full bars be weighed.  Under 'Retests,' para. 14.4 "If a weight [mass] test fails...a retest shall be permitted on two random specimens from the same lot." -- sort of implies full length bars as specimens.
  
Best to get an accurate balance capable of weighing full bars (50-lb capacity electronic toploaders are quite cheap).  Simply weighing the 3 pieces & dividing by 3 neglects cutting losses.  The 2 cuts per bar lose maybe 0.7% of the bar (length & mass).  

Or, correct for the cuts: Accurately measure both the length & mass of each piece, then divide: (sum of weights)/(sum of lengths).  Any error of lost weight is thus cancelled by the lost length.

rc63,

Perhaps you could refer your question to the appropriate (sub)committee for clarification.

Good luck.

Jeff

Thanks all for the comments, I came across a newer spec today a615/a615m-05a, it states that the test specimen shall be at least 94 % of the applicable weight [mass] per unit length prescribed in table 1.  Table one prescribes the unit length per foot, which leads you to think of it as being a one foot sample.  Also looked in a370 which covers the testing procedures for rebar,  this does not cover the weighing procedure but it does state that all test specimens shall be the full section of the bar as rolled, which would be three foot, the diameter of the roll. Since this sort of contradicts itself I think I will refer my question to the sub committee for clarification.

A 370 Appendix A9 covers the testing procedure. A 615 is just the specification.

Unfortunately I do not have a copy of A 370 around..all the same, I have some thoughts to share on this subject.

Weighing three ft long sections and then dividing by length in feet to determine nominal weight in plf units is not uncommon. This can be done on same specimens used for tensile properties and bend tests.

Two or three ft long sections are also obtained in field for nominal weight determination. For instance, rebar in the field may appear very rusty. In order to ascertain that the nominal weight is in compliance,  one or more 2 to 3 ft section(s) is/are cut, hand wire brushed, and then weighed...see ACI 318 Sec 7.4.2. The value obtained must not be less than 94% of nominal weight in lb/ft units.

rc63, in your post dated 18 Feb 07 22:10, you wrote "....it does state that all test specimens shall be the full section of the bar as rolled,...". I believe they mean full cross-section as opposed to a reduced cross-section which is obtained by machining the specimen. For plain rebar, does A370 Appendix A9 say use full section, or reduced section for determination of tensile properties?