Simple Particle Packing Material: Recycled Glass Issue: When mixing granular materials with bonding agents (e.g. cement with aggregate),
it is sometimes critical to achieve the highest possible “particle
pack,” that is, the combination of materials and gradations that has
the greatest density when blended dry.
Finding the highest particle pack can significantly improve
strengths of bonded materials by increasing bonded surface area per
weight of material. It also reduces liquid requirements for wetting
mixtures. Best Practice: Given two granular materials, one coarse and one fine,
each different percentage combination of the two materials will have
a different density, measured in grams per cubic centimeter. The maximum particle pack is the combination
of the two gradations that has the highest density. This is a description of a quick and easy way to determine the maximum
particle pack for two materials, or three if one material has a pre-defined
percentage in the mixture.
1.
Obtain a
one-inch inside diameter glass tube, called the “packing tube,” at
least three feet long, a flexible plastic or cloth centimeter scale,
a gram weight scale, and a supply of the two granular materials to
be packed, as they are to be delivered for production.
A glass or Pyrex tube is better than plastic because it stays
straight and will not scratch as quickly.
2.
Plug one
end of the tube and tape the centimeter scale to the tube so that
zero starts at the plugged end.
3.
Weigh out
a combination of the two granular materials, recording the weight
of each, for a total of 400 grams.
Mix the two (or three) granular materials thoroughly outside
of the packing tube and pour them, through a funnel, into the packing
tube.
4.
Tap the bottom
of the packing tube a defined number of times on a cushioned surface.
A piece of all-weather carpeting works well.
200 taps may be sufficient.
The number of taps must be such that no discernible packing
is occurring after an additional 10 taps. For large percentages of very fine materials,
even a large number of taps may not settle the material. That can be disregarded. Large percentages of fines cannot be as efficiently
packed as combinations of coarse and fine.
5.
Record the
height of the tapped column, empty the mixed materials, mix new materials
at different percentages, and begin again.
Continue until the point of minimum column height is found. That is the maximum particle pack. Example:
Assume that a maximum particle
pack is needed for three granular materials, with one of the materials
being cement, to be combined in a 3:1 ratio with two aggregates. By
repeating steps 3-5 above, the following table is created: Graphed, the table above looks
like this:
Therefore, the maximum particle
pack for a 3:1 aggregate:cement mixture is achieved with 25%
cement 19%
olivine 120 mesh 56% copper slag 16x30 mesh It is also possible to perform
the same type of analysis with three variable aggregates, but a three-dimensional
graphing surface is necessary and the number of iterations can be
daunting. Implementation: This kind of analysis can be
performed in a shop environment in a few minutes. Records should always be kept of past results. Any time a new source of granular material
is received, new tests should be run, even if the gradation analysis
is the same as one previously used.
This is because different processing equipment generates differently
shaped grains, resulting in surprisingly different particle packs.
Benefits: Optimizing particle packing when combining aggregates
with binders can dramatically increase the strength of the composition
material and decrease shrinkage during curing. Application Sites: Small businesses, shops, and
laboratories. Contact: For more information about
this Best Practice, contact CWC, mailto:info@cwc.org. References:
Most ceramics texts treat the
characteristics of particle packing, including Grimshaw, Rex
W., The Chemistry and Physics
of Clays and Other Ceramic Materials, Wiley-Interscience, 1971,
pp 407ff.
Issue
Date / Update: November 1996 |
