To
compact a road base using a slag product will only require 50% of the
effort that a typical aggregate would need.
A vibratory compactor will quickly work the surface into nearly
100% compaction in only a fraction of the time.
As
an added benefit, because of the way slag interlocks, the surface remains
planar and sound even under a heavy load.
For example, if a vehicle is driven over a compacted limestone road
base, the surface would indent and swell around a tire’s surface.
In direct and vivid contrast, the slag surface remains undisturbed
and sound. The higher angle
of repose, or the steepness of a natural stockpile, for slag further
testifies to the inherent stability of the interlocking granules.
There
is also a yield savings when you use slag, because less slag is required
for a given job than conventional aggregates.
This is because slag was formed in the blistering hot temperatures
of a blast furnace, under molten conditions, and pores or vesicles were
formed as the slag cooled and gases were being released into the
atmosphere. This is why when
you look at a piece of slag up close, it is literally riddled with holes.
The percent porosity is the fraction of volume that a piece of slag
has that is taken up by these holes.
Since slag has similar strength and soundness characteristics that
natural stone has, but a large volume percentage is taken up with air (the
pores, or holes), a ton of slag can be used further than a ton of stone.
This is simply because a ton of slag takes up more space.
There is also a further freight savings, because more volume of
slag can be placed on every truckload of slag going to the job site.
Click
here to use an interactive spreadsheet analysis that demonstrates the cost savings of
using Beaver Valley Slag.
The
blistering high blast furnace temperatures also created an additional
benefit: high product purity. Impurities,
such as dirt and clay, which are typically found in naturally occurring
limestone are nonexistent in blast furnace slags.
The 2700 degree furnace, which literally melts rock, chemically
recombines any impurities into slag’s molecular structure.
This structure is chemically uniform, and displays strong abrasion
resistance because of its high purity.
Beaver
Valley Slag must meet, or exceed, the stringent requirements established
by Penn D.O.T. to maintain their certification of its washed and unwashed
slag products. The
established systems are critical to assure to our customers that our
products meet the gradation requirements, are chemically inert, and that
they have low abrasion losses. We
can also work with customers to establishing QA/QC procedures for any
requirements that they might have, such as chemical composition.
Three
examples of test methods that Beaver Valley Slag must comply with are the
L.A. Abrasion test, the Sulfate Soundness test, and the particle size
analysis (gradation test).
The
requirements for sampling and testing are established by Penn D.O.T.
Source verification samples are taken for every 5000 tons (or
monthly) shipped
to state jobs. Field
verification samples are taken at state certified jobs.
Requalification samples are taken biannually, at a minimum, for
Beaver Valley Slag to maintain its certification.
A quality control plan is submitted annually for approval to the
District Materials Engineer. Any
deviation from this plan or failure to meet specifications can result in
the suspension or removal from Penn D.O.T.’s approved list.
Stockpiles and testing records are further checked by Penn D.O.T.
inspectors.
The
first test is used by ASTM, Penn D.O.T. and AASHTO to measure the
aggregates susceptibility to breakdown.
A sample is tumbled for 500 revolutions inside a steel drum with
six to twelve 15 ounce steel balls. The
rotating drum lifts the slag aggregate and smashes it between the tumbling
steel balls. The test method
runs the slag material through a sieve screen and measures the percent
broken down into fine particles. Beaver
Valley Slag products consistently beat the Penn D.O.T. requirement of 45%
abrasion loss. A typical
round of 10 Beaver Valley Slag samples yields a 28% abrasion loss.
The
second test is the Sodium Sulfate Soundness Test. This test is used to measure the aggregates vulnerability to
freezing and thawing degradation. Water
absorbed into the particles can freeze, causing an increase in volume
which can breakdown aggregates. In
this method, a sample is immersed in a salt solution for 16 to 18 hours
and dried. Five cycles of
this imitates five freezing and thawing cycles.
The salt crystallizes inside the particles exerting forces that
cause a breakdown of the aggregate. The
sample is then sieved to determine the percent degradation.
Beaver Valley Slag
products consistently beat the Penn D.O.T. requirement of 10% breakdown.
A typical round of 10 Beaver Valley Slag samples yields a 1.36% breakdown.
The
third test checks the size distribution of the slag aggregates using sieve
screens. A dry sample is run through a mechanical shaker containing
a series of progressively smaller screens. After shaking, the amount
of material retained on each screen is weighed to determine the percent
passing to the next larger screen size. Each material must be within
PennDOT's gradation specifications. Beaver Valley Slag’s products are sampled and
tested by Penn D.O.T. certified aggregate technician before being put into
approved stockpiles. Beaver Valley Slag meets these requirements
about 98% of the time, where the nonconforming material is stockpiled
separately.
Unfortunately, slag has gotten an undeserved "bad reputation" for
expanding in place. Stories of "brand new parking lots cracking
because of the sub-base expanding" have unfortunately substantiated this
further. However, Beaver Valley Slag's, both Blast Furnace and
Steel, display no expansion characteristics. They can be used with
complete peace of mind in any sub-base applications.
Click
here to read more about Slag Expansion... (Adobe
Acrobat® PDF)
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