ANDED SLATE LIGHTWEIGHT AGGREGATE

When suitable shales, clays, and slates are heated in rotary kilns to temperatures
in excess of 1100° C (2012°F), a cellular structure is formed of essentially
nonnterconnected spherical pores surrounded by a strong, durable ceramic
matrix that has characteristics similar to those of vitrified clay brick. **
ASTM procedures prescribe measuring the saturated (misnamed in the case of
LWAs; partially saturated after a 1-day soak is more accurate) specific gravity in
a pycnometer and then determining the moisture content on the sample that had
been immersed in water for 24 hours. After a 1-day immersion in water, the rate
of moisture absorption into the lightweight aggregate will be so low that the
partially saturated specific gravity will be essentially unchanged during the time
necessary to take weight measurements in the pycnometer.
1
MATRIX

**
Lightweight Aggregate Soil Mechanics: Properties and Applications
T.A. Holm and A.J. Valsangkar


Research at Stalite has shown that the non-interconnected spherical pores in
Stalite expanded slate lightweight aggregate do not completely fill when
submerged in water. The research has shown that only the exterior pores and
interior pores connected by micro cracks or fissures fill with water.
The below
picture is of expanded slate lightweight aggregate produced in North Carolina. In
the research the material was submerged in water containing florescent water
based dye for a
period of six
months. The
material was
removed from
the water and
the absorption
percentage was
determined.
The absorption
percentage of
the materials
averaged 8.0%.
Sample was
then dried and
broken to reveal
the interior pore
structure. The
exposed pore structure was viewed under a black light to determine penetration
of the water and dye. The water and dye had only penetrated the
exterior pores
and interior pores connected by micro cracks or fissures.
photo by Darren Friedlein, Judy Johnson and
Jody Wall


SPECIFIC GRAVITY VS ABSORPTION OF STALITE LIGHTWEIGHT
AGGREGATE

The following tests were performed at Stalites lab in Gold Hill, North Carolina.
The material tested was the ½ structural aggregates from our production
stockpile. The material was washed over a #4 screen and oven dried at the
beginning of the test. The material was submerged in water at 73
°
F for durations
as shown below. The original sample mass was large enough to allow for
portions to be removed and tested for absorption and specific gravity while the
remainder of the sample remained submerged. This allowed for continuous
submersions as listed below. The specific gravity was tested by the pycnometer
method as described in ACI-211. The absorption was tested after towel drying
the aggregate as described in ASTM C-127.

Time submerged
Specific Gravity
Absorption %
Dry 1.43
0
1hr 1.46
3.4
4 hr
1.46
3.8
8 hr
1.47
4.1
24 hr
1.50
6.6
48 hr
1.50
7.2
120 hr
1.51
7.9
336 hr
1.51
8

Absorption vs Submersion Time
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9
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Hours
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