Stalite’s strong end-use products begin with the production processing of our raw material slate. Slate possesses the high strength and lasting durability necessary to create a superior lightweight aggregate. Unlike shale or clay deposits formed from mineral or organic sediments, the slate used in STALITE was formed from volcanic ash. This volcanic ejecta, free of impurities which were burned away at very high temperatures, was deposited in a wet environment and compressed under extreme pressures for millions of years. The resulting material is an extraordinary slate deposit whose unique properties contribute to making STALITE the very finest high performance lightweight aggregate in the world. In the foothills of NC, east of Charlotte, NC is the only known source of slate that is being used as a raw material for rotary kiln expanded slate lightweight aggregate.
Slate vs. Clay and Shale
Several types of raw material can be expanded in a rotary kiln to produce structural lightweight aggregates. These materials can be classified as clays, shales and slates. The primary difference in these three classifications of materials in their strength, density and absorption. Clays and shales are naturally softer, and less dense than slate. After processing in a rotary kiln, clays and shales have 24-hour absorptions ranging between 15% and 30% (compared to 6% for STALITE). During mixing or pumping concrete, clay and shale absorptions can be as high as 50% (compared to 9% for STALITE). Due to the higher material strength of STALITE slate aggregate, higher strength concretes can be achieved with lower cement contents allowing for more economical concrete mixes. BEGIN STRONGER = END STRONG.
More Information on the Physical Characteristics of Slate
The raw material mined by Stalite is an argillite slate located in a geological area known as the Tillery Formation. It is a thinly laminated, gray, fine-grained siltstone, composed of clastic (transported) rock fragments. The Tillery Formation is a complex system that must be selectively mined in order to separate the desirable product from the non-desirable to manufacture a high quality expanded slate aggregate.
The geologic history of the Tillery Formation began 550 million years ago in the Cambrian Period, approximately 330 million years before dinosaurs. Rock fragments of volcanic ash origin were deposited in a water environment (sedimentation) and later solidified into solid rock (lithification). Consequent burial and tectonic pressure then changed (metamorphosed) the rock into argillite slate. Along with the deposition of the volcanic ash was an occasional ash (debris) flow or gravitational mud-type flow into the same deposition basin. Additional layers, consisting of volcanic tuff with high calcite concentrations, formed within the system. Subsequent millions of years of geologic forces caused the alternating layers of material to fold and fault, causing disorder to the once ordered, layered system. Along with this disorder came diabase dike rock intrusion of Triassic-Jurassic age (about 180-220 million years ago), which caused additional rock structures of vertical emplacement that further complicated the system.
The calcareous tuff impedes the bloating process of lightweight aggregate production. At 2,000 degrees F (1,000 degrees C), the calcite simply calcines. At high temperatures of over 2,200 degrees F (1,200 degrees C). diabase rock (specific gravity of 3.0) melts to a glassy type of rock with no specific gravity change. Because this high specific gravity creates havoc on a desired lightweight specific gravity material, it should be avoided totally. The only way to avoid this material is through a process of selective mining. Extensive core drilling must be performed along with microscopic, chemical, and laboratory test bloating of the core in order to “map” the subsurface material and identify desirable versus non-desirable aggregate. Computer software must then be used to identify high-quality cross-sections of desirable versus non-desirable rock zones. Mining computer software can then be used to design the selective mining sequence. A modern fractionation plant with controllable radial stackers and feed systems then crushes the high-quality bloatable material to optimum size for processing and separates it to be conveyed to the raw feed storage silos.