There is a fixed quantity of construction aggregate in the crust of the earth, and there is also only a fixed amount of area in which to dump waste materials. With this in mind, new technologies are being developed to improve these materials so they can benefit construction.
In November 1999, Lafarge Canada received a patent for its "Process for Producing Cement Clinker Containing Blast Furnace Slag" (U.S. Patent 5,976,243, Nov. 2, 1999). This came directly on the heels of the company's patent for a "Process and Apparatus for Making Expanded Slag" (U.S. Patent 5,944,861, Aug. 31, 1999).
Lafarge's processes entail pelletizing the slag with the addition of a controlled amount of water while the slag is still hot from the smelting process. The result is expanded slag pellets suitable for use as aggregate. The water gasifies and expands the slag in almost exactly the same way as popcorn turns from a hard, dense kernel to a lightweight, palatable treat.
Lafarge's technologically enhanced slag products have found their way into a variety of construction products, including its highly touted True Lite lightweight aggregate. The product reduces the weight of the finished product, and it provides concrete with similar or superior physical performance characteristics compared with normal weight concrete.
Fire ratings for products that use this lightweight aggregate, such as concrete block, are 30% to 50% higher. As for thermal insulation, concrete block made with this aggregate has roughly 2.5 to 4.8 times the thermal efficiency (k value) of normal weight units. Also, block that uses this aggregate absorbs 45% of incident noise compared with normal weight concrete block, which absorbs 27% of incident noise.