"Lightweight Concrete" - The Industry Misnomer
Mar 11
2 min read
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I always have found it interesting that "lightweight concrete" or "LWC" is such a broadly used term intended to describe a wide array of composite structural roof deck types, some of which are not cementitious at all...
The misnomer "LWC" can be broken down into many various types:
- Lightweight concrete consisting of lightweight aggregate such as perlite or vermiculite. These aggregates are also referred to as "expanded aggregates". Lightweight aggregate makes for lightweight concrete.
Lightweight concrete consisting of an injected foam solution. This variant is known as "cellular concrete" (Picture 1) and can be confirmed by the small air bubbles visible within a cured pour.
- Lightweight concrete that integrates fluted expanded polystyrene boards to assist with providing a lightweight, insulative, and cost-effective structural drainage slope (Picture 2).
(The above three variants are all commonly referred to as "lightweight insulating concrete" or "LWIC" as they all have insulative properties through lightweight aggregate, injected foam solution, or integrated expanded polystyrene.)
- Poured gypsum decks, which actually are not cementitious at all. As expected, gypsum decks exhibit similar to how drywall exhibits. Picture 3 shows a gypsum form panel and poured gypsum (notched to show boundary between form panel and poured gypsum).
As with any composite deck system, the underside of a structural roof deck provides invaluable clues including but limited to the form board type (compressed fiberglass panel, gypsum panel, compressed wood fiber panel, steel panels) as well as other components such as bulb tees (Picture 4).
To make matters more confusing, there are precast lightweight concrete interlocking panels, alleviating the need for form panels or bulb tees. More information can be learned about these here:
Onward and upward!
Andrew M. Behrens, RRC®
President
Construction Analytics Group, Ltd.
