When I saw the PRO-RING manhole repair system at the 2010 Pumper & Cleaner Expo, I had a strange experience. I saw a stack of black rings of various thicknesses that from a distance of several yards looked like cast iron. Yet people in the Cretex Specialty Products booth were lifting them with one hand to show them to attendees.

All right then, I said to myself. These are plastic foam models of the actual iron rings, made specifically for trade show exhibit purposes. Wrong. Those were the actual products. The rings come in a series of components that combine to finish a manhole to within a quarter-inch of grade. There are three basic components.

Grade rings 2, 4 or 6 inches thick are installed on the top of the concrete cone section of a vault or brick structure and stacked to add the required height. A finish ring is engineered to provide a watertight seal. An optional angle ring enables the manhole to conform to sloped road surfaces.

So, what are these magic rings made from? It's expanded polypropylene (EPP), an extremely light yet very strong material used extensively in the automotive industry for making interior components and some items in the engine compartment. It is known for a high strength-to-weight ratio, stability, chemical resistance, and long service life under harsh conditions. A Cretex brochure shows a tracked excavator driving over a manhole built with the components. The captions reads, "Is PRO-Ring tough enough? Oh yeah."

Municipal Sewer & Water is looking forward to reporting on a demonstration of this product in a manhole repair. In the meantime you can learn more at www.cretexseals.com.