Glass fiber reinforced concrete, usually referred to as GFRC, is made of a Portland cement and aggregate slurry reinforced with short glass fibers. GFRC is a composite in which the reinforcement is randomly dispersed throughout the materials, thus differing from conventional reinforced concrete where steel is placed primarily in tensile stress areas. The fibers in GFRC help to stop cracks. Normally, when a microcrack occurs in concrete, finding little resistance in the brittle matrix, it travels quickly and causes a break. In GFRC, however, when the first microcrack occurs, the glass fibers pick up the load, thus preventing many cracks from propagating. Consequently, GFRC does not fail abruptly but yields gradually. Only when the fibers pull out or break does the concrete finally fracture.

GFRC can be used to build new structures or renovate old ones. Panels made of GFRC weigh substantially less than conventional concrete panels, making them less costly to transport and erect. Consequently, using GFRC as the skin of new buildings allows construction to be lighter and more economical. Using GFRC in renovation projects for recladding minimizes the load added to the existing structure.

When GFRC is mixed in batches as normal concrete would be, the maximum fiber content possible is about 2 percent by volume. With the sprayup process, the fiber content is generally about 4 to 5 percent. Regardless, the flexural strength of GFRC (which can be 2 to 3 times that of conventional unreinforced concrete) does not increase further with fiber contents above 7 percent. Fibers range in length from 1 to 2 « inches. Typically the cement contents are higher and the amount and sizes of coarse aggregate are smaller than for regular concretes. GFRC is desirable because of worldwide availability, comparatively low-cost raw materials, simple fabrication processes and its ability to replace asbestos in many applications.