Civil Engineering Reference
In-Depth Information
Fiber modifications to improve long-term durability
involve (1) specially formulated chemical coatings to help
combat hydration-induced embrittlement, and (2) em-
ployment of a dispersed microsilica slurry to adequately
fill fiber voids, thereby reducing potential for calcium
hydroxide infiltration.
A low-alkaline cement has been developed in Japan
that produces no calcium hydroxide during hydration.
Accelerated tests with the cement in alkali-resistant-glass
fiber-reinforced concrete samples have shown greater
long-term durability than previously achieved.
Metakaolin can be used in glass-fiber-reinforced con-
crete without significantly affecting flexural strength,
strain, modulus of elasticity, and toughness. (
Marikunte,
Aldea, Shah 1997
).
The single largest application of glass-fiber concrete
has been the manufacture of exterior building façade panels
(Fig. 7-5). Other applications are listed in
PCA (1991)
.
Fig. 7-4. Tightly bunched steel fibers are placed in a form,
before cement slurry is poured into this application of
slurry-infiltrated steel-fiber concrete (SIFCON). (60672)
Glass Fibers
The first research on glass fibers in the early 1960s used
conventional borosilicate glass (E-glass) (Table 7-1) and
soda-lime-silica glass fibers (A-glass). The test results
showed that alkali reactivity between the E-glass fibers
and the cement-paste reduced the strength of the concrete.
Continued research resulted in alkali-resistant glass fibers
(AR-glass) (Table 7-1), that improved long-term durability,
but sources of other strength-loss trends were observed.
One acknowledged source was fiber embrittlement stem-
ming from infiltration of calcium hydroxide particles, by-
products of cement hydration, into fiber bundles. Alkali
reactivity and cement hydration are the basis for the fol-
lowing two widely held theories explaining strength and
ductility loss, particularly in exterior glass fiber concrete:
• Alkali attack on glass-fiber surfaces reduces fiber ten-
sile strength and, subsequently, lowers compressive
strength.
• Ongoing cement hydration causes calcium hydroxide
particle penetration of fiber bundles, thereby
increasing fiber-to-matrix bond strength and embrit-
tlement; the latter lowers tensile strength by inhibit-
ing fiber pullout.
Fig. 7-5. (top) Glass-fiber-reinforced concrete panels are light
and strong enough to reduce this building's structural
requirements. (bottom) Spray-up fabrication made it easy to
create their contoured profiles. (60671, 46228)
