Gas Concrete (See cellular concrete)
GFRC - Glass Fiber Reinforced Concrete Concrete panels, usually
architectural designs, reinforced with a high zirconia (16% minimum),
alkali-resistant glass fiber. Optimum glass fiber content of 5% by
weight. Lower fiber content results in lower early ultimate strengths,
higher fiber content can produce composite compaction and consolidation
Gillmore Needle A device used in determining time of setting of
hydraulic cement, described in ASTM 0 266. Gradation The sizing of
granular materials; for concrete materials, usually expressed in terms
of cumulative percentages larger or smaller than each of a series of
sieve openings or the percentages between certain ranges of sieve
Grout A fluid mixture of (1) cement, sand, and water or (2) cement
and water: the hardened equivalent of such mixtures.
Gunite A term sometimes used to designate dry-mix shotcrete.
Heat of Hydration The quantity of heat expressed in calories per
gram, evolved upon complete hydration of portland cement at a given
Holding Period Period In the manufacture of concrete products, the
period between completion of casting and the introduction of additional
heat or the steam curing period.
HRM High Reactivity Metakaolin. Refined form of an ASTM C618, Class
N (natural) pozzolan. A high performance, mineral admixture, similar in
performance to silica fume, additionally comparable in cost. Pure white
powdered in form will, not effect the natural color or darken concrete
as silica fume does. Suitable for high-performance color matching in
architectural concrete. Dosage at 5% to 10%, of cement by weight. No
bleed water, better finishability, more creamy, cleanup is easier with
slightly higher 28 day strengths and 25% - 35% less plasticizer is
required than silica fume.
Process: Produced by heating a purified
kaolinite clay to a specific high temperature to alter the physical
composition (calcined). Through a carefully controlled refining
process, impurities are removed producing an almost 100% reactive,
pure white, pozzolanic powder, very evenly distributed in particle size
and results in a mineral admixture which is consistent in appearance and
performance from lot to lot.
Hydration Formation of a compound by the union of water with some
other substance. In concrete it is the chemical reaction between water
and the cement. A concrete slab needs to completely hydrate prior to
the application of paints, coatings, and flooring materials.
Hydraulic Cement A cement that is capable of setting and hardening
under water due to interaction of water and the constituents of the
cement (ASTM 219).
Hydrogenesis Another term for condensation. The term is especially
applied to base and soil substrates under highway pavements. where the
barometric pump causes the inhalation of humid air, which then condenses
in those structures, causing an ever increasing moisture content and
Hydrologic Cycle The Hydrologic Cycle consists of the evaporation of
water from oceans and other bodies of open water; condensation to
produce cloud formations; precipitation of rain, snow, sleet or hail
upon land surfaces; dissipation of rain or melted solids by direct
run-off into lakes and by seepage into the soil. Thereby producing a
continuing endless source of water in the sub-grade.
Impermeable The ability of a material or product to reduce or
eliminate gaseous transmissions through it's mass; measured as the rate
of Water Vapor Transmission (WVT). Note: Not all materials that are
waterproof are vaporproof; all materials that are vaporproof are
Initial Set A degree of stiffening of the cement and water mixture.
This is a degree lees than final set and is generally stated as an
empirical value, indicating the time in hours and minutes required for a
cement paste to stiffen sufficiently to resist to an established degree
the penetration of a weighted test needle. (Refer to ASTM C191 or C286
for weight and penetration data.)
Initial stress In prestressed concrete, the stresses occurring in
the prestressed members before any losses occur.
Jacking Equipment In prestress concrete, the device used to stress
Jacking Force The temporary force exerted by the jacking device
which introduces tension into the tendons. Jacking Stress In prestress
concrete, the maximum stress occurring in a tendon during stressing.
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