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 Reactive
Aggregate (See alkali-aggregate reaction)
Rebound Wet shotcrete or sand and cement which bounces away from a
surface again at which pneumatically applied mortar is being projected.
Refractory Concrete Concrete having refractory properties, suitable
for use at high temperatures. Calcium-aluminate cement and refractory
aggregates are normally used for the manufacture of this product.
Reinforced Concrete
A. Concrete
in which reinforcement, other than that provided for temperature changes
for shrinkage, has been embedded in such a- manner that the two
materials act together in resisting forces.
B. Concrete
in which steel bars have been placed to sustain the tensile stresses.
Retardation Delaying
the hardening or strength gain of fresh concrete, mortar or grout.
Retarder An admixture
which extends the setting time of cement paste, and therefore of
mixtures such as concrete, mortar, or grout.
Retempering The addition of water and remixing of concrete which has
started to stiffen: usually not allowed as it may affect the ultimate
strength.
Revibration Delayed vibration of concrete that has already been
placed and consolidated. Most effective when done at the latest time a
running vibrator will sink of its own weight into the concrete and make
it plastic and workable again.
Rock Pocket Area or portion of hardened concrete which is deficient
in mortar and consisting primarily of coarse aggregate and open voids;
caused by insufficient consolidation or separation during placement, or
both; by leakage from form.
Rod (tamping) (ASTM C24l) A round, straight steel rod, 5/8' in
diameter and approximately 24' in length, having the tamping end rounded
into a hemispherical tip, the diameter of which is 5/8'. |
