Lightweight Concrete for High Strength - Expanded Shale & Clay

E = 44,000
c
' wc
fc
145
(7.1)
where
E c =
concrete modulus of elasticity (psi)
f c ’ =
concrete compressive strength (psi)
w c = unit weight of concrete (lb/ft 3 )
7.8.2 Transfer Length
Use the current AASHTO and ACI equations to conservatively predict transfer length in
pretensioned girders constructed with slate HPLC and 0.6-in pretensioning strands. For a more
accurate prediction that is still conservative, use equation 7.2.
50
d
b
6000
f '
ci
( 7 .2 )
where
d b = diameter of prestressing strand
f ci ' = concrete compressive strength at strand release (psi)
7.8.3 Flexural Behavior
Do not use the modulus of rupture test, ASTM C 78, for determining the cracking stress
and cracking moment for pretensioned slate HPLC girders.
More research is required to examine a potential tension strength ceiling for HPLC, as
related to flexural cracking, and adjustments to lambda for concrete compressive strengths over
10,000 psi.
Use the current AASHTO procedure for ultimate moment calculation for slate HPLC
girders with normal weight concrete decks having a compressive strength under 6,000 psi.
7.8.4 Shear Behavior
Use the current AASHTO Standard specification to provide a conservative prediction of
concrete and ultimate shear capacity in slate HPLC pretensioned girders when shear steel
capacity is capped at a yield strength of 60 ksi.
7-5