Lightweight Concrete for High Strength - Expanded Shale & Clay

More research is required to examine a potential tension strength ceiling for HPLC, as
related to diagonal tension cracking, and adjustments to lambda for concrete compressive
strengths over 10,000 psi. Examination of the alternate design procedure listed in ACI-318
Section 11.4.2.2 for predicting shear strength, V c , is necessary for concrete compressive
strengths over 10,000 psi.
The AASHTO Standard Specification can be used to conservatively predict interface
shear strength between slate HPLC and normal weight concrete.
The AASHTO LRFD Specification can be used to conservatively predict ultimate shear
strength in slate HPLC pretensioned girders.
7.8.5 Development Length
The current AASHTO and ACI provisions can be used to conservatively predict
development length in pretensioned girders constructed with slate HPLC and 0.6-in diameter
pretensioning strands. For a more accurate prediction that is still conservative, use equation 7.3.
where
⎛
⎜
⎝
5000
+
f
−
⎟ ⎞
⎠
50 f
' ps
fse
db
ci
d b = diameter of prestressing strand
f ci ' = concrete compressive strength at strand release (psi)
f se = effective prestressing stress after losses (psi)
f ps = stress in prestressed reinforcement at nominal strength of member (psi)
(7.3)
In the transfer length region, use two times the stirrup density currently specified by the
AASHTO Standard Specification to limit strand slip in the event of shear cracking.
7.8.6 Prestress Losses
The current AASHTO techniques may be used to conservatively estimate prestress losses
in HPLC girders. Considering creep and shrinkage performance, the Shams and Kahn model
was the best model for predicting long-term strains of HPLC made with locally available
materials in Georgia. The AASHTO-LRFD refined method for estimating prestress losses was
7-6