Lightweight Concrete for High Strength - Expanded Shale & Clay

A statistical evaluation based on field studies concluded that the mean strength of HPLC
should be 600 psi greater than the required design strength. The elastic moduli of the specimens
ranged from 2,980 ksi to 4,680 ksi, and Equation S.1 was developed to predict the moduli of
expanded slate HPLC.
' wc
E
c
= 44,000 fc
(S.1)
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The rupture modulus ranged from 545 psi to 1,283 psi, conservatively predicted as
7.5λ
fc
' , where the λ can be taken as 0.85 for sand-lightweight concrete. The HPLC developed
in this project was found to possess a low to negligible chloride permeability classification
according to ASTM 1202. The low chloride permeability is believed to be the result of
incorporating silica fume into the mix designs. The average coefficient of thermal expansion
value (CTE) was 5.3 x 10 -6 , approximately the same as high strength, normal weight concrete.
The long-term creep and shrinkage studies showed that the creep of HPLC was less than
that of normal weight high performance concrete while the shrinkage was somewhat greater. The
620-day creep of 8,000-psi HPLC was about 1,650 µε and 2,000 µε when loaded to 40% and
60% of initial strength, respectively. On the other hand, the 620-day creep of 10,000-psi HPLC
was approximately 1,160 µε and 1,500 µε when loaded to 40% and 60% of initial strength. The
620-day shrinkage was approximately 820 µε for the 8,000-psi HPLC mix and 610 µε for the
10,000-psi HPLC mix. Considering creep and shrinkage performance, the Shams and Kahn
(2000) model was the best model for predicting long-term strains of HPLC made with locally
available materials in Georgia.
The AASHTO-LRFD (1998) refined method for estimating prestress losses was
conservative when compared to measured long-term losses found in six AASHTO Type II
precast, prestressed girders made with HPLC. The AASHTO-LRFD lump sum method was
conservative for estimating prestress losses on the 10,000-psi girders made with HPLC. Overall,
the AASHTO-LRFD refined method may be used conservatively for predicting prestress losses
in girders made of high performance lightweight concrete.
Overall, expanded slate HPLC is applicable for construction of precast bridge girders
with design strengths up to 10,000 psi.
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