Lightweight Concrete for High Strength - Expanded Shale & Clay

Raithby and Lydon described the use of LWC for highway bridges in North America and
various countries in Europe. Their overall summary of said bridges was that performance was
satisfactory and durability was at least as good as NWC. In cases where performance was not
satisfactory, improper detailing or quality control was at fault. They describe several
advantageous aspects of LWC including weight savings and reduced superstructure
requirements, reduced cost of foundations, and reduced handling costs.
Bender (1980) made many of the same conclusions as Raithby and Lydon after
performing a cost analysis on the construction of a prestressed concrete bridge. His main
assertion was that the reduced weight of LWC allowed the casting of fewer larger pieces thus
less total pieces were required to be moved during construction.
Brown and Davis conducted a study on the long-term performance of a prestressed LWC
used in a bridge in Fanning Springs, Florida. Initially built in the early 1960s with 121.5-ft
AASHTO Type IV girders using 6,500-psi concrete weighing 120 pcf; the bridge underwent a
comprehensive load test in 1968 and again in 1992. In comparing data from the two tests, the
deflections were very close. Taking into account a margin of error, there was no change in the
deflection values. Overall, Brown and Davis felt the bridge performed very well.
Janssen wrote about the Shelby Creek Bridge in Pike County, Kentucky. The use of
7,000 psi HSLC reduced hauling and lifting weights and reduced dead loads on the structure.
The post-tensioned girders were 8.5 feet deep and were made with SLWC having a unit weight
of 130 pcf.
Roberts reported on the use of LWC for bridges in California again emphasizing the
importance of reduced weight. He noted that successful use of LWC demanded accurate
knowledge of shrinkage, creep and modulus coefficients.
Murillo, Thoman and Smith described the use of LWC for design on the Benicia-
Martinez Bridge across San Pablo Bay, California. In addition to being the least expensive
alternative, the reduced weight of the structure was also more appealing from the standpoint of
seismic design.
A publication from the Expanded Shale, Clay and Slate Institute (ESCSI) provided a
listing of the most significant uses of LWC for bridges worldwide. Of particular note were three
bridges using pretensioned bridge girders including the Coronado Bay Bridge in California, the
Lewiston Pump-Generating Plant Bridge in New York, and the Sebastian Inlet Bridge in Florida.
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