Lightweight Concrete for High Strength - Expanded Shale & Clay

All constructed in the 1960s, the bridge girders used LWC with a compressive strength between
5,000 and 6,000 psi. When the publication was issued in 1994, all the bridges were reported to
be in excellent condition.
Melby, Jordet and Hansvold described the use of HSLC for long-span bridges in Norway.
The authors commented that LWC has been used for bridges in Norway since 1987. Their
recommendations focused on testing mix designs thoroughly and ensuring excellent quality
control to obtain consistent properties. They stated that the use of LWC was economical for long
span bridges, but that bridge geometry would determine the amount of savings. Compressive
strengths up to 8,700 psi with a unit weight of 125 pcf were successfully used to construct the
Raftsundet Bridge.
Holm and Bremner noted that LWC was a very promising alternative for the replacement
of functionally obsolete bridges throughout the United States. In many cases, the use of LWC
for deck replacement would allow upgrading bridge capacity based on lower deck dead load.
The authors cited as an example the Woodrow Wilson Memorial Bridge in Washington, D. C.
By replacing the bridge deck with LWC, engineers reduced the dead load on the structure and
were able to add an additional lane of traffic without exceeding the load carrying capacity of the
structure.
2.5 HSLC Mix Designs
A.5.1 Coarse Aggregate
Coarse aggregate is a primary factor in developing a mix design that is lightweight, highstrength,
and cost effective. Manufactured lightweight coarse aggregates include expanded
clays, expanded shales, expanded slates, expanded perlite, exfoliated vermiculite, and sintered
fly ash. Lightweight coarse aggregates also occur naturally in the form of pumice and tuff.
Depending on the source of the aggregate, the particle shape and surface texture vary
significantly impacting all other aspects of the mix design and the placement characteristics of
the concrete. Numerous authors commented on the need for specifications by particular
aggregate manufacturer or source with respect to design characteristics.
The raw material from which the LWA is produced determines the strength of the
aggregate and thus the strength that can be achieved in the concrete. Expanded slate aggregates
A-4