Lightweight Concrete for High Strength - Expanded Shale & Clay

Chapter 1. Introduction
1.1 Purpose and Objectives
The purpose of the research was to determine if lightweight aggregate, high strength
concrete is applicable for construction of precast prestressed bridge girders. Specific objectives
were as follows: (1) analytically determine if a high strength/high performance lightweight
concrete (HPLC) could be used to effectively increase the span length of bridge structures and to
provide a span of 150 ft. with a girder plus truck weight less than 150,000 lbs.; (2) to develop
HPLC mixes with design strengths of 8,000 psi, 10,000 psi, and 12,000 psi; (3) determine the
short and long term properties of selected HPLC mixes; (4) verify that the HPLC mixes could be
produced at precast concrete plants; and (5) determine if precast prestressed girders made with
HPLC behave in conformance with AASHTO design specifications.
1.2 Scope
The scope of the research was limited to using expanded slate lightweight aggregate; all
lightweight aggregate was obtained from Carolina Stalite Company. Only six AASHTO Type II
girders were tested, three made from an 8,000 psi design mix and three from a 10,000 psi design
mix.
1.3 High Performance Lightweight Concrete
The Federal Highway Administration (FHWA) definition of high performance concrete
(HPC) can be seen in Table 1.1 (Goodspeed et al. 1996). In general, lightweight concrete (LWC)
is concrete that possesses a unit weight of less than 120 pcf (Murillo et al. 1994). In this report,
all controlled density concrete with a unit weight less than 125 pcf and design strengths greater
than 6,000 psi is termed High-Performance Lightweight Concrete (HPLC) and applies to
concrete with lightweight fine and coarse aggregate and to concrete with natural sand and
lightweight coarse aggregate.
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