Lightweight Concrete for High Strength - Expanded Shale & Clay

Appendix A. Background
A.1 Introduction
Much research has been published on lightweight concrete, however, only a small portion
of it focuses on high-strength lightweight concrete used for pretensioned bridge girders. In most
cases the research involved concrete with compressive strengths less than 7,500 psi. While this
research is important and in most cases relevant, it does not verify current code provisions for
use on high strength lightweight concretes (HSLC) commercially available today. The term high
performance lightweight concrete (HPLC) is synonymous with HSLC. In addition, since the
properties of lightweight aggregate (LWA) vary based on the raw material from which it is made
and the production technique, a direct comparison is not always possible.
This review provides information on both HSLC and normal weight concrete. Initially,
the review covers terms and definitions related to lightweight concrete. The production of slate
lightweight aggregate is described and a review of the use of HSLC in prestressed bridge
applications is provided. Previously developed HSLC mix designs are described and comments
about their production in a field environment are discussed. The development of equations to
predict transfer length in normal weight concrete is reviewed and current research on transfer
length is summarized. Information on shear relating to findings in this research is provided as
well as a review of other ongoing research. The review culminates with a summary of the
development of equations to predict prestressing strand development length as well as a review
of other related research.
A.2 Terms and Definitions Related to Lightweight Concrete
The following terms are used throughout this appendix:
Lightweight Aggregate (LWA) – Aggregate with a dry, loose unit weight of 70 lb/ft 3 or less.
Lightweight Concrete (LWC) - A general term that includes “all-lightweight concrete” and
“sand-lightweight concrete” defined below.
All-Lightweight Concrete (ALWC) - Concrete containing all lightweight aggregate and does
not exceed 115 lb/ft 3 .
Sand-Lightweight Concrete (SLWC) - Lightweight concrete in which all the all of the fine
aggregate consists of normal weight sand.
A-1