Lightweight Concrete for High Strength - Expanded Shale & Clay

aggregate must be saturated by presoaking if the concrete is to be pumped. In the event of dry
aggregate, pumping could force mix water into the LWA pores reducing the workability of the
mix.
Valum and Nilsskog reported on field production of HSLC having a compressive strength
of 8,700 psi for the construction of the Raftsundet Bridge in Norway. Field production included
steps to insure expanded slate aggregate absorption was maintained between 7 and 9 percent to
prevent mix water absorption. The time from batching until concrete placement could be as long
as 2 hours. In addition, bulk density and surface moisture were determined prior to each
concrete placement to insure proper mix proportioning. Prior to a concrete truck leaving the
batch plant, concrete temperature, slump, air content and wet density were checked for
compliance with design specifications. Any results out of specification resulted in the mix being
discarded. While these standards would be common for the production of normal weight HPC,
the more exacting control of aggregate moisture content was evident for HSLC. In addition,
exact control of moisture also enabled better control of unit weight.
Hoff described field production of HSLC for offshore platform construction. Many of
the same steps were followed as mentioned by Valum and Nilsskog. Hoff reiterated the
importance of moisture control and the impact it could have on slump loss during placement and
also commented that excessive moisture could result in unsuitable resistance to freezing and
thawing damage.
A.7 HSLC Short and Long-Term Material Properties
The following sections address specific material properties and material related
phenomenon where differences were noted between HSLC and NWC.
2.7.1 Modulus of Elasticity
An in-depth explanation of the determination of modulus of elasticity is covered in
Chapter 3, Analytical Investigation on HSLC for Pretensioned Bridge Girders.
The current ACI equation for modulus of elasticity is:
E
c =
33w
1.5
c
f
'
c
( A.1)
where
E c =
concrete modulus of elasticity (psi)
A-7