Lightweight Concrete for High Strength - Expanded Shale & Clay

Chapter 3. Mix Designs, Field Evaluation, and Short-term Properties
3.1 Preliminary Laboratory Investigation
The purpose of the preliminary laboratory study (Task 2) was to develop the most promising
mixes to satisfy the 8,000 psi, 10,000 psi, and 12,000 psi strength requirements. Over 75
preliminary mixes were batched, and over 700 4-in. diameter x 8-in. long (4x8) cylinders were
tested. To develop the preliminary mixes, a base mix given in Table 4.1 was used initially and
then modified.
Table 3.1 Base Mix Components Provided by Carolina Stalite Company
Material Quantity (lbs) Specific Gravity
Sand 1221 2.63
1/2” Stalite 950 1.52
Cement 500 3.15
Silica Fume 35 2.2
Class “C” flyash 200 2.25
Water 266.6 1
Admixtures*
air-entrainer Daravair 1000
water-reducer WRDA 35
------
high range water reducer
ADVA Flow
Target Air Content 4 % ------
*Admixtures dosed in accordance with manufacturer specification
Mixes were varied by modifying one parameter at a time: maximum size aggregate, cement
paste ratio, coarse-to-fine aggregate ratio, pozzolan contents, and water/cementitious materials
ratio. Mixes were compared using concrete strength. All cylinders were first cured for 24 hours
in an insulated box to mimic curing conditions in a precast girder. Thereafter, the cylinders were
cured in a fog room at 70 o F until time of testing.
To study aggregate size, 3 different size aggregates, 3/8-in., 1/2-in., and 3/4-in., were
substituted into the base mix. Figure 3.1 shows the strength data for 1 day and 28 day strength
tests. Further mixes using normal weight granite aggregate as a replacement for the lightweight
aggregate showed that there was a strength ceiling of about 11,500 psi for HPLC.
3-1