Effects of Ground Granulated Blast Furnace Slag in Portland Cement ...

cycles. They cast 3 in. by 6 in. by 12 in. blocks and moist cured them for 14 days followed by
14 days of air curing. Water was added to the blocks, and they were subjected to a
freeze/thaw regimen at -17.8°C and 21.1°C, respectively. Flaked calcium chloride was added
to the ice at the start of each thawing and the block was washed off at the finish of each
thawing cycle. ACI Committee 233 bases their stand partly on this study. This may be
unjustified since the salt was added after freezing took place and washed clean before being
refrozen. This would eliminate the additional osmotic pressures caused by the deicer salt.
While it is known that GGBFS has a detrimental impact on strength development and deicer
scaling resistance, it is less clear as how this information should be used for Wisconsin
paving projects. Unlike earlier studies, this study aimed to determine GGBFS concrete
performance variations over a range of concrete-making materials used in Wisconsin. The
research plan sought to quantify the effects on GGBFS concrete of Type I portland cement
from four different manufacturers, three GGBFS replacement levels, and two types of coarse
aggregate. This research represents the most comprehensive assessment of GGBFS to date.
The research plan consisted of four tasks:
Task 1: documentation of Midwest GGBFS experiences and a literature survey
update,
Task 2: monitoring of the variability of GGBFS composition,
Task 3: strength gain and air void development with 4 different brands of Type I
portland cement at varying temperatures, and
Task 4: deicer scaling tests with two different cements and with four different curing
methods.
The strength gain and deicer scaling tests used GGBFS as a replacement of portland cement
at 0%, 30%, and 50% levels. Thirty mixes were evaluated in the Task 2 regarding strength
gain task, and thirteen mixes were evaluated in Task 3 regarding the deicer scaling task.
Freeze-thaw testing for the deicer scaling tests followed a modified ASTM C672 procedure
where testing was extended to 100 cycles, and the scaled off material from the block surface
was weighed every 5 cycles.
Research Process
The methodologies of the four tasks of the research followed accepted procedures with some
modifications to enhance the level of meaningful data. Task 1 established the recent
experiences with GGBFS in paving concrete. A survey of neighboring Midwestern state
DOT’s attempted to find potential commonality of field and performance problems. Task 2
was targeted at assessing the variability of GGBFS from one producer as delivered to a local
ready-mix plant. The tests used to quantify variability were chemical composition of the
portland cement and GGBFS (ASTM C114), slag-activity tests (ASTM C989), and particle
size distribution. Task 3 was directed at measurement of air dry shrinkage, hardened air
void, and compressive strength test results using the appropriate ASTM standards. Thirty
mixes were completed in Task 3. The mix variables were cement brand, curing temperature,
GGBFS replacement level, and aggregate type. The purpose of Task 4 was to quantify the
deicer scaling resistance of the GGBFS concrete using a modified ASTM C672 procedure.
Task 4 had similar mix variables to Task 3, except that the test concrete utilized only two
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