114 / 140
November 2018
112 \
World Cement
working with only portland cement. Slag cement
enhances the consolidation and pumping of concrete by
improving its rheology or flowable nature. This leads to
an easier paste and a smoother concrete finish.
Most concrete made with slag cement will have less
bleed water than concrete made with portland cement
alone. Bleeding rates are slowed by having a more
finely ground cement, and virtually all slag cement used
in the US is ground more finely than Type I or Type II
cements.
Case studies
The SCA runs an annual awards programme that honours
outstanding projects utilising slag cement in innovative
and exemplary ways. These case studies serve as real-life
examples that showcase the positive impact slag cement
can have on concrete performance. The following are
two examples (more can be found on the SCA website).
St. Croix River Crossing
St. Croix River Crossing won an award from the SCA this
year for innovative applications. This US$646 million
project involved two states, multiple communities,
many individuals, and decades of debate. The bridge
contains five sets of piers in the river, seven sets of piers
on land in Minnesota, and one set on land in Wisconsin.
The length of the bridge span is 5074 ft (nearly one
mile) with a width of 100 ft. There were 988 concrete
segments used and the total concrete for the project
was 140 000 yd
3
. The project team created 19 mix
designs, which required extensive testing including
compressive strength, hardened air, freeze/thaw
durability, surface scaling, shrinkage, rapid chloride
permeability, alkali silica reactivity, cement diffusion,
and modulus of elasticity and creep. Slag cement was
critical to the success of mix testing.
There were over 200 mass concrete placements on
the project (most mass concrete included 65 – 70% slag
cement), all requiring thermal models and temperature
monitoring. Much of the concrete had to be placed in
the river. The team decided to deliver concrete to the
shore, pump the concrete into two ready–mixed trucks
that were fixed on a barge, barge them out to the
element, then pump the concrete into the element.
The Minnesota Department of Transportation
required that the mixes used for placement over the
water have a 180 min. range. This meant that the
project team had to prove the concrete could be
batched with the slump and air content within the
tolerance of the specification; then the concrete had to
maintain a slump and air content with the allowable
range for the entire 180 min. The concrete was tested
every 30 min. during the 180 min. duration for trial
batch compliance.
University of Notre Dame’s Campus Crossroads
Stadium
Another award-winning project from the SCA was the
University of Notre Dame’s Campus Crossroads Stadium
project, receiving the Green Design category award in
2017. This US$400 million, LEED Silver project consisted
of attaching three new buildings onto the existing iconic
football stadium, increasing its capacity by 750 000 ft.
The project included over 13 000 yd
3
of mass
concrete, which could not exceed 158°F at its core.
Therefore, the mass concrete contained 70% slag
cement to help control core temperature rise,
which was vital to the success of the mass concrete
foundations. Thermocouples placed into the mass
concrete revealed that no foundation exceeded 130°F.
Some mass concrete structures required pours of over
1000 yd. Despite utilising the slag cement at 7%, the
28 day design strengths were typically obtained in only
seven days.
Advancing industry practice
Fine tuning the relationship between construction
materials to produce high-quality concrete structures
with easy-to-replicate results is the goal of most
construction professionals. Relying on associations like
the SCA can help connect the dots when it comes to
introducing slag cement to a project. Over 25 technical
information sheets can be downloaded from the SCA
website. These cover many different slag cement topics,
such as precast use, soil stabilisation, high performance
use, residential use, and more. As mentioned above, the
case studies section of the website holds award-winning
profiles on different project types, including highways,
stadiums, bridges, hospitals, buildings, and airports.
To highlight its impact on concrete sustainability, a
downloadable Life Cycle Assessment Calculator and
Environmental Product Declaration for slag cement is
also available on the association website.
The complex thing about concrete mix design is that
no one mix will work for every single project: finding
the right balance of available materials to achieve the
desired concrete results is critical to structural success.
While making the switch to a new material can be
unsettling, industry tools and resources from associations
like the SCA help make the transition easier.
Whether the project goals are to reduce concrete
permeability, mitigate corrosive attacks, or simply to
produce lighter colored and stronger concrete, slag
cement can help. When considering optimising concrete
performance, think about slag cement and the benefits
this material has to offer.
About the author
Drew Burns started working with the Slag Cement
Association in January 2017 as Marketing Coordinator.
Promoted to Director of Operations earlier this year, his role
has expanded to help with association management and
strategic planning. Burns worked with the SCA Technical
Marketing Committee using association resources to
develop the content in this article. Before joining the SCA,
Burns worked for Planterra Inc. as their National Accounts,
Marketing and Brand Manager, and with Strive RTS as
Special Projects Director before that.