December 2013
CONSTRUCTION WORLD
60
Specialist Contractors or Suppliers
B
Supply of fly ash for the construction of
Medupi Power Station
W
hen construction began in 2008 on Medupi, Eskom’s
6 x 800MWcoal-fired power station at Lephalale in Limpopo
Province, it was the largest dry-cooled coal-fired power
station in the world.
In the early stages of construction, the concrete was mainly
pumped because of the extremely crowded nature of the site where
foundations and bases were being poured for a huge number of
structures. The main challenges were to deliver the volumes of
concrete required and to manage the heat of hydration in the large
pours. The concrete designs are tightly specified and most are based
on a 70/30 CEM I /fly ash mix, with the use of a 60/40 mix approved
to help control temperatures in the larger mass pours. Since Eskom
built its last coal-fired power station over twenty-five years before
the Medupi project, the use of fly ash has become a virtual standard
component of concrete for controlling the heat of hydration: not only
contributing to lower temperatures but the peak temperatures also
occurring at a later age.
In addition to controlling heat of hydration, concrete mixes had
to be developed and approved to meet very tight shrinkage speci-
fications. The use of Ash Resources’ classified fly ash DuraPozz® and
DuraPozz®Pro™contributed to highly effective mix designs. They also
featured excellent workability and‘pumpability’, which helped achieve
good flow through the congested reinforcing without segregation
or settlement.
Flexibility in delivery rate and, above all, reliability of fly ash supply
were paramount requirements in delivering approximately 60 000
tons of classified fly ash to meet the project’s requirement for over
600 000 m³ of total concrete to be placed. The critical importance of
the concrete work on a project such as Medupi and its tight timeline
meant that it simply could not afford to run out of fly ash or have
quality problems. Ash Resources supplies by road from their Matla
plant and is able to effect efficient back up supply arrangements from
their other facilities should it be necessary.
Themix designbeingemployed for the structural concrete reached
60 MPa in 28 days and would have been virtually impossible to break
down to correct any errors. Because of the high daytime temperatures
at Lephalale, the larger pours were done at night. Pours averaged
6 000 - 8 000 m³ a week, with nightshifts achieving pours of up to
1 500 m³. These large pours reflected the fact that many of the power
station structures are essentiallymonolithic.The turbine hall is a good
example with its raft foundation for the turbine up to 4 m deep. The
pours had to be completed without interruption to avoid cold joints.
The main concrete structure of the Medupi power station is now
all but complete with Ash Resources nearing the end of the fly ash
supply for the remaining concrete work involved in completing
associated infrastructure facilities and service plant.
Project information
• Name of project: Supply of fly ash for the construction
of Medupi Power Station
• Company entering: Ash Resources
