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CONSTRUCTION WORLD
JUNE
2015
PROJECT PROFILE
Project background
The Metolong Dam project is the major struc-
ture in the Metolong Dam and Water Supply
Programme (MDWSP) that will provide a
new raw water supply for Lesotho’s capital,
Maseru, and the generally impoverished
surrounding areas.
The region has historically suffered
from water shortages and the scheme will
improve water delivery to domestic users
and the country’s textile industry, an impor-
tant source of employment.
Metolong Dam is a 83 m high roller
compacted concrete (RCC) dam with a
design crest length of 280 m, constructed
on the Phuthiatsana River, approximately
35 km from Maseru. Contractor, Sino-
hydro, established an on-site batch facility
to provide the estimated requirement of
330 000 m³ of RCC and 40 000 m³ of conven-
tional vibrated concrete (CVC). The Beijing
based contractor is a global top-ranking
construction and hydropower group that is
involved in a range of projects on the African
continent, and has worked on major interna-
tional projects such as China’s Three Gorges
Dam, the world’s largest dam.
Fly ash
Ash Resources, Lafarge South Africa’s
leading fly ash company, had established
a relationship with Sinohydro three years
previously on a project in Zambia and were
also supplying fly ash for other sections
of the MDWSP. This facilitated the initial
introduction of Lafarge South Africa to
Sinohydro as a major, technically sophis-
ticated company that could supply all of
the contractor’s requirements for cement
and fly ash. It was both commercially and
practically of interest to Sinohydro and was
in line with the recently introduced ‘One
Lafarge’ approach to major infrastructure
developments, aimed at ensuring customers
receive the optimum all-round benefits from
the company’s resources. It further reflects
Lafarge South Africa’s policy of building long
term relationships by delivering true value.
In South Africa, cement for water infra-
structure projects is traditionally dominated
by CEM I products. Engineers and contrac-
tors are cautious about changing estab-
lished practice, whereas Lafarge SA had
phased out CEM I cements and, some years
earlier, had developed a complete range of
innovative fly ash extended products. The
challenge that the company faced was to
convince the project team of the merits of its
CEM II product.
Technical innovation
Realising that Heat of Hydration would be
a significant concern, Lafarge SA proposed
their premium technical cement, Power-
crete Plus CEM II 42,5R. This formulation is
a Low Heat cement and also has the capa-
bility of being extended further on site
with additional fly ash. The engineers and
the contractor were not familiar with this
versatile, high performance product. It took
a two-year determined selling campaign,
with strong technical support from Lafarge
SA’s highly regarded accredited civil engi-
neering testing facility, Quality Department
Southern Africa (QDSA), to achieve a change
in the technical mindset and the commercial
breakthrough. A significant selling point was
the same quality and source of fly ash being
incorporated in the cement as would be
used for on-site concrete batching.
The role of QDSA
Arising from discussions with the consult-
ants and main contractor Sinohydro, QDSA
was requested to conduct laboratory eval-
uations of the RCC (Roller Compacted
Concrete) mix and the CVC (Conventional
Vibrated Concrete) mix. The outcome was
that based on QDSA’s recommendation,
Powercrete Plus premium technical cement
and DuraPozz® classified siliceous fly ash
from Ash Resources’ Lethabo facility were
used as binder material, with the RCC mix
containing 66% and the CVC mix (grade
25/38) 52% fly ash respectively.
Trials using the CEM II Powercrete Plus
achieved similar results to those obtained
during a trial mix programme by the consult-
ants using a type CEM I product. This
impressed both the consultants and the
contractor, whose previous experience did
not include RCC dams constructed using a
CEM II cement. A significant factor in favour
of Powercrete Plus was that it is a Low Heat
Cement with a typical Heat of Hydration
value of 227 J/g, compared with the EN 197-1
criterion of < 270 J/g at 41 h.
Throughout the dam’s construction,
QDSA has continued to provide technical
support. Its laboratory is equipped to under-
take Heat of Hydration testing in accord-
ance with EN 196-9, and Lafarge’s cement
team supplies the consultants with Heat of
Hydration results, together with Powercrete
Plus batch chemical analyses on a monthly
basis. This gives the client the security of
confirmed consistent levels of fly ash exten-
sion in the product.
Cement performance
Lafarge’s Powercrete Plus has performed
exceptionally well, exceeding the contrac-
tor’s expectations. The consistent quality
of the product and its good strength
performance has enabled the contractor
to systematically reduce the cement
content of some of the mixes from the initial
design levels.
Quality fly ash extending
concrete performance
The use of Ash Resources’ classified fly ash,
DuraPozz®, has become virtually a standard
component of concrete for controlling the
heat of hydration in major water retaining
structures. This is now especially the case
since DuraPozz® complies with the new and
more stringent SANS 50450 specification
for category ‘S’ fly ashes. The consistent
CEMENT
and
FLY ASH
Metolong’s innovative
Project information
• Client:
Sinohydro
• Project start date:
2012
• Project end date:
End of 2014
• Main contractor:
Sinohydro
• Principal agent:
Metolong Authority
• Consulting engineer:
Arcus GIBB
It was both commercially and practically of interest to
Sinohydro and was in line with the recently introduced ‘One
Lafarge’ approach to major infrastructure developments,
aimed at ensuring customers receive the optimum all-round
benefits from the company’s resources.