The Civil Engineering Contractor June 2019 | Page 20

THIS IS CIVIL ENGINEERING
The Maputo Bridge, now the longest suspension
bridge in Africa with 3 300m of connecting bridge
structures, required a specific and durable building
material – concrete – that would not only meet the
100-year design life mandated by the Mozambican
government but be visually acceptable and as
sustainable as possible.
This stipulation led to the substitution of up to
40% of the cement with fly ash, leading to what
GAUFF calls ‘fantastic results and the construction
of arguably one of the most durable structures on the
African continent’. A requirement that had a drastic
effect on the quality of the overall project was the
decision to appoint an internal independent quality
control consultant. GAUFF Engineering – a German
company with head offices in Nuremburg and over
40 years of experience in Africa – was appointed to
this position.
The Maputo Bridge project is made up of two
140m tall reinforced concrete pylons and two 170
000t anchor blocks that support the suspension
bridge. Also included are 3km of connecting viaducts
constructed from precast post-tensioned T-beams
in the south and a composite structure in the north
consisting of T-beams as well as in-situ cast post-
tensioned box girders. These were constructed
utilising
the
balanced
cantilever
method
as
construction took place over an extremely active
industrial area.
In total, more than 340 000m 3 of concrete were
cast, calling for a staggering 850 000 bags of 50kg
cement. Both sides of the bay were equipped
with computerised 120m 3 /hour batch plants, each
with individual chiller plants to cope with the high
temperatures often experienced in Maputo.
For the various structures involved in the project,
over 300 piles were constructed varying in depth
from 110m for the pylons to an average depth of 50m
for the overall project. This required a workable self-
compacting concrete so 21 mix designs were done
to facilitate the different requirements for individual
structures and components. Design strengths varied
from 20Mpa to 50Mpa for the pylons, T-beams, box
girders, piers, piles, crash barriers, curbing and
hydraulic structures.
The
Portland
limestone
cement
comprises
between 80 to 94% clinker and between 6 to 20%
limestone with the capacity to produce cement
strengths between 42.5MPa and 62.5MPa.
The project’s massive workforce – peaking at 2 370
people – included Mozambicans and Chinese staff, with
quality control engineering and supervision staff totalling
36. In total, 14 526 940 man-hours were recorded on the
project until the end of October 2018.
18 | CEC June 2019
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