The voice of concrete products - British Precast

BRITISH PRECAST BEST PRACTICE AWARDS 2008
Gallagher. The pouring process was quite intense and everyone
involved had to be fully aware of their position in the
team. Keeping the same people in the same positions for
the length of the project ensured their safety and a goodquality
consistent product.
The two production teams on the project were shown
DVDs of the barriers being produced in the US and a team
from California came over to take Milton staff through the
first few weeks of barrier production. A full risk assessment
and safe working procedure were written to ensure
that everyone would be kept safe.
Operators were ‘walked through’ the production process
to ensure they understood their roles. Demarcation
lines and a one-way system were mapped out to segregate
the two teams and to ensure that the ready-mixed concrete
trucks were kept to specific areas. Each operator knew his
role in the process, from demoulding to pouring, to reassembling
to moulds. This continuity made for a safe, slick
operation.
The production and quality control had to equal the
dynamic simplistic approach to the end usage of the QMB
– the goal being one unit per mould per day.
The reo-dynamic high-flowing concrete has been
designed to allow for minimal compaction with little to no
voids present. The mix was designed to withstand large
changes in temperature ranging from 5° to 35°C to allow
the concrete to be cast outside; the use of superplasticisers
allowed for high workability with the capability of
demoulding after 24 hours. The required strength was
31MPa at 28 days, typically reaching 21MPa at two days.
The decision to use ready-mixed concrete allowed large
volumes of concrete to be discharged in limited time.
Slump tests and cube samples being taken from each truck
delivered ensured the quality and consistency of concrete
poured, allowing 8m3 of concrete to be discharged into
moulds and the truck being able to leave within 30 minutes
of arrival on-site. Each operation needed to be quick to
allow for smooth production of the units, as casting was
not the only task needing to be completed within the day:
preparation of the reinforcement and accessories were
required for the following day.
The QMB barrier system had three main processes
before the finished article could be used: casting, addition
of the feet and jointing together in pairs. None of the processes
could be undertaken until a strict quality regime had
been completed, as strength goals were required for each
process.
The entire production operation from the arrival of the
first container to the making of the final barrier took
approximately three months. In this time, 4500 barriers
were produced at 100 per day. In the entire project only one
day’s production was lost and this was due to bad weather.
Concluding remarks
Milton Precast is convinced that QMB will bring major
benefits to both contractors and road users, in terms of
safety, efficiency and improved traffic flows. By allowing
rapid lane changes, even at peak times, QMB helps ensure
that work is completed more quickly, safely and cost-effectively
– and that’s got to be good news for everyone using,
and paying for, Britain’s roads.
n
Figures 2 and 3:
Installation on the M20.
“QMB will bring
major benefits to
both contractors
and road users, in
terms of safety,
efficiency and
improved traffic
flows.”
Reproduced f ro m CONCRETE December 2008/January 2009 © The Concrete So c i e t y, 2008 19