RICHARD COWLING, ALFRED McALPINE CAPITAL PROJECTS
Blast cleaning laitence and debris during bridge construction
was an effective alternative to traditional techniques.
A4146 BYPASS
A simple telephone enquiry gave us the opportunity to
play a crucial role in the construction of a new bypass
near Milton Keynes.
From reading our website, main contractors Alfred
McAlpine knew we used blast cleaning technology to
remove graffiti. They asked if we could transfer that
expertise to the removal of laitence from the base of
part-constructed bridge piers on the new A4146. We
were on site within three days.
Laitence is fine cement powder which floats to the
surface of all poured concrete work. It must be removed
(along with any other dirt or debris) to ensure a positive
bond is formed between the existing and newly-poured
concrete. To remove it, we blast-cleaned the surface
with recycled iron silica.
Top for health and safety
The project is ongoing, as more bridges are built, but
McAlpine are delighted with the results so far. We were
equally delighted to learn that of all the sub-contractors
McAlpine had evaluated, we scored highest in terms of
our health and safety procedures.
The final stage of the project for us will be to apply
a new non-hazardous protective impregnation sealer
(this replaces the use of Silanes) to all 15 completed
structures. The product is called Protect All P1 and its
use on this contract has been approved by Atkins on
behalf of the Highways Agency. The sealer prevents water,
oil, road salt and other contaminants from permeating the
concrete and corroding the steel reinforcing bars. It has
the additional benefit of being resistant to solvents and,
thus, aids the removal of graffiti.
