1.
CASE STUDY – SAFELY WORKING WITH SYLENTMITE®
Concrete and Rock Solutions worked with UK company AWCS Holdings Ltd to excavate a lift pit safely
within a building so as not to disturb the existing works and structure.
AWCS Holdings Ltd is a small specialist civil engineering company based in Launceston, Cornwall. They
carry out sheet piling works, installation of temporary works and civil engineering /building works that
usually different to the norm and this work takes them all over the country working for many of the
main and regional contractors.
All their operatives are fully trained and multi‐skilled, and are used to dealing and adapting to the
unusual or unexpected.
AWCS were contracted by BAM Construction Ltd to undertake the excavation of a lift pit (1600mm wide
by 2000mm long and 1100mm deep) within an existing building which forms part of the new University
Technical College (UTC) Plymouth.
Alastair Hegarty, Construction Director of AWCS Holdings Ltd explains, “There was an existing lift shaft
but the pit itself needed to be deepened to accommodate the new lift. Preliminary investigations led
the contractor to believe the existing “ground” consisted of 1200mm of mass concrete and the contract
was let on this basis.”
After looking at all the possibilities AWCS met with CRS and Colin Gaunt explained and demonstrated
the unique qualities of Sylentmite® and why it was the best option for this project.
Colin Gaunt, Sales Director of CRS, describes how Sylentmite® would work in this situation, “Sylentmite®
fitted the profile for its qualities of noise reduction, limited space, no heavy equipment needed and its
green ecological capability. Additionally, there would be no contamination with the waste as
Sylentmite® is pH neutral when used, as a result there were no additional costs for waste disposal.”
From this, AWCS proposed using Sylentmite® to break this concrete out minimising the amount of
noise, dust and disturbance inside a building that was nearing completion.
Their initial proposal was to stitch drill around the perimeter of the lift shaft to create a movement
zone for the concrete to expand into and then drill 40mm holes in a grid at 200mm centres to pour the
Sylentmite® into.
However on commencement of drilling it soon became clear that the existing mass concrete was not as
initially expected. Further test drilling revealed a 300 thick slab, on top of a bitumen based
waterproofing membrane on top of a 500mm thick heavily reinforced concrete slab. A re‐ appraisal of
their methods was required as the rock drill struggled to penetrate the bitumen layer and was unable to
touch the reinforcement bars.
Their chosen method, therefore, was to stitch drill around the perimeter of the lift shaft as previously
but this time they used a 100mm diamond core drill bit, which allowed them to drill and remove the
bitumen layer and also allowed them to drill straight through the reinforcement.
A grid of 42mm holes were then drilled using the diamond drilling rig again on the top 300mm of the
slab. Sylentmite® Pour ‘N’ Crack was then poured into the slab and left overnight. The slab cracked and
split as predicted into manageable lumps, which could be removed by hand from the lift pit area.

2. Photograph 02* shows the lumps of concrete after removal, as well as the core bits from the
perimeter of the lift shaft.
After the area was cleaned up the grid of 42 mm hole was repeated again through the reinforced
concrete slab. Sylentmite® was poured into these holes and left overnight. The following morning the
concrete was shattered around the reinforcement bars. The small lumps of concrete were removed by
hand and small hand breakers were used merely to prise lumps away from each other. The whole slab
was removed in a couple of hours. Photograph 17* shows the broken out lumps of concrete with the
reinforcement bar removed lying behind.
Hegarty concluded, “The use of Sylentmite® exceeded all expectations from both ourselves and the
main contractor and allowed us to remove both mass and heavily reinforced concrete quickly and
efficiently. We had no health and safety concerns either from the product itself but also with regards to
vibration, noise, dust, fumes etc inside a building. It was a very successful product to use.”
www.awcsholdings.co.uk