Authors:
John Read and David Whiteoak
Editor: Robert Hunter
Date: July 2003
ISBN: 0 7277 3220 X
Compiled by the Shell Bitumen European Technical Team
The Shell Bitumen Handbook is intended to be of daily
use to civil engineers in pavement construction and maintenance,
and also to students and researchers.
Considerable attention is given to the different aspects
of asphalts, detailing types of mixture, their manufacture
and testing, mechanical properties, transport, laying
and compaction and mixture design. This excellent reference
also devotes chapters to the important topics of analytical
design of flexible pavements and the technology of surface
dressing.
Chapter 19 - Surface Dressings and
Other Specialist Treatments
Page 415...
19.7 Grouted macadams
Grouted macadams are proprietary products, the most well
known being ‘Hardicrete’. They are not controlled
by a British Standard but are the subject of an Agrément
Certificate. Grouted macadams are available in two variants,
cementitious grouted macadams and asphaltic grouted macadams.
|
 |
19.7.1 Cementitious grouted macadams
Grouted macadams are used in areas where loading is particularly
heavy or concentrated, where there is likely to be spillages
of aggressive materials or in areas that require high surface
rigidity.
Typical uses include:
. container handling and storage areas and docks
. vehicle maintenance and refuelling areas
. runway thresholds and areas subjected to jet blast
. areas used by tracked vehicles
. bus lanes
. industrial areas and mooring
. roundabouts
. car parks.
19.7.2 Asphaltic grouted macadams
Asphaltic grouted macadams evolved from the long-term use of
cementitious grouted macadams. The essential difference between
asphaltic and cementitious grouted macadams is the nature of
the grout which, in the former, is based on bitumen rather than
cement. Manufacturers claim that the materials, when laid, improve
flexibility and resistance to permanent deformation whilst,
via increased bitumen content, possessing increased resistance
to oxidisation leading to longer life. The material is marketed
as a carriageway surface course and is particularly
suited to use on airfields.
19.7.3 Development
Grouted macadams originated in France where development of the
first ‘Salviacim’ took place in the early 1950s.
‘Gercim’ appeared in the early 1960s and others
were developed and appeared over time. The use of these French
materials has now spread to other countries through licensing
agreements. Their use in the UK started in the mid 1960s, mostly
for industrial mooring and areas subject to oil spillage. UK
use remained relatively constant until the late 1990s when a
need for materials capable of withstanding more severe working
conditions prompted a rise in their usage.
19.7.4 Laying
There are two stages in laying these materials. The first stage
is to lay a single layer of open textured coated macadam designed
with a controlled void content. A resin/cementitious grout or
asphaltic grout is then vibrated into this ‘receiving
coat’, filling the voids and sealing the surface. The
resulting product, in the case of the cementitious grouted macadam,
exhibits properties that lie between those of a flexible asphaltic
layer and one constructed of rigid concrete.
Grouted macadams may be laid onto any existing clean, sound
and level surface. A layer of regulating course is normally
required over an irregular surface.
When laying over existing concrete, all joints should be
inspected and any loose joint compound removed. Where edges
have spalled, these should first be treated with a suitable
material such as fine graded asphalt or bituminous sealant
before the application of the receiving coat. For new construction,
grouted macadams should be considered as an alternative surface
course.
Grouted macadams are generally laid at a nominal thickness
of 40mm but this may be varied to suit the particular application.
The thickness of this layer and the necessary void content
controls the aggregate size used in the receiving course.
The design of the traditional matrix can be altered to produce
a range of material strengths suitable for use from general
carriageways to heavy industrial areas.
The type of coarse aggregate used is governed by the application.
However, it is essential to use an aggregate that is hard
and durable. Thus, if polishing of the aggregate is not a
consideration then macadams containing carboniferous limestone
can be successfully used. However, in locations where severe
abrasion is likely, igneous rock sources would produce a superior
material.
Normally 100/150 penetration grade bitumen is used as the
binder, although 160/220 penetration grade bitumen may be
used where ambient temperatures so warrant. Use of a softer
bitumen will assist where the material is laid by hand. Conversely,
the use of a harder grade of bitumen such as 40/60 pen may
be adopted in areas where high ambient temperatures occur.
|
