Road Purpose
Modular roads using concrete block paving are a modern
equivalent of 'sets' first seen in the building of roman
roads throughout Europe. Using modern materials the modular
road is both durable and easily maintained as well a
providing a good appearance.
 Road
Structure and Design
Concrete block paving used in the are 80mm thick and in
footways 60mm thick unless used for vehicle crossings. The
blocks come in a variety of shapes an colours and have a
minimum crushing strength of 50N/mm² for use in the
carriageway. There are principally two types of
modular surfaces, they are High Amenity and High Duty. High
amenity areas are designed to look pleasing by using
decorative patterns, there is no limit to the patterns used.
With High duty areas the 'look' is not as important but the
durability is.
 High
Amenity
 High
Duty
The blocks are manufactured
with skid resistance built into them by providing a textured
finish. Chamfered edges are provided to allow for handling
and ease of laying. Blocks can be almost any colour or shape
with some shapes being more suitable for carriageways by
providing resistance to movement, such as interlock paving.
Block paved areas are to a certain degree flexible, in that
it can move vertically during traffic loading. This is an
important point to remember when reinstating because poor
compaction of the sub-base, bedding or blocks can cause
reinstatement failure.
Edge restraints or kerbs are used to prevent the blocks from
spreading under load. Care is taken to ensure that concrete
haunching or bedding do not make the blocks stand proud.
Blocks are laid on a 'bed' of sand which is often treated
with a weed killer. The bed is normally 50mm compacted layer
thickness. Some high trafficked areas also include a
bituminous road base or lean mix concrete to provide extra
strength to the road.
The bond or pattern used is
very important to the integrity of the road. A 45° or 90°
bond is used to provide good load spreading capabilities in
high duty areas. Often an interlocking block is used where
traffic capacity and loading is expected. Laying an
unsuitable pattern would allow the blocks to spread or kick
up under load. During reinstatement it is important to
maintain the bond pattern used in the original surface.
Tactile paving is being used more at crossing places to help
the visually impaired, this must be replaced when
reinstating.
Kiln dried sand which is also treated with a proprietary
weed killer is used to fill the joints. The kiln dried sand
also provides resistance to movement of the blocks during
loading and allows the load to be transferred to adjacent
blocks.
The blocks are laid about 5mm proud of the edge restraints
to allow for compaction to their finished level using a
vibrating plate fitted with a rubber mat to prevent damage
to the blocks during compaction.
Another type of paving is element block paving, these are
paviors that are 450 x 450 square and often 65mm thick.
Small element paving is laid in the same way as concrete
block paving and are often used in high amenity areas.
Sub-Base
The sub-base is designed to assist in the load spread over
the sub-grade. It also allows drainage into the sub-grade
and is often used during construction as a temporary running
surface and is the main platform on which to build the road.
The sub-base is also used to make up the thickness of the
pavement to at least 450mm to give frost protection to the
sub-grade in frost susceptible soils. Sub-base is always
made up with unbound granular materials.
Reinstatement of Modular
Roads
The 'Specification for the Reinstatement of Openings in
Highways' is used when designing the reinstatement and
deciding the materials to be used. The specification also
gives the permitted tolerances and intervention limits on
all reinstatements.
Main Considerations for
Reinstatement
When reinstating the road there must be great efforts to see
that the workmanship and quality are of the highest
standard. This will ensure that the reinstatement will stand
up to the expected loading and prevent further visits to the
site thus more expense. Time should be allowed for to ensure
quality is maintained.
Where an interim reinstatement is used every effort should
be made to complete a permanent repair. This must be in
accordance with the NRASWA. An interim repair can be done
using deferred set macadam, damaged blocks or concrete to
open the road to traffic. In high amenity areas this would
be unsightly and not advised.
There must be an agreement with the local authority on
materials used in areas of special needs. Using unsuitable
materials, even if well compacted, may lead to a defect
notice being served.
In some situations a bituminous roadbase is used to provide
extra strength to the structure of the road. When
reinstating the bituminous material must be replaced as
existing and compacted in accordance with the
Specifications.
Where reinstating a modular road the blocks or paviors used
must match the existing. The authority should advise on
sources and also retain a quantity of spares for such
reinstatement purposes. Where materials are no longer
available a suitable replacement must be agreed with the
authority.
The sub-base material and sand bed must be well compacted
prior to relaying the blocks.
Damaged kerbs or edge restraints must be replaced as well as
making good any disturbed ironwork.
In some roads a bituminous roadbase is used and must be
replaced as existing to the same depth or a minimum of
100mm.
Foamed concrete is used with the permission of the
authority. If used, there must be operational safety
measures taken to avoid people stepping onto the mix until
it has set. Loading would not be allowed until the foamed
mix has reached a minimum crushing strength defined in the
specifications as 4N/mm² at 28 days up to a maximum of
14N/mm² at 28 days.
Lean mixed concrete may only be used on small reinstatements
of less than 2m² and less than 300mm in width.
The reinstatement should be 'like for like' in colour and
type of block and the existing bond or pattern matched.
Tactile paving must be replaced as existing.
Removal of blocks or paviors where an existing edge,
ironwork or reinstatement is necessary to ensure that
disturbed areas are made good. It is important to remove any
adjacent disturbed blocks or at least two rows prior to
relaying. This will ensure a good bond is made and help
replace the last blocks.
The blocks laid so that they stand 5mm proud of the adjacent
surface and are compacted using a plate compactor with a
rubber mat fitted to prevent chipping the blocks, 5-6
compaction passes are made to ensure that the blocks are
well bedded in, some sand will push up into the joints. Kiln
dried fine sand to match the existing is swept into the
joints and vibrated using the plate compactor to fill the
voids. The main purpose of joint filling is to assist in
load spreading and prevent blocks coming loose. If the area
is to be cleansed using mechanical sweepers the kiln dried
sand may need to be reapplied. Joints wider than 6mm are
grouted using a mortar mix and care taken to prevent
discolouring the surface.
Whilst the as laid profile given in the 'Specifications' is
+ or - 6mm, this would be unacceptable in the footway as
there should be no significant 'trip' between the existing
surface level and the reinstatement.
This list
is not exhaustive
Back to
top......
|
