ROAD PAVEMENTS – BITUMINOUS BOUND MATERIALS Contents

Volume 2 Series NG 900
Notes for Guidance on the Specification for Road Works Road Pavements – Bituminous Bound Materials
method from BS 598 part 110 to IS EN 12697-
22, which uses similar equipment but
different duration and loading. Further
information is given in the note to SR28 Table
4 and Table NG 9/9. Work is in hand to
establish criteria for the new method, but in
the interim, requirements should be based on
the BS 598 test but with data provided to
show the values for the same mix tested to the
IS EN 12697 method.
8 Sub-clause 18 requires a minimum stiffness
category of 1800 MPa for mixtures containing
40/60 grade binder. This is a minimum default
value for these mixtures and should not be
confused with the design stiffness. Further
information on design stiffness can be found in
HD 26 (DMRB 7.2.3). There is no protocol
covering stiffness determination for dense
base and binder asphalt concrete mixtures in
BS 594987. Therefore, the following Type
Testing protocol should be adopted:
‘Following the general protocol in BS 594987
Annex C, take an additional, three adjacent
core pairs as described in C.3.2. Cut test
specimens from these cores and determine
stiffness in accordance with IS EN 12697-26
(ITSM method 20 o C). The mean of the set of
six values shall not be less than 1800 MPa for
mixtures containing 40/60 grade binder.’
9 Indirect density gauges, including nuclear
density gauges, are specified for compaction
control. It is important that these are
calibrated across an appropriate range of
densities as required by BS 594987. Such
gauges have a penetration depth of
approximately 80 mm and where layer
thicknesses exceed this it is especially
important that cores are visually inspected to
ensure that they are uniformly compacted.
10 A new requirement for density control close to
joints has been introduced. Experience has
shown that in-situ void content requirements
in the wheeltracks are generally achieved.
Therefore, the frequency of testing in this
position has been reduced. Compaction at
joints is considered to be a primary factor in
affecting the durability of asphalt pavements
and testing at this location has therefore been
introduced. Contractors may need to adopt
special measures of joint compaction in order
to comply with this requirement.
11 Where dense asphalt concrete base and binder
course mixtures are to run on directly by
normal highway traffic (due to traffic
management requirements) it is recommended
that they be surface dressed to prevent water
ingress and to provide adequate skid
resistance.
Declared Declared Specifications
Specifications
Specifications
12 The following tables provide examples of
declared specifications derived from the target
composition
specification.
criteria set out in the
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