New Roads and Street Works Act 1991 Specification for the Reinstatement of Openings in Roads Third Edition (Scotland) June 2012

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Publication Date: 
07/12/2012

Appendix A2 Key to Materials

A2.0 Introduction

1) This Specification covers the reinstatement of excavations made by Undertakers. Whilst the Specification captures all forms and sizes of excavations, the substantial majority of reinstatements carried out by Undertakers are small rectangular-type openings and trenches. By implication these reinstatements can be considered to be carried out in restricted or confined areas.

2) Undertakers primarily adopt hand laying operations in their reinstatements, rather than machine laying operations, which are allied to new-build and larger surface area situations, i.e. those which are not necessarily restricted or confined. In addition to the final compaction of asphalt layers, hand laying operations also include the on-site transportation and handling of the asphalt materials.

3) The preferred and permissible materials set out in this Appendix are predominantly for hand laying operations by Undertakers, and have been selected accordingly, which supports other end-performance criteria, generally set out through the Specification.

A2.0.1 Roads - General

1) In types 3 and 4 roads for small excavations and narrow trenches, the preferred binder course mixture may be replaced by any surface course mixture that complies with the Specification for the respective road type, provided that the same mixture is used as the surface course, see Section S6.4.10.

A2.0.2 Footways, Footpaths and Cycle Tracks - General

1) In all excavations, the preferred binder course mixture may be replaced by any surface course mixture that complies with this Appendix and with Section S8. This substitution is limited solely to the binder course layer. Void contents shall meet the requirements of Table S10.1 for footways.

A2.1 Hot Rolled Asphalt (HRA) Mixtures

1) All HRA shall conform to BS EN 13108-4. Conformity shall be established in accordance with BS EN 13108-20 and BS EN 13108-21. Natural gravels are not permitted as coarse aggregate for use in Types 0, 1 and 2 roads.

2) Requirements for deformation resistance as assessed by wheel tracking performance (WTR) are in accordance with PD6691 Appendix C, Table C.3

3) Design Type C mixtures listed in this section may only be used by agreement where satisfactory local experience has been gained in their use.

4) Chippings for surface application to HRA surface course mixtures shall be coarse aggregate conforming to PD 6691 Appendix C, C.2.3 and meet the requirements of C.2.8. The size and grading of chippings shall be 14/20 as in Table C.5. Where the existing surface has 8/14 chippings these may be used In the reinstatement.

A2.1.1 Surface Course Mixtures

The following HRA surface course mixture options are permitted. The preferred HRA mixtures may be replaced by one of the other alternative permitted mixtures.

1) Roads Type 0 and 1

The preferred HRA surface course mixture shall be: HRA 35/14 F surf PMB des WTR 2

Alternative permitted mixtures are:

a) HRA 30/14 F surf PMB des WTR 2

b) HRA 35/14 F surf 40/60 des WTR 2

c) HRA 30/14 C surf 40/60 des WTR 2 (before use refer to A2.1.(3))

2) Roads Type 2, 3 and 4

The preferred HRA surface course mixture shall be: HRA 35/14 F surf 40/60 des WTR 1

Alternative permitted mixtures are:

a) HRA 30/14 F surf 40/60 rec WTR 1

b) HRA 30/14 F surf 40/60 des WTR 1

c) HRA 30/14 C surf 40/60 des WTR 1 (before use refer to A2.1. (3))

3) Footways, Footpaths and Cycle Tracks

HRA surface course mixture shall be HRA 15/10F surf 100/150 rec or, HRA 15/10F surf 70/100 rec or HRA 15/10F surf 40/60 rec.

Areas which exhibit signs of regular trafficking by commercial vehicles or, such sites notified to the Undertaker by the Authority, shall be reinstated in accordance with Section S8.4. In such situations 100/150 pen material shall not be used.

A2.1.2 HRA Binder Course Mixtures

1) Road Type 0 & 1

The HRA binder course mixture shall be HRA 60/20 F bin 40/60 des WTR 2.

2) Road Types 2, 3 and 4

The preferred HRA binder course mixture shall be HRA 50/20 F bin 40/60.

Alternative permitted mixtures (a) and (b) below may be used by agreement where satisfactory local experience has been gained in their use.

a) Openings up to 500 mm width - HRA 50/14 F bin 40/60.

b) Openings over 500 mm width - HRA 60/20 F bin 40/60.

3) Footways, Footpaths and Cycle Tracks

The preferred HRA binder course mixture shall be HRA 50/20 F bin 100/150 or, HRA 50/20 F bin 70/100 or HRA 50/20 F bin 40/60.

Alternative permitted mixtures (b) and (c) below may be used by agreement where satisfactory local experience has been gained in the use of these mixtures.

a) Openings up to 500 mm width - HRA 50/14 F bin 100/150 or, HRA 50/14 F bin 70/100 or HRA 50/14 F bin 40/60.

b) Openings over 500 mm width - HRA 60/20 F bin 100/150 or, HRA 60/20 F bin 70/100 or HRA 60/20 F bin 40/60.

Areas which exhibit signs of regular trafficking by commercial vehicles or, such sites notified to the Undertaker by the Authority shall be reinstated in accordance with Section S8.4. In such situations the preferred binder course mixture may not be replaced by any carriageway surface course mixture and 100/150 pen material shall not be used.

In areas not subject to vehicular trafficking the preferred binder course mixture may also be replaced by any permitted carriageway surface course mixture.

A2.2 Stone Mastic Asphalt (SMA) Mixtures

1) SMA shall conform to BS EN 13108-5 and PD 6691. Conformity shall be established in accordance with BS EN 13108-20 and BS EN 13108-21.The following SMA mixtures are permitted by this Specification, depending upon the detail requirements of the relevant section.

2) Requirements for deformation resistance as assessed by wheel tracking performance (WTR) are in accordance with PD6691 Appendix D, Table D.2 and the note to that table.

A2.2.1 Surface Course Mixtures

The required performance properties are to be set by agreement with the Authority. Some Authorities, e.g., Transport Scotland, will generally require the use of:

HAPAS certificated Thin Surface Course Systems, e.g., TSCS 14 or TSCS 10.

Where the Authority requires the use of generic SMA mixtures the SMA surface course mixture shall match the existing nominal size unless otherwise agreed.

1) Roads Type 0 and 1

The permitted mixtures are:

a) SMA 14 surf PMB WTR 2

b) SMA 14 surf 40/60 WTR 2

c) SMA 10 surf PMB WTR 2

d) SMA 10 surf 40/60 WTR 2

Alternative permitted mixtures subject to the Authority's approval are:

e) SMA 6 surf PMB WTR 2

f) SMA 6 surf 40/60 WTR 2

2) Roads Type 2, 3 and 4

The permitted SMA mixtures are:

a) SMA 14 surf PMB or 40/60 or 70/100 WTR 1 or 2

b) SMA 10 surf PMB or 40/60 or 70/100 WTR 1 or 2

Alternative permitted mixtures subject to the Authority's approval are:

c) SMA 6 surf PMB or 40/60 or 70/100 WTR 1 or 2

(see Section S6.4.2)

3) Footways, Footpaths and Cycle Tracks

The permitted surface course mixtures, unless advised otherwise by the Authority, shall be:

a) SMA 6 surf 40/60

b) SMA 6 surf 70/100

c) SMA 6 surf 100/150

A2.2.2 SMA Binder Course Mixtures

1) Roads Type 0 and 1

The preferred SMA binder course mixture shall be SMA 20 bin 40/60 WTR 2.

Alternative permitted mixtures shall be SMA 14 bin 40/60 WTR 2.

2) Roads Type 2, 3 and 4

The preferred SMA binder course mixtures shall be:

a) SMA 20 bin 40/60 WTR 1 or SMA 20 bin 70/100 WTR 1.

b) Openings up to 500 mm width - as a) or SMA 14 bin 40/60 WTR 1 or SMA 14 bin 70/100 WTR 1.

A2.3 Asphalt Concrete Mixtures

1) All asphalt concrete shall conform to BS EN 13108-1. Conformity shall be established in accordance with BS EN 13108-20 and BS EN 13108-21. The following coated mixtures to BS EN 13108-1 and PD 6691 are permitted by this Specification depending upon the detailed requirements of the relevant section.

2) Where the existing mixture is HDM (Heavy Duty Macadam to the now superseded BS 4987-1) or HMB (High Modulus Base) and the Authority requires the reinstatement to be completed using a similar mixture, the Authority shall notify the Undertaker accordingly.

3) Requirements for deformation resistance as assessed by wheel tracking performance (WTR) are in accordance with PD6691 Appendix B, Table B.4 and the note to that table.

A2.3.1 Surface Course Mixtures

1) All Road Types

The coated surface course mixtures to PD 6691 shall be AC10 close surf 100/150.

2) Footways, Footpaths and Cycle Tracks

a) The preferred coated surface course mixtures shall be AC 6 dense surf 100/150 or AC 6 dense surf 160/220.

b) The preferred mixture may be replaced by other agreed, alternative materials where the existing surface is a coated mixture to the now superseded BS 4987 or current PD 6691 of aggregate size significantly finer than 6 mm nominal size, see Section S8.3 3.

A2.3.2 Binder Course Mixtures

1) Road Type 0 & 1

The preferred binder course mixture to PD 6691 shall be AC 20 dense bin 40/60 WTR 2.

2) Road Types 2, 3 & 4

The preferred binder course mixture to PD 6691 shall be AC 20 dense bin 100/150 WTR 2.

3) Footways, Footpaths and Cycle Tracks

The preferred binder course mixture shall be AC 20 dense bin 100/150 or AC 20 dense bin 160/220.

A2.4 Cold-lay Surfacing Materials

A2.4.1 Permanent Cold-lay Surfacing Materials (PCSMs)

1) Only PCSMs with a current HAPAS certificate shall be used for the permanent reinstatement of openings.

PCSMs shall be stored, transported, handled and used strictly in accordance with the manufacturer's requirements contained in the HAPAS certificate for that material.

Approved PCSMs, laid and compacted in accordance with the HAPAS certificate may be used in substitution for any permitted equivalent bituminous material type, e.g., an SMA, AC etc., at the discretion of the Undertaker, as follows:

a) Permanent Cold-lay Surfacing Material (PCSM), at any position, in all reinstatements in footways, footpaths and cycle tracks.

b) Permanent Cold-lay Binder Course (PCBC) in all reinstatements in Type 3 & 4 roads.

c) Permanent Cold-lay Surface Course (PCSC) in all reinstatements in Types 3 & 4 roads.

2) The required thickness of the PCSM in a), b) & c) shall be as stated in the HAPAS certificate.

3) Whenever a potential PCSM binder has begun a HAPAS PCSM Approval Trial, regardless of aggregate or material formulation under trial, then any material manufactured using that binder shall be considered to be an approved Deferred Set Material to PD 6691 for interim use only, with immediate effect.

A2.4.2 Deferred Set Mixtures (DSMs)

1) Deferred set coated mixtures shall be in accordance with PD 6691 and shall be AC 6 dense surf 160/220 DS (6 mm Surface Course) or AC 10 close surf 160/220 DS (10 mm Surface Course) or AC 20 dense bin 160/220 DS (20 mm dense Binder Course).

The binder grade & amount of flux oil may need to be amended as necessary to meet the performance requirements for surfacing mixtures for the duration of the interim reinstatement period. Advice on this is contained in PD 6691 Appendix B.2.3.

The binder viscosity should be adjusted to give approximately the equivalent to 10 days deferred set.

2) Deferred set coated mixtures can be used at any position, in all interim and immediate reinstatements, but are not permitted within permanent reinstatements.

A2.5 Structural Layer Thickness Tolerances

1) Several individual layers of material, commonly termed "lifts", may be required to reinstate a structural layer.

2) The thickness of each complete structural layer is specified as a nominal value.

3) The lower tolerance for the thickness of a structural layer shall be as follows:

a) -5 mm for the surface course

b) -10 mm for any other structural layer comprising bound material

c) -20 mm for any other structural layer comprising unbound material

4) The upper tolerance for a structural layer thickness is not subject to any restriction although an excessive thickness of surface course is not expected. Where large thicknesses of surface course are used:

a) the requirements for compacted lift thicknesses under Appendix A2.6 shall be met, as shall the in-situ air-voids through the full depth of the as-laid surface course layer, as set out in Section S10.2.3.

b) the required combined binder and base course material thickness is still required, unless the binder course mixture is replaced with surface course mixture, as permitted by Appendix A2.0.1(1) and A2.0.2(1).

c) the surface profile performance requirements set out in Section S2.2 shall not be exceeded.

5) The combination of permitted tolerances for the thickness of each structural layer of bituminous and/or cement bound mixtures shall not result in any of the following:

a) An overall reduction in thickness of the bound pavement, excluding the sub-base, of more than 15 mm from the specified nominal thickness in a road, subject to an absolute minimum of 100 mm of bound materials.

b) An overall reduction in the thickness of the bound pavement, excluding the sub-base, of more than 10 mm from the specified nominal thickness in a footway, subject to an absolute minimum of 60 mm of bound materials.

c) A non-compliance with the Specification if the combined thickness of the relevant layers equals or exceeds that of the Specification requirements, provided that each individual lift meets the thickness requirements of Tables A2.1 or A2.2 and the bituminous mixtures meet the void requirements of S10.2.3.

A2.6 Compacted Lift Thickness

The compacted thickness of all individual lifts of reinstatement mixtures, within all reinstatement structural layers, shall be in accordance with the following requirements:

A2.6.1 Bituminous Mixtures

The compacted thickness of all individual 'lifts' of bituminous mixtures shall be in accordance with Table A2.1.

Table A2.1 Compacted Lift Thickness (mm) - Bituminous Mixtures
Compacted Lift Thickness (mm)
Material Type PD 6691 Reference Minimum at any point Nominal Lift Thickness Maximum at any point
6mm DSC AC 6 dense surf 15 20 - 30 40
10mm CGSC AC 10 close surf 25 30 - 40 50
15/10 HRA HRA 15/10 F surf 25 30 50
30/14 HRA HRA 30/14 F surf
HRA 30/14 C surf
35 40 50
35/14 HRA HRA 35/14 F surf HRA 35/14 C surf 45 50 60
6mm SMA SMA 6 surf 15 20 - 40 45
10mm SMA SMA 10 surf 20 25 - 50 55
14mm SMA SMA 14 surf 30 35 - 50 55
10mm Porous Asphalt No reference* 25* 30 - 35* 40*
20mm Porous Asphalt No reference* 40* 45 - 60* 65*
50/20 HRA BC HRA 50/20 bin 40 45 - 80 100
60/20 HRA BC HRA 60/20 bin 40 45 - 80 100
14mm SMA BC SMA 14 bin 25 30 - 60 65
20mm SMA BC SMA 20 bin 40 50 - 100 110
20 mm DBC AC 20 dense bin 40 50 - 100 110

* The use of porous asphalt is now very limited in the UK except for specialist uses such as sustainable drainage systems. Where porous asphalt surfaces are encountered refer to S6.4.5.3. (BS EN 13108 - 7 contains specifications for this group of asphalts and guidance on the appropriate material should be obtained from the Authority).

A2.6.2 Non-Bituminous Materials

The compacted thickness of all individual 'lifts' of non-bituminous materials shall be in accordance with Table A2.2.

Table A2.2 - Compacted Lift Thickness - Non-Bituminous Materials
Material Compacted Lift Thickness (mm)
Minimum at any point Nominal Lift Thickness Maximum at any point
CBGM B 75 100 to 150 200
C25/30 Concrete 100 As Required As Existing
C32/40 Concrete 100 As Required As Existing
GSB1 75 100 to 150 200
Classes A & B 75 100 to 150 200
Classes C & D 75 100 to 150 200
SMF-A & SMF-B 75 100 to 150 200
SMF-C & SMF-D 75 100 to 150 200

A2.7 Bituminous Laying Temperatures

The laying temperatures for bituminous mixtures shall be in accordance with Table A2.3.

Table A2.3 - Laying Temperatures - Bituminous Materials
Material Binder Grade Maximum Temperature at any Stage (ºC) Minimum Temperatures (ºC)
Arrival Minimum Rolling#
CGSC 100/150 170 120 95
DSC 160/220 170 110 85
DBC 40/60 190 130 100
70/100 180 125 95
100/150 170 120 90
160/220 170 110 80
HRA SC# 40/60 190 140 110
70/100 180 125 90
100/150 170 120 85
HRA BC 40/60 190 130 105
70/100 180 125 90
100/150 170 120 85
SMA SC 40/60 200 130 100
SMA BC 70/100 180 125 90
100/150 170 120 85
Porous 125 135 110 85
Asphalt 190 145

Notes to Table A2.3:

1 = In the lorry within 30 minutes after arrival on site.
2 For coated slag mixtures temperatures may be 10ºC lower than the recommended values.
3 Greater compactive effort may be required to achieve an acceptable air voids ratio as the temperature approaches the lower limit.
4 # = See table A2.4 for the final rolling temperatures when chippings are applied to HRA surface courses.

Table A2.4 - Final Rolling Temperatures - HRA
Binder Grade Minimum temperature (°C) at completion of rolling
40/60 85
70/100 80
100/150 75

Note: When using modified bitumen or additives, different temperatures might be applicable.

A2.8 Identification of Structural Layers

A2.8.1 Road Structures

1) For the purposes of defining permissible material options, layer thickness etc, this Specification classifies road structures as being of flexible, composite, rigid or modular design. The road structures assumed to be representative of each of these designs are shown in Figure A2.1. For each design, a typical reinstatement structure, identifying the principal structural layers, is also shown.

Figure A2.1

2) Permitted materials and layer thickness for road structures are specified as follows:

a) Flexible Design - see Appendix A3.0 to A3.4

b) Flexible Sub-structure - see Appendix A3.5

c) Composite Design - see Appendix A4.0 to A4.3

d) Composite Sub-structure - see Appendix A4.4 to A4.5

e) Rigid Design - see Appendix A5.0 to A5.2

f) Modular Design - see Appendix A6.1 to A6.3

3) All layer thicknesses are in millimetres.

A2.8.2 Footway, Footpath and Cycle Track Structures

1) For the purposes of defining permissible material options, layer thickness, etc. this Specification classifies footway, footpath and cycle track structures as being of flexible, rigid or modular design. The structures assumed to be representative of each of these designs are shown in Figure A2.2. For each design, a typical reinstatement structure, identifying the principal structural layers, is also shown.

2) Permitted materials and layer thickness for footway, footpath and cycle track structures are specified as follows:

a) Flexible Design see Appendix A7.1

b) Rigid Design see Appendix A7.2

c) Modular Design see Appendix A7.3.

3) All layer thicknesses are in millimetres.

Figure A2.2

A2.9 Key to Materials

1) For the purposes of defining the main material options, layer thickness, etc. required by this Specification, Appendices A3 to A7, inclusive, show the principal structural layers within cross-sections of typical reinstatement designs in each of the main surface categories. Materials are denoted by the symbols in Table A2.5.

2) Proprietary asphalt materials are not included in Table A2.5, given their specialist and limited application, an example being flowable mastic asphalts, which may be used in footway surface courses and access surrounds to larger apparatus in roads.

3) ARMs are not shown, given the wide range of options and material variations.

Table A2.5

A2.10 Key to Reinstatement Methods

Sections S6.1, S7.1 and S8.1 set out the permissible reinstatement methods for all of the main types of construction categories covered by the Specification. Appendices A3 to A7, inclusive, indicate different materials and material thicknesses for each permissible reinstatement method, which may also vary between different Road Categories. Table A2.6 summarises these permissible reinstatement methods.

Table A2.6

A2.11 Summarised Selection Process for Hot Lay Flexible Materials

Specific to the hot-lay reinstatement of flexible roads and footways (including footpaths and cycle tracks), different parts of the Specification set out the following criteria:

  • overall class, layer designation and mixture design for Hot Rolled Asphalts, Stone Mastic Asphalts and Asphalt Concretes (A2.1 to A2.3);
  • different thicknesses of mixture layers (A3 and A7);
  • specific requirements and limitations for surface courses (Sections S6.4 and S8.3).

The overall process for selecting the correct materials to reinstate flexible roads and footways is particularly more complex at the reinstatement design selection stage. Figure S0.1 provides a generic overview of this process, but to assist practitioners, Figures A2.3, A2.4 and A2.5 respectively set out the summarised overall processes specific to:

  • Types 0 and 1 Flexible Roads
  • Types 2, 3 and 4 Flexible Roads
  • Flexible Footways, Footpaths and Cycle Tracks

Figures A2.3

Figures A2.3

Figures A2.4

Figures A2.4

Figures A2.5

Figures A2.5


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