Quality manual for hydraulically bound mixtures - Wrap

Notes for guidance

Quality manual for hydraulically

bound mixtures

This manual provides guidance on the selection, design and quality production of hydraulically bound mixtures through a factory production control system that is compliant with harmonised British and European standards.

Project code: MRF106 ISBN: [Add reference]

Research date: August 2008 to March 2009 Date: August 2009

WRAP helps individuals, businesses and

local authorities to reduce waste and

recycle more, making better use of

resources and helping to tackle climate

change.

Document reference: WRAP, 2009, Quality manual for hydraulically bound mixtures: Notes for guidance. (WRAP Project

MRF106). Report prepared by J Edwards, J Kennedy and P Edwards. Banbury, WRAP

Written by: J Edwards (Scott Wilson Ltd), J Kennedy (JK Pavement Consulting Ltd) and

P Edwards (Lafarge A&C UK)

Front cover photography: Mobile mixing plant producing HBM on construction site (courtesy of The Independent Stabilising Company Ltd).

WRAP and Scott Wilson Ltd believe the content of this report to be correct as at the date of writing. However, factors such as prices, levels of recycled content and

regulatory requirements are subject to change and users of the report should check with their suppliers to confirm the current situation. In addition, care should be taken

in using any of the cost information provided as it is based upon numerous project-specific assumptions (such as scale, location, tender context, etc.).

The report does not claim to be exhaustive, nor does it claim to cover all relevant products and specifications available on the market. While steps have been taken to

ensure accuracy, WRAP cannot accept responsibility or be held liable to any person for any loss or damage arising out of or in connection with this information being

inaccurate, incomplete or misleading. It is the responsibility of the potential user of a material or product to consult with the supplier or manufacturer and ascertain

whether a particular product will satisfy their specific requirements. The listing or featuring of a particular product or company does not constitute an endorsement by

WRAP and WRAP cannot guarantee the performance of individual products or materials. This material is copyrighted. It may be reproduced free of charge subject to the

material being accurate and not used in a misleading context. The source of the material must be identified and the copyright status acknowledged. This material must

not be used to endorse or used to suggest WRAP’s endorsement of a commercial product or service. For more detail, please refer to WRAP’s Terms & Conditions on its

web site: www.wrap.org.uk

Quality manual for hydraulically bound mixtures 1

Contents

1.0 Stage 1: HBM selection............................................................................................................... 5 2.0 Stage 2: Constituent selection ................................................................................................... 6 3.0 Stage 3: HBM design................................................................................................................... 7 4.0 Stage 4: HBM production............................................................................................................ 8

4.1 Stage 4a: Aggregate processing ...........................................................................................9 5.0 Stage 5: HBM storage ............................................................................................................... 10 6.0 Stage 6: HBM application ......................................................................................................... 11 Appendix A: Tables to aid HBM selection ............................................................................................. 12 Appendix B: HBM properties................................................................................................................. 14

Figures

Figure 1: Overview of the process for producing an HBM ...............................................................................4 Figure 2: HBM production ...........................................................................................................................8 Figure 3: Soil and aggregate process options depending on source.................................................................9

Tables

Table 1: Suggested HBM production choices .................................................................................................8


Glossary

ABS Air-cooled blastfurnace slag

ASS Air-cooled steel slag

BS British standard

CBGM Cement bound granular mixture

CBM Cement bound material

CBR California bearing ratio

Compacity A theoretical density requirement used to maximise density & limit air voids

DMRB Design manual for roads and bridges

EN European Norm, known as a European standard

ENV A European pre-standard

FA

Fly ash, also known in the UK as pulverised-fuel ash (PFA). There are 2 types: siliceous

fly ash which results from the burning of low sulfate coals and is a pozzolan; and

calcareous fly ash which results from the combustion of high sulfate coals and is both

pozzolanic and hydraulic.

FABM Fly ash bound mixture

GBS

Granulated blastfurnace slag, a slow setting and hardening (or latent hydraulic) binder

which can be ground to enhance its hydraulic potential. Depending on the degree of

grinding, GBS can be designated as partially ground (PGBS) or ground (GGBS).

Gypsum Calcium sulfate dihydrate [CaSO4.2H2O]

HBM Hydraulically bound mixture

HRB Hydraulic road binder, a factory produced hydraulic binder blended specifically for HBM

use

HRBBM Hydraulic road binder bound mixture

Hydraulic binder A material that sets and hardens with water. Examples of hydraulic binders include;

cement, calcareous FA and HRB

IBI Immediate bearing index, a measure of traffickability for fresh HBM

Lime Quick lime [CaO] or hydrated lime [Ca(OH)2] (also known as the UK as slaked lime); this

does not refer to agricultural lime (ground CaCO3) which is inert.

MCHW Manual of contract documents for highway works

Pozzolan A material that, when combined with lime, sets and hardens with water

Rc Resistance in compression, also known as compressive strength

Rit Resistance in indirect tension, also known as indirect tensile strength or Brazilian split

cylinder test

Rt Resistance in direct tension, also known as direct tensile strength

SBM Slag bound mixture

SC Soil treated with cement

SFA Soil treated with fly ash

SHRB Soil treated with HRB

SHW Specification for highway works, Volume 1 of the MCHW – also known as MCHW1

SL Soil treated with lime

SROH Specification for the reinstatement of openings in highways

SS Soil treated with slag


Table of Standards

Standard number Standard title

BS EN 13242 Aggregates for unbound and hydraulically bound materials for use in civil engineering work and road construction.

BS EN 13285 Unbound mixtures. Specifications.

BS EN 13286-1 Unbound and hydraulically bound mixtures – Part 1: Test methods for laboratory reference density and water content – Introduction, general requirements and sampling.

BS EN 13286-2 Unbound and hydraulically bound mixtures – Part 2: Test methods for the determination of the laboratory reference density and water content – Proctor compaction.

BS EN 13286-3 Unbound and hydraulically bound mixtures – Part 3: Test methods for laboratory

reference density and water content – Vibrocompression with controlled parameters.

BS EN 13286-4 Unbound and hydraulically bound mixtures – Part 4: Test methods for laboratory reference density and water content – Vibrating hammer.

BS EN 13286-5 Unbound and hydraulically bound mixtures – Part 5: Test methods for laboratory reference density and water content – Vibrating table.

BS EN 13286-40 Unbound and hydraulically bound mixtures – Part 40: Test method for the determination

of the direct tensile strength of hydraulically bound mixtures.

BS EN 13286-41 Unbound and hydraulically bound mixtures – Part 41: Test method for the determination of the compressive strength of hydraulically bound mixtures.

BS EN 13286-42 Unbound and hydraulically bound mixtures – Part 42: Test method for the determination of the indirect tensile strength of hydraulically bound mixtures.

BS EN 13286-43 Unbound and hydraulically bound mixtures – Part 43: Test method for the determination

of the modulus of elasticity of hydraulically bound mixtures.

BS EN 13286-47 Unbound and hydraulically bound mixtures – Part 47: Test method for the determination of the California bearing ratio: immediate bearing index and linear swelling.

BS EN 13286-50 Unbound and hydraulically bound mixtures – Part 50: Method for the manufacture of test specimens of hydraulically bound mixtures using Proctor equipment or vibrating

table compaction.

BS EN 13286-51 Unbound and hydraulically bound mixtures – Part 51: Method for the manufacture of

test specimens of hydraulically bound mixtures by vibrating hammer compaction.

BS EN 13286-52 Unbound and hydraulically bound mixtures – Part 52: Method for the manufacture of

test specimens of hydraulically bound mixtures using vibrocompression.

BS EN 13286-53 Unbound and hydraulically bound mixtures – Part 53: Method for the manufacture of test specimens of hydraulically bound mixtures by axial compression.

BS EN 14227-1 Hydraulically bound mixtures. Specifications. Cement bound granular mixtures.

BS EN 14227-2 Hydraulically bound mixtures. Specifications. Slag bound mixtures.

BS EN 14227-3 Hydraulically bound mixtures. Specifications. Fly ash bound mixtures.

BS EN 14227-4 Hydraulically bound mixtures. Specifications. Fly ash for hydraulically bound mixtures.

BS EN 14227-5 Hydraulically bound mixtures. Specifications. Hydraulic road binder bound mixtures.

BS EN 14227-10 Hydraulically bound mixtures. Specifications. Soil treated by cement.

BS EN 14227-11 Hydraulically bound mixtures. Specifications. Soil treated by lime.

BS EN 14227-12 Hydraulically bound mixtures. Specifications. Soil treated by slag.

BS EN 14227-13 Hydraulically bound mixtures. Specifications. Soil treated by hydraulic road binder.

BS EN 14227-14 Hydraulically bound mixtures. Specifications. Soil treated by fly ash.

BS EN 197-1 Cement: Composition, specifications and conformity criteria of common cements.

BS EN 933-1 Tests for geometrical properties of aggregates – Part 1: Determination of particle size

distribution – Sieving method.

ENV 13282 Hydraulic road binders – Composition, specifications and conformity criteria.

PD 6682-6 Aggregates. Aggregates for unbound and hydraulically bound materials for use in civil engineering works and road construction. Guidance on the use of BS EN 13242.


This manual outlines the process for the selection, design and quality production of hydraulically bound mixtures

(HBMs). It is written to provide guidance to HBM producers and those involved in specifying and auditing HBM

production. The focus of the manual is on mix-in-plant HBM production, also known as ex situ, plant-mixed, hub

recycled and ready-mix HBM production. Where appropriate, guidance in this manual includes integration of the

waste recovery process for recycled aggregate into HBM production.

HBMs are versatile products which offer benefits in the efficient use of materials; including the potential to

increase the value of the material being recycled (up-cycling), and the ability to consume a range of feedstocks -

including soils and aggregates. HBMs can be designed for almost all projects and applications, and to utilise

locally available, cost effective constituents. The importance of HBM design highlights that HBM production is only

one stage within the overall production process of an HBM (Figure 1). The Sections of this manual outline the

stages of the overall production process, with detailed guidance contained in Appendices.

Quality assurance of HBMs is achieved by initial development of a robust mixture design, which ensures that the

HBM is fit for purpose, and the subsequent application of production control, suitable storage and accompanying

guidance/training for the application. It is the responsibility of the producer to demonstrate that the HBM has

been produced in a consistent manner using necessary process controls. A template quality management

scheme1, based upon the factory production control requirements of BS EN 14227 and incorporating the

principles of the WRAP Quality Protocol for the production of aggregate from inert waste2 is also available from

the WRAP website.

Figure 1: Overview of the process for producing an HBM

1 WRAP, 2009, Template quality management scheme for the production of a hydraulically bound mixture (WRAP project MRF 106). Report prepared by J Edwards. Banbury, WRAP. Available on line via www.wrap.org.uk

2 WRAP. 2005. The Quality Protocol for the production of aggregates from inert waste. Available on line via www.aggregain.org.uk/quality/quality_protocols/

Stage 3: HBM Design

Design HBM to comply with appropriate standards and specifications.

Stage 1: HBM Selection

HBM selection will depend on the specification for use, the vicinity and availability of constituents to be exploited,

and other market factors.

Stage 4: HBM Production

In accordance with factory production control BS EN 14227.

Production may also include aggregate processing/ recovery depending on source (Stage 4a).

Stage 5: HBM Storage

Ensure the material is suitably protected from the elements to maintain optimum water content and used within the

product shelf life (only applicable to HBMs that have a shelf life).

Stage 6: HBM Application

The product should be used within the recommended shelf life and installed in accordance with the manufacturer’s

recommendations or appropriate specification.

Stage 2: Constituent Selection

Test aggregate or soil in accordance with BS EN 13242 and declare property classes.

Recycled aggregate must conform to the WRAP Quality Protocol1

Select HBM properties and constituent

proportions

Conduct laboratory testing to confirm

design


1.0 Stage 1: HBM selection The selection of the type of HBM (and the selection of the appropriate BS EN) is based on whether a particular

market or specification is to be satisfied or whether the production process is being established to exploit a

source(s) of possible constituents for HBM. The latter will dictate the type of HBM that can be produced and thus

the market of specification that can be targeted. The specific HBM type will be a function of the particle size

distribution of the mixture and the selected hydraulic binder. The hydraulic constituents covered by the BS ENs

are; cement, slag, fly ash, lime and hydraulic road binder (the latter being a proprietary product). It should be

noted that;

� Hydraulically bound mixtures can be made from aggregate complying with a recognised standard such as

BS EN 13242 (aggregate for unbound and hydraulically bound mixtures) or BS EN 14227-4 (specification for

fly ash). Such an HBM will then comply with mixtures included in BS EN 14227 parts 1, 2, 3 and 5 (see the

Table of standards).

� HBMs can also result from the treatment of soil or material that does not comply with the aggregate standard

but still comply with BS EN 14227, specifically parts 10 to 14 (see the Table of standards).

All recycled aggregates must be recovered in accordance with the WRAP Quality Protocol2.

Suitability of HBM for a specific application is generally based on mechanical performance (typically compressive

strength but also tensile strength and elastic modulus) and durability requirements. These requirements are

defined in specifications such as:

� BS ENs (see the Table of standards);

� Manual of contract documents for highway works3 (MCHW);

� Specification for the reinstatement of openings in highways4 (SROH).

The tables contained in Appendix A have been developed to help with the selection of mixture type. They should

enable the HBM selection to be made taking into account what has been specified or what is being targeted and

relating this to the local availability of binders, binder constituents, aggregates and soils.

3 Highways Agency, 2009, Manual of contract documents for highway works. Volume 1, Specification for highway works. The Stationery Office. Available on line via www.standardsforhighways.co.uk/mchw/vol1/index.htm

4 Highway Authorities and Utilities Committee, 2002, Specification for the reinstatement of openings in highways, Second edition. Available on line via www.dft.gov.uk/pgr/roads/network/local/streetworks/cop/roo

Stage 1: HBM Selection

Select the HBM to suit application / specification / market.

For more detail see Appendix A.


2.0 Stage 2: Constituent selection

This stage determines the properties of the aggregate which the producer wishes to exploit, or it covers the

selection of the aggregate or soil to meet the requirements of the HBM type selected in Stage 1.

Provided it complies with the selected property classes from BS EN 13242, the aggregate can be natural,

manufactured (also known as secondary) or recycled material, or a combination of these types. To achieve the

desired properties, the aggregate may have to be processed and, in the case of aggregate recycled from inert

waste, recovered in accordance with the WRAP Quality Protocol2.

Since grading is usually specified for the different HBM types, the main aggregate properties for consideration

include particle shape and hardness. These, together with the overall HBM grading, are the relevant properties to

control long term performance. They are also relevant in the case of short term performance, such as the ability

to withstand immediate traffic. However, to understand this short term performance aspect it is usually better to

examine the character of the total mixture using the immediate bearing index test, standardised in

BS EN 13286-47 and discussed in Stage 3.

Particle hardness has a significant bearing on the strength that can be achieved by the HBM and may affect the

potential market or specification to be satisfied. For example, irrespective of binder content, the strength of HBM

made with soft chalk aggregate is a function of the strength of the chalk particles and will be limited to a

maximum compressive strength class of C3/4. Thus, it would be prudent to examine issues related to aggregate

strength when considering the HBM type in Stage 1, where using a particular type of aggregate is more important

to the HBM producer than the targeted market or exact HBM type.

Aggregate particle shape and hardness classes are found in the aggregate standard, BS EN 13242. The relevant

classes should be selected / determined for the intended HBM application.

In addition, fines quality, chemical properties and physical impurities will need examination in relation to

volumetric stability and durability although, as with immediate traffickability, these are better considered by

examining the mixture (as discussed in Stage 3) and are further discussed in Appendix B. The available methods

for the determination of laboratory mechanical performance (such as compressive and tensile strength) which

have a significant bearing on long term performance are also discussed in Appendix B.

Stage 2: Constituent selection

Use BS EN 13242 (if applicable) and state the ‘no-requirement’ class where appropriate, declare aggregate

properties including: particle shape; hardness; fines content / nature; impurities and sulfates. Recover recycled aggregates in accordance with the WRAP Quality Protocol.


3.0 Stage 3: HBM design

This stage covers the design process to achieve mixture properties such as:

� strength;

� durability;

� range of suitable water content for installation;

� volumetric stability; and

� immediate use / traffickability.

If complying with a specification / design, the strength will be specified as a strength class (described in

Appendix B). For example:

� HD26/065 requires, depending on pavement layer thickness, HBM with strength classes of at least C8/10,

C9/12, or T3.

� the SROH4 requires minimum strength classes C1.5/2 or C3/4 and a maximum strength class C8/10.

If not working to a specification, the producer has to choose the strength class that they wish to offer. This will

depend on the constituents available and/or markets they wish to exploit. In this case, the producer may require

expert assistance to match binder content & strength with design issues, volume stability (ability to resist internal

disruption/expansion) and durability (water and frost resistance) requirements. Where immediate use / overlaying

/ trafficking are required, the capabilities of the fresh mixture will also need examination. Where storage either at

the production facility or elsewhere is anticipated, the properties relevant to time of actual use will need

determination. All these aspects are also discussed in Appendix B.

The effective completion of this Stage requires laboratory mixture design testing (on which guidance can be

found in the MCHW3 and in other industry guidance6,7). This testing will determine the necessary constituent

proportions, which, in accordance with BS EN 14227, will need to be declared.

5 Highways Agency, Design manual for roads and bridges, pavement foundation design. Volume 7 Section 2 Part 3 (HD 26/06), The Stationery Office.

6 Kennedy J, 2006, Hydraulically bound mixtures for pavements. Performance, behaviour, materials, mixture design, construction, control testing. CCIP-009, BCA and Concrete Centre.

7 Fly ash in highways construction, Datasheet 6.0 – 6.4, UK Quality Ash Association. Available on line at www.ukqaa.org.uk

Stage 3: HBM design

Design HBM to comply with appropriate standards and specifications.

Declare constituents and mixture proportions. Conduct laboratory testing on mixture and declare properties (probably strength class, volumetric stability,

resistance to frost, optimum water content/moisture condition value and immediate traffickability).

For more detail see Appendix B.


4.0 Stage 4: HBM production HBM production is outlined in Figure 2 and can be carried out using the mix-in-plant method in accordance with

either Clause 814 (batching by mass) or Clause 815 (batching by volume) of the MCHW3. Guidance on the

appropriateness of Clauses 814 or 815 is provided in Table 1.

Figure 2: HBM production

Table 1: Suggested HBM production choices

HBM Types to BS EN 14227 Mix-In-Plant Method From MCHW3

CBGM B, FABM 1, HRBBM 1,

SBM A, SBM B1, CBGM B Clause 814

CBGM C, FABM 2, HRBBM 2,

SBM B2 Clause 814 with aggregate batched in not less than 2 fractions

CBGM A, FABM 3 & 4,

HRBBM 3 & 4, SBM B3 & B4 Clause 814 or 815 depending on application*

FABM 5 Clause 814 or 815 depending on application*

except 814 only for ‘lime + gypsum’ binder

SC, SFA, SHRB, SS Clause 814 or 815 depending on application*

* Clause 814 is recommended for stop/start production such as HBM on a ready-mixed basis

Whether batching by mass or volume, factory production control should be exercised to demonstrate the

production of a quality and consistent product. Recommendations for a production control system are given in the

annex of BS EN 14227. The annex states that the producer should establish and maintain their policy and

procedures for production control in a quality manual that includes:

� the producer’s organisational structure relating to quality;

� control of constituents (including water) and mixtures;

� process control, calibration and maintenance;

� requirements for the handling and storage of the mixture when appropriate;

� inspection, calibration and control of the measuring equipment in the process, and laboratory testing

equipment for the mixture; and

� procedures for handling non conforming mixtures.

A template quality management scheme for HBM production is also available from WRAP.

Source Binder

To suit the selected

HBM (Stage 1) and

comply with

BS EN 14227.

Mix constituents In accordance with MCHW Clause 814 or 815 and following a production

control procedure to demonstrate quality and consistency.

Source Aggregate

To suit the selected HBM (Stage 1). Aggregate to comply with BS EN 13242 and recycled aggregate recovered in

accordance with the WRAP Quality Protocol. Fly ash to comply with BS EN 14227-4.

Add water In accordance with BS EN 14227.


4.1 Stage 4a: Aggregate processing Aggregates from natural sources may need to be crushed, screened, washed and/or blended as appropriate. This

will normally be carried out at the aggregate source but can be carried out at the HBM production facility by the

HBM producer.

Aggregates derived from inert waste must be recovered in accordance with the WRAP Quality Protocol2, and

manufactured or other industrial waste in accordance with the relevant Protocol8 or recovery procedure. Recycled

aggregates, including recycled trench arisings, can produce HBMs which comply with either BS EN 14227-1 to 3

and 5 (for aggregate mixtures) or BS EN 14227-10 to 14 (for treated soils).

In the case of BS EN 14227-10 to 14 (for treated soils), the soil may be used ‘as found’ with no intention (or the

need in most instances) to classify in accordance with BS EN 13242 (aggregates for HBMs). Alternatively, the soil

may undergo processing to meet the requirements of BS EN 13242.

Figure 3: Soil and aggregate process options depending on source

8 Waste Protocols Project, Environment Agency. Last Accessed February 2009 at http://www.environment-agency.gov.uk/business/topics/waste/32154.aspx

Wash,

screen,

blend as

appropriate.

Crush, screen, blend as appropriate.

Recover in

accordance with the

WRAP Quality

Protocol for inert

waste2.

Recover in accordance

with the appropriate

Protocol8 or procedure.

Soil Aggregate

Natural Inert waste Manufactured or

industrial waste

Classify to BS EN 13242 (or BS EN 14227-4 in the case of fly ash)

Use as found

to BS EN

14227 Parts

10 to 14


5.0 Stage 5: HBM storage Any HBM should be used before setting begins and the producer should give advice on setting times of their

products.

Where a HBM is to be stored, it is imperative that the producer has laboratory evidence of the performance

properties relevant to the time of use and that these are quoted for design purposes. In addition, samples for

compliance specimens and testing should be taken at the time of use.

Whether it is the producer or the purchaser that finds storage is necessary, the HBM should be stored under

cover and protected from wind and rain to prevent loss or gain of moisture, and protected from extreme

temperature changes to prevent deterioration.

Care should be taken to prevent segregation which can occur when a HBM is loaded on top of a conical stockpile

or in one large dump from a truck; under these circumstances the larger aggregate sizes tend to roll to the

outside and bottom. Further mixing may be required prior to placement to compensate for segregation during

storage and/or transportation.


6.0 Stage 6: HBM application It is normally the responsibility of the contractor using the material to install the HBM in accordance with the

manufacturer’s recommendations and to ensure that trained personnel are undertaking the activity in accordance

with their own quality management system.

It is good practice for the producer to provide recommendations on the installation of their HBM in different

applications to enable contractors to achieve optimum performance from the product. Recommendations may

include:

� setting times;

� strength development;

� shelf life and storage methods;

� affect of storage on properties such as strength and long term performance;

� methods of laying, compaction and protection;

� weather implications during installation, and in the short term;

� design advice for particular applications;

� site control methods and tests; and

� immediate traffickability.


Appendix A: Tables to aid HBM selection

Table A1: BS EN 14227 for HBM using aggregates from BS EN 13242

BS EN 14227: Hydraulically bound mixtures - Specifications

Part 1. Cement

bound granular

mixtures

Part 1 covers mixtures bound with cement or cement with ground granulated blastfurnace

slag added separately at the mixing stage.

Part 2. Slag

bound mixtures

Part 2 covers binder combinations based on the hardening properties of slag which results

from the manufacturing of iron and steel.

Part 3. Fly ash

bound mixtures

Part 3 covers binder combinations based on the hydraulic and/or pozzolanic properties of fly

ash from coal-fired electricity generation (also known as pulverised-fuel ash in the UK). Two

types of ash are covered: siliceous fly ash and calcareous fly ash. The type of ash depends

on the nature of the coal that is burnt in the power station.

Part 5. Hydraulic

road binder

bound mixtures

Part 5 covers hydraulic road binders. These are proprietary; factory produced finely ground

blends of cement, fly ash and or granulated blastfurnace slag usually with, but not

exclusively, small quantities of lime and gypsum.

Note that soil mixtures are specified in BS EN 14227 Parts 10 and 12 to 14.

In addition, BS EN 14227 Part 11 covers soil treated by lime

Table A2: Types and designation of HBM covered by BS EN 14227 Parts 1 to 3 and 5

BS EN 14227-

Part 1

BS EN 14227-

Part 2

BS EN 14227-

Part 3

BS EN 14227-

Part 5

Type of mixture Cement bound

granular

mixtures

Slag bound

mixtures

Fly ash bound

mixtures

Hydraulic road

binder bound

mixtures

Graded slag mixtures without

specified binder requirements SBM A1 – A5

31.5 mm wide graded mixture

(includes sand mixtures) CBGM A

31.5 mm well graded mixtures CBGM B SBM B1 FABM 1 HRBBM 1

0/20, 0/14 and 0/10 mm well

graded mixtures with compacity

requirement

CBGM C

0/20, 0/14, 0/10

SBM B2

0/20, 0/14, 0/10

FABM 2 0/20,

0/14, 0/10

HRBBM 2 0/20,

0/14, 0/10

Sand mixtures with Immediate

Bearing Index (IBI) requirement SBM B3 FABM 3 HRBBM 3

Mixtures with declared grading

and other properties if

appropriate

SBM B4 FABM 4 HRBBM 4

Treated fly ash mixture FABM 5

For the mixtures above, the quality of the aggregate used is at the discretion of the specifier / user / producer.

Since grading is specified in the relevant mixture clause, the main aggregate properties for consideration include

particle shape and hardness. These, together with grading are relevant properties for immediate traffickability.

These properties and their classes are found in the aggregate standard BS EN 13242. In addition, fines quality

and chemical and physical impurities may need consideration in relation to volumetric stability and durability

(although these are better considered by examining the HBM).

Note that soil mixtures are specified in BS EN 14227 Parts 10 to 14.


Table A3: Permitted binder constituents for HBM to BS EN 14227-Parts 1 to 3 and 5

BS EN

14227

Cement

CEM I to

CEM V

GBS Air-cooled

steel slag Lime Gypsum

Siliceous

fly ash

Calcareous

fly ash

Hydraulic

road binder

-Part 1 BS EN

197-1

GGBS to

National

regulations

N/A N/A N/A N/A N/A

HRB 22.5E or

HRB 32.5E to

ENV 13282

-Part 2 N/A

GBS or

GGBS to BS

EN 14227-2

BS EN

14227-2

BS EN

14227-11 N/R N/A N/A N/A

-Part 3 BS EN

197-1

GBS or

GGBS to BS

EN 14227-2

N/A BS EN

14227-11

BS EN

14227-3

BS EN

14227-4

BS EN

14227-4 N/A

-Part 5 N/A N/A N/A N/A N/A N/A N/A ENV 13282

CEM I = Portland cement;

CEM II = Portland-composite cement;

CEM III = blastfurnace cement;

CEM IV = pozzolanic cement;

CEM V = composite cement.

GBS = Granulated blastfurnace slag;

GGBS = Ground granulated blastfurnace slag.

HRB = Hydraulic road binder

.


Appendix B: HBM properties

The test methods of (and classes for) laboratory mechanical performance are described in Table B1. The

performance requirements should be selected from Table B1. The European test method standards for the

manufacture and testing of specimens are listed in the Table of standards.

Table B1: Laboratory mechanical performance

BS EN HBM and treated soil laboratory mechanical performance are similar. The CBGM, FABM and HRBBM

standards permit classification by either compressive strength (Rc) or the combination of direct tensile strength

(Rt) and elastic stiffness (E) - designated RtE classification. In addition to these test methods, the SBM standard

and the standards for treated soils also permit classification by CBR where appropriate. Whatever method is used,

a wide range of classes exists for each method. The specifier or user is free to select the appropriate class

depending on application.

Rc classes are designated Cxx/yy and range from C0.4/0.5 to C27/36. The first number in the notation - xx - is the

minimum compressive strength of cylinders with height/diameter (or slenderness) ratios of 2. The second number

- yy - is the minimum strength of cubes or cylinders with slenderness ratio of 1. It is important that the full

notation is always used since, if a single value is used, it will not be clear which notation it relates to.

The strength classes are slightly different for the CBGM standard compared to the other mixture standards. Those

numerically close can be deemed equivalent. Thus C8/10 for CBGM can be considered equivalent to C9/12 for

FABM.

When using the CBGM standard, it should be recognised that the notation relates to minimum characteristic

strength at 28 days using 20°C curing. In the case of the other HBM standards, the notation relates to the

minimum strength of the mixture using curing conditions and age of testing as specified in the country of use. For

example, in the MCHW3, the notation has been chosen to relate to the minimum average strength of groups of 5

specimens tested at 28 days, using 40°C curing with non-cement mixtures and 20°C with cement based mixtures,

with no individual test result being less than 85% of the characteristic strength.

The RtE classes are designated Tsuffix. The suffix ranges from 0 to 5 with performance increasing as the number

increases. In the classification, Rt refers to strength measured in direct tension. Rt can be deduced from the

indirect tensile strength (Rit) using the relationship Rt = 0.8Rit.

CBR classes are designated CBRxx/yyThe first number in the notation - xx - designates the immediate CBR (either

30 or 50) and second number - yy - the percentage change in CBR value after 28 days (either 25, 35 or 50%).

Thus, for mechanical performance purposes, the range of CBR values at 28 days will be 40 to 75.

With respect to the long term properties of volumetric stability and durability, it is possible (using aggregate

property categories from in BS EN 13242) to specify the aggregate requirements to avoid problems in this area.

However, since it is the final mixture rather than the aggregate that ultimately determines volumetric stability and

durability, it can be argued that tests on the hardened mixture are more appropriate than restrictions on the

aggregate. These mixture tests are not included in the European standards so it is recommended that the

specifier / user / producer includes relevant testing either at set up or in the project specification.

Evaluation of volumetric stability of the HBM, is normally carried out by comparing the strength of specimens

after immersion in water to the strength of non immersed specimens. Experience has found that the volumetric

stability of the HBM will be satisfactory if the loss of strength does not exceed 80%. Clause 880 in the MCHW3

describes how testing and evaluation should be carried out. This immersion comparison also checks the durability

of the hardened HBM to water.

In terms of durability to frost and, in particular, resistance to frost heave, usually HBMs can be assumed to resist

frost heave if the compressive strength of specimens with a slenderness ratio of 1 exceeds 2 or 2.5 MPa. In the

case of an HBM that will never meet this level of compressive strength (for example, some treated clays), an

indirect tensile strength in excess of 0.2 or 0.25 MPa has been found satisfactory.


It should be noted that strength (and associated volumetric stability and durability) is particularly dependant on

the aggregate that is to be processed - such that the poorer the properties of the aggregate the lower the likely

achievable strength class. Thus for highway bases (HD26/065), good quality aggregate is required to meet the

requirement for relatively high strength classes. For trench reinstatements (SROH4) and pavement foundations

(given in the Highways Agency’s IAN739), where lower strengths are specified, lower quality aggregate and soils

can be used.

The various methods of specimen manufacture are covered by BS EN 13286 Parts 50 to 53, to accommodate the

different shapes and density of specimens. Each method of manufacture will yield a different strength; hence, it

is important that the specifier / user / producer specifies what is required. Common UK practice is:

� for Rc classification, either cylindrical or cubic specimens compacted to refusal by a vibrating hammer;

� for RtE classification, cylindrical specimens compacted to refusal by vibrating hammer;

� CBR classification is rarely used.

Short term concerns of immediate use or traffickability are normally addressed by ensuring that the HBM is well

graded, that the aggregate is hard, and it consists of at least 50% crushed particles. Alternatively, or for other

HBM where these aggregate factors do not apply, the Immediate Bearing Index (IBI) of the mixture may be

declared. A range of IBI values for immediate trafficking of a variety of treated soils and mixtures is given in

industry guidance10,11.

The capability to withstand trafficking without detriment to long term performance can be checked by using a

pneumatic tyred roller (PTR) for finishing rolling. Provided there is a load of at least 3 tonnes on each pneumatic

tyre and the deformation without stress cracks under the tyre is less than approximately 10 mm after at least 10

passes of the roller, the HBM layer can usually be considered to be able to support immediate traffic.

Mixture design advice can be found in the MCHW3 and other industry guidance6,7.

9 Highways Agency’s Interim advice note 73/09 Design guidance for road pavement foundations (Draft HD25), The Stationery Office. Available on line at www.standardsforhighways.co.uk/ians/index.htm.

10 Britpave. Stabilised soils as subbase or base for roads and other pavements. Technical data sheet. Available on line at www.soilstabilisation.org.uk/assets/pdf/stabilised_soils.pdf.

11 Britpave. Immediate trafficking of cement bound materials. Technical report. Available on line at www.soilstabilisation.org.uk/assets/pdf/5413%20CBM%20Traffic.pdf.

www.wrap.org.uk/construction

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Quality manual for hydraulically bound mixtures - Wrap

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