Quality manual for hydraulically bound mixtures

Transcription

1 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

2 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:

3 Contents Stage 1: HBM selection... 5 Stage 2: Constituent selection Stage 3: HBM design Stage 4: HBM production Stage 4a: Aggregate processing...9 Stage 5: HBM storage Stage 6: HBM application Appendix A: Tables to aid HBM selection Appendix B: HBM properties 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 Quality manual for hydraulically bound mixtures 1

4 Glossary ABS ASS BS CBGM CBM CBR Compacity DMRB EN ENV FA FABM GBS Air-cooled blastfurnace slag Air-cooled steel slag British standard Cement bound granular mixture Cement bound material California bearing ratio A theoretical density requirement used to maximise density & limit air voids Design manual for roads and bridges European Norm, known as a European standard A European pre-standard 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. Fly ash bound mixture 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 [CaSO 4.2H 2 O] HBM HRB HRBBM Hydraulic binder IBI Lime MCHW Pozzolan R c R it R t SBM SC SFA SHRB SHW SL SROH SS Hydraulically bound mixture Hydraulic road binder, a factory produced hydraulic binder blended specifically for HBM use Hydraulic road binder bound mixture A material that sets and hardens with water. Examples of hydraulic binders include; cement, calcareous FA and HRB Immediate bearing index, a measure of traffickability for fresh HBM 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 CaCO 3 ) which is inert. Manual of contract documents for highway works A material that, when combined with lime, sets and hardens with water Resistance in compression, also known as compressive strength Resistance in indirect tension, also known as indirect tensile strength or Brazilian split cylinder test Resistance in direct tension, also known as direct tensile strength Slag bound mixture Soil treated with cement Soil treated with fly ash Soil treated with HRB Specification for highway works, Volume 1 of the MCHW also known as MCHW1 Soil treated with lime Specification for the reinstatement of openings in highways Soil treated with slag Quality manual for hydraulically bound mixtures 2

5 Table of Standards Standard number BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN BS EN ENV PD Standard title Aggregates for unbound and hydraulically bound materials for use in civil engineering work and road construction. Unbound mixtures. Specifications. Unbound and hydraulically bound mixtures Part 1: Test methods for laboratory reference density and water content Introduction, general requirements and sampling. Unbound and hydraulically bound mixtures Part 2: Test methods for the determination of the laboratory reference density and water content Proctor compaction. Unbound and hydraulically bound mixtures Part 3: Test methods for laboratory reference density and water content Vibrocompression with controlled parameters. Unbound and hydraulically bound mixtures Part 4: Test methods for laboratory reference density and water content Vibrating hammer. Unbound and hydraulically bound mixtures Part 5: Test methods for laboratory reference density and water content Vibrating table. Unbound and hydraulically bound mixtures Part 40: Test method for the determination of the direct tensile strength of hydraulically bound mixtures. Unbound and hydraulically bound mixtures Part 41: Test method for the determination of the compressive strength of hydraulically bound mixtures. Unbound and hydraulically bound mixtures Part 42: Test method for the determination of the indirect tensile strength of hydraulically bound mixtures. Unbound and hydraulically bound mixtures Part 43: Test method for the determination of the modulus of elasticity of hydraulically bound mixtures. Unbound and hydraulically bound mixtures Part 47: Test method for the determination of the California bearing ratio: immediate bearing index and linear swelling. 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. Unbound and hydraulically bound mixtures Part 51: Method for the manufacture of test specimens of hydraulically bound mixtures by vibrating hammer compaction. Unbound and hydraulically bound mixtures Part 52: Method for the manufacture of test specimens of hydraulically bound mixtures using vibrocompression. Unbound and hydraulically bound mixtures Part 53: Method for the manufacture of test specimens of hydraulically bound mixtures by axial compression. Hydraulically bound mixtures. Specifications. Cement bound granular mixtures. Hydraulically bound mixtures. Specifications. Slag bound mixtures. Hydraulically bound mixtures. Specifications. Fly ash bound mixtures. Hydraulically bound mixtures. Specifications. Fly ash for hydraulically bound mixtures. Hydraulically bound mixtures. Specifications. Hydraulic road binder bound mixtures. Hydraulically bound mixtures. Specifications. Soil treated by cement. Hydraulically bound mixtures. Specifications. Soil treated by lime. Hydraulically bound mixtures. Specifications. Soil treated by slag. Hydraulically bound mixtures. Specifications. Soil treated by hydraulic road binder. Hydraulically bound mixtures. Specifications. Soil treated by fly ash. Cement: Composition, specifications and conformity criteria of common cements. Tests for geometrical properties of aggregates Part 1: Determination of particle size distribution Sieving method. Hydraulic road binders Composition, specifications and conformity criteria. Aggregates. Aggregates for unbound and hydraulically bound materials for use in civil engineering works and road construction. Guidance on the use of BS EN Quality manual for hydraulically bound mixtures 3

6 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 scheme 1, based upon the factory production control requirements of BS EN and incorporating the principles of the WRAP Quality Protocol for the production of aggregate from inert waste 2 is also available from the WRAP website. Figure 1: Overview of the process for producing an HBM 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 2: Constituent Selection Test aggregate or soil in accordance with BS EN and declare property classes. Recycled aggregate must conform to the WRAP Quality Protocol 1 Stage 3: HBM Design Design HBM to comply with appropriate standards and specifications. Select HBM properties and constituent proportions Conduct laboratory testing to confirm design Stage 4: HBM Production In accordance with factory production control BS EN 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. 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 2 WRAP The Quality Protocol for the production of aggregates from inert waste. Available on line via Quality manual for hydraulically bound mixtures 4

7 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 (aggregate for unbound and hydraulically bound mixtures) or BS EN (specification for fly ash). Such an HBM will then comply with mixtures included in BS EN 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 Protocol 2. 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 works 3 (MCHW); Specification for the reinstatement of openings in highways 4 (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. Stage 1: HBM Selection Select the HBM to suit application / specification / market. For more detail see Appendix A. 3 4 Highways Agency, 2009, Manual of contract documents for highway works. Volume 1, Specification for highway works. The Stationery Office. Available on line via Highway Authorities and Utilities Committee, 2002, Specification for the reinstatement of openings in highways, Second edition. Available on line via Quality manual for hydraulically bound mixtures 5

8 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 Protocol 2. 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 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 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 (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. Quality manual for hydraulically bound mixtures 6

9 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: HD26/06 5 requires, depending on pavement layer thickness, HBM with strength classes of at least C8/10, C9/12, or T3. the SROH 4 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 MCHW 3 and in other industry guidance 6,7 ). This testing will determine the necessary constituent proportions, which, in accordance with BS EN 14227, will need to be declared. 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 Highways Agency, Design manual for roads and bridges, pavement foundation design. Volume 7 Section 2 Part 3 (HD 26/06), The Stationery Office. Kennedy J, 2006, Hydraulically bound mixtures for pavements. Performance, behaviour, materials, mixture design, construction, control testing. CCIP-009, BCA and Concrete Centre. Fly ash in highways construction, Datasheet , UK Quality Ash Association. Available on line at Quality manual for hydraulically bound mixtures 7

10 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 MCHW 3. Guidance on the appropriateness of Clauses 814 or 815 is provided in Table 1. Figure 2: HBM production Source Binder To suit the selected HBM (Stage 1) and comply with BS EN Source Aggregate To suit the selected HBM (Stage 1). Aggregate to comply with BS EN and recycled aggregate recovered in accordance with the WRAP Quality Protocol. Fly ash to comply with BS EN Mix constituents In accordance with MCHW Clause 814 or 815 and following a production control procedure to demonstrate quality and consistency. Add water In accordance with BS EN Table 1: Suggested HBM production choices HBM Types to BS EN Mix-In-Plant Method From MCHW 3 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 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. Quality manual for hydraulically bound mixtures 8

11 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 Protocol 2, and manufactured or other industrial waste in accordance with the relevant Protocol 8 or recovery procedure. Recycled aggregates, including recycled trench arisings, can produce HBMs which comply with either BS EN to 3 and 5 (for aggregate mixtures) or BS EN to 14 (for treated soils). In the case of BS EN 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 (aggregates for HBMs). Alternatively, the soil may undergo processing to meet the requirements of BS EN Figure 3: Soil and aggregate process options depending on source Soil Aggregate Natural Inert waste Manufactured or industrial waste Wash, screen, blend as appropriate. Recover in accordance with the WRAP Quality Protocol for inert waste 2. Recover in accordance with the appropriate Protocol 8 or procedure. Use as found to BS EN Parts 10 to 14 Crush, screen, blend as appropriate. Classify to BS EN (or BS EN in the case of fly ash) 8 Waste Protocols Project, Environment Agency. Last Accessed February 2009 at Quality manual for hydraulically bound mixtures 9

12 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. Quality manual for hydraulically bound mixtures 10

13 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. Quality manual for hydraulically bound mixtures 11

14 Appendix A: Tables to aid HBM selection Table A1: BS EN for HBM using aggregates from BS EN BS EN 14227: Hydraulically bound mixtures - Specifications Part 1. Cement bound granular mixtures Part 2. Slag bound mixtures Part 3. Fly ash bound mixtures Part 5. Hydraulic road binder bound mixtures Part 1 covers mixtures bound with cement or cement with ground granulated blastfurnace slag added separately at the mixing stage. Part 2 covers binder combinations based on the hardening properties of slag which results from the manufacturing of iron and steel. 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 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 Parts 10 and 12 to 14. In addition, BS EN Part 11 covers soil treated by lime Table A2: Types and designation of HBM covered by BS EN Parts 1 to 3 and 5 BS EN Part 1 BS EN Part 2 BS EN Part 3 Type of mixture Cement bound granular mixtures Slag bound mixtures Fly ash bound mixtures BS EN Part 5 Hydraulic road binder bound mixtures Graded slag mixtures without specified binder requirements SBM A1 A 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 CBGM C SBM B2 FABM 2 0/20, HRBBM 2 0/20, graded mixtures with compacity 0/20, 0/14, 0/10 0/20, 0/14, 0/10 0/14, 0/10 0/14, 0/10 requirement Sand mixtures with Immediate Bearing Index (IBI) requirement SBM B3 FABM 3 HRBBM 3 Mixtures with declared grading and other properties if SBM B4 FABM 4 HRBBM 4 appropriate 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 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 Parts 10 to 14. Quality manual for hydraulically bound mixtures 12

15 Table A3: Permitted binder constituents for HBM to BS EN Parts 1 to 3 and 5 BS EN GBS Lime Gypsum -Part 1 -Part 2 -Part 3 Cement CEM I to CEM V BS EN N/A BS EN GGBS to National regulations GBS or GGBS to BS EN GBS or GGBS to BS EN Air-cooled steel slag Siliceous fly ash Calcareous fly ash N/A N/A N/A N/A N/A BS EN N/A BS EN BS EN Hydraulic road binder HRB 22.5E or HRB 32.5E to ENV N/R N/A N/A N/A BS EN BS EN BS EN Part 5 N/A N/A N/A N/A N/A N/A N/A ENV CEM I = Portland cement; CEM II = Portland-composite cement; CEM III = blastfurnace cement; GBS = Granulated blastfurnace slag; GGBS = Ground granulated blastfurnace slag. HRB = Hydraulic road binder CEM IV = pozzolanic cement; CEM V = composite cement.. N/A Quality manual for hydraulically bound mixtures 13

16 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 (R c ) or the combination of direct tensile strength (R t ) and elastic stiffness (E) - designated R t E 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. R c classes are designated C xx/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 MCHW 3, 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 R t E classes are designated T suffix. The suffix ranges from 0 to 5 with performance increasing as the number increases. In the classification, R t refers to strength measured in direct tension. R t can be deduced from the indirect tensile strength (R it ) using the relationship R t = 0.8R it. CBR classes are designated CBR xx/yy The 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 MCHW 3 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. Quality manual for hydraulically bound mixtures 14

17 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 (HD26/06 5 ), good quality aggregate is required to meet the requirement for relatively high strength classes. For trench reinstatements (SROH 4 ) and pavement foundations (given in the Highways Agency s IAN73 9 ), where lower strengths are specified, lower quality aggregate and soils can be used. The various methods of specimen manufacture are covered by BS EN 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 R c classification, either cylindrical or cubic specimens compacted to refusal by a vibrating hammer; for R t E 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 guidance 10,11. 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 MCHW 3 and other industry guidance 6,7. 9 Highways Agency s Interim advice note 73/09 Design guidance for road pavement foundations (Draft HD25), The Stationery Office. Available on line at 10 Britpave. Stabilised soils as subbase or base for roads and other pavements. Technical data sheet. Available on line at 11 Britpave. Immediate trafficking of cement bound materials. Technical report. Available on line at Quality manual for hydraulically bound mixtures 15

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