Model Specification for Pavement Layers made from Soil Stabilised by Lime and Hydraulic Binders BRITISH LIME ASSOCIATION 1. General This model specification describes the requirements for the constituents, composition and performance of sub-base and base layers made from soil stabilised with combinations of lime, ground granulated blast furnace slag, pulverised fuel ash, cement and hydraulic road binder. The specification relates primarily to mix-in-place treatment but can be adapted for central plant mixing. 2. Standards Lime - BS EN 459-1: 2001 Cement - BS12 Ground granulated blast furnace slag - BS6699: 1992. Fly ash - BS 3892 part 1: EN450 Hydraulic road binders - DD ENV 13282: 2000 Methods of test for stabilised soils - BS1924: 1990 3. Definitions, symbols and abbreviations PFA - pulverised fuel ash also known as (coal) fly ash. GGBS - ground granulated blast-furnace slag. HRB - hydraulic road binder (a factory blended hydraulic binder specifically for roads and pavements) HB - hydraulic binder (a material that hardens both under water and in air, when mixed with water) e.g. cement, HRB, and the lime/PFA or lime/GGBS combination. SHB - soil treated or stabilised by an hydraulic binder OMC - optimum moisture content MCV - moisture condition value 4. Constituents 4.1 Soil Soil for SHB shall be naturally occurring material, artificial material, recycled material, or a combination of these. When wet sieved, not less than 95% of the soil shall pass the 63mm sieve. Organic matter, if present, shall not adversely affect the performance of the mixture. If this exceeds 2% by weight, laboratory tests shall be carried out to confirm that the required strength can be achieved. Soil, particularly that containing or suspected of containing sulfates or other potentially disruptive material, shall be deemed suitable for treatment provided the requirements of clause 8.13 are satisfied both at laboratory mixture design stage and during construction. 4.2 Lime Lime shall be quicklime to EN459-1: 2001 and the following specification: CaO + MgO content > 80% MgO content < 10% Reactivity with water, established in accordance with EN459-2, shall achieve a temperature of at least 60 degrees C within 25 minutes. (Less reactive Quicklimes may be used providing complete hydration is ensured before final compaction.) Particle size: For in-situ treatments 100% passing a 10mm sieve and at least 95% passing a 5mm sieve or finer. Where airborne dust is less critical, such as a sealed static mixing plant, finer grades of quicklime may be used. Where a sealed mixing plant is to be used and dust is not a concern Hydrated Lime to BS EN 459-1: 2001, CL90 may be considered. The drying reaction achieved with Quicklime will not be present using Hydrated Lime. 4.3 GGBS GGBS shall comply with BS6699: 1992. 4.4 PFA PFA shall comply with BS 3892 part 1 or EN450. The Engineer may also approve dry or conditioned (wet) run-of-station ash providing recent supplier certificates indicating the physical and chemical characteristics of the material are available. Before use, conditioned PFA shall be stored for at least 3 days at minimum moisture content of 10% and screened to remove particles greater than 10mm. 4.5 HRB HRB shall comply with DD ENV 13282: 2000. 4.6 Cement Cement shall be portland cement complying with BS EN 197-1: 2000. 4.7 Water Water shall not contain components that affect the performance of the SHB. 5. Composition 5.1 SHB shall be made from constituents selected from section 4 using proportions that satisfy the requirements of this section and the performance requirements of section 8, particularly noting the requirements of sections 8.10, 8.11 and 8.12 on strength, trafficking and frost resistance respectively. 5.2 Unless otherwise agreed by the Engineer, the minimum proportions of a constituent in any mix, by dry weight of the total mix, shall be; lime 1.5%, GGBS 3%, PFA 5% (8% in the case of conditioned PFA), HRB 3% and cement 3%. 6. Method Statement 6.1 Before commencement of the main works, the contractor shall provide a full method statement. This shall specify the operational procedure for the works, site preparation, type of plant and programme. Specific details shall be supplied regarding estimated durations and intervals between the main stages of the treatment, lime amelioration stages (if applicable) and the hydraulic binder addition, curing and protection. 6.2 In particular, the method statement should specify the procedures, controls and production checks with respect to site preparation, powder spreading, pulverisation (if applicable), water addition, MCV, depth of mixing, compaction, insitu density measurement, level control, finishing rolling, curing and protection. 6.3 The method statement shall include the intended mixture proportions, the supportive data to justify the proportions, the moisture content and related MCV limits and binder additions for all stages of the work. 6.4 The method statement shall include a sample record sheet to be completed for each construction bay detailing; construction times, sample and test locations and check results for all control parameters including those in clause 6.2. 6.5 The main works shall not commence until receipt of a satisfactory method statement and record sheet. 7. Demonstration area 7.1 Prior to the commencement of the main works, the contractor shall undertake a demonstration area of at least 800m 2 conforming to his method statement. The demonstration area shall consist of at least 2 full-width bays so as to include a transverse end-of-bay joint. 7.2 The demonstration area may be accepted into the permanent works with the agreement of the Engineer. 8. Mixture Performance and Construction Requirements The frequency of tests, controls and checks shall be in accordance with 8.14. 8.1 Spread rates With the exception of conditioned PFA, which shall be spread by blade, dry powders shall be spread by purpose-made spreaders at rates high enough to avoid non-uniformity and low enough to minimise displacement by plant that traverse the area just spread. This will normally be between the ranges 8 – 20 kg/m 2 . 8.2 Amelioration Where lime is used to ameliorate (break down) cohesive soils prior to the addition of GGBS, PFA, HRB or cement, it shall be added and mixed with the soil not less than 24 hours nor more than 72 hours before the subsequent addition. For sulfate bearing cohesive soils this period shall be between 48 and 72 hours. During this period it must be ensured that any quicklime added to the soil is fully hydrated. The moisture content at this stage shall be not less than the OMC (or more than the equivalent MCV) for the lime modified mixture determined in accordance with the 2.5kg Proctor method of BS1924. 8.3 Mixing and pulverisation Mixing and pulverisation shall be carried out by one or more passes of a purpose made mixer until uniformity is achieved. In the case of amelioration of cohesive soils (8.2), the degree of pulverisation of the full depth of treatment after lime addition shall be in excess of 30%, or other agreed value, determined in accordance with BS1924. For cohesive mixtures after final mixing of the final constituent addition, the degree of pulverisation of the full depth of layer shall be in excess of 60% or other agreed value. NOTE: The measurement of the degree of pulverisation may be difficult with mixtures at or wetter than the OMC. 8.4 Depth of mixing. The depth of mixing at all relevant stages of the process shall be checked using suitable reference stations to ensure that after final trim and compaction, the final thickness of the layer is to specification. 8.5 Final water content At final compaction, the moisture content for granular mixtures shall be not less than 0.9 OMC determined in accordance with the vibrating hammer method of BS1924, and for cohesive mixtures not less than the OMC (or more than the equivalent MCV) determined in accordance with the 2.5 kg Proctor method of BS1924. 8.6 Compaction Final compaction, including finishing rolling, shall be completed within 2 hours of mixing of cement, 4 hours for GGBS and HRB, and 6 hours for PFA.Where a single powder is added over 2 operations, the time shall apply from the mixing of the first application. 8.7 Surface finish On completion of final compaction, the surface of the layer shall be well closed, free from movement under compaction plant, and free from ridges, cracks, loose material, segregated areas, pot holes, ruts and other defects. On no account is it permissible to add thin layers of material to build up areas that are low once rolling has started. 8.8 Density The full depth of the layer shall be compacted to an average density of not less than 95% of the average fresh wet density of the strength specimens made in accordance with clause 8.10. The insitu wet density shall be measured using a nuclear density gauge in accordance with BS1924: 1990. The average insitu densities shall relate to the mean of the results for one day production samples specified in Table SHB. 8.9 Sealing Immediately on completion of compaction, the surface of the layer shall be sealed with a bitumen emulsion applied at the rate of 0.5 litre/m 2 . Alternatively another approved product at an equivalent application may be used or a single surface dressing (see 8.11) to achieve a continuous and consistent seal across the whole area of the works. 8.10 Strength Strength shall be measured using samples of the mixture representing the full depth of the layer after final mixing. Groups of cubic or 1:1 cylindrical specimens representing one day’s work shall determine the average compressive strength. They shall be made in rigid plastic (HDPE) moulds and compacted to refusal within one hour of the final constituent addition in accordance with either BS1924 or using MCV apparatus. The specimens shall be sealed and cured as described in BS1924-2, section 4.1.6, using the recommendations for cement to cover SHB that contain cement and the recommendations for lime to cover SHB that do not contain cement. The strengths recorded shall be not less than 1 MPa or other specified value (see 8.11 and 8.12). NOTE 1: Whatever the age of testing and curing conditions, it should be noted that SHB made from high plasticity clays may struggle to reach compressive strengths of 1 MPa. NOTE 2: As an alternative to, or in conjunction with, compressive strength, laboratory or insitu surface stiffness can be specified. For guidance, in comparison with the above compressive strength, laboratory NAT stiffness would range upwards from 1000 MPa and, depending on age and temperature, insitu surface stiffness from 200 MPa. MCV apparatus has been found suitable for the manufacture of NAT stiffness specimens. NOTE 3: As a further alternative to compressive strength, soaked CBR testing may be employed. Typically, a CBR value of 100% may be considered equivalent to 1 MPa compressive strength. 8.11 Trafficability Unless agreed otherwise, construction plant and traffic shall not run on the layer other than to enable construction of the overlying layer. Note: Experience suggests that SHB meeting the strength level of 1 MPa specified in 8.10 should provide a sufficiently robust layer for site trafficking associated with the next layer and possibly for drainage and edge detail work. Where trafficking will be light, a specified strength as low as 0.5 MPa may suffice. Where heavy trafficking is expected then a specified strength of at least 1.5 MPa will be necessary. In the later case, consideration should be given to the application of a surface dressing. lime think 21425_specPav1_sheet 13/1/06 12:12 pm Page 1