SPECIALTY MIX 5 - COLD IN-PLACE RECYCLING

JKR/SPJ/2008
Cold in-place recycling (CIPR) is a structural pavement rehabilitation technique. It re-uses the
existing pavement materials. This technique involves scarifying, stabilising and re-laying the
recycled materials with minimal off-site hauling or mixing.

CIPR involves the processing and stabilising of the existing pavement layers without heating to
produce a rejuvenated pavement layer. There are many types of stabilising agents that can be
used in CIPR but the most common are bitumen emulsion, foamed bitumen, lime, Portland
Cement and fly ash. Stabilising agents can be injected directly into the recycler mixing chamber
while the scarifying operation is carried out, ensuring excellent mixing of the stabilizing agent
with the scarified materials. Where required, the scarified materials may be modified by the
addition of fresh aggregates and/or bitumen.
The main advantages of CIPR technique include conservation of materials and energy, full
utilisation of local materials, minimise use of new materials, reduction of traffic
disruption, improved pavement strength, and lower capital costs.

CIPR is applied to older pavements that are structurally deficient and no longer are
candidates for a simple overlay. Most pavement distresses, such as fatigue cracking,
transverse thermal cracking, reflective cracking can be successfully corrected using cold in
place pavement recycling technique. Generally, CIPR technique costs lower than full
reconstruction method.

CIPR should not be used to rehabilitate pavement that has failed due to poor
embankment or foundation support. Normally, a surfacing layer is required on top of the
recycled pavement layer
4.10 SPECIALTY MIX 5 - COLD IN-PLACE RECYCLING

4.10.1 Description

This work shall include all activities in connection with the construction of a new pavement layer using the
cold in-place recycling process to recycle material from the pavement layers of an existing road. The work
shall include;

i. breaking down and recovering material of an existing pavement using a purpose-built recycling
machine;

ii. where required, modifying the characteristics of the recovered material by the addition of
imported material;

iii. the provision and application of stabilising agents and water; and

iv. mixing, placing, compacting and shaping the recycled material to achieve a new
pavement layer.

New pavement layers shall conform to the lines, grades, thickness and typical crosssections shown on the
Drawings and/or described in detailed pavement design report and/or as required by the S.O.
4.10.2 Materials
4.10.2.1 Existing Pavement Material
Investigations carried out, together with the results of tests conducted on representative samples of materials in the
existing pavement structure, shall be detailed in pavement design report and/or issued separately by the S.O. As a minimum,
these shall include;
i. a description of the pavement structures that is/are likely to be encountered when cold in-place recycling;

ii. anticipated grading, plasticity and other relevant properties of the materials to be recycled from the
pavement layers;

iii. in-situ moisture contents measured at the time of investigation;

iv. structural and mix designs.

These information shall be supplied in good faith but any reliance placed by the Contractor on these information shall be at
his own risk, and he shall undertake his own separate testing programme to determine the conditions prevailing at the time
of construction.
Any significant deviation in the physical or mechanical properties of the material recovered by recycling that are indicative
of changes in the existing pavement shall be immediately reported to the S.O. The Contractor shall take whatever action he
deems necessary to ensure that the new pavement layer produced in the cold in-place recycling process complies with the
design requirements, unless otherwise directed by the S.O.
4.10.2.2 Imported Pavement Material

Natural material (sand, gravel, etc), crushed stone products (graded products, crusher dust, etc)
and/or salvaged Recycled Asphalt Pavements (RAP) from other sites may be required to be mixed with
the recycled material for the purposes of;

i. altering the grading of the recycled material; and/or

ii. supplementing the volume of the recycled material (e.g. for shape correction);

iii. improving the structural properties of the pavements.

The specific requirements for imported materials shall be detailed out in pavement design report
and/or as directed by the S.O.
4.10.2.3 Stabilising Agents

(a) General

All stabilising agents shall be of the quality and type specified, and the Contractor shall provide
documentary evidence to this effect when required by the S.O. Any stabilising agent that is not
satisfactory shall be rejected.

(b) Cement

Cement used in the cold in-place recycling process shall be ordinary Portland cement complying
with MS 522.

The use of any other class or type of cement shall only be considered if the Contractor can
demonstrate that it will provide a cost benefit without any technical detriment to the Works,
subject always to the written approval from the S.O.

(c) Water

Water used in the cold in-place recycling process shall be potable, clean and free of harmful
matter.
4.10.3 Mix design

4.10.3.1 General

Details regarding materials to be used, application rates of stabilising agent, type and application rate of any
required additives, any specific pre-treatment requirements and the compacted thickness of the recycled
stabilised layer shall be determined in advance of the Work.

Laboratory tests on materials sampled from the existing pavement and/or borrow areas shall be carried out to
determine the basic properties of the recycled pavement material prior to addition of stabilising agent. Samples
taken from the existing pavement material shall be representative of the material that will be recycled for the
particular section.

The preliminary laboratory testing shall form the basis for determining the feasibility of cold in-place recycling and
indicating the most appropriate method.
For sections determined as feasible for cold in-place recycling, further laboratory tests shall then be
undertaken to determine the following key parameters;

i. the volume of any additional material to be imported from specific borrow areas;

ii. the type and optimal application rate of the stabilising agent;

iii. the amount and type of any required additives.

The additional laboratory tests shall be as specified in Sub-Section 4.10.5 for each of the stabilising agents to
which this Specification apply.
4.10.3.2 Preliminary Laboratory Testing

Testing of the existing pavement material shall be undertaken and shall conform to the following
physical and mechanical quality requirements;

i. the plasticity index shall be not more than 6 for unbound material;

ii. the aggregate crushing value when tested in accordance with MS 30 shall be not more
than 25%;

iii. the flakiness index when tested in accordance with MS 30 shall be not more than 25%;

iv. the material shall have a CBR value of not less than 80% when compacted to 95% of the
maximum dry density determined in the BS 1377 Compaction Test (4.5kg rammer method)
and soaked for 4 days under a surcharge of 4.5kg;

v. the gradation shall comply with the envelope shown in Table 4.10.2.
TABLE 4.10.2: GRADATION LIMITS FOR RECYCLED LAYER MATERIAL

Sieve Size (mm) % passing

50 100
37.5 85-100
20 60-100
10 40-90
5 30-75
2.36 20-60
0.425 10-45
0.075 2-20
Compliance with the conformance requirements of Sub-Section 4.10.3.3 shall not be deemed as acceptance
for its use in cold in-place recycling. It shall be regarded as indicating potential suitability.

Non-compliance with the conformance requirements of Sub-Section 4.10.3.3 shall not be deemed as non-
acceptance for its use in cold in-place recycling. It shall be regarded as indicating deficiencies that require
attention to render it potentially suitable.

Where the existing pavement material is deemed potentially suitable for cold in-place recycling, the
Contractor shall provide the S.O. with recommendations of proposed stabilisation type and additional
material/ treatment required. Such additional material/ treatment shall be used to correct any deficiencies in
the properties of the existing pavement material that would otherwise render it unsuitable for stabilisation.

Subject to no objection by the S.O. to the recommendations, the Contractor shall undertake detailed testing
as specified in Sub-Section 4.10.5.
4.10.3.3 Compliance Requirements for Recycled Layer Materials

(a) General Requirements

The following sub-sections set out the specific compliance requirements for the recycled pavement layer. The
Contractor shall provide the S.O. with the results of all tests together with his proposals for the mix and
pavement designs for each section of the road. The minimum length of any one section shall be 500m. After
review, the S.O. shall either accept such proposals, in writing, or describe his concerns and suggest that
specific changes be made.

The untreated material shall comprise existing pavement layer material and any other additional
material/treatment required as recommended in Sub-Section 4.10.4, and its physical and chemical
composition shall be representative of the material expected on site immediately prior to the addition of
stabilising agent.

The stabilising agent shall be in conformance with the requirements of Sub-Section 4.10.2.3 and shall be
applied such that the resulting material shall be representative of the recycled material expected on site.
Laboratory tests on stabilised material shall be undertaken to determine the application rate of
the stabilising agent. Specimens shall be prepared at the optimum fluid content for the particular
stabilising agent based on and derived from the optimum moisture content of the untreated
material determined in the AASHTO T 180 (modified moisture density relationship) or BS 812 /BS
1924.

Modification of the specimen moisture content to attain the appropriate optimum fluid content
for the particular stabilising agent shall be in accordance with current best practice and the
Contractor’s own experience.

(b) Cement Stabilisation

The compliance requirements for cement stabilised cold-in-place recycled layer material
requirements are given in Table 4.10.3.
 TABLE 4.10.3: REQUIREMENTS FOR CEMENT STABILISED COLD IN-PLACE RECYCLED LAYER MATERIAL

Parameter Requirement
Unconfined
Compression Test
(UCS), in accordance Minimum 97% of Range (MPa)
with B.S. 1881, part Modified AASHTO (minimum and 2–5
116. 7day strength, density maximum limits)
moist curing @ 25oC,
height/width 1:1
Indirect tensile test
(ITS) on 150mm
diameter briquette Minimum 97% of
cured as for UCS Modified AASHTO Minimum (MPa) 0.2
specimens, in density
accordance with
AASHTO T-198
Maximum cement content by weight 5%

The job mix stabilising agent content shall be determined from the testing and submitted to the S.O., together with all
other details of the mix for quality control purposes, including target moisture content and density.
4.10.3.4 Trial Sections

Trial (pilot) section construction shall be undertaken on each contract section for which the layer and/or material
design requirements are expected to change. Each accepted trial section shall demonstrate compliance with the
specification requirements to the satisfaction of the S.O., prior to cold-in place recycling continuing on the section. As
a minimum, the following details shall be included;

i. Gradation of the recycled material;

ii. Compaction requirements including type of roller and rolling pattern to be employed to achieve the
required density;

iii. Strength of the recycled layer material in terms of UCS and ITS as specified in Table 4.10.8;

iv. Recycling depth and compacted thickness of new recycled layer material as specified in detailed
pavement design report;

v. In-situ moisture content in order to determine the application rate of water to achieve the OMC;

vi. Percentage by weight of the stabilising agent used as specified in Table 4.10.8, and

vii. Speed of advance of the recycler machine as specified in Table 4.10.8.

The trial section shall have a minimum 150m length at the proposed laying width. Quality control
sampling and testing frequency shall be at least double that specified for normal job production
as directed by the S.O.

If the trial lay results are within the permissible tolerance, then the trial lay results shall be
designated as Job Standard Mix (JSM).

Trial sections deemed to comply with the specification requirements shall be accepted as part of
the permanent works and the Contractor shall be permitted to proceed on the specific section.

For trial sections deemed as non-compliance with the specification requirements, the Contractor
shall submit a work proposal for making good such sections for approval by the S.O. Trial sub-
sections made good and subsequently approved as being in compliance with the specification
requirements shall be paid for at the same nominal rate as the normal job for the particular
section of work.
4.10.4 Equipment

4.10.4.1 General

All equipment shall be supplied and operated in such a manner as to recycle the in situ pavement to the
specified depth and construct a new pavement layer, all in accordance with the requirements of the
specifications. All equipment deployed on the site shall be of adequate rated capacity and in good working
order. Obsolete, poorly maintained or dilapidated equipment shall not be allowed on site.

The minimum compliance requirements for the equipment to be used for cold in-place recycling are given
in the following sub-sections. The Contractor shall provide the S.O. with details and technical
specifications of the equipment at least two weeks in advance of the first proposed usage.
4.10.4.2 Equipment for Cold In-Place Recycling

Cold in-place recycling shall be carried out using a modified milling machine or a purpose-
built recycling machine to;

i. add the required amounts of water and stabilising agents;

ii. mix all ingredients together to achieve a uniform consistency; and

iii. place the reconstituted material within the excavation created by the initial
milling.

Unless specified in the detailed pavement design report or directed by the S.O., all the
operations described above shall be effected simultaneously in a single pass of the machine.

Unless otherwise specifically permitted within the contract documents, the modified milling
machine or recycler to be used for cold in-place recycling shall meet the following minimum
requirements;
i. It shall be factory-built by a manufacturer having a demonstrable track record and manufacturing history in
the particular type of equipment.

ii. The milling drum shall have a minimum cut width of 2 metres with the capability of changing the speed of
rotation.

iii. A level control system that maintains the depth of milling within a tolerance of ± 10 millimetres of the
required depth during continuous operation.

iv. The milling drum shall rotate within an enclosed chamber inside which water and stabilising agents are added
to the recovered material at the rate required to achieve compliance with the specified laboratory design
mixture during continuous operation.

v. All spray systems fitted to the recycler shall be controlled by micro-processor to regulate the flow rate with
the speed of advance of the machine. All spray systems shall also have the ability to allow variable widths of
application.

vi. It shall have sufficient power to mix the recycled material together with all additives to produce a uniform
homogenous reconstituted material during continuous operation.

All ancillary equipment for supplying water, stabilising agents and other additives to the recycler during
operation shall be in accordance with the recycler manufacturer's recommendations.
4.10.4.3 Additional Requirements when Stabilising with Cement

Where the cement stabilising agent is not applied directly on the surface of the road prior to recycling, the
recycler shall be fed with cement slurry that is produced in a separate mobile mixing unit pushed ahead of the
recycler. Such a mixing unit shall be equipped as follows;

i. It shall have the capability to supply the cement slurry at the required rate to comply with the mix
design during continuous operation.

ii. It shall be capable of regulating the application rate of cement slurry in accordance with the speed
of advance of the recycler and volume of material during continuous operation.

iii. It shall provide uniform mixture of the cement slurry to the recycler to produce a homogenous
recycled mixture.

iv. There shall be a method for monitoring cement usage during operation that can be validated by
simple physical measurement for control purposes.
4.10.5 Construction Method

4.10.5.1 General

(a) Surface Preparation

Prior to commencement of cold in-place recycling, the surface of the existing section to be recycled shall;

i. be cleared of all foreign matter and standing water from the entire width of cut and to a
minimum of one metre to either side;

ii. be accurately marked showing the proposed cut lines.

(b) Production Plan

Prior to commencement of cold in-place recycling, the Contractor shall prepare a production plan detailing
the proposed day's work, which shall include the following;
 i. an annotated sketch showing the overall layout of the existing section intended for
recycling during the day showing the proposed cut pattern, sequence of cut and overlap
dimensions between cuts;

ii. the estimated time required for proposed day's production;

iii. the amount and type of stabilising agents to be applied to each cut;

iv. the proposed control testing programme;

v. any other information relevant to the intended work.

(c) Weather Limitations

No cold in-place recycling work shall be undertaken during wet conditions or in such other conditions
that may result in the work quality being negatively compromised, unless otherwise directed by the
S.O.
(d) Equipment, Materials and Material Delivery

The Contractor shall ensure that all logistical requirements for unhindered production of the day's proposed work are
prepared prior to commencement of the Work. All equipment for the cold in-place recycling process, from milling to final
compaction and finishing, shall be on site and in good working condition, as described in Sub-Section 4.10.4.

All materials required for the day's production, including stabilising agents and any additional material, shall be available.

All ancillary equipment for the delivery of stabilising agents and any additional material to the site shall be available as
required and in good working condition.

Specific equipment checks to be undertaken prior to the start of each production run shall include;
i. All supply pipes, chambers and jets for supply of stabilising agent, water, or other additives, are free of blockage
and primed;

ii. Sufficient quantities of stabilising agent, water, or other additives, are available in their supply equipment for
unhindered continuous production during the run;

iii. Bitumen temperature (where foamed bitumen is applied) is correct;

iv. All equipment settings are correct and gauges and monitoring equipment are functioning;

v. Equipment operators and crew are ready, and equipped as appropriate to undertake their tasks and fulfill their
responsibilities.
(e) Time Limitations

The maximum permissible time between mixing the recycled material with any stabilising agent and final
compaction of the placed material is given in Table 4.10.6.

TABLE 4.10.6: MAXIMUM TIMES BETWEEN MIXING AND FINAL COMPACTION

Stabilising agent Time Limit (hours)

Cement 3

(f) Application Quantities of Stabilising Agents, and any additional materials

The Contractor shall record the area of application and quantity of stabilising agent and any additional materials
used per run, and shall keep these records for at least 12 months after completion of the project.

(g) Others

The Contractor shall undertake the cold in-place recycling process with due diligence and shall instigate immediate
corrective measures in the event of any other occurrence or event that may lead to a sub-standard end product.
4.10.5.2 Laying

The mixed material shall be continuously placed back in the excavation created by milling as the
recycler advances. The recycler shall be equipped to place mixed material to the thickness and
uniformity required to achieve the design properties of the layer after trimming and final
compaction, in accordance with the design and specifications.

The Contractor shall provide necessary ancillary equipment and resources to ensure that
deficiencies in thickness or uniformity of the re-placed layer material can be corrected
immediately, and prior to initial compaction.
4.10.5.3 Compaction

(a) Initial Compaction

The recycled layer shall be initially compacted immediately, or as soon as any deficiencies are made good in accordance
with Sub-Section 4.10.5 above. Initial compaction shall be undertaken by a smooth-drum or pad foot vibrating roller,
operating on high-amplitude vibration. The static mass of the roller shall be selected in accordance with Table 4.10.7.

TABLE 4.10.7: MINIMUM STATIC ROLLER MASS

Thickness of compacted layer Minimum static mass of roller (tonne)
< 150mm 12
150mm to 200mm 15
200mm to 250mm 19
> 250mm 24

Note: The operating speed of the primary roller shall never exceed 3km/hr and rolling shall be applied over the
full width of each cut.
(b) Trimming and Final Compaction

After primary rolling has been completed, a grader shall be used if required to cut the final surface levels. Grader work shall
be limited to the minimum necessary to achieve the required final surface shape, evenness and texture. Skimmed material
shall be removed and under no account compacted into the trimmed layer.

Final compaction shall commence as soon as possible after trimming. Final compaction comprises secondary rolling, to
achieve the specified density, and finishing. Secondary rolling shall be undertaken using a smooth-drum vibrating roller
(nominal 12 tonne static mass) operating on low-amplitude vibration. Any additional moisture required maintaining
workability and achieving the specified density requirements shall be applied by spraying the surface with multiple light
applications from a water tanker.

Finishing shall be undertaken with a pneumatic-tyred roller to achieve a close-knit surface appearance.

For cement stabilised layer materials, water shall be sprayed regularly using full-width spray bar fitted with fine nozzles to
prevent the surface from drying out and for curing purposes. Alternatively, if early opening to traffic is required, a rapid
setting bitumen emulsion curing membrane with a minimum spray rate of 0.6 litre/m2, or such other curing membrane as
otherwise approved by the S.O., shall be applied immediately after finishing operations.
4.10.5.4 Joints

Two types of joint can be required during the cold in-place recycling process longitudinal (between adjacent cut
sections), transverse construction/operational joints); formed transverse (in cement stabilised layers). Joints shall be
constructed to avoid built-in weakness using best practice techniques, and in accordance with the following;

(a) Longitudinal Joints

Longitudinal joints between adjacent cuts shall overlap by at least 100mm to ensure complete treatment across the
full width of the road. Guidelines marked on the road surface for each cut shall be checked to ensure that only the
first cut is the same width as the milling drum. All successive cut widths into existing original material shall be less
than the drum width by at least 100mm.

(b) Transverse Joints

Transverse joints, created at the start and end of each cut and each time the recycling process stops, shall be formed
to ensure that there is continuity of treatment across the resulting joint. The overlap shall be at least 1.5m or equal to
the diameter of the milling drum.
4.10.5.5 Protection and Maintenance

The Contractor shall protect and maintain the completed layer until the next pavement layer or surfacing is applied.

Curing agents or a temporary surfacing in the forms of sand blinding, surface dressing, slurry seal or other method as
approved in the contractor's work plan shall be applied after finishing as required. The treatment shall be appropriate to
the cold in-place recycled material type, and the time and trafficking levels prior to application of the next pavement
layer.

Minimum curing time of 72 hours shall be allowed for cement stabilised layer prior to overlaying of hot mix over the
treated layer. For foamed and bitumen emulsion stabilised layers a minimum curing period of 48 hours shall be allowed.
The Contractor shall overlay with hot mix immediately, after the minimum curing time has been achieved.

The Contractor shall undertake necessary maintenance activities to ensure that the curing agent or temporary surfacing
remains intact and protects the cold in-place recycled pavement layer against deterioration prior to application of the
next pavement layer. The contractor shall also make good any damage to the stabilised surface at his own cost by using
approved method prior to laying of the hot mix.
4.10.5.6 Quality of Materials and Workmanship
The general quality control requirements applicable to cold in-place recycling that shall be complied with during normal
operation are given in Table 4.10.8.
Tolerances on horizontal alignment, surface levels and surface regularity for the cold in place recycled layers shall conform to
the following requirements;

(a) Horizontal Alignment

The horizontal alignment shall be determined from the centre-line of the pavement surface shown on the Drawings. The
edges of the pavement as constructed and all other parallel construction lines shall be correct within a tolerance of + 50mm
and minus 0 mm from the centre-line, except for kerbs, channel blocks and edge lines which shall be laid with a smooth
alignment within a tolerance of + 25mm and minus 0mm from the centreline.

(b) Surface Levels of Pavement Courses

The design levels of pavement courses shall be calculated from the vertical profile, cross fall and pavement course thickness
shown on the Drawings. The level of any point on the constructed surface of a pavement course shall be the design level
subject to the appropriate tolerances given in Table 4.10.9.

(c) Surface Regularity of Recycled Layer

The transverse regularity of completed recycled surface shall be measured with a 3m straight-edge and no depression shall
exceed 10mm. Any individual irregularity measured with the rolling straight-edge, or 3m straight-edge, laid parallel to the
road centre-line shall not exceed 10mm.
TABLE 4.10.8: GENERAL QUALITY CONTROL REQUIREMENTS FOR COLD IN-PLACE RECYCLING
Parameter Test Method Frequency Acceptance

Field compaction (Density) B.S. 1377 Sand Replacement One test per 500m2 and at least 95% for natural gravel/crushed
Method one test per daily operation aggregates; 97% for mixture of
crushed aggregates and RAP; 98%
for RAP of JSM
Stabilising agent application rate Consumption records reconciled Every completed section and daily ± 10% of target rate
with theoretical usage.
Unconfined Compression Strength As defined in Table 1.4, 1.5 or 1.6 One test per 2000m2 and at least No result less than the minimum
(UCS) for the particular stabilising agent one test per daily operation, each required strength for the particular
test comprising four (4) specimens stabilising agent. For cement
stabilised layer no result shall fall
outside specified range.
Indirect Tensile Strength (ITS) As defined in Table 1.4, 1.5 or 1.6 One test per 2000m2 and at least No result less than the minimum
for the particular stabilising agent one test per daily operation, each required strength.
test comprising four (4) specimens
Depth of recycling Physical measurement of cutting At least two tests per 50m linear ±10mm of target depth
depth relative to final surface progress
elevation
Thickness of new recycled layer Small inspection holes cut through One test per 250m of completed ±10mm of specified layer thickness
completed layer layer
Moisture content B.S 1377: Part 2 1990 At least once each 500m length of ±20% of the Optimum Moisture
cut Content (OMC) determined from
AASHTO test T180.
Speed of advance Manufacturer’s advisory note. At least once each 250m length of 5m/min - 12m/min.
cut.
TABLE 4.10.9: TOLERANCES IN SURFACE LEVELS OF PAVEMENT COURSES

Pavement Course Tolerance

Wearing Course +/- 5 mm
Binder Course +/- 5 mm
Roadbase + 0 mm
- 20 mm
Sub-base + 10 mm
- 20 mm

The combination of permitted tolerances in the levels of different pavement courses shall
not result in a pavement thickness less than that shown on the Drawings. Each pavement
course shall have an average thickness not less than that shown on the Drawings.