Cold-Mix Recycling

8/7/2019 Cold-Mix Recycling

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METHODOLOGY FOR

ASPHALT COLD MIX RECYCLING


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Methodology For Asphalt Cold-Mix Recycling.

1.1 General

1.1.1 Purpose / aim of the Method Statement submission:

Laying of Asphalt Cold-Mix recycling over remaining portion of old granular base asshown in working drawings.

1.1.2 Scope of the Method of Statement:

Construction of Asphalt Cold-mix recycling thickness varies depends on designrecommendation / as per Tech. Specifications and contract drawings.

1.1.3 Reference to other controlling documents where appropriate:

As per Tech. Specifications A 6, MOST Cl. 519, BOQ item No. 4.06 and as per workingdrawings.

1.2 Temporary Works

Temporary diversion will be constructed for vehicular traffic in a manner creating leastinterference to the flow of traffic.

1.3 Surveys

Asphalt cold recycling mix will be laid after completion of necessary survey checks onremaining portion of old granular base surface by supervision staff.

1.4 Utilities

All identified utilities will be relocated before starting of the Asphalt cold recycling mixprocessing.

1.5 Traffic arrangements and Control

Traffic will be diverted on another carriageway by providing traffic signals and safetymeasures. More over necessary extra man power and display boards will be placed toregulate the flow of traffic without causing any congestion or stagnation.

1.6 Access

Land access will be provided with the temporary diversion where necessary.


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1.7 Work Sequence Program

a) Prepare the sketch showing the overall layout of the length and width of roadintended for recycling during the day, broken into the number of parallel cuts

required to achieve the stated width, and the over lap dimensions at each jointbetween cuts.

b) The sequence and length of each cut to be recycled before starting on theadjacent or following cut.

c) Estimate the time required for milling, mixing and compacting each cut.

d) The location where samples were taken for determing in-situ moisture contentsand the results of the tests.

e) Proposed water addition for each cut, and the location at which any change is tobe made with in that sequence.

f) The locations and quantity of material to be imported.

g) Proposed control testing program.

1.8 Work Methodology

a) Field Samples: The locations for sampling should be selected by randomsampling techniques. A minimum of 5 samples per kilometer should be taken forlaboratory analysis.

b) Reclaimed Asphalt pavement & Aggregate materials: The aggregate andAsphalt contained in reclaimed Asphalt pavement must be evaluatedindependently.

(i) Aggregate materials: The gradation of the aggregate separate from theAsphalt and found by sieve analysis by ASTM C 136 and found the all physical

analysis like shape, AIV, stripping and water absorption.

(ii) Asphalt Content: The Asphalt is extracted and found the existing asphaltcontent in the pavement by ASTM D 2172.

c) New Aggregate: If new aggregate is needed to correct the gradation of thereclaimed aggregate material or to increase the thickness of the recycledpavement and satisfy the requirements as specified in MOST Table 500-3 and

Table 500-4 (Gr.I).

d) Asphalt Stabilizing Agent: Asphalt stabilizing agent shall be Medium Setting(MS) Bitumen Emulsion.


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e) Mix Design:

(i) Gradation of Recycled Mixture: Fix the gradation as per MOST Table 500.4 (Gr.I) with combination of the reclaimed aggregates and new

aggregates (if any).

(ii) Select the Grade of New Asphalt: A grade of Asphalt is selected asspecified in Tech. Specifications A 6.2.3 (i.e. Medium Setting (MS)Bitumen Emulsion).

(iii) Percent Asphalt demand of the combined Aggregate: Asphaltdemand of the combined aggregate may be calculated by the followingempirical formula.

Pc = (0.035 a + 0.045 b + K c + F) / R

Where,

Pc = Percent of Asphalt by weight of total mix.

K = Constant 0.18 for 6 10% passing 75 mic. Sieve.- 0.20 for < 5% passing 75 mic. Sieve.

a = Percent of aggregate retained on 2.36 mm sieve.

b = Percent of aggregate passing on 2.36 mm & retained on75 mic. Sieve.

c = Percent of aggregate passing 75 mic. Sieve.

F = Percent of water absorption ( 0 2%).

R = Constant 0.60 to 0.65 for Bitumen Emulsion.

(iv) Percent of New Bitumen in Mix: The quantity of new asphalt to beadded to the recycled mixtures equals the calculated asphalt demandminus the percentage of asphalt in the reclaimed asphalt pavement.

Formula is Pr = Pc (Pa X Pp) / R

Where,

Pr = Percent of new asphalt in the recycled mix.

Pc = Percent of asphalt by weight of total mix.

Pp = Decimal percent reclaimed asphalt pavement in therecycled mix.

R = Constant 0.60 to 0.65 for Bitumen Emulsion.


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f) Construction operations:

(i) Weather and seasonal limitations: Construction with cold mix must notbe under taken when temperature below 10

0C, during rain, in standing

water or generally when poor weather is predicted.

(ii) Preparation of Base: The base on which cold mix is to be laid shall beprepared, shaped and leveled to the required profile as mentioned in Sl.No. 1.7, and a prime coat, where specified shall be applied in accordancewith clause 502. A tack coat in accordance with clause 503 shall beapplied over the base on which the cold mix is to be laid, where specifiedin the contract.

(iii) Preparation of the Mixture: Constructing recycled pavements usingboth in-place and central plant production methods.

In-place recycling: The first step in In-place recycling is to break up theroad surface up to the depth indicated by the structural design (i.e..160mm). Using pull type rippers in a single pass.

Mixing the Bitumen Emulsion uniformly with the sized asphalt pavement,old granular base and new aggregate if used. When new aggregate isadded to In-place materials, a spreader box or windrow size should beused to ensure the required quantity is evenly placed.

Cold mix prepare with proper proportioning of the asphalt and uniformlyby using blade mixing / rotary mixing / travel plant mixing. The entireoperation will be in a single pass.

The Milling and Recycling machine shall have the followingfeatures.

Capacity of milling to depths up to 300 mm in a single pass and fittedwith an automatic sensor system to accurately maintain the depth of

cutting.

Milling drum which rotates up wards into the direction of advance andachieves at least 2.0 m of cut width in a single pass.

Mix the milled material with stabilizing agent, the recycling machineshall have the following features.

A microprocessor controlled system to regulate the application ofstabilizing agent in relation to travel speed and mass of material beingrecycled.

The pumping system for stabilizing agents shall be calibrated to deliverwith a tolerance of + / - 3% of volume.

A system of self cleaning nozzles that promotes an uniform application ofstabilizing agent across the full width of treatment.


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(iv) Spreading: Mixtures that have been windrowed by a travel plant or byblade mixing are spread and shaped to the desired cross section bysuccessive passes with a motor grader.

Mixtures that do not required aeration may be spread to the required

thickness immediately after mixing.

The thickness of layer should not exceed 150 mm, when multiple lifts arerequired, curing time must be allowed between 2 to 5 days under goodcuring conditions.

Note: Emulsified asphalt mixes gain stability as the fluids (mainly water)evaporate. It is important not to retard this process. Therefore, liftthickness must be limited by the rate at which the mixture loses its fluids.

(v) Compaction: Initial compaction (breakdown rolling) of the laid materialshall be carried out using a pneumatic tyred roller a weight 12 15tonnes weight having nine wheels, with a tyre pressure of at least 5.6kg/sqcm (or 15 25 tonnes weight having seven wheels, with a tyrepressure of at least 7.0 kg/sqcm).

Intermediate rolling shall be done with 8 10 tonnes vibratory roller orsteel wheeled pneumatic roller.

Finishing rolling shall be done with 6 8 tonnes smooth wheeled tandemroller.

(vi) Open to Traffic: Traffic shall not be allowed to run on new work until thewater or volatile in the mixture have evaporated.

Cold-Mix Recycling

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