large scale cold mix construction for rural roads in india

7th ISSA WorldCongress, Lyon 2010

LARGE SCALE COLD MIX CONSTRUCTION FOR RURAL ROADS IN INDIA

ABSTRACT

India lives in its villages. With this basic belief in the mind of our technical and commercial team in

BitChem, we started the foundation of COLD MIX Implementation in Assam, India. After 20 years and

continued research by CRRI, New Delhi no private or public company was coming ahead for

promoting this novel concept of roads construction. Allaying fears for fellow engineers in the

government department and the basic thought of water in bitumen very few were ready to help us

and let our team precede ahead. A regular focus on R&D (Trial and Error) helped us understand the

need of different viscosities and setting time for the aggregates found at different locations. Further,

lack of central hot mix plants added to the business opportunity as conventional hot construction is

time consuming, slow progress, hazardous, polluting and requires more investment than cold mix

construction. Today after completing 1000 Kms of rural roads in place of Hot Mix construction

learnings are still coming from the field.

We understand the basic need of designing practical solutions as all will not match with THEORY in

the worksite.

Making workers sensitive to use of aggregates with more than allowable moisture and to maintain

the correct binder content in the mix are still being imparted.

As the first Indian company we are proud to start commercialisation of COLD MIX in the field and are

only increasing our commitment in penetrating COLD MIX construction in not only Assam but the

entire North-East India. With strong focus on economic construction for contractors and cost

comparison with hot mix, we feel challenges have been only encountered now.

The mixed rumours on failure on COLD MIX in thicker construction and highways construction further

motivate us to explore the truth here today

Authors:

1. Agarwal Rajeev, CEO, Bitchem Asphalt Technologies Limited

2. Goswami Ramen, Head-Applications, Bitchem

3. Jain Dr Pramod Kumar, Senior Scientist, Central Road Research Institute, New Delhi

4. Das Kr. Ranjeet, Director, Road Research Laboratory, Public Works Dept., Assam

1. INTRODUCTION & BACKGROUND

In India, hot mix construction using central small plants and conventional mobile type mixing

equipments is very prevalent. Assam has got the due share of Central Ministry policies on rural

connectivity. Hence, rural roads construction using conventional mixing equipments are gradually

increasing in absence of hot mix plants. Intermittent rains, slow progress using conventional mixing

equipments, unviability of central hot mix plants, site preparations and overall headache related to

site hot-mix construction paved the way for acceptance of cold mix methodology using bitumen

emulsions in the last 2 years. Another key highlight for the government is the carbon footprint

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reduction without compromising on the road quality using this Green Technology.

This paper presents a summary of large scale Cold Mix Implementation in North-Eastern India. The

key purpose of this paper is to discuss the working process of cold mix and requirements to

implement cold mix system in an error free manner.

2. PRESENT WAY OF DOING BITUMINOUS WORK IN INDIA

2.1 Heating and Mixing process: Generally, the heating and mixing process is carried out in central

Hot Mixing Plant and the mixed materials are carried out to the site by tipper trucks. The laying

activity is carried out by using paver. For rural road construction (in maximum cases) the mixing is

carried out with the help of small portable hot mixing plant and the laying is carried out manually.

Finally, it is rolled using the standard 10 Tonne Static Roller.

2.2 Different Bituminous layer adopted in India:

In rural road network, bituminous construction is carried out only of a thin layer where it works as a

wearing course on a Water-Bound Macadam (WBM). A 20 mm open graded premix carpeting1

(OGPC) is applied followed by a seal Coat using 6.7 mm aggregates with 5-10% fines.

For non-rural heavy traffic road where design of structural layer gets more important the following

bituminous layers are adopted in Base Course2 with different thickness over the Sub Base course

Bituminous Macadam (BM)

Semi Dense Bituminous Concrete (SDBC)

Dense Bituminous Macadam (DBM)

Bituminous Concrete (BC)

2.3 Aggregates and Bitumen requirement for 20 mm (OGPC) open graded premix carpeting and seal

Coat:

Table -13: Quantity of Aggregates & Bitumen for 20 mm premix carpeting

Aggregates Qty per 10 sqm

(a) Coarse Aggregate- Nominal Size 13.2 mm 0.18 cu.m.

(b) Coarse Aggregate Nominal Size 11.2 mm 0.09 cu.m.

Total quantity of aggregate 0.27 cu.m

Binder (Normal grade Bitumen) Qnty per 10 sqm

(a) For 0.18 m3 of 13.2mm nominal size aggregates at 52 kg bitumen per m3 9.5 kg

(b) For 0.09 m3 of 11.2mm nominal size aggregates at 56 kg bitumen per m3 5.1 kg

Total Bitumen 14.6 kg

(1)IRC specification for open graded premix carpeting, IRC:14:2004

(2) Specifications for road & Bridge works , published by IRC for Ministry of Road transport &

highways , India.

(3) IRC: 14-2004, MoRT&H specifications

Table 24: Quantity of Aggregates & Bitumen for Seal Coat

Seal Coat Type/ Aggregate Size Qty. of aggregates /10 m2 Qty of Bitumen / 10 m2

Type A Seal Coat (liquid seal coat ) - Aggregate Size 6.7 mm (passing 11.2 mm & retained on 2.36

mm ) 0.09 cu.m 9.8 kg

Type B Seal Coat (premixed seal coat) - Fine Aggregates- Medium coarse sand or fine grit (Passing

2.36 mm and retained on 180 micron sieve) 0.06 cu.m. 6.8 kg

Type C Seal Coat (Premixed seal coat)- Aggregate Size 6.7 mm (passing 9.5 mm & retained on 2.36

mm )

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0.09 cu.m 6.8 kg (4.5 % by wt.)

3. HOT MIX METHODOLOGY IN NORTH EASTERN REGION

During the construction of hot mix-hot laid bituminous work the following issues are observed in NE

India-

a) Preparation Time- As central hot mix plants are not viable for rural roads construction, the

preparation time for site hot mix construction is quite long which ultimately affects the output and

delays the connectivity.

b) Slow progress- Due to use of site mobile mixing equipments, the progress level is very slow in

conventional hot mixing. This affects the contractors business cycle.

c) Smaller Paving Season- Due to longer rainy season the paving period for hot mix is quite less in

North Eastern States of India. Hence, work completion always suffers compared to other parts of

India and as desired.

Overall, the delay in project completion time is generally termed as Low Fund Absorption Capacity of

the States and this lapse the scope of participation in future development funds of the central

government.

4. COLD MIX IMPLEMENTATION IN NORTH-EAST INDIA

In India, Indian Road Congress (IRC), the apex body for developing specifications and procedures for

roads and bridge construction, has developed guidelines for 20 mm thickness (OGPC) premix

carpeting. The basic system of cold mix methodology is to use higher quantity of bitumen emulsion

as a binder to get the desired bitumen content on the road surface as evaporation of water shall take

place. Bitumen Emulsions used are as per Specifications developed by Bureau of Indian Standards

code IS 8887:2004-

4.1. Aggregates: Aggregate quality and grading requirement for 20 mm Open graded premix

carpeting (OGPC) with Bitumen Emulsion (Cold Mix) is similar to the aggregates used in Hot Mix as

described earlier in Table 1.

4.2 Binder for OGPC: Medium setting grade with a medium to high viscosity range of Cationic

Bitumen Emulsions is used for carpeting works in India having minimum 65 % of binder content,

where open graded aggregates are used. (Refer Table-3)

4.3 Binder for Seal Coat: Slow setting grade low viscosity range 20-40 and type Cationic Bitumen

emulsions are used having minimum 60% binder content for seal coat applications.

The following table indicates the quantity of Bitumen Emulsion normally used for 20mm premix

carpeting in India (Refer Table-4)

(4) Refer IRC: 14-2004 & MoRT&H Specifications.

Table 35: Quantity of Binder (Bitumen Emulsion) for OGPC 20 mm

ITEM Qty per 10 sqm area

For 13.2 mm size coarse aggregate 13-15 kg ( MS Grade)

For 11.2 mm size coarse aggregate 6-7 kg (MS Grade)

Total 19-22 kg

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Table -46 : Quantity of Binder (Bitumen Emulsion) for Seal Coat

ITEM Qty. per 10 sqm area

For Type A Seal Coat (Liquid seal coat) 12-14 kg (RS-2 Grade )

For Type B Seal Coat (Premix seal coat) 10-12 kg (SS -2 Grade )

For Type C Seal Coat ( Premix Type ) 9-11 g ( SS-2 Grade)

5. DIFFERENT ISSUES OBSERVED DURING CONSTRUCTION OF COLD MIX WORK :

The main issues for using bitumen emulsion as a binder is to coat aggregates properly, have good

workability for paving, acceptable curing time after rolling and adequate final asphalt mixture

properties.

5.1 Moisture: The moisture present with the aggregates plays a major in maintaining proper quality

of Cold Mixes. Having a small percentage (0.5-1.0 %) of moisture gives very good effect in coating of

aggregates. Aggregates are generally non-porous so they do not hold moisture more than 3%-4%. At

the same time, these levels of moisture lead to run-off of binder from the mixes. Hence, the moisture

present in the aggregates plays an important role to control the run-off characteristics and have the

correct residue properties in the mix. Our experience shows that during rainy season, aggregates

heaps require spreading of the entire collection so that water can evaporate faster for starting the

work without such problems.

5.2 Equipments: Concrete Mixers are the approved equipment for producing the aggregate mixes in

rural roads construction. But if there are cases of huge work volume then pug-mill concept to

produce the mixes with automatic flow control measures can be adopted. In such cases difference in

the setting properties of emulsion is increased for the lead time to the site and with the challenge to

maintain the product viscosity as per the mix design needs to get the proper coating and workability.

5.3 Strength: The breaking of emulsion and curing behaviour of the mixes is largely influenced by

the type of aggregate and bitumen emulsion, environmental conditions, mechanical pressure and

moisture content of the aggregate. The curing process and build-up of binder cohesion and

consequent mixture strength takes place gradually after passage of time and traffic. A cold mix

pavement layer can be trafficked immediately after rolling, although the mix does continue to gain

strength over a period of time. Up to some extent considerable improvement can be made easily by

using different types of emulsion by understanding the time gap required between mixing and

laying.

5.4 Emulsion: The Bitumen emulsions used are required to have properties which would not only

provide good coating of emulsions on the aggregates but also that of bitumen once the coating dries

after the breaking of the emulsions. Practically it is not possible to get the same quality of

aggregates maintaining a constant gradation in all the area. It is very much necessary to make the

emulsion viscosity suitable for the selected aggregates. Depending upon the environment conditions

and external mechanical forces, the breaking of emulsion varies and hence setting properties of

emulsions also needs adequate design.

(5) IRC specification for OGPC, IRC-14:2004 & MoRT&H Specifications for Road & Bridge works

(6) IRC specification for OGPC, IRC-14:2004 & MoRT&H Specifications for Road & Bridge works

5.5 Compatibility of emulsion with the aggregates- Cold Mix Design procedure:

A laboratory evaluation for compatibility of the aggregates and emulsion named as a Cold Mix

Design Procedure plays a major role for finding better quality of cold mixes.

The following table is self explanatory

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Emulsion Aggregate for 20 mm OGPC Emulsion

% by wt Moisture

% by wt

Workability Initial

Coating Coating

After drying

Type

(Viscosity Range 50-300) Viscosity in Secs Aggregate Characteristics

MS

94 Sample C1 High Fines/ Below Gradation 5.5 % Nil Very Poor Very poor NA

MS

94 Sample C1 High Fines/ Below Gradation 5.5 % 2 % Average Good Good

MS-

Slow Type 68 Sample C1 High Fines/ Below Gradation 6 % 1 % Very good Very good Good

MS 68 Sample C2 Pea Gravel/ No Fines 5.5 % 2 % Very good Run Off Poor

MS 110 Sample C2 Pea Gravel/ No Fines 5.5 % Nil Not workable Good Good

MS 110 Sample C2 Pea Gravel/ No Fines 5.5 % 1 % High Workability Good Good

MS 110 Sample C3 Quarry Crushed/ Proper Gradation 5.5 % 1 % Poor Poor NA

MS 65 Sample C3 Quarry Crushed/Proper Gradation 5.5 % 1 % Poor Poor NA

MS-Slow Type 65 Sample C3 Quarry Crushed/ Proper Gradation 4.5 % Nil Very good Very good Dull

MS-Slow Type 65 Sample C3 Quarry Crushed/ Proper Gradation 5.5 % Nil Very Good Very Good Very

Good

5.6 Important Parameters to be notice during the Mixing and Laying of Cold Mix

Few parameters were found to be very critical for proper product indexing and sometimes new

product designing as per the

Product Indexing on basis of Gradation and Fines Content of the aggregates

Workability and Coating ability of the emulsion with the aggregates

Moisture in the Aggregates

Breaking of emulsion and Curing of Mixes for maintaining quality of surface under traffic

6. Cold Mix design and Implementations

Successful implementation of Cold Mix successfully depends upon the Mix Design of the mixes prior

to the start of the work. The emulsion manufacturer has to play a major role in selection and

indexing of appropriate quality of emulsions based on various parameters noticed in the Cold Mix

Design Laboratory. A close co-operation with the emulsion manufacturer, contractor and government

department is the main criteria for successful implementation of cold mixes on site using the

application support service.

7. CONCLUSION

To promote this novel concept of using Bitumen Emulsion in road construction, policy formulation in

international level is required for building more awareness in developing countries. More emphasis

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has to be given in R & D activities immediately for different environment and for different layers

thicknesses to enable cold mix enter the higher thicknesses application. Industry initiative and

knowledge sharing among the industry about their experiences is important.

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large scale cold mix construction for rural roads in india

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