Cold Mix Bituminous PlantPrepared By : Rahul Pitroda

Guide by : Prof. Manish Jain

Introduction

• Cold placed asphalt pavement mixtures are generally mixes made with emulsified or cutback asphalt. Emulsified asphalts may be anionic or cationic. Cutback asphalts may be MC (medium curing) or SC (slow curing)grades.

• Aggregate material may be anything from a dense-graded crushed aggregate to a granular soil having a relatively high percentage of dust. The aggregate at the time of mixing may be either damp, air-dry, or artificially heated and dried.

• Mixing methods may be performed either in the roadway, along the roadway, or in a stationary mixing facility

Asphalt

• The type and grade of asphalt selected for use in cold-laid pavement construction depends a great deal upon the aggregate, mixing method, and climatic conditions.

• Mixtures prepared at a stationary mixing facility generally permit a more viscous grade of asphalt than used in the road-mixing method. Cool weather conditions require a lower viscosity grade and permit a faster curing or setting type of asphalt to be selected than for warmer or hot weather mixing conditions. 

• Mixtures prepared with emulsified asphalt do not require aggregates as dry as those prepared with cutback asphalts

Cold mix asphalt & hot mix asphalt

• Cold mix is a mixture of unheated aggregate and emulsion or cutback and filler. The main difference between cold mix and hot mix asphalt is that aggregates and emulsion or cutbacks are mixed at ambient temperature (10°C-30°C) in case of cold mix and aggregates and binder are mixed at high temperature (138°C-160°C) in case of HMA. Dense graded cold mixtures have far lower permeability and good resistance to deformation. Open graded mixtures are storable and semi dense mixtures have good adhesion and lower permeability.

ADVANTAGES

• It eliminates heating of aggregate and binder. • It is environmental friendly and conserves energy. Cold mix pavement can provide

energy savings of over 50% compared with hot mix . So it can be considered as green bituminous mix for rural road construction.

• It can be easily prepared using small set up on site. It can be produced manually for small scale job. Laying of HMA for rural road construction sometimes is not economical because setting up of a hot mix plant for small scale job increases the project cost.

Aggregates Selection

• In India aggregates should conform the physical requirement laid by MoRTH(Ministry of Road Transport and Highways)

• specification (2001). Testing of aggregate like sieve analysis, specific gravity, aggregate impact value and soundness is necessary.

Emulsion Selection

• Selection of emulsion depends on aggregate type and aggregate gradation and ability of emulsion to coat the aggregate. According IS 8887:2004 specifications, five grade of emulsion; RS-1, RS-2, MS, SS-1 and SS-2 are used to prepare cold mix. Quality tests should be carried out on the selected emulsion according to IS 8887:2004

Mix Composition• A wide variety of aggregates and soil-aggregate combinations can be processed. There

are many cases where material from road cuts, pits, or nearby quarry sites may be economically crushed or used.

• Often the entire output below a certain maximum size from a rock crusher is used. Suitable local materials also include granular soils having up to 20 percent passing the 75 um (No. 200) sieve, as well as clean sands and gravels. Granular materials that are mostly fine aggregate and have relatively high percentage mineral dust may cause mixing, aeration, and compaction problems. 

• Well-graded aggregates are always desirable for any course of the asphalt pavement structure, but many poorly graded and gap-graded aggregates are adequate for base courses when properly prepared by road mixing methods and procedures.

Formulas may be used for approximating the asphalt content for initial mixing.For estimating the approximate emulsified asphalt content in dense-graded mixes the following empirical formula may be used:

P = (0.05A + 0.1B + 0.5C) x (0.7)where:P = percent of total emulsified asphalt by weight of dry aggregate,A = percent of aggregate retained on the 2.36 mm (No. 8) sieve,B = percent of aggregate passing 2.36 mm (No. 8) and retained on 75 um (No. 200) andC = percent of aggregate passing 75 um (No. 200).(All above percentages should be expressed as whole numbers.)

Mix component Percentage on aggregate

Granite aggregate 20mm

26

14 mm 15 10 mm 9 6 mm 15 Dust 35 OPC 0 1 2 3 4

Pre-wet water 2.5 2.5 3 3.5 4 Bitumen Emulsion 8.06

USE OF ADDITIVES IN COLD MIX

• Additives are used to accelerate curing rate imparting initial strength to mix in early life. Portland cement and lime are the common additives used in emulsion mixes. These additives are typically used by 1 to 3 percent of total weight of dry aggregate. Additive imparts some charges to emulsion which help emulsion to break quickly and bitumen droplets come out from emulsion and stick to aggregate giving binding properties

Suitability for Pavement Construction• Cold-laid asphalt mixes may be used for surface, base, or subbase courses if the

pavement structure is properly designed. Cold-laid surface courses are suitable for light and medium traffic.

• When used in the base or subbase, they may be suitable for all types of traffic. Cold-laid pavements have special advantages in outlying areas where economic problems exist in getting the necessary improved mileage. Also used on large jobs, cold-laid paving mixtures reduce construction costs, but not necessarily the strength orquality of the pavement structure. 

• Asphalt pavements made by cold-laid methods can be designed and built to meet current traffic requirements.

• They can also be increased in thickness, as may be dictated for subsequent traffic, by adding additional pavement courses.

Cutback Cold Mix Asphalt Manufacture

• Cold-mix asphalt is not a sophisticated preparation. Generally, placing and compacting do not normally call for equipment as sophisticated as that required for hot-mix asphalt.

• This type of pavement construction, however, is no less important since a large percentage of the nation's roadways have cold-mix asphalt bases and even surfaces.

• Less control is required for cold-mix preparation with a distributor and motor-grader operation. But possibilities for as great a control as for hot-mix asphalt are present in a plant-mix operation. However, many plants used for producing cold mixes do not use or have all the means for maintaining close uniformity of control. Wherever suitable materials are available, such plant mixing procedures are employed for high production and low cost.

• Cold-mix recycling or reworking of existing asphalt pavement or aggregate structures is another important pavement construction alternative.

Cold - mix asphalt with bitumen foam• Water is sprayed through nozzles into the hot bitumen under pressure.

The water expands explosively when the pressure is released, resulting in a fine bitumen foam that can easily be used to coat the cold aggregate substances. The quality of the cold mix can be influenced as desired by adding cement.

http://www.e-asphalt.com/ingles/cutbackcoldmix/index.htm

www.ammann-group.com/en/home/asphalt-mixing-plant/continuous-asphalt-mixing-plant/coldmix-130-400-th/

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