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Dense Graded Mixes

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Dense Graded Mixes

Dense graded mixes are medium air void mixes that are high in strength and use affordable crusher-run aggregates. Low water impermeability greatly improves freeze/thaw characteristics.

Design Criteria

When designing a dense graded mix a number of factors have to be examined and assessed to ensure a proper surface will be placed that will perform for its service life. The following factors can have a tremendous effect on the performance of a dense graded mix; aggregate shape, mix workability, aggregate type, coating ability and residual asphalt content. If these factors are addressed the chances of a good dense graded mix being placed are greatly increased.

Aggregate Shape and Type: 

The overall shape of the mix aggregate can influence the quantity of aggregate as well as the amount of asphalt emulsion to be used. The more graded the aggregate is the higher the emulsion quantity needed. The compatibility of the emulsion used with the aggregate is critical.

Mix Workability: 

The emulsion used should give the finished mix enough workability to be laid evenly and homogeneously and be designed for the intended method of processing be it immediate placement or in a stockpile.

Coating Ability:

The asphalt emulsion should have the ability to coat the fine aggregate (pass 4.75 mm) without the fine aggregate balling up. With some emulsions the use of mixing water will aid in coating the fines.

Asphalt Residual in the Emulsion: 

The quantity of asphalt residual in the emulsion can affect the quantity of emulsion needed to coat the aggregate. The lower the residual the higher the quantity of asphalt emulsion needed.

During the design process the two key factors that are needed is a well coated mix combined with adequate strength and stability which will be able to handle the traffic load and volume.

If these factors are taken into consideration in designing the dense graded mix then the chances of a successful mix are greatly improved. Typically a dense graded mix would require an emulsion content of 5.5 – 7.0%, a minimum of 2500 Newtons stability at 25°C and air voids of 7 – 11%.

Materials

Asphalt Emulsions:

Several factors have to be taken into account when choosing the emulsion to be used. The type and grade of emulsion is affected by the aggregate, the coating ability, the compatibility, the mixing method, the environmental conditions as well as the laying and compaction process. The most widely used grades of asphalt emulsion used in dense graded mixes are SS-1, CSS-1, MS-2 and CMS-2. In recent years proprietary type emulsions have been developed for use in dense graded mixes.

Mix Aggregate:

The mix aggregate used in dense graded mixes can be processed or semi-processed crusher, pit or bank run aggregates. Most are graded from a maximum size of 25 mm with material passing the 75 micron sieve. They should have very low clay content and not have an excessive amount of pass 75 micron material.

Performance Guidelines

In order to construct a proper well designed dense graded mix the following guidelines should be followed:

Safety Data Sheets

DescriptionPdf File
SDS – MacPatch
SDS – Rapid Curing Cutback

Related Resources

DescriptionPdf File
Research – A Laboratory Investigation of the Compaction of Dense Graded Asphalt Concrete
Research – Progress in Cold Mix Processes in Canada
Research – A Review of Cold mix Processes In Canada
Research – Mixture Design and Field Experience: Coloured Hot Mix Asphalt on Bus Rapid Transit (BRT) Lanes in Ontario
Research – Development of a Performance-Based Asphalt Mixture Overlay for Usage In A LowBudget Pavement Management System CTAA
Research – Development and Field Experience of Performance-Based Low Permeability Asphalt Mixture Used to Overlay Bridge Decks
Research – Comprehensive Evaluation of Warm Mix Asphalt Moisture Susceptibility
Research – Development and Field Evaluation of High Performance and Fuel Resistant Asphalt Mixture
Pavement Process Overview – Dense Graded Cold Mixes

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