Method Statement for Wet Mix Macadam (WMM) on Granular Sub Base

This macadam work method statement covers laying and compacting clean, crushed, graded aggregate and granular materials premixed with water into a dense mass on a prepared Granular Sub base Course to specified lines, grades and cross sections as shown in drawings, subject to a minimum thickness of 75 mm and max. of 200 mm.

References and Standards

Contract Agreement

Ministry of Roads Transport & highways Specification

Relevant drawings

International and National codes.

Necessary Plant & Equipment

• Wet Mix Plant
• Mechanical Paver
• Grader
• Vibratory Rollers (80/100 kN)
• Dumpers
• Water tanker/ Browser
• Back Hoe cum Loader

Materials shall be obtained from nearby approved quarry.

Vertical Shaft Impactor (VSI) crusher will be installed at the quarry/camp sites, if required.

This crusher shall produce aggregates cubical / angular type so that flakiness and elongation index are within the specified limit.

If the water absorption of the coarse aggregate is not more than 2%, soundness tests shall be carried as per the local standards.

Grading Requirements

The aggregate shall conform to the grading given in specifications.

Material finer than 425micron, shall be non-plastic in nature.

The final gradation approved within these limits shall be well graded from coarse to fine and shall not vary from low limit on one sieve to high limit of adjacent sieve or vice versa.

Field Trial Test

A trial bay shall be laid with the wet mix macadam using paver finisher.

Loose thickness of the layer, number of passes of vibro-roller to achieve 98% modified proctor density, allowance for evaporation of moisture content, and line, level & cross fall shall be established during the trial.

Size of trial bay for wet mix macadam WMM shall be minimum 10m x 70m.

Wet Mix Macadam Laying Procedure

Preparation of Base

Wet mix macadam shall be laid on the already approved layer of the granular sub base.

The aggregates mix shall be spread to proper profile by using mechanical paver having hydraulic control suitable for initial adjustment and maintaining the same to achieve the specified slope and grade.

Surface shall be made free of dust & other extra materials.

Any ruts or soft yielding places shall be corrected in an approved manner, if necessary, by sprinkling water and light compaction as per density requirements.

While constructing Wet Mix Macadam arrangement shall be made for the lateral confinement of wet mix.

This shall be done by laying materials on adjoining shoulder along-with that of WMM layer.

The preparation of mix, spreading of mix and compaction are done sequentially.

Preparation and Transportation of Mix

WMM shall be prepared in the Wet Mix Plant of adequate capacity.

The mixed material shall be immediately transported to prepared sites by using tipper trucks.

Spreading

The plant mix WMM at Moisture Content as decided in the trial mix be transported to the site in dumpers and shall be spread uniformly upon the prepared Sub-Base/Base in required quantities.

Mix shall be spread by mechanical paver finisher, and where it is not possible for the paver to be used, mechanical means like motor grader shall be used with the prior approval of the consulting engineer.

For portions where, mechanical means cannot be used, manual means as per approved by the Engineer shall be used.

The level and gradient will be controlled with the level pegs.

Surface of the laid material shall be checked with templates, level and any high/low points shall be rectified by removing / adding material before rolling.

Compaction Method

After the mix has been laid on site to the required thickness, on grade and camber, then compaction is carried out with suitable roller to the full width.

Up to 200 mm thick material shall be compacted in single layer, compaction shall be done with vibratory roller of 80 to 100 kN static weight with plain drum or equivalent capacity roller.

The speed of the rollers shall not exceed 5 km/hour to ensure smooth finish and better compaction.

In portions having unidirectional cross fall / super elevation, rolling shall commence from the lower edge and progress gradually towards the upper edge.

Progressing parallel to the center line of the road, uniformly over lapping each preceding track by at least one third width until the entire surface is rolled.

Where rolling cannot be done by rollers, it shall be compacted with mechanical tampers or a plate compactor.

Any undulations / displacement found as a result of reversing of the direction of roller or due to some other reasons shall be rectified as specified or removed and made good to the satisfaction of the consultant.

Rolling shall not be done when the GSB surface is soft or yielding or when it causes a wave like motion.

The rolling shall be done to achieve 98% compaction as compared to laboratory maximum dry density MDD.

Surface of the layer on completion shall be well-closed, free from movement under compaction equipment & free from compaction planes, ridges, cracks or loose materials.

All loose segregated or otherwise defective areas shall be made good to the full thickness of the layer & re compacted.

Testing of wet mix macadam layer

On completion of compaction of the layer, it shall be tested for its density and other tests as per the specifications and got approved from the client before start of next pavement layer.

Opening to traffic

After final compaction of WMM course the layer shall be allowed to dry for 24 hours.

No vehicular traffic should be allowed on the finished WMM surface till it has dried and covered with next layer.

Test frequency and surface finish shall conform to the requirements of approved inspection and test plan.

Health, Safety and Environmental Requirements

During construction of wet mix macadam on new carriageway, adequate safety & traffic signs shall be installed adjacent to the working area to protect the ongoing works.

For locations where the paving of wet mix macadam is done a minimum two flagman with reflection vests holding red flags each shall be deployed to regulate the traffic affected by the construction operation.

The safety officer shall make frequent patrols along the highway to ensure that the safety equipment and signs are operational.

Note: Safety plan for diversions, roads sign fixing and for other aspects of safety shall be as per the approved project safety plan.

Vehicle tracks shall be kept moist to prevent flying of dust particles.

Stone dust shall be sprinkled with water prior to its feeding to plant hopper.

Water sprinklers or vacuum suction arrangements shall be employed on crushing plants to prevent the dust particles from polluting the atmosphere.

Plantation shall be done around the plant to make the atmosphere free from heavy particles and access carbon dioxide

Provisions given in the Contract Agreement, specifications, drawings, approved mix designs & ITP shall get precedence over this wmm method statement.