Wet Mix Macadam Construction and Quality Control

Wet Mix Macadam(WMM) work includes laying and compacting clean, crushed, graded aggregate and granular material premixed with water to a dense mass on a prepared GSB layer or existing pavement as per the requirement of the project. WMM can be laid in one or more layers, but the thickness of the single compacted layer is not less than 75mm, and the maximum of 200mm when vibrating or other approved types of compacting equipment are used.

Also, Read: Sieve Analysis of Coarse Aggregate Test – Construction Civil

Plants, Equipment and Machinery for Wet Mix Macadam:

The following plants and equipment are necessary for wet mix macadam works.

• WMM plant – 01 No
• Loader – 1 No
• WMM Paver (Sensor) – 01 No.
• Motor Grader – 01 No
• Vibratory Rollers, capacity 80-100KN static wt – 2 Nos.
• Tipper/Dumpers, Cap – 10T/20T (As per site requirement)
• Plate compactor (as per site requirement)

The above equipment deployment list is for a single WMM setup, whereas the number of sets shall be mobilized per the program’s requirement.

Also, Read: Site Clearance – Clearing and Grubbing for Highway Construction

Also, Read: Granular Sub Base Construction and Quality Control

Wet Mix Macadam Material:

Coarse aggregate The coarse aggregate shall be crushed stone of identified quarry having the following physical characteristics. The WMM material should conform to the physical requirement and strength per the technical specifications and standards. The aggregate for wet mix macadam shall conform to requirements specified in table 400-10 of MORTH and Technical Specifications.

• If the water absorption of the coarse aggregate is more than 2.0%, the soundness test shall be carried out on the WMM material as per IS: 2386 (Part-5).
• A mix of crushed stone and aggregates should be proportioned to achieve the grading specified per MORTH & Technical Specifications.

Also, Read: Subgrade – Steps for Preparation of Subgrade

Also, Read: Embankment Meaning – Construction – Quality Control

Also, Read: Dense Bituminous Macadam (DBM) Construction Requirements

• The Proportioning shall be completed by determining the individual gradation of the individual ingredients and the blend determined by trial and error method to achieve the gradation specified. 
• Wet Mix Macadam shall be constructed per MORTH Specifications, clause 406, and as per change made to various Sub-Clauses in clause 406.
• MDD & OMC shall be determined as per MORTH clause 406 for the material so blended.
• Mix design with the proportion of all materials, grading/test reports shall be submitted to Engineer, and a trial patch of appropriate length shall be constructed before the actual commencement of Wet Mix Macadam work. 
• The trial patch shall be laid on an approved granular sub-base layer on the road alignment as approved by the Engineer. 
• If the trial patch result does not meet the specified requirements, the same shall be repeated unless the requirement is fulfilled.
• In case of different gradation in the course of work should be furnished to Engineer for their approval.

Wet Mix Macadam Construction Operations:

Also, Read: Asphalt Concrete/Bituminous Concrete(BC) Construction Guide

Preparation of Base for WMM:

• The surface to receive the Wet Mix Macadam layer shall be prepared to the specified lines and cross-fall (camber) and made free of dust and other extraneous material. 
• Rain cuts and surface irregularities, if any, shall be repaired before placing of WMM layer. 
• Base preparation should be done as per clause 404.3.1 of MORTH technical specification.

Lateral Confinement of WMM Layer:

While constructing wet mix macadam, the arrangement shall be made for lateral confinement of the wet mix macadam. This shall be completed by laying materials in adjacent shoulders along with the WMM layer and following the sequence of operations described in clause 407.4.1 of MORTH specifications.

Preparation of WMM Mix :

• Suitable ingredients in required proportion shall be mixed with required OMC in a WMM mixing plant, with the provision of controlled addition of water and forced or favourable mixing arrangements like pug mill or pan type of mixer.
• Optimum moisture for mixing shall be obtained by following IS 2720(Part-8) after replacing the aggregate fraction retained on the 22.40 mm sieve with the material of 4.75mm to 22.4mm size. 
• While adding water, the due allowance shall be made for the evaporation loss. 
• During compaction, water in the wet mix shall not vary from the optimum value by more than the agreed limit. 
• The mixed material should be adequately wet, and no segregation shall be permitted.

Transportation, Spreading, Compaction and Finishing of Wet Mix Macadam:

Also, Read: Dense Bituminous Macadam (DBM) Preparation and Laying Methodology

Transportation:

• The material shall be thoroughly mixed in the Wet Mix plant as per the approved mix formula.
• The material shall be loaded onto the dumpers directly from the wet mix plant for transporting to the WMM location.
• Mark the lines of WMM with lime powder or pegs on the completed GSB layer.
• Lateral confinement shall be provided by laying the material for the shoulder prior to the wet mix laying operation as described above.
• The WMM shall be laid and compacted in two layers of uniform thickness as defined in the scope of work, and the compacted layer shall not be less than 75 mm and not more than 200 mm. 

Spreading of Wet Mix Macadam:

• The first layer shall be spread by a motor grader, whereas the second layer shall be spread with a Sensor Paver. 
• The motor grader shall be capable of laying the WMM material uniformly all over the surfaces. Its blade shall have some hydraulic control suitable for initial adjustments and maintaining the same to achieve the specified slope and grade. 
• The paver finisher shall be self-propelled, having loading hoppers and distribution mechanism along with a tamping and vibrating arrangement for the compaction control mechanism to ensure the finished surface free from surface blemishes.

Also, Read: Determination of Sieve Analysis For Fine Aggregate

Also, Read: Construction of Mastic Asphalt for Roads and bridges

 Compaction of Wet Mix Macadam:

• Compaction of WMM shall start immediately after laying is completed. The compaction shall be completed with the help of a vibratory compactor. The compaction pattern, including the number of passes required, shall be finalized after full-scale trials at the site to achieve 98% of MDD determined as per IS: 2720 (Part-8).
• One pass of the roller shall include both forward and reverse movement, and the roller speed shall not exceed 5Km/Hr. Considering the above, the general pattern of rolling shall be as follows:
  • Initial rolling – 2 static passes with a Vibratory roller.
  • Subsequent rolling – 4 vibratory pass
• The compaction shall commence from the lower edge and shall move to the upper edge, width by width. 
• The roller shall progress parallel to the road’s centerline, uniformly over-lapping each preceding track by at least 1/3rd width until the total area/surface has been rolled. 
• Alternate vibratory roller trips shall be terminated at stops at least one meter away from any preceding stop. 
• Quality control tests shall be carried out prior to the commencement of the next layer.
• The second layer of WMM shall then be laid to the limits and compacted.

Also, Read: Aggregate Impact Test Procedure for Determining AIV as Per IS 2386 Part-4

Finishing and Opening to Traffic:

• After the final compaction of Wet Mix Macadam, the same shall be allowed to dry for 24 Hours.
• The surface of Wet Mix Macadam shall have a suitable cross fall to enable efficient surface drainage. 
• The finished WMM top surface level shall be within the tolerance limits specified in Table 900-1. (i.e +10 mm to –10mm).
• Vehicular traffic or heavy movement should not be allowed on the finished WMM top surface until it has dried and the wearing course is laid.
• During the construction period, the traffic arrangement shall be made as per clause 112 of MORTH technical specification.

Summary

Article Name

Wet Mix Macadam Construction and Quality Control

Description

Wet Mix Macadam(WMM) work includes laying and compacting clean, crushed, graded aggregate and granular material, premixed with water, to a dense mass on a prepared GSB layer or existing pavement as per the requirement of the project.

Author

WhiteHelmet

Publisher Name

Construction Civil

Publisher Logo