Wet Mix Macadam consist of laying spreading and compacting of clean, crushed, well-graded granular materials on a prepared and approved Granular sub-Base. The material is well mixed with water and rolled to a dense mass. It shall be laid on one or more layers as per line and level, grade and cross section shown in the drawing or as directed by the Engineer. The thickness of single compacted Wet Mixed Macadam (WMM) Base shall not be less than 75 mm. Maximum thickness of single compacted layer base can be up to 250 mm upon approval of Engineer.
2. Setting Out.
3. Selection of Material.
5. Methods of Operation.
6. Quality Control.
7. Work Safety.
8. Environmental Safety.
I) Ministry of Road Transport& Highways Specifications
II) Technical Specifications
III) Relevant Drawings.
IV) IS 2720 Codes.
2.0 Setting Out
After the layer of GSB Sub-Base has been approved, then line and level are carried out to fix the Wet Mix Macadam base layer (herein after called WMM Base). Pegs are fixed at regular intervals on the safe side of the road edge where blade of grader should not disturb the peg while blending of the Base materials. On each peg’s top level of Base layer is marked. The chainage boards and working bench mark shall be set out side the limits of construction areas.
3.0 Selection of Material
Coarse aggregate shall be crushed stone or crusher run as per IRC 109 or clause 406.2.1 of MORT&H specification.
3.2 Physical requirement
The constituents of the aggregates shall be produced by integrated crushing and screening plant (Impact or Cone type) and, unless otherwise instructed by the Engineer, crushing shall be carried out in at least two stages. The fraction of material passing through 4.75mm sieve shall also be crusher run screening only. The aggregate shall conform to the physical requirements set forth in Table 400-12 of MORT&H. or IRC 109 clause 3.1.1
If the water absorption value test of coarse aggregate is greater than 2 per cent, the soundness test shall be carried out on the materials delivered to site.
3.3 Grading Requirement
The aggregate shall conform to the grading given in table 406.2.1.2 of technical specification or IRC 109 -2015. Material finer than 425 micron, shall have Plasticity Index (PI) less than 6. 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.
The following equipments shall be carried out for the WMM
1. Wet Mix Macadam Plant
2. Dumper / Tippers.
3. Vibro Roller (80 to 100 KN)
4. Water Tanker
5. Paver capable of paving more than 9 meter width.
6. Survey kit / instrument
5.0 Method of Operation
5.1 Preparation of WMM Base (As per clause 406.3.1):
5.1.a Provision of lateral confinement of aggregates
Proper arrangement shall be made for the lateral confinement of wet mix during laying. 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.
The sequence of operation shall be followed as described in clause: 406.3.3 of MORT&H.
5.2 Preparation of mix
Wet mix Macadam shall be prepared in an approved WMM mixing plant having provision for controlled addition of water and forced/positive mixing arrangement. Optimum moisture for mixing shall be determined in accordance with IS: 2720 (Part 8) after replacing the aggregate fraction retained on 22.4 mm sieve with materials of passing from 22.4 and retained on 4.75 mm. While adding water, evaporation loss shall also be taken into account. The mixed material should be uniformly wet and no segregation shall be permitted.
5.3 Spreading of mix
Immediately after mixing, the aggregate shall be spread uniformly and evenly upon the approved GSB layer. Materials should neither be dumped in heap nor their hauling over a partly completed stretch. The first layer will be laid by motor grader and the second layer mix shall be spread by a WMM paver finisher capable of paving minimum 4.5m to 9.0m width. The layer may be tested by depth block during construction. No segregation of materials are allowed. The aggregates should be of uniform gradation with no pockets of fine materials.
After the mix has been laid on site to the required thickness, grade and camber, then compaction is carried out with suitable roller to the full depth. For a thickness up to 200mm in a single layer, compaction shall be done with vibratory roller of 80 to 100 KN static weights with plain drum or equivalent capacity roller. Rolling is done from lower edge towards upper edge longitudinally for the portion having unidirectional cross fall and super elevation.
Each pass of the roller shall uniformly overlap not less than one third of the track made in the previous pass. During rolling, grade and cross fall shall be checked and any high spot or depressions, which become apparent, corrected by adding or removing fresh materials. The speed of roller shall not exceed 5km/h. Rolling shall be continued till the density of the layer is achieved 98% of the Maximum Dry Density.
Rolling should not be done when the WMM layer is soft or yielding or when it causes a wave like motion. If level difference or irregularities develop during rolling which exceeds 12 mm when tested with 3 metre straight edge, the surface should be loosened and premixed materials added or removed as required before rolling again. In no case the unmixed material be permitted to make up the depressions.
5.5 Opening to traffic
After testing the compaction & level of WMM course the road shall be allowed to dry for 24 hours. Preferably no vehicular traffic should be allowed on the finished WMM surface till it has dried and covered with wearing course.
6.0 Quality Control
Table 400-12 Physical Requirement of coarse aggregate for Wet Mix Macadam for Sub-base /Base Courses
406 WET MIX MACADAM SUB BASE /BASE
Table 400- 13: Grading Requirement of Aggregate for Wet Mix Macadam
- Control Tests for Granular WMM Base: Post Construction
- Tolerance in Surface Level : +10 mm
- permissible undulation (with 3 m straight edge) : 8 mm
- no. of undulations permitted in any 300 m length, exceeding 12 mm: 20
- Control on quality of materials and works shall be in accordance to section 900 of MORT&H.
7.0 Work Safety
1.Safety will be provided location specific safety plan.
8.0 Environmental Safety
1.Nearby Streams, water courses, lakes, reservoir shall be protected from contamination by the soil erosion from areas exposed during excavation by constructing temporary berms, dykes, sediment Basins, slopes, drains & by the use of temporary mulches, seeding or other control devices.
2.Vehicles tracks shall be kept moist to prevent flying of dust particles with the vehicle movement.