Construction Methodology of Wet Mix Macadam(WMM)
This work shall consist of laying spreading and compacting clean, crushed, graded aggregate and granular material, pre-mixed with water, to a dense mass on prepared and approved granular sub-base in accordance with clause 406 of MORT&H specification.
Wet Mix Macadam is also known as “John Macadam”.
- Wet mix plant
- Paver finisher or Motor grader
- The smooth wheeled vibratory roller of 80 to 100 KN
- Survey kit
As per clause 406.2 of MORT&H, the material Wet Mix Macadam to be used for the construction of Wet Mix Macadam (WMM) shall satisfy the following requirements.
- Aggregate impact value shall not be more than 30%.
- Combined flakiness and elongation indices shall not be more than 35%.
- The water absorption value of aggregate shall not be more than 2%.
- Materials finer than 425mocrons shall have a plasticity index (PI) not exceeding 6.
- The mix graduation shall be satisfied as per MORT&H table no. 400-13.
In other words, it is a mixture of 40mm, 20mm, 12mm aggregates and dust with the assistance of water.
- The base of the approved GSB layer shall be leaned off all foreign matter and marking shall be done to its length and breadth.
- The wet mix produced from the plant shall be transported to the site by means of end dumpers.
- As the mix is laid by means of a paver finisher or motor grader, the string line shall be given as per MORT&H intervals to its gradient.
- The mix shall be unloaded gently into the paver hopper and paving shall be started uniformly, In the exceptional case where it is not possible for the paver to be utilized, mechanical means like motor grader may be used with prior approval of the engineer,
- The motor grader shall be capable of spreading the material uniformly all over the surface. For petitions where mechanical means can’t be used, manual means as approved by the engineer shall be used only in restricted areas.
- The levels shall be checked just after paving or grading and after compaction with respect to designed levels. If there is variation in the levels, the same shall be adjusted in further paving.
- While constructing the WMM layer, the proper arrangement shall be made for the lateral confinement of the wet mix.
- If there is any segregation after spreading or paving, the same shall be rectified by spreading fines before rolling.
- In either case, the rolling shall be carried out from lower edge to upper edge with 80 to 100KN smooth wheeled vibratory roller at a speed not more than 5km/hr.
- Rolling shall be continued until there are no tyre impressions or drum impressions on the surface and specified field densities are achieved.
- The surface shall be protected from vehicular movement until covered with asphalt layer after the final compaction of the WMM layer the same shall be allowed to dry for 24 hours.
- The surface layer shall be brushed or broomed to loose dust particles until the rough texture is exposed.
- The top layer shall be primed with approved prime coat material at the rate of 7 to 10kg/10m^2.
- The laying trail/test section shall be carried out on a suitable area as approved by the Engineer for confirming the performance of the mix design and density. The area of the laying trails shall be a minimum of 100sqm.
Quality control for the above work shall be as per table 900-3 of MORT&H specification.
- The gradation and moisture content of the mix shall be controlled at the plant as per the approved design mix.
- The compacted surface shall be checked for field density at the frequency of 1 test per 1000sqm. The degree of compaction should not be less than 98%.
- The surface shall be checked for levels per MORT&H intervals longitudinally and transversely and the same shall be within +/- 10mm.
- Surface irregularities shall be checked as per MORT&H clause 900.
- While producing or crushing of aggregates in the crusher plant care should be taken in respect of controlling and minimizing flow of dust, noise and use of blasting materials such as dynamites, etc., safety aspects to workers are also vital and should be taken of.
- Care will be taken to prevent spilling of material from the trucks during transportation.
If there is any change in the quality of aggregates or in the gradation of the individual aggregates a fresh mix to be worked out. Proper proportioning of materials and production of uniform mix shall be ensured. Proper quality control I required to achieve the design mix and adequate compaction in the field.
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