Wet Mix Macadam construction is an improvement upon the conventional Wet Bound Macadam (WBM) and is intended to be as an alternative and more durable pavement layer in roads and highway works .
It generally consists of clean, crushed, graded aggregates premixed with other granular materials and water and rolled to a dense mass on a prepared surface.
- It is generally used as a base course of Flexible Pavement.
- WMM provides a uniform and strong support, high resistance to deformation and distress.
Material Requirement for WMM
- Material to be used for WMM shall be
- Crushed Gravel
- Crushed Stone
- WMM material shall be free from organic or other deleterious constituents.
- It shall conform the Grading requirements as per MORTH V Table 400-13.
Grading Requirements WMM-MORTH V Table 400-13:
|IS Sieve Designation||Percentage by weight passing|
Grading Curve for WMM-Morth V:
Quality Control Tests and Frequency
|Tests Performed||Relevance IS Code||Frequency of Tests||Limits|
|Sieve Analysis||IS 2720 (Part4)||1/200 m³||As per Morth-V|
|AIV/Wet AIV||IS 2386 (Part4) / IS5640||1/1000 m³||As by Engineer|
|Los Angles Abrasion Value||IS 2386 (Part4)||1/1000 m³||≤30%|
|FI & EI||IS 2386 (Part1)||1/500 m³||≤40%|
|Liquid Limit||IS 2720 (Part5)||1/200 m³||≤35%|
|Plasticity Index||IS 2720 (Part5)||1/200 m³||≤6|
|MDD & OMC||IS 2720 (Part8)||1 test per source||As per material|
|Water Absorption||IS 2386 (Part3)||1 test per source||Max 2%|
|Soundness Test||IS 2386 (Part5)||1 test per source||<12% with Na2SO4 <18% with MgSO4|
|Moisture Content||IS 2720 (Part5)||As per Engineer||As by Engineer|
|Field Dry Density||IS 2720 (Part28)||3 test/1000 m²||>98% of MDD|
Method of Construction:
Preparation of WMM from plant:
- Wet Mix Macadam shall be prepared, as per approved design proportion. In the pug mill plant with controlled addition of water. Water to be maintained within limit.
- Gradation of the mix shall be checked at the start of plant for the day work.
- Generally, 1-2% extra moisture that of OMC shall be maintained in the mix to compensate the evaporation losses depending up on lead and season.
- Mix shall be transported from the plant to the laying site by dumpers with tarpaulin.
Spreading/Paving of WMM:
- If the GSB layer surface is found to be dry, water shall be sprinkled before laying of WMM.
- While constructing Wet Mix Design, arrangement shall be made for the lateral confinement of Wet Mix where WMM is laid on the outer edge of carriageway.
- Control pegs shall be fixed at every 10m along CL on both sides of the bed in such a manner that they are not distributed by paver movement.
- Required level shall be marked on the pegs with suitable vertical offset and string wire shall be fixed over the pegs to hold the sensor of paver.
- The string wire shall be tightened by using hand winch.
- The paver shall be set over the GSB layer considering loose thickness and shall be kept 15-17% extra than compacted thickness.
- Paver shall be check for skid and sensor before unloading WMM mix.
- Special care is required for cambering and grade to be maintained.
- Test trail shall be done to check the number of passes required for achieving 98% of FDD and approved from clients.
- The number of passes shall be made as:
Plain Pass- 1, Low vibration- 2, Plain Pass- 1
- The speed of roller during compaction shall not exceed 5kmph.
- The acceptance criteria for the test on density shall be subject to condition that mean density shall be less than the specified density plus [1.65-1.65/(no. of samples)^0.5] times standard deviation.
- Moisture Content, sampling of raw material is very important aspect.
- If the surface is found high or low, the top 75mm shall be scarified, re-shaped with freshly mixed WMM material.
- The surface shall be watered thoroughly up to 75 mm for scarifying by using Mechanical Grader.
- Care shall be taken to ensure the line and levels including surface regularity to the specified requirement.
- Surface level- The level of finished layer shall not vary from the project design level for a particular layer.
- Tolerance on surface levels: ±10mm.
- For checking compliance with the above requirement, measurements of the surface levels shall be taken on a grid of points placed at 6.25m longitudinally and 3.5m transversely along the pavement. The average of 10 measurements shall not be more than 3mm above the permitted limit.
- Wet Mix Macadam productivity: 25000 m³/Month/team/shift
- Paver productivity : 60 m³/hr
- Roller productivity : 60 m³/hr
- The above details are considered for 5km lead and 8-10 hr of working time.
- For WMM 160 TPH plant is considered for production.