4. wbm roads 10 sep

WBM Roads

1. WBM Roads Definition: The pavement base course made of crushed or broken aggregates mechanically interlocked by rolling and voids filled by screening and binding material with the assistance of water

2. Salient Features of WBM Roads WBM means W ater B ound M acadam. The word Macadam comes from the name of Scottish Engineer John L. Macadam. Wearing surface is formed by cleaned, crushed aggregates which are spread and rolled by sprinkling water.

3. Salient Features of WBM Roads Low cost Thickness range: 8cm to 30 cm Camber : 2.5% to 3% OR 1:36 to 1:48 Surface is better than earthen road but rough as compared to bituminous or Concrete roads Can be used as Base Course for Bituminous or Concrete roads.

4. Materials to be used in WBM roads Crushed trap rock – Most Suitable Crushed slag Burnt Brick bats Kankar Aggregate Laterite Screenings to be used as filler material

5. IRC Recommendations for Course Aggregate Grading for WBM Roads Grading No Size Range (mm) Sieve Size (mm) % Passing the sieve by weight 1 2 3 90 to 40 63-40 50-20 100 80 63 40 20 83 63 50 40 20 63 50 40 20 10 100 65-85 25-60 0-15 0-5 100 90-100 30-70 0-15 0-5 100 95-100 35-70 0-10 0-5

6. IRC Recommendations for Grading of Screenings Classification Grading Size of Screenings mm Sieve size mm % by weight passing the sieve A B 12.5 10.0 12.5 10.0 4.75 0.15 10.0 4.75 0.15 100 90-100 10-30 0-8 100 85-100 10-30

7. Construction Procedure of WBM Roads 1. Preparation of Sub Grade 2. Preparation of Base Course 3. Intermediate Layer 4. Wearing Surface 5. Shoulders Shoulder Shoulder

8. Precautions in Rolling WBM Roads Roller to be used- 8-10 Tonnes Rolling should be done from edges to the centre The successive rolling strips should be overlapped Length of each rolling should be <=200m. Water should be sprinkled and not poured by buckets The rolling should be done for 80 passes or until the aggregates are broken.