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Cement Bound Material



  1. Milling or excavation shall be carried-out on the demarcated area to the required depth.
  2. Upon reaching the required depth, the surface of the existing road base shall be cleaned from any dust and debris etc.  Manual dipping shall be carried out jointly with the Engineer representative at site.
  3. The moisture content of the designated areas will be taken accordingly prior to recycle works.
  4. Cement (in bags) is distributed at specified intervals throughout the construction area. The propose length of cement distribution is 100 meters instead of 200 meters (per stage). This is to ensure the recycle and final compaction time is within 2 hours (Series 820.1, clause 13). Then, the bags are opened and cement is uniformly spread out (manually).
  5. If cement distributor is used, the operator shall calibrate the rate of cement distribution per area as required prior to operation.
  6. The materials are mixed without any additive using milling machine. When the moisture content in the materials is insufficient, water is added during the mixing or pulverisation process.
  7. The above procedure shall be followed with prime compaction in which the road base is levelled and shaped to its required depth with back-pusher or motor-grader, the mixture to be thoroughly compacted until the required density and approximate optimum moisture content is obtained. The mixture can be effectively compacted though using of combination of rollers.
  8. The recycle and compaction works will do in two stages. Each stage in 2 meters as milling machine width is 2 meters in 1 hour operating. Next 1 hour is for touch up and spraying of prime coat on the new laid recycle surface.
  9. At transverse construction joints, the finished end should be vertically cut and removed before fresh materials are placed against the cut section after a period of time, the construction joints could develop cracks.
  10. The prime coat should be applied manually (hand spray) immediately after completion of the CBM layer.  The prime coat layer is to serve as a protection layer against adverse weather condition.
  11. To prevent water ponding during the curing period, trench shall be dug up across the shoulder at the lowest point to clear of any ponding water. 
  12. The newly laid CBM layer is allowed to cure for 72 hours prior to overlaying with hot mix over the treated (Series 820.3, clause 16).
Calculation of Cement Usage:
  1. The cement percentage shall be as approved by the Engineer.
    The calculation for 1 m2 of area shall be as below:

    Cq = Cratio x d x ρ

    Cq, Cement quantity (kg/m2)
    Cratio, cement ratio (%)
    d, depth of treatment (m)
    ρ, density of compacted CBM, kg/m3
      
    The sample calculation for cement usage of 4% at depth of 250 mm is as below:

    Cq =  4/100 x 0.250 x 2300

    Cq = 23.0 kg for 1 m2 or 1 bag of 50 kg of cement bag can cover an area of 2.17 m2.

    Based on the above calculation, we know that per pass the machine can cover 2.00 meter width per process.  Thus, at site the following grid system shall be implemented: the grid shall be at 2000 mm x 1085 mm for one cement bag.  The grid is system is shown in the following diagram.
     

    The above distribution interval shall be followed throughout the project unless there changes in depth and cement ratio.
Posted by Engineer Malaysia