The full-scale laying and compaction of Dense Bituminous Macadam shall be carried out with the help of approved material, and mix design proposed for the permanent works using the Plants, Equipment, Machinery and approved methodology.
Acceptance Criteria of Construction Materials for Dense Bituminous Macadam:
The following materials shall be used for the activity
Bitumen for DBM work:
Paving Bitumen of penetration grade S-65 complying with Indian Standard Specifications for Paving Bitumen IS:73 and Contract Technical Specification shall be used.
Specification of Coarse Aggregates for DBM:
Coarse Aggregates shall be of crushed rock retained on the 2.36 mm sieve. Aggregates shall be as per specified in table 500-8, of MORTH for DBM and satisfy the physical requirements.
Specification of Fine Aggregates for DBM:
Fine Aggregates shall be of crushed stone passing on 2.36 mm sieve and retained on 75.00-micron sieve. It should be clean, hard, durable, dry and free from dust and soft or friable matter, organic and other deleterious matter. Fine Aggregates shall have a sand equivalent value of not less not than 50 when tested in accordance with IS:2720 part-37, and PI shall not exceed 4.0 when tested in accordance with IS:2720 part-5. This shall comply with the requirements as per clause 507.2.3 of MORTH.
Filler Specification for DBM:
Filler shall conform to 507.2.4 of MORTH specification and consist of finely divided mineral matter such as cement, rock dust, hydrated lime.
The filler gradation limits for DBM:
IS Sieve % Passing by weight
600 micron 100
300 micron 95-100
075 micron 85-100
The filler material shall be free from organic contaminants and have plasticity Index not greater than four. The plasticity index(PI) requirement shall not implement if the filler is cement or lime.
Aggregate Gradation for Dense Bituminous Macadam:
The combined coarse, fine aggregates and filler shall satisfy the grading requirements as indicated in table 500-9 of MORTH. The grading of the aggregate mix as used in work, shall be a smooth curve within and approximately parallel to the envelope in Table 500-9.
Job Mix Design Requirements for Dense Bituminous Macadam :
In addition to the grading and quality requirements of individual ingredients, the Job Mix shall meet the following requirements as per Table 500-10 of MORT&H technical specification.
|1||Marshall stability with 75 blows||Minimum 820 kg|
|2||Marshall flow||2 to 4 mm|
|3||Air voids||3% to 5%|
|4||Voids in mineral aggregates (VMA)||12% to 14%|
|5||Voids in mineral aggregates filled with bitumen (VFB)||65% to 75%|
|6||Bitumen content||Not less than 4%|
|7||Stability to Flow ratio||205 to 410|
|8||Water Sensitivity||Not less than 75%|
|9||Filler Bitumen ratio||0.6 to 1.2|
The permissible variations of actual mix from the job mix design shall be within the specified limits of Table 500-13 of MORT&H specification.
Prime Coat / Tack Coat for Dense Bituminous Macadam:
It shall be Bitumen Emulsion of grade- CSS 1h as per ASTM D – 2397 from an approved source (As per clause 502.2.3 & 503.2.1 of Contract Technical Specification).
Construction Requirement for Dense Bituminous Macadam Laying:
Plants and Equipment for DBM Operation:
The following Plants, Equipment and Machinery shall be deployed for the execution of the DBM works.
- Self-propelled Bitumen pressure sprayer equipped for spraying emulsion of 7000 ltr capacity – 01 No.
- Mobile Air compressor – 01 No.
- Hot Mix Plant of capacity 150 TPH -01 No.
- Automatic Sensor Paver – 01 No
- Smooth wheel Rollers, Cap 8 to 10 mt. dead wt – 02 Nos
- Pneumatic tyre Rollers, Cap 12 to 15 mt. dead wt – 02 Nos.
- Tipper/Dumpers of capacity. 15 mt. – Adequate nos as per the site requirement
- Water Tanker, capacity – 10,000 lit – 1 No.
- Survey related accessories and equipment
- Other accessories as per the site requirements.
Site Trials for DBM:
The full-scale laying and compaction trials shall be carried out with the approved mix design of DBM materials proposed for the permanent works using the Plants, Equipment, Machinery and methods proposed. The trials shall be done with the consent and under the supervision of the Engineer or his representative.
The trial shall be carried out to demonstrate the suitability of the Plants, Equipment, machinery and work procedures to provide and compact the material to the specified proportions, density and voids content and to confirm that the other specified criteria of the finished Asphalt Pavement can be achieved. The trial length shall be for the full construction width and depth for the layer. The trial of pavement layer shall be undertaken ahead of the proposed work to commence full-scale work on that layer.
Data to be recorded during the site trial of DBM:
- Type and grade of bitumen used shall be recorded
- The composition and grading of the construction material, including bitumen content
- The temperature of bitumen and aggregate shall be recorded immediately prior to entering the mixer, and the temperature of the mix after discharge from the mixer prior to dispatch from the plant, on commencement of laying, on commencement of compaction and on completion of compaction
- The type, mass, number of wheels, frequency of vibration and the number of passes of the compaction equipment, as appropriate for each roller type.
- The per cent air voids in the mix at the lab, voids in mineral aggregate (VMA), voids filled with bitumen (VFB), stability and flow,
- The air voids achieved at site, the compacted thickness of the layer, per cent compaction achieved and any other important, relevant information as required by the Supervision Consultant. The site trial shall be deemed to be successful if all specified sets of results over the range of combined effort meet the specified requirements for the material. The above data, as recorded in the site trial shall become the agreed basis on which the particular material shall be provided and processed to achieve the specified requirements.
Surveys and Setting out Works for DBM:
After completion of the Wet Mix Macadam layers as per the construction drawings, the limits of Dense Bituminous Macadam shall be marked as per established grid lines and Bench Marks etc. and as per approved construction drawings.
Preparation of Base for DBM:
- Where DBM is to be laid over WMM surface, Prime coat shall be applied over the granular surface before laying of DBM in accordance with provisions of clause 502 of MORTH
- The tack coat shall be applied over the previously primed surface or even previously laid Bitumen surface before laying of DBM in accordance with the provisions of clause 503 of MORTH
- The base on which DBM is to be laid shall be prepared, shaped and conditioned to the specified lines, grades and cross-sections in accordance with Clause 501 & 920 of MORTH or as directed by the Engineer. Loose materials and any foreign matters shall be removed by thorough brushing with mechanical brooms and/or blown off by compressed air or any other acceptable methods. Any defect of the surface shall be made good as instructed by the Engineer.
Edges Protection Work:
Edges on shoulder side or on the side where Kerb has not been provided shall be well protected and aligned by fixing angles of size 100 mm x 100 mm properly anchored. It shall be ensured that mix at edges is well compacted, and proper line and levels are maintained.