Construction Methodology of Bituminous Concrete

Bituminous Concrete (herein after referred as “BC”) is a type of construction material that is used to build highways, driveways, and parking lots.

It is composed of a binding agent and a mixture of stone and other types of aggregate materials. This binding agent is known as “bitumen,” and it is produced as a residue of petroleum refining. When heated, it has a thick, sticky texture similar to tar, and when dry, it forms a dense solid surface.

Machinery

1. Hot mix plant of suitable capacity
2. End Dumpers
3. Paver Finisher
4. Vibratory Rollers of capacity 80-100 KN static weight or pneumatic tyred roller of capacity 120-150KN weight.
5. Bitumen sprayer
6. Camber board and 3 m straight edge
7. Mechanical broom
8. Air Compressor
9. Survey kit etc.,

Material

1. Paving Bitumen of penetration grade VG 30/VG 40 shall be used generally and in accordance with clause 507.2.1 of MoRT&H.
2. Coarse aggregate shall be of clean, strong, durable, cubical shape and free from other deleterious matter and adherent coating as per clause 507.2.2 of MoRT&H.
3. Los Angeles Abrasion value shall not be more than 30% when tested as per IS: 2386 (Part 4).
4. Aggregate Impact Value shall not be more than 24% when tested as per IS: 2386 (Part 4).
5. Flakiness and Elongation Indices (Combined) shall not be more than 35% when tested as per IS: 2386 (Part 1).
6. Stripping value of bitumen aggregate mixtures shall be of minimum retained coating 95% when tested as per IS 6241.
7. Water absorption of the aggregate shall not be more than 2% when tested as per IS: 2386 (Part 5).
8. Plasticity Index of the filler shall not be greater than 4.
9. Sand equivalent value of fine aggregate should not be less than 50 when tested in accordance with the requirements of IS: 2720 (Part 37).
10. The stone polishing value of aggregate shall not be less than 55 when tested as per BS: 812 (Part 114).
11. The filler shall be satisfy as per MoRT&H specification.
12. The aggregate gradation shall be as per MoRT&H table no. 500-17.

Preparation of Material

Bituminous Concrete works shall be carried as per the MoRT&H Clause 507.

The aggregate for bituminous concrete shall conform to requirements specified in the table 500.16 of MoRT&H specifications.

Bitumen: Viscosity grade paving bitumen confirming to IS: 73-2006. The grade shall be used as per requirement.

A mix of crushed stone and aggregates shall be so proportioned so as to achieve the grading specified as per MoRT&H table 500.17 of Grading-2.

The proportioning shall be done by determining the individual gradation of the individual ingredients and the blend determined by trail and error method so as to achieve the gradation specified. Bituminous Concrete shall be constructed as per the MoRT&H specifications, Clause 507.

As per MS-2 sixth edition, VA (Air Voids), VMA (Voids in Mineral Aggregates), VFB (Voids filled with Bitumen), Stability and flow shall be determined for the material so blended.

The mixture shall meet the requirements as per MoRT&H table 500.11.

Mix Design with proportion of all materials grading/test reports shall be submitted to respective authorities and trail patch shall be constructed before actual commencement of Bituminous Concrete work.

In case of variation of gradation in the course of work the proportion shall be suitably modifies so as to achieve the desired gradation.

Procedure

1. The base shall be thoroughly swept clean free from dust and foreign matter by means of mechanical broom and compressed air.
2. Marking shall be done by adjusting paver sensor to its lines, grades and cross sections.
3. Tack coat shall be applied over the prepared base by using approved material to the required quantity.
4. Mix produced from the hot mix plant shall be transported to the site by means of end dumpers.
5. The mix shall be unloaded gently into the paver hopper and paving shall be started uniformly.
6. The levels shall be checked before paving and after compaction with respect to the designated levels. If there is any variation in the levels, the same shall be adjusted in further paving.
7. Initial or break down rolling shall be carried out immediately following close to the paver in longitudinal direction from lower edge to upper edge with 80 – 100 KN static weight of smooth wheeled roller. The speed of the roller shall be maintained not more than 5 Km/hr.
8. Intermediate rolling shall be done with 80-100 KN static weight of vibratory roller or with a pneumatic tyred roller of 120-150 KN weight having Tyre pressure of atleast 0.56 Mpa.
9. Traffic shall be allowed after completion of the final rolling when the mix has cooled down to the surrounding temperature.
10. Laying trail/test section shall be carried out on a suitable area after conforming performance of the mix design and density. The area of the laying trails shall be a minimum of 100 Sqm.

Quality Control

This shall be done as per table 900-3 of MOST (Ministry of Surface Transport).

1. The gradation of the mix shall be controlled at plant as per approved designed mix.
2. Mix temperature shall be controlled at plant within the range of 150-165°C and the temperature less than 140°C shall not be used for paving.
3. The compacted surface shall be checked for field density by taking cores at the frequency of 1 test for 700 Sqm. The degree of compaction shall have a minimum field density equal to or more than 92% of the average theoretical maximum specific gravity obtained on the day of compaction in accordance with ASTM-D-2041.
4. The surface shall be checked for levels at 5 m intervals longitudinally and transversely and the same shall be within +/-6 mm.
5. The thickness of the compacted layer of BC shall be checked from cores and levels.
6. The requirements for BC material and laid each day shall be confirmed by laboratory and field tests as per Clause 509.3.1 of MoRT&H.

Environmental Control

1. While producing or crushing of aggregates in the crusher plant care should be taken in respect  of controlling and minimizing flow of duct, noise and use of blasting materials such as dynamite, safety aspects to workers are also vital and should be taken of.
2. Care will be taken to prevent spilling of material from the trucks during transportation.
3. Excess material, if any, after using in the pavement should be carefully disposed off in the designated area.

Above all, this is the general procedure of Bituminous Concrete. The procedure varies on type of road, design, pavement characteristics etc.

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Also Read: Construction Methodology of Dense Bituminous Macadam