13-WEARING COAT



WEARING COAT AND APPURTENANCES

1. GENERAL

This part deals with wearing coat and bridge appurtenances such as railing, crash barrier, approach slab, drainage spout and weep holes. The work shall be executed in conformity with details shown in the Drawings and MoRTH Specifications or as approved by the Engineer.

2. WEARING COAT

2.1 Bituminous wearing coat

The construction operations and bituminous mixes shall conform to the MoRTH Specifications or as specified in the Contract.

  1. Bituminous wearing coat shall generally comprise of following types:

i) Type 1: Bituminous concrete 50 mm thick laid in single layer.

ii) Type 2: Bituminous concrete 40 mm thick overlaid with 25 mm thick mastic asphalt.

iii) Type 3: Stone matrix asphalt 50 mm thick laid in single layer.

iv) Type 4: Mastic asphalt 50 mm thick laid in single layer.

  1. Before laying wearing coat, the deck surface shall be thoroughly cleaned and tack coat shall be applied.

2.2 Cement concrete wearing coat

  1. Cement concrete wearing coat shall be laid separately over the bridge deck as per the Drawing. If the same is not mentioned in the Drawing the following details shall be followed:

i)  The thickness of wearing coat shall be 75 mm. The concrete shall be of minimum M30 grade.

ii)  Steel reinforcement of 8 mm diameter at 150 mm spacing in both directions shall be provided at mid depth of the wearing coat.

iii) In a length of 1 m near the expansion joint, additional reinforcement of 8 mm diameter bars shall be provided in both directions to make the spacing as 75 mm.

  1. Cement concrete and steel reinforcement shall conform to the respective Sections of this Manual.

2.3 Workmanship

  1. Curing of wearing coat shall start as early as possible.
  2. All carriageway and footpath surfaces shall have non-skid characteristics.
  3. The cross slope in the deck shall be kept as 2.5% or as specified in the Drawing.
  4. For the structures with flat deck surface, camber/superelevation in the wearing coat shall be achieved as below:

i) In bituminous wearing coat provide profile making course before laying wearing coat. The profile making course shall be of the same material as of wearing coat. The thickness of wearing coat at any point shall not be less than that given above.

ii) In case of cement concrete wearing coat, provide profile corrective course along with wearing coat, in single layer.

  1. Overlay on the existing wearing coat on bridge decks shall not be permitted.
  2. In case the wearing coat is damaged, it shall be repaired or replaced. The dismantling of wearing coat shall be as per MoRTH Specifications.

3. RAILING AND CRASH BARRIER

  1. Bridge railing/crash barrier includes the portion of the structure erected on and above the kerb.
  2. Railing/crash barrier shall not be constructed until the centering false work for the span has been released and the span is self-supporting.
  3. For concrete with steel reinforcement, requirements for the items of concrete and reinforcement mentioned under relevant Sections of this Manual shall be applicable.
  4. The railing/crash barrier shall be carefully erected true to line and grade. Posts shall be vertical with a tolerance not exceeding 6 mm in 3 m. The pockets left for posts shall be filled with non-shrink mortar.
  5. The type of railing/crash barrier to be constructed shall be as shown in the Drawings and shall conform to IRC: 5 and IRC: 6.
  6. Care shall be exercised in assembling expansion joints in the railing/crash barrier to ensure that they function properly.
  7. The railing/crash barrier shall be of such design as to be amenable to quick repairs.
  8. The material of metal railing/crash barrier shall be handled and stored with care, so that it remains clean and free from damage. Railing/crash barrier materials shall be stored above the ground on platforms, skids, or other supports and kept free from grease, dirt and other contaminants.
  9. Methods of repairs shall be such that they do not damage the material or protective coating.

3.1. Metal railing/crash barrier

  1. Materials, fabrication, transportation, erection and painting for bridge railing / crash barrier shall conform to the requirements of specifications of structural steel.
  2. All steel railing elements, pipe terminal sections, posts, bolts, nuts, hardware and other steel fittings shall be galvanised or painted with an approved paint.
  3. If galvanised, all elements of the railing/crash barrier shall be free from abrasions, rough or sharp edges, and shall not be kinked, twisted or bent.
  4. If straightening is necessary, it shall be done as per method approved by the Engineer.
  5. Damaged galvanised surfaces, edges of holes and ends of steel railing/crash barrier cut after galvanising shall be cleaned and re-galvanised.
  6. The railing/crash barrier shall be carefully adjusted prior to fixing in place to ensure proper matching at abutting joints and correct alignment and camber throughout its length.
  7. Holes for field connections shall be drilled with the railing/crash barrier in place in the structure at proper grade and alignment.
  8. Unless otherwise specified in the Drawings, metal railing/crash barrier shall be given one shop coat of paint and three coats of paint after erection, if sections are not galvanised.
  9. Railing/crash barrier shall follow the alignment of the deck as per the Drawing.

3.2. Cast in-situ concrete railing/crash barrier

  1. The portion of the railing/crash barrier or parapet which is to be cast in-situ shall be constructed in accordance with the requirements of Section 600 of this Manual.
  2. Forms shall be fabricated conforming to the shape of railing/crash barrier shown in the Drawings. It shall be ensured that no form joint appears on plane surfaces. For bridges/viaducts of length more than 500 m, horizontal slip forms shall be used for casting of crash barriers.
  3. All mouldings, panel work and bevel strips shall be constructed according to the details shown in the Drawings. All corners in the finished work shall be true, sharp and clean-cut and shall be free from cracks, spalls or other defects. Castings of posts shall be done in single pour.

3.3. Precast concrete railing/crash barrier

  1. Precast members for railing/crash barrier shall be of reinforced cement concrete and shall conform to the requirements of Section 600 of this Manual.
  2. The maximum size of the aggregate shall be limited to 12 mm and minimum concrete grade shall be M30 for railings and M40 for crash barriers.
  3. The precast members shall be removed from the moulds as soon as practicable and shall be kept damp for a period of at least 10 days, during which they shall be protected from sun and wind. Any precast member that becomes chipped, marred or cracked before or during the process of placing shall be rejected.

4. APPROACH SLAB

  1. Reinforced concrete approach slab with 12 mm dia bars at 150 mm c/c in each direction both at top and bottom in M30 grade of concrete covering the entire width of the roadway, shall be provided as per details given in the Drawing or as approved by the Engineer. Minimum length and thickness of approach slab shall be 3.5 m and 300 mm respectively.
  2. Reinforced cement concrete and reinforcement shall conform to the requirements of Section 600 of this Manual.
  3. The approach slab shall rest on a base of 150 mm thick M15 grade concrete or as shown in the Drawings or as directed by the Engineer.

5. DRAINAGE SPOUTS

  1. Drainage along longitudinal direction shall be ensured by providing sufficient number of drainage fixtures embedded in the deck slab.
  2. The spouts shall be of not less than 100 mm in diameter and shall be of corrosion resistant material such as galvanised steel with suitable cleanout fixtures.
  3. The spacing of drainage spouts shall not exceed 10 m. The discharge from drainage spout shall be kept away from the deck structure by means of suitable down pipes up to 500 mm above High Flood Level.
  4. In case of viaducts in urban areas, the drainage spouts shall be connected with suitably located runners and down pipes to discharge the surface run-off into drains provided at ground level.
  5. The galvanised assembly shall be given two coats of bituminous paint before placement. The whole assembly shall be placed in true position, lines and levels as shown in the Drawings with necessary cutouts in the shuttering for deck slab and held in place firmly. Where the reinforcements of the deck are required to be cut, equivalent reinforcements shall be placed at the corners of the cutout.
  6. After setting of the deck slab concrete, the shrinkage cracks around the assembly shall be sealed with polysulphide sealant or bituminous sealant as per 1S:1834 and the excess sealant trimmed to receive the wearing coat. After the wearing coat is completed, similar sealant shall be provided to cover at least 50 mm on the wearing coat surface all round the drainage assembly.

6. WEEP HOLES

  1. Weep holes shall be provided on all plain concrete, reinforced concrete, brick masonry and stone masonry structures such as abutment, wing wall and return walls as shown in the Drawings or as directed by the Engineer to permit water to flow out without building up pressure in the back fill.
  2. Weep holes shall be provided with 100 mm diameter AC/PVC/HDPE pipe for structures in plain/reinforced concrete or brick masonry. In case of stone masonry, weep holes shall be of rectangular shape 80 mm wide, 150 mm high or circular with 150 mm diameter.
  3. Weep holes shall extend through the full width of concrete/masonry with slope of about 1 vertical to 20 horizontal, towards the draining face.
  4. The spacing of weep holes shall be 1 m in either direction or as shown in the Drawings with the lowest at 150 mm above the low water level or ground level whichever is higher or as directed by the Engineer.

RELATED CODES:

1.IRC: 5:-Standard specification and code of practice for road bridges: General features of design.

2.IRC: 78:-Standard specification and code of practice for road bridges: Foundations and substructures.

3.MoRTH:-Specifications for Road and Bridge works (5th revision).

*****