Method of placing Neoprene bearings in position

(A) For solid slab super structure

Preparing Seating

Strip in concrete cap

During concreting of the pier/abutment caps, a continuous strip of width 'B' (slightly more than width of bearing) and depth of 10 to 15 mm. shall be kept in concrete this can be done by removing concrete carefully when green.

Bearings in position: Levelling & Placing the Bearings

A few days before placing of superstructure:

1. Concrete the strip as formed in above image shall be completely filled in by stiff cement mortar 1:1 proportion with water cement ratio not exceeding that of parent concrete of pier cap. Very fine sand with size between 3 mm. shall be used for preparing this mortar. The top surface shall be perfectly levelled.

2. Centre line positions of the bearings shall be marked accurately on pier and abutment caps in both the directions. The plan dimensions of the bearings shall then be marked.
3. The bearings shall be placed on the green mortar by light tamping if necessary. The mortar shall be cured for atleast 7 days.

Erection of centering and casting the slab

a) Casting in situ deck.

The area around the bearings shall be filled with well rammed, selected fine damp sand. The thickness being equal to that of the bearing. The sand shall be covered with polythene layer. The side gap between soffit and pier cap may be sealed off by timber packing pieces.

The rest of the centering shall be erected as standard practice. The reinforcement for the solid slab shall be fixed in position as usual. During concreting great care shall be taken to avoid puncturing of the polythene membrane and displacement of the bearings.

Draining out Sand

After 14 days from casting of the solid slab, the side timber packings shall be removed and the sand shall be drained out by water jets.

(B) For T Beam and slab superstructure

Preparing Seating

Same as above.

Levelling and placing the bearings in position

same as above.

iii) In case where M. S. plate is to be placed below the bearings, the plate shall be placed in position on the green mortar by light tamping. The position of bearing shall then be marked on these plates. The bearings shall then be placed in position. Epoxy grout shall be applied to the top and bottom surfaces of the bearing, wherever specified. The mortar shall be cured for minimum 7 days.

Erection of centering and casting superstructure

1. For cast in situ decks. The procedure will be same as for solid slab. The sand packing will be required only under the main girders and not all over pier cap.
2. For Precast Decks. Precast beam shall be placed on these bearings after a minimum period of 7 days from placement of the mortar, to allow mortar to develop adequate strength.

Additional insight (per IRC:83 Part-II and MoRTH practices): The 1:1 stiff cement mortar bedding (low w/c ratio, fine sand ≤3 mm) ensures uniform support and full contact under the bearing. Cure for minimum 7 days (often 14 days recommended) before loading to achieve strength. Sand bedding (fine, damp, rammed + polythene) is a standard temporary support for in-situ casting to prevent leakage and allow precise positioning; remove by jetting after concrete gains strength (14+ days) to avoid long-term settlement. For T-beams/precast, epoxy grout on interfaces (if specified) bonds effectively; ensure no displacement during girder erection. Bearings must be clean, protected from contamination during concreting, and inspected for full seating post-installation. Avoid over-tamping to prevent tilting.

Best practices note: Align bearings precisely with marked centerlines in both directions. Use leveling tools (spirit level) during placement. For skew/curved bridges or high loads, verify no uplift or twisting. Protect bearings from mortar splash/debris; clean immediately if contaminated. Follow IRC:83 for material quality (e.g., neoprene shear modulus, hardness) and testing.