BRIDGE DECK POURS - METHOD STATEMENT

1)   Scope of Work

a)   The bridge decks consist out of cast in-situ post tensioned multi cell concrete structures with a top deck. A final road surface is provided by an overlay of asphalt.

2)   Construction Sequence

a)   The deck of concern Bridge (maybe) divided into 2 or more construction stages with optional construction joints at 6m offset from the piers transversely across the decks. Stage 1 comprise of several no. spans running from Pier no.(x) to Pier no. (xi) and stage 2 out of (x) no. spans running from abutment 1 to Pier(x). Thus in total (x) no. major pours with (x) no. infill pours.

b)   Please refer to the attached drawing (which should be attached) for pour sequence. First cast partly the webs moving on the bottom slab and then back to cast the balance of webs (from lowest point level forward to the upper point).

c) after 7 days of completion the bottom slab ,de-shuttering the interior  shutter of webs to be done and fix scaffolding and top slab formwork ,steel reinforcement and pouring of concrete to be done  

c)   Staging of the bridge will remain in place for full duration until all post tensioning works are done.

3)   False Work

a)   A supporting system will be used for staging out the full plan area of each deck. The staging consists out of a braced structure with supporting primary and secondary beams (timber, steel and / or aluminium beams) separately submitted designs and layout regarding /supporting system.

b)   All above will be overlaid with 18mm marine plywood to provide final finishes as per specification.

c)   The cantilever slab will be supported by a light weight braced structure with primary and secondary beams (timber, steel and / or aluminium beams). This support structure will be removed after 14 days of casting the top deck.

d)   A cup lock support system with adjustable jacks, primary and secondary beams (timber and aluminium beams) will be used for top deck. A layer of 18mm marine plywood will cover this support system to provide finishes as per specification. This system to be removed in 7 days after casting the top deck.

4)   Placement & Finishes of Concrete

a)   Concrete Supply

i)          Approved Batching plant concrete to the approved mix design will be supplied by approved supplier. The average deliver time for the concrete trucks from plant to site is + 30 minutes.

ii)         Concrete will be batched from a fully automated batch plant capable of batching 100m³/hr. Average delivery production rate from the plant is in the region of 30 - 70m³/hr.

iii)        Placement of the concrete will be via truck mounted pumps. Generally/ 2 no’s pumps per pouring. A 3^rd pump is necessary will be on standby even if not used.

iv)        The pour rate will be + 30 – 40m³/hr for each truck mounted pump

v)         Where temperature permits the deck pours will be carried out during day or night.

b)   Pre – Pour Inspections

i)          All false work openings and support works to be inspected for structural integrity and in accordance with approved support layout drawings

ii)         All formwork to be re-checked for level, cross falls and camber if required. The check / approval will be carried out prior to fixing of the reinforcement.

iii)        Ensure that control stations are setup to check horizontal alignment back to known points and check the overall width at several locations along the length of the deck.

iv)        Inspect all formwork surfaces to ensure tightness and alignment of joints, surface finish, cleanliness and cover.

v)         Inspect all reinforcement to ensure compliance to approved working drawings including size, number, position and laps. Also ensure that the correct cover is maintained and that sufficient concrete spacer blocks are provided.

vi)        Inspect all post tensioning ducts for position, spacing, profile alignment, fixing and joint preparation.

vii)       Ensure that all construction joints stop ends are securely fixed.

viii)      Ensure all formwork to webs are in accordance with approved drawing. Also check the cover between reinforcement and formwork.

ix)        On completion of above, fetch Engineer for inspection and approval.

x)         After obtaining approval from Engineer, concrete will be ordered.

xi)        When high ambient temperature exist a fog mist of water will be sprayed in the air during the concreting process.

c)   Web Pours

Divide the total length of cast into equal length(about 7 to 10 )meters prior to control pouring the concrete with good compaction, Complete the 1^st Part section before moving to next Part section

           

*Start web pouring at the lowest point of the bridge deck section.

           

Commenced with the webs first with the 1^st layer filling up the haunch section followed by the 2^nd   layer and up to top slab formwork level. Compaction in haunch to be done by using pokers from the bottom and from the top jointly. Continue to vibrate until concrete flow freely from underneath formwork to form haunch section. Proceed with 2^nd layer after this. After completion of the 2^nd layer commenced with the bottom slab and moved back to do the balance of webs. Each layer not to exceed maximum thickness of 400mm as per specifications. Compaction of 1^st layer in haunch section will be with 75mm and 50mm vibrating pokers. The number of pokers will be depended upon size and length of pour.

After completing casting full height of web, vibrate down to haunch section again, stop vibrating when movement of concrete is visible to eye from underneath the web shutters. Struck off to the correct level at top of webs to form a construction joint. The construction joint between the web/top slab will be prepared using approved retarder and washing away later any laitance by high pressure water jet. Washing down the construction joint will depend on the final setting of the concrete and in accordance of the manufacturers instructions, any additional roughness later to be done by mechanical means.

d)   Bottom Slab

i)          For each slab pour, a drawing will be prepared showing the following:

            a)         Location of slab

            b)         Truck mounted pump locations

            c)         Volume rate of pour and + quantity of trucks

            d)         Direction of concrete placement

ii)         Placement of the concrete will commence from the lowest point of the bridge section. (Same as per the webs) Commence with bottom slab only after the casting of the 2^nd layer in web.

iii)        Divide bottom slab also in  equal lengths as per webs

iv)        Compaction to be done with 75mm and 50mm vibrating pours. The number of pokers will be depended upon size and length of pour.

v)         Steel pipes will be installed to control the concrete level. The surface to be floated to produce a uniform surface free from screed marks as per specification.

e)   Deck Top Slab

i)          Temporary false work will be constructed between the webs to support the deck slab soffit.

ii)            The profile of the soffit to be checked in conjunction with the Engineers and Surveyors.

iii)        Reinforcement to be fixed in accordance with approved drawing.

iv)        Timber / steel rails to be provided to control the finish level with particular attention to grade or camber changes.

v)         Concrete will be placed by truck mounted pumps in a single layer commencing from the lowest point of bridge section. The concrete will be compacted by using 75mm vibrating pokers and top surface by vibrating screed beam, the number of pokers will be generally three/pump with a fourth on standby.

vi)        When the concrete hardened sufficiently the surface will be floated by hand, apply a brush finish transversely across the deck.

f)    Curing

i)          After the brush finish has hardened enough clean water will be sprayed over the surface. Wet hessian will then be kept on the fresh concrete. For normal water curing the wet hessian is to be covered with plastic sheeting to retain the moisture.

4)   Plant & Labour

i)    General

      Concrete Type                                                          45/20 (OPC/MC)

      Rate of Pour                                                             70m³/hr (2 nos. Pumps)

      No. of Pumps                                                            2 + 1 Standby

      Anticipated Pour Period                                         (x) hours(depend of quantity) +

                                                                                       I hour to finish

ii)   Plant

      Power                                                                         1 Generator set + 1 standby

      Inverters                                                                     6 nos. + 2 standby

      3” Pokers                                                                   6 Nos.

      2” – 2 ½ “ Pokers                                                      6 Nos.

      1 ½ “ Pokers                                                              4 Nos.

      Compressor                                                              1 No.

      High Pressure Water Jet                                        1 No.

Lights (Fixed)                                                            Adequate Lighting will be provided

Lights (Mobile)                                                          8 Nos.

iii)  Manpower

      Engineer                                                                   1 No.

      Foreman (3 Box)                                                      2 Nos.

      Charge Hand            (3 Box)                                              2 Nos.

      Steel Fixers                                                               4 Nos.

      Carpenters                                                                6 Nos.

Mason                                                                        20 Nos.

Labour (Concrete)                                                   12 Nos.

Labour (Cleaning)                                                   8 Nos.

Labour / Mason (Pump)                                          2 Nos.

Electrician (Charge Hand)                                     1 No.

Electrician (Lab)                                                       3 Nos.

Labour (Mobile Lights)                                            8  Nos.

                                                                                    69 Nos.

iv)  QA/QC

      Lab Technician                                                        2 Nos.

      Lab Helper                                                                2 Nos.

                             

                                                                                          4 Nos.