Concrete Work 



 Bonding Agent

Bonding Agent – EMACO 157 D Primer (Barra Emulsion 57 D)

Before concreting, Barra Emulsion was applied to the existing concrete surface to have proper bonding of already casted concrete and new casting member.

Properties

•      Supply form: Liquid

•      Color: Milky White

•      pH Value: approximately 9 – 10.5

•      Application Temperature: not below 5° C Toxicity: non-toxic 

 

 Column Concreting

There were two types of concrete used in this site. They were Ready Mix and Site mix. The difference between these two were, Ready Mix was weight batched and Site Mix was volume batched. Ready mix concrete batching was done in onsite batching plant. There are two onsite batching plants and backup plant from Tokyo Super 10 km far from the site.

 

Surface Preparation was done after concreting slab, ideally the concrete in the column area was chipped and cleaned  using  pressurized  air  from  a compressor  to remove  any  loose  particles  and  grout  from  the  bonding  surface  and  reinforcement  bars  are  cleaned  to  remove  any  grout before erecting formwork. This gives a rough clean surface for the concrete to bond.  

 

Scaffolding was arranged around the column for the workers to operated and checked to see if they were braced properly to ensure safety.  In  determining  whether  scaffolding  arrangement was adequate,  the best method is to have a person from the concreting  gang  to  confirm  that  was  sufficiently safe for them to work on. Otherwise, there have been a few instances where there have been lapses in scaffolding during concreting that potentially caused injuries. Especially when working at upper levels, columns in the edges of the building it was of utmost importance to eliminate any safety hazards. All workers should properly wear safety belts during concreting when working at heights.

G30 RM concrete was used for columns. Concrete pouring was done using mobile crane, and concrete buckets. (Figure 1.11). Concreting height was controlled under 1800 mm to avoid segregation. Ordering concrete with a proper slump was important, because if the mix was too stiff it will be unworkable and will require longer compaction. This increases the chance of segregation at bottom of the column, therefore, a proper mix should be used. Therefore, slump needs to be checked after batching especially in column concreting to make sure it’s within the required range. 






Figure 1.11. Column Concreting

After the concrete has been placed, it contain air voids. Concrete compaction was done for avoid the air voids in fresh concrete. Poker vibrator was used for compacting concrete. It consists short straight tube about 750 mm long and 25mm – 50mm diameter. The tube was attached to an electric motor or petrol engine with flexible hose. Poker must be insert to the concrete quickly and allow to penetrate to the bottom of the layer as soon as possible under its’ own weight. The vibrator should let in concrete around 15 seconds. Poker should be withdraw slowly and insert back nearly about 300 mm away from its’ last position. The vibrator was kept away 75mm-100mm from formwork because formwork can be damaged. Also kept away from reinforcement unless steel bars can be leave from correct position. Also formwork was tapped using rubber hammer after concrete pouring to avoid the concrete having hollow ditches.

 

Slab Concreting 

The slab thickness of a floor is 150mm & 200mm. Concrete levels are dropped on some areas in the floor. A slab is concreted in 2 - 3 stages. This method was implemented in project planning to improve progress, better utilize labor, and avoid bottlenecks in the construction process. When planning the concreting process, arrangements are made in advance according to the methods decided. If concrete was batched at site two truck mixers were used to avoid the delay during batching concrete. If a pump car was arranged, location of placing the pump car should be determined and clear access provided in advance. If a concrete was stopped between grids, it is done at 1/3rd or 2/3rd of the distance between the grids. The construction joint between the two successive concretes was comparatively a weak plane through the continuous slab. Therefore the position of the construction joint was determined thus to give the least bending moment and shear force as possible.

Surface Preparation of the formwork was cleaned  and  blasted  with  pressurized  air  to  remove  any  saw dust  and  other  debris; this  gives a  smooth  finished  surface  to  the  concrete.  Formwork  panel  joints  and  stop  board  gaps  were  covered  with  masking  tape  and  sponge  to prevent  grout  leaking. Construction joints were chipped and cleaned to give rough profile for better bonding. If  concreting  was  done  at  night  adequate  lighting  needs  to  be arranged and similar precautions (to that of column concreting) were taken on scaffolding arrangements if required (for concreting beams at the edges of the slab) and equipment used . 

Concrete should be poured uniformly as possible and formation of heaps should be avoided, if so the concrete heap needs to be dispersed before using the vibrating poker. Concrete was placed along the shorter span of the panel; this avoids formation of cold joints since time between successive concrete pours was less. (Figure 1.12) Compacting concrete was done with a poker vibrator. The concrete was leveled using gauge and troweled. An officer and a worker from the formwork section should check grout leakage underneath slab and repaired immediately.


Figure 1.12. Slab Concreting