Formwork Blog

Archive for the ‘Formwork’ Category

Here is two more pedestal formwork examples. The pedestal forms will be used on typical pedestal bases (shown below). We begin by forming up the bases.

Pedestal Base Formwork

After the base concrete is poured, the formwork is stripped leaving the pedestal steel starters exposed. After the steelfixers fix the remaining steel to the starters, it is time to assemble the pedestal formwork.

Typical Pedestal Base

On this job there are many pedestals this particular size (1200mm H x 1100mm x 1100mm) so we are using conventional timber and plywood formwork along with prefabricated steel forms.

Example #1 – Conventional Pedestal Formwork

One box composed of four small formwork shutters held together with z-bars and strong-backs.

Conventional Pedestal Formwork

Example #2 – Prefabricated Steel Pedestal Formwork

One box composed of two steel forms held together with nuts and bolts.

Prefabricated Steel Pedestal Formwork

There is several of these steel forms on this job because there are lots of these typical (exactly the same) pedestals.

Prefabricated Steel Pedestal Formwork

A closer look at the bolt template, bolts, tolerance tubes and shear key.

Pedestal Bolt Template and Shear Key Formwork

Here is the finished pedestal. If you look closely, you will notice that the shear key formwork is yet to be stripped.

Finished Pedestal

Here is an example of a very simple formwork box which is ready for concrete. It is held together with z-bars at the top and bottom on the corners while the centers are held together with z-bars at the top with pins and wedges at the bottom.

Pedestal Base Formwork

The pedestal formwork will be assembled after the concrete base is poured and set.

Dimensions: 2000mm x 2000mm wide x 1200mm high.

Location: Port Adelaide SA

Precasting six cone shaped concrete structures 2 at a time for the Adelaide Aqua Port Stanvac Desalination project.

Scaffolding

The 400 mm thick bases for the concrete units was poured first and the 2600 mm cone shaped section will be added on top. After the bases are poured, the scaffolding is added to enable steel fixing, formwork erection and pouring of concrete.

Tube and Fitting Scaffold

Internal Formwork

The internal formwork is 1800 mm diameter (not cone shaped) which includes 2 x 6mm plywood layers bent into shape and screwed into the vertical timbers one layer at a time.

Cone Formwork Internal

External Formwork

The external formwork below is cone shaped. It will also be skinned with 2 x 6mm plywood layers. It will take a bit longer to screw the ply to the external formwork because of all the extra cutting into the cone shape.

Cone Formwork External

Below we see the skinned external formwork being added to the structure in 2 parts. There is no way this formwork would fit around the steel in one piece, so we split it in half, lifted it in two crane lifts and joined it all up in position.

Cone Formwork

Finished Precast Concrete Unit

Below we see the finished 30 tonne pre-casted concrete unit. It will later be placed on a barge with the other 5 units and floated out to Port Stanvac Desalination Project.

Cone Shaped Pre Cast Concrete

Plain old circular formwork is a bit easier than cone shaped formwork.

Location: Northern Expressway Adelaide SA

When Z-Bars become difficult to extract because concrete slurry has leaked into the conduit, it may be necessary to make a heavy duty Z-Bar extracting tool.

Z-Bar Extractor

Simply cut a notch in the plate of a Prop-Inner, Screw-Jack or similar item. The notch should be slightly bigger than the diameter of the Z-Bars being extracted.

The length of the Prop Inner tube should be cut down to a manageable length while keeping in mind that the longer the tube (handle) is, the more effective it will be for extracting stubborn Z-Bars. (The longer the handle, the heavier the tool.)

Z-Bar Extractor In Action

To use the Z-Bar Extracting tool, remove the Z-Bar plate (washer) and replace only the nut. Then simply slide it along the Z-Bar towards yourself smashing the nut.

The photo above shows us using the Z-Bar Extractor to pull out a stubborn 4 meter long, 25 mm thick Z-Bar from a poured concrete pier. The Z-Bar Extracting tool made light work from what would otherwise have been one of those crappy never-ending jobs.

Pitfalls To Avoid

Important! Don’t be a bozo and smash your fingers into something while pulling back with the Z-Bar Extracting tool! Look around before you start smashing.

Tip: The length of the handle should be determined by your surroundings. For example, you would not have a 2400mm handle if you were working from a tight scaffold. You would cut it down to say 900mm – 1500mm max.

Tip: Using the Z-Bar Extracting tool on Z-Bars that are not so stubborn is also a good idea because it will reduce the number of times the ends need to be ground-down in order for the nut to fit properly.

Smashing Z-Bars out the regular way with a hammer will burr the ends, increase servicing requirements and produce down-time when someone goes to screw a nut onto a burred Z-Bar.

Location: Bolivar Water Treatment Plant SA

While this slab formwork “may” hold the concrete, it could be done a bit more professionally by using plywood rips and a bedlog to straighten the edgeform instead of wire. I can’t believe the formworkers that did this job recon it was ready for concrete.

Dodgy Formwork

Using wire back to a single pin to pull the formwork into line is dodgy and time-consuming because the pin can flex (or the wire can break) and put a “dog leg” in the formwork.

Dodgy Formwork Braced without a Bedlog

Tip: If it is important to have nice straight formwork (it should be), always use a bedlog. A bedlog enables you to push and pull the formwork into the exact position, secure it properly and “walk away”.

Even if it is not important to have nice straight formwork because the crooked concrete will “never be seen”, it is not a good look to have dog-legs in a concrete slab. By the way – It will be seen before it is never seen. It will be seen by bosses and inspectors.

Location: Whyalla Pellet Plant South Australia

Here’s another thrust block formwork job we had to do, but this time it was below the water table which means that water would be continually pouring into the job the whole time.

Thrust Block Excavation

Imagine arriving at this job and they say they want a couple of thrust blocks around these pipes, and they want it quick coz it’s “just a couple of thrust blocks”

Pumping the Water Out

Not only that, Des had to be very careful while digging out this watery goop to avoid damage to the fiber optic telecomminications and electrical cables while the pump pumps water out all day long. Des named this job The Swamp Monster

Concrete Thrust Blocks (Pump Still Pumping)

Finally the job is done and the Concrete Thrust Blocks are in position. The formwork for this job was almost the same as this other thrust block formwork we did.

Location: Port Adelaide South Australia

This is the formwork which will be used to cast the bridge bearings into position on top of the concrete columns. Silicon sealer was used to completely seal the formwork in order to stop any grout leakage, while at the same time holding the formwork securely in position.

Bridge Bearing Grout Formwork

You’ll notice that the original holes that were voided out during the concrete pour have been filled in with grout and new holes have been core-drilled. Why? ..

This happened because either the wrong hole centers were supplied to the formworkers, or a different size Bearing Pad was supplied in the end. Every column top had to be core-drilled in this way

You’ll also notice that the surface has been scabbled. This is specified as part of the job to ensure that the grout bonds properly to the concrete.

Tip: Don’t try and get away without scabbling the concrete if instructions were not given to do this job. Treat it as part of the job and do it without being told.

Pins and wedges are often used to secure many types of timber formwork in order to prevent concrete blow out while at the same time define a nice straight “edge of concrete” line.

Pins and Wedges used to secure Formwork

How it works is you drill a hole into the slab, put a steel pin into the hole, then use a timber wedge to secure the formwork hard onto the previously installed fiberglass pins which define the edge of concrete.

Formwork Tip

Drilling a hole slightly larger than the pin allows for the pin to be extracted with little or no effort. For example, if you are using a 12mm pin, then the correct drill bit is 14mm. If you are using a 16mm pin, then drill an 18mm hole, etc.

To any observer, the pins and wedges in these photos look normal, however, there was extra labour involved to extract the pins because the holes were drilled the same size as the pin.

Close-up of Pins and Wedges Method

Bozo

Too often I see formworkers smashing a 12mm pin into a 12mm hole

What happens next is the pin cannot easily be extracted, so then an angle grinder, grinder blades, full face shield, generator, a crane to bring the generator, fuel for the generator, power leads, lead stands, RCD box, etc etc, must be organized just to cut the pins off.

On big mining and civil construction jobs, this “small” job could take over a day depending on the availability of all the above tools, plant and equipment. For example, the crane could be busy with much higher priority jobs, so you get no generator until the crane is free.

To me it makes much more sense to simply keep some extra drill bits in the drill box!

And Worse – On some jobs, the specifications require that the tops of those cut off pins be sealed with special epoxy resins which supposedly prevents corrosion of the slab.

This too however is incorrect because only the top of the pin is sealed which means the slab will eventually corrode due to the fact that there is steel with less than the required cover. In reality, the concrete around the pin should be jack-hammered down to the required “cover” and then epoxy sealed.

Conclusion

Taking short-cuts is not necessarily quicker!

• There is no future in being a fraud by creating the illusion of getting the job done quickly. This form of bullshitting only works on the gullible, and on those who have not been around the traps of the building industry.
• There is no freaking point in creating more work on the job.
• Credibility really goes to the formworker who takes the time to think ahead.

The above conclusions do not only apply to formworkers, they apply to all construction personnel.

Location: Road Bridge – Port Adelaide South Australia

After each column concrete pour, the column formwork gets stripped down to be cleaned with high pressure water blasting and grinding with a wire wheel to remove all the slurry.

Cleaning Column Formwork

After cleaning, a special oil is applied to the forms which ensures they will strip off easy next time, and also helps provide a nice smooth finish on the concrete.

Location: Turner River Rail Bridge Mining Construction Site Pilbara Region, WA

The formwork used for the first concrete pour of this concrete bridge abutment.

Formworker Getting Ready to Concrete this Abutment Formwork

The red “spreader timbers” were also used to support the template which will leave the required penetrations for the Structural Bearings (also called bearer pads, bearing pads, bridge bearings). The Bearer Pads will fit neatly into these penetrations which will then support the bridge spans.

Concretors could not be hired for this job because Turner River Camp is only a small 70 person camp and all dongers were full. For this reason, the three formwork carpenters were required to do the concreting jobs as well.