Step 7 - Creating the Columns

Continuing the theme of trying to demystify the building process (and at the significant risk of making it sound too easy and losing my job to a team from grade 3!) the next step in the process now we have created the foundations are the columns. These very important often unappreciated part of the building will support the floors above.....This building is challenging as it has a number of spaces such as the exam hall, the small theatre and the drama studios that require column fee space (imagine watching a show with a column in the middle of the stage!) To reduce some of the complexity we elected to move these functions to the top most floor as they the structure above them is comparatively light..

Lets go back to the foundations... you might remember seeing the squares containing more steel, these marked the column positions, you can see the columns are laid out in very regular grid.

 This extra steel that you can see is added reinforcement to prevent 'punching shear'  A simple description of this would be the column punching through the structure...  Mr Hulk to the right is imparting some punching shear on this unfortunate wall. Even Mr Hulk would have problem punching through our column positions with our extra steel in place. An added bonus of the current design of the building I feel....

So now we have attached the steel work into the foundation and ensuring that they can take the pressure of the building above we can start making the actual columns...

As if to prove that its all common sense, we actually make a huge metal mould which is clipped around the steel reinforcing bars and then

Step 1 

Step 2 - Add more steel

Step 3 - Add the mould

Step 4 - Pour in the concrete

Step 5 - All Finished - Repeat 72 times per floor!

Further Progress on the other side of the foundations

We finished one side of the foundations and now we are using this platform to work to finish the other side of the building, with another HUGE continuous pour of concrete - Even bigger than the first one!

It took us 16 hours, 2 pepperoni pizzas, 3 portions of char siew rice, 12 coffees and 2 changes of clothes to finish this continuous concrete pour and the majority of the foundation...phew

Step 6 - the start of the building proper - Casting the foundations

Today is a milestone day as it represents the start of the some real visible construction - Yipeee!

Today we are going to casting zones 1 and 2 of 6 zones of the foundations that we eventually need to construct.




These 2 zones consists of 600 tons of rebar, which we will fill with 2295 m3 of concrete. This is one of the largest single casts in Singapore this year and certainly the largest one I have been involved in, we should be finished in around 16 hours. This is about as exciting as concrete gets!

Each concrete truck that you see on the road can carry around 8.5m3  This cast will take around 270 concrete trucks who will have to come constantly throughout the day..

Heres one of the delivery notes for the concrete. The concrete we are using is grade 40 PBFC (portland, blast furnace, cement) instead of OPC (Ordinary portland cement) This is considered a green concrete as it uses the by product of industrial blast furnaces to replace the sand  More information on this type of concrete here.

We need the concrete to set slowly to prevent cracking, so as well as thinking carefully about its chemical composition and adding some extra chemicals, we also chill the concrete to around 27 - 30 degrees celsius before it is sent from the concrete mixing plant and we pour it all in a single 16 hour session without stopping...


The concrete will take around 4 weeks to fully gain its strength and we do a number of tests on the concrete both on delivery and progressively as the concrete drys to ensure that the concrete is performing as we would expect and can reach its required strength.

We are using three elephant pumps (yes they look like an elephant with a 35m trunk and minus the ears!) The concrete trucks back up to the pump and discharge their load, the pump them can move it to the far corners of the site!

Each pump can discharge around 60 m3 per hour and so we are estimating around 14 hours non- stop casting depending on site conditions.

Once the concrete is pumped into the metal cages, a team of men with vibrating metal probes help add some vibration to the thick concrete which helps it flow into all the nooks and crannies of the raft.

 Nearing midnight and almost finished.... The weather was kind to us.. and all the planning paid off.

 Our First Casting....2500M3 of Concrete, 16 hours!

Step 5 - Making the foundations - Designing and testing the quality of the concrete.

Testing the quality of the concrete.. 

Throughout the project, we will use huge amounts of concrete. Concrete is made up of a number of materials and these materials can be adjusted in quantities to give the concrete various properties. These properties could be in its eventual strength, in the way it flows, the speed it drys and even in its ability to resist water.

Getting this concrete mix right is essential - The ultimate strength of the building depends on it!

Like making a less than yummy cake?

The first stage of this journey is the design of the concrete mix, this is a theoretical design of the various components that might be used to make the concrete, sort of like making a huge, very unpleasant tasting cake!

This trial mix is then made and put through a number of test before being selected for the project.

Throughout the project , whenever concrete is delivered to site the same tests are done to ensure that the concrete delivered is the same as the concrete trial mix that was done at the start of the project...

A sample of the concrete delivered  to site and used in any construction is stored and labelled in these steel boxes 15cm x 15cm for later testing




After a few weeks it is then sent to a special outside lab for testing on its composition and also its compressive strength.......

Here is an example of the concrete test certificate, this one is from the grade 40 concrete for the raft, around 2 days from casting, you can see it is nearing 70% of its strength as it progressively dries.



The concrete also goes through a slump test before it is allowed on the site. This very simple test is designed to quickly check that the concrete does not have a too high water content as this would ultimately affect the ability of the concrete to chemically react and harden properly...





UPDATE: Here are some example of the tests of the concrete from the foundations