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Wednesday, December 8, 2010

House Construction 9: Milk Foam Nozzle for Concrete

I like to watch baristas at work at Coffee Bean. They stand behind the counter and pull out all sorts of tubes and nozzles to concoct milk foam and other stuff that's good to drink.

Now, imagine a 3 storey high contraption on wheels with a steel arm that reaches over the fence and gate all the way from the road to the back of a longish piece of land. The steel arm holds a nozzle that dispenses concrete mix straight into the formworks (i.e., the wooden planks all nailed together to form a mould for the concrete mix).

I've never seen any machine this large. We went off on an early and short vacation in order to be around to supervise the house construction. We still feel like we're on holiday though... because so many interesting things have been happening to the house and every day holds new learning and fresh insights into the building process.

The concrete was mixed by specialists instead of on site. The clerk of works was present to examine the quality and strength of the concrete mix. It was interesting to see them do the slump test. Too much water in the concrete mix is not good (because when water dries, the concrete will crack from water evaporation). Too little water in the concrete mix is also not good (because then it's not easy to apply - I think). The concrete specialists provided a document that gave the tolerance envelope for the slump test. Ours envelope was between 75mm to 105mm. Our slump test came up to be 80mm. See picture below.

80mm shows that the concrete was on the dry side (the lesser the slump, the more viscous the mixture), but since it was still liquid enough to work on, the cement mixer poured the whole truckload into the huge 3-storey concrete nozzle machine. Out the nozzle end (guided by one tiny human) came the gray concrete into the humongous wooden mould. Tiny humans waded into the mix to level it properly into the mould.

And voila... the entire slab that will be our 1st storey floor is done. Now, we wait for it to harden like a plate of agar agar.

By the way, I also learnt that it isn't good for concrete to dry too fast. One is supposed to spray it with water during the "curing" (i.e., drying process) so that it takes 28 days to dry out. That way, it reaches its maximum strength. Hence, some slight rain is actually good when one is building one's house.


Lee Chao Rui said...

Informative posting.

Lee Chao Rui said...

Thanks for sharing. Informative postings. Will your contractor wait for 28 days to cure the concrete on the ground floor before they start further construction?