Vacuum Concrete

For almost a whole week, me and my boss was stuck with translating Japanese design documents into English. As the task was such a pain, a part of me was elated because it was a chance for me to tank up on my Japanese while looking back at my specification writing.

In one of the construction notes, I came across a concreting method loosely translated as "vacuum concrete" (shinkuu konkuri-to). The english outcome was 'vacuum casted concrete', this spiked my intrest.

I searched the web and found out that this method is used to make the poured concrete useable as early as possible. This is mostly used for slab constuction.

As the Nakayashiki site explains, when this system is applied, the freshly casted concrete attains its rigidity and strength faster, creates a more durable hard surface after curing, and decreases the amount shrinkage (cracking) that occurs in concrete after setting.

These features are attained by laying a mat over the concrete and attach it to a vacuum pump. The mat maintains the atmospheric pressure required while the pump sucks out the surplus water used in the cement mixing. After this process, the concrete is dehydrated by 15 to 20 percent, enough to make a RC slab treadable. Another element of this system is the metal O-ring which raises the vacuum mat over the slab.

As the pressure is decreased, the metal rings emboss themselves into the concrete which leaves a tell-tale mark of its use. Some users even out the surface afterwards, some users leave it there as a floor pattern.

Like the 'punched concrete' presumably started by Tadao Ando, this might spark another building feature that started as 'purely Japanese' and integrated into the International Style.