First Architecture built using “SHIRASU” Concrete
The house is located in the center of Tokyo, on a site merely 66 square meters in area. The clients are a married couple both working in the field of chemistry, sharing a passion for architecture and art. “We want to see exposed concrete finish inside and out. A distinctive piece of architecture that is at the same time environmentally conscious”, were the initial requests of the clients. With these words as a starting point, we conducted various studies and researches and the house saw its completion after two and a half years.
In high density residential area in Tokyo, such as this site, you seldom have the luxury of large open spaces, let alone vast nature. The only direction that we can turn for those factors is the “Sky”. We have been repeatedly studying this approach to the sky as an element of nature in previous projects and one way of establishing it is by pruning away the corner of a rectangular volume at an angle. Because the building footprint is only 30 square meters, large openings facing the sky becomes an effective means to incorporate the feeling of vastness onto the compact internal space. The chamfered corners, the result of which are large openings, not only provide the interior space with a view to the sky, but also allow for a more open view to the sky for the people on the street.
To secure a comfortable interior climate, a “thermal circulation system” was incorporated with the help of environmental engineer Hiroyuki Yamada. This system makes use of the stacking effect in the 4 story stair well that is opened to the living space on each floor. In the winter, the warm air that accumulates in the upper part of the house is transferred to the pit below the basement floor automatically through a ventilation duct and reversible fan connected to a thermostat. An electrical radiator is added in the pit for the extra heat needed in the coldest season. In the summer, the chilled air from the pit is sent up to the 3rd floor to flow down into the pit again cooling the entire house.
The building itself is made from 100% recyclable concrete, what contributes to a society of low carbon and recycling of resources.
For this project we developed a 100% recyclable concrete which, instead of sand, contains SHIRASU. “SHIRASU” is a general term for the deposit of pyroclastic flow of volcanic ash found in south of Kyushu. It covers almost half of Kagoshima prefecture (4,600 km2) with an average thickness of 60m. The amount of deposits are estimated to be 75 billion m3, enough to replace all the sand used in the manufacture of concrete in Japan for 2000 years. Since it is not suitable for agriculture due too high drainage and scarce nutritive substances, and corrosion and mudslides easily happen at the time of heavy rain, it is regarded as an unwelcome troublesome material. It also has not been used as a concrete material for architecture, as it does not meet the criteria of Japanese architectural regulations. On the other hand, Japan is lacking in fine aggregate used for the manufacture of concrete. The good river sand is getting scarce and has been replaced by gravel scraped from seabeds. However, most local governments have banned the collection from the sea considering the negative impact to the environment.
The advantage of this concrete is its strength and durability that increases over a long period of time because of the pozzolanic reaction of SHIRASU. Also its density, which comes from the fine granularity of SHIRASU, protects the concrete from neutralization. SHIRASU also contains micro closed-cells which gives the concrete humidity control and deodorizing qualities. This development and use of SHIRASU concrete can be a huge asset to those areas where SHIRASU can be excavated.
As it’s being self-consolidating concrete, it reduces the noise, vibration and energy at the construction site as well. The world’s irst architecture, R torso C was built using environmentally friendly concrete, as well as incorporating a sectional thermal circulation system.
Thinking about the environment through materials.
In the 20th century, the production of concrete which was the driving force for the building industry, it has been making constant increase in synchronicity with economic growth.
It is expected that the production of cement, being the main ingredient of concrete, will continue to rise. It is assumed that the consumption will be doubled by 2050 compared to the turn of the century. Additionally, cement is produced by heating natural limestone with other materials through a process known as calcination. In order to calcine at the high temperature of 1450 °C, a lot of heat energy is required that results in vast CO2 emission. The aggregate for concrete are gravel and sand. Both are natural resources. Up until the economic boom, these materials were extracted from dry river beds or mountains resulting in drainage of good resources. Instead manufactures started to use sand from the seas. This results not only in the rusting of the reinforcement bars in concrete, but also contains many chlorides that originate from the sea water, which causes a general deterioration of quality of the concrete. Moreover, the extraction of beach sand is being regulated or banned by many local governments, because of the bad effects it has on the marine environment.
It is a matter of utmost urgency with in the concrete industry, clearly an industry that is indispensable to contemporary architecture, to search for alternative resource that could be utilized instead of sand and gravel. Also to change the formation of the recycling process of concrete, develop a more durable and multifunctional concrete.
This is how we came up with the idea for the practical use of volcanic “SHIRASU” as a fine aggregate.
Characteristics of Environmentally Conscious “SHIRASU” Concrete:
1. Contribution to the preservation of natural resources.
・ up to 80% of sand in concrete, which is becoming a scarce resource, can be replaced by “SHIRASU” .
2. Environmentally friendly.
・The concrete becomes completely recyclable as a cement raw material at the time of demolition.
・ Calcination energy [of the cement] and CO2 emission can be reduced.
3. Strength and durability
・Strength and durability that increases to grow over a long period of time because of the pozzolanic reaction of “SHIRASU”, resistant to sulfuric acid and salt-damage
・Also its density, which comes from the fine granularity of “SHIRASU”, protects the concrete from neutralization
4. Smooth surface, humidity controlling qualities
・Smooth texture allows to have exposed concrete as fine finish.
・ “Shirasu” also contains micro closed-cells which give the concrete humidity control and deodorizing qualities.
Located on a corner site, a mere 30 m2 plot of land in the city center, the height of about 10m, the external form derived by pruning off the corners from a generally rectangular volume.
The external form is determined by a balance adjusted to suit the needs for wall for seismic resistance, an opening to the sky assuring a sense of vastness and the need for securing internal privacy.