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May 15, 2000
New Superhigh-Strength Concrete with Advanced Fire
Resistance that can Expand Floor Space and Reduce the Costs and Construction
Time of 50-Story-Class RC Condominium High-Rises
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Takenaka Corporation
Shimizu Corporation
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In order to promote the construction of more 50-story-class deluxe condominium
high-rises, Takenaka Corporation and Shimizu Corporation have jointly
developed Advanced Fire Resistance Concrete (AFR)* that does not peel
or shatter even under the extreme heat of a major fire. This is the
first time in the industry that such a concrete has been developed and
put to actual use. AFR can also help to increase floor space
and reduce the costs and time needed for construction. Shimizu
is currently planning to build two high-rise RC condominiums with AFR in Saitama Prefecture, and Takenaka is planning to build one in Tokyo.
Already the General Building Research Corporation of Japan** has certified
the performance of AFR's fire resistance. Applications for patents and
registered trademarks are currently pending.
We have now entered the age of 50-story RC condominium buildings, and
plans are being drawn to build such buildings that are 200 meters
or higher. The technology that supports such lofty edifices lies with
Superhigh-Strength Concrete, which is of the 80-100 N/mm2
class that can withstand 800-1000 kg of force per square centimeter.
However, at forces above 80 N/mm2,
the intense heat from a fire can cause peeling and shattering at the
surface of the concrete, so it is urgent that such damage be prevented.
Although the mechanism for peeling and shattering is not completely
understood, it appears at this point in time that the causes are severe
swelling of concrete induced by the intensive heat of a fire, and dramatic
vaporization and swelling of water contained in the concrete. The stronger
the concrete, the denser it is, so the intensive heat of a fire would
greatly increase heat-swelling, and the expansion of gases in the interior,
without an escape path, would raise the pressure inside to a dangerous
level. Therefore, Superhigh-Strength Concrete of 80 N/mm2
strength or over usually covered with a fire-resistant material. However,
the covering increases column diameter by five percent, which reduces the living
area and adds to construction time and cost.
Thus, Takenaka and Shimizu worked together to develop AFR.
This is Superhigh-Strength Concrete that contains a mixture of synthetic
fabrics such as polypropylene. During a fire, these fabrics melt and
vaporize, leaving minute spaces in the concrete that act as release
valves for gas pressure and as swelling repressors on the surface. This
helps to prevent peeling and shattering of the surface. With a diameter
of 0.012- 0.2 mm and length of 5-20 mm, the fibers are mixed into 80-120 N/mm2
concrete at the rate of about 0.10- 0.35 volume percentage. Performance tests have
not only proven the excellent fire resistance of this concrete, but
have also confirmed that it has the same strength, workability and durability
as regular Superhigh-Strength Concrete.
Merits of AFR
1. Since this new concrete can prevent peeling and shattering in the
concrete surface, there is no need for fire-resistant covering. Thus,
columns do not have to be so thick as those with fire-resistant covering.
This not only helps to increase available floor space, it adds absolutely
no extra work on site, and has no adverse effect on construction time.
2. This concrete can be used at 1/10 or less the cost of regular Superhigh-Strength
Concrete that is covered with fire-resistant materials.
3. Since this new concrete can be made just by adding a small amount
of synthetic fibers to concrete while it is in the mixer truck, no special
production equipment is required.
Both Takenaka Corporation and Shimizu Corporation have had good results
with 80 N/mm2 AFR, and its
workability has been confirmed at actual construction sites. The two
companies plan to recommend AFR to large real estate companies,
etc., who commission the construction of high-rise RC condominium buildings.
* The meaning of AFR
"AFR" stands for the trade name "Advanced Fire Resistance" concrete.
** Brief Description of the General Building Research Corporation of Japan
The General Building Research Corporation of Japan is a public corporation
jointly operated by the Ministry of Construction and the Ministry of
International Trade and Industry. It works for the public good by performing
third-party testing, inspections, and diagnostics to improve the quality
of structures, ensure safety, and so forth.
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