License Granted for Fire-Resistant "AFR Concrete®"
February 19, 2010
Takenaka Corporation
Shimizu Corporation
Takenaka Corporation (President: Toichi Takenaka) and Shimizu Corporation (President: Yoichi Miyamoto) have begun licensing of "Advanced Fire Resistant (AFR) Concrete®," the super high-strength fire-resistant concrete, jointly developed and used by the two companies, to other companies such as construction companies, concrete companies and manufacturers of precast concrete members. Specifically, the companies are planning to license 80 newtons per square millimeter and the 100 newtons per square millimeter specified design strength concretes, for 1,000 yen per cubic meter.
These photos show 80 N/mm² concrete column test specimens that have been heated up to 1,100 degrees C over a 2-hour period. On the left is conventional superhigh-strength concrete; on the right is AFR Concrete®.
80 newtons per square millimeter and above specified design strength concrete is used in the lower stories of superhigh-rise apartment buildings around 50-stories class. The characteristic of 80 newtons per square millimeter and above strength concrete leads to significant spalling of the surface in high-heat conditions such as under fire, so there is a need for measures against spalling such as fire resistive covering.
"AFR Concrete®," with just a little synthetic fiber mixed in, displays excellent fire resistance. There is no need for fire resistive covering, so not only can the work cost and processes be reduced, there is also the merit of being able to maintain more living space. This has led to many construction companies wanting to use the technology under license. As a result of consultations between Takenaka and Shimizu, the companies agreed to grant licenses, limited to the 80 newtons per square millimeter and the 100 newtons per square millimeter specified design strength concretes.
In order for quality control, the following conditions have been applied.
- If the applicant is an individual company, with regard to the manufacture of work with 80 newtons per square millimeter and above specified design strength concrete, the company must have received ministerial approval, as stipulated in Section 37 of the Building Standards Law. Otherwise, the company must receive approval from the Japan Prefabricated Construction Suppliers & Manufacturers Association for members using 80 newtons per square millimeter and above specified design strength concrete, as per that association's PC Members Quality Approval System.
- If the applicant is a joint venture, the sponsor must meet the above conditions.
■Where to apply for license
- For concrete companies, and manufacturers of precast concrete members:
- Intellectual Property
Technology Planning Department
Takenaka Corporation - Phone: 03-6810-5692
- For construction companies:
- Intellectual Property Department
Technology Planning Office
Shimizu Corporation - Phone: 03-5441-0422
<<Reference>>
1. The spalling mechanism of superhigh-strength concrete
Spalling is thought to be caused by the severe swelling of concrete induced by the intensive heat of a fire, and the 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 greatly increases heat-swelling, and the expansion of gases in the interior, without an escape path, raises the pressure inside to a dangerous level. Therefore, fire-resistant measures are required for superhigh-strength concrete of 80 newtons per square millimeter strength or above.
2. AFR Concrete®
This is superhigh-strength concrete that contains a mixture of synthetic fibers. During a fire, these faiber 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 spalling of the concrete. The fibers have a diameter of 0.005 to 0.1 millimeters and a length of 5-40 millimeters. Between the two companies, Takenaka and Shimizu, already have a track record of using the concrete in 33 buildings with a capacity of 87,000 cubic meters. The fibers are mixed into 80 newtons per square millimeter and 100 newtons per square millimeter concrete at the rate of 0.10 to 0.20 volume percentage. Since this new concrete can be made just by adding a small amount of synthetic fibers to concrete while it is in the agitator truck, no special production equipment is required. With regard to the fire-resistance of the AFR Concrete® now being licensed, technology certification has been received from the General Building Research Corporation of Japan.
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