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Improving the durability of concrete structures |
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Iron and steel slag products are used in a variety of areas where their unique characteristics are put to effective use. The majority of the demand for these products comes from the field of cement. Approximately 40% of iron and steel slag products, and 60% of blast furnace slag, are used in cement. Most of these products are used as a raw material in Portland blast furnace slag cement.
Portland blast furnace slag cement has the following characteristics.
(1) It has high resistance to seawater and to chemicals, and can improve durability.
(2) It has a low chloride ion diffusion coefficient (resists rebar corrosion).
(3) It can reduce alkali-aggregate reaction.
(4) Its strength increases over time.
(5) It produces little elution of hexavalent chrome when used in ground improvement.
This product is also increasingly being used in construction projects. For reasons including the generally large material cross-sections, ease of ensuring concrete curing time, and the relatively large cover it provides, Portland blast furnace slag cement is suitable for use in structures such as piles, foundations, underground beams, and continuous walls. With the CASBEE evaluation system that is increasingly being instituted by local governments and under the Tokyo Metropolitan Environmental Building System, the use of Portland blast furnace slag cement adds points to the evaluation score. The Tokyo system was started in FY 2002, and Portland blast furnace slag cement is used in approximately 50% of the buildings that have been designated under this system.
Reducing CO2 emissions |
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Expanding the use of Portland blast furnace slag cement is one measure included in the plan to achieve the targets of the Kyoto Protocol, and there are large expectations for its ability to help reduce CO2 emissions. Under the Kyoto Protocol, Japan has made a commitment to the world to reduce its 2008 – 2012 emissions of greenhouse gases by 6% from 1990 levels. The plan for achieving this public commitment includes a reduction in CO2 emissions of 1.12 million tons resulting from a 16% increase in the production ratio of blended cement (FY 2004 result: 21.4% → FY 2010 planned value: 24.8%).
The majority of the blended cement that is produced in Japan is Portland blast furnace slag cement. If we were to assume that Portland blast furnace slag cement accounted for all of the 16% increase in the production ratio of blended cement, this would contribute to an annual reduction in CO2 emissions of 640,000 tons. Specifically, the use of 20% Portland blast furnace slag cement in the construction of a single apartment complex would result in a per-household CO2 reduction of approximately 1,200 kg. These effects have been recognized by the national government, local governmental organizations, and private companies, and there is growing momentum toward stopping global warming by expanding the use of Portland blast furnace slag cement.
Examples of structures that utilize Portland blast furnace slag cement |
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| Koyama Dam (Ibaraki Prefecture) |
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Akashi-Kaikyo Bridge |
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Tokyo Bay Aqua-Line |
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Kansai Branch of the National Diet Library |
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