The Concrete Committee of Japan Society of Civil Engineers was commissioned in June, 2008 by Sumitomo (SEI) Steel Wire Corp., Shinko Wire Company Ltd., Suzuki Metal Industry Co., Ltd., and Neturen Co., Ltd. to publish a draft of “Recommendations for Design and Construction of Pre-stressed Concrete Structures Using Advanced Pre-stressing Steel Coated with Epoxy Resin.” The committee then decided to establish a Subcommittee to draft “Recommendations for Design and Construction of Pre-stressed Concrete Structures Using Advanced Pre-stressing Steel Coated with Epoxy Resin” (Subcomittee 276) under Steering Committee to carry out investigation and research activities until March, 2010.

Advanced pre-stressing steel coated with epoxy resin include epoxy coated and filled strand (ECF strand) and pre-grouted tendon. It was decided to issue a draft of recommendations for design and construction for each of them. These advanced pre-stressing steels have high level of anti-corrosion performance due to epoxy resin coatings. Further, pre-stressed concrete structures using such pre-stressing steels will also be highly durable. As a result, they contribute to the social infrastructure by being more durable and having longer life cycles.

The committee had held three committee meetings and eight secretariat meetings during the 2-year period. Five working groups were set up to take part in the discussions in the committee meetings and secretariat meetings can proceed smoothly. The draft of recommendations was completed in July 2010 and a seminar referring to it was held in August 2010.

The following three points will be emphasized in this draft of recommendations.

1. In addition to issuing a draft of design and construction for pre-stressed concrete structure using ECF strand and pre-grouted tendon, inspection methods, quality standards and so on, which are related to such advanced pre-stressing steels were prepared.
No such public standards existed in Japan and the industry had been confused because there were many kinds of recommendations and inspection methods. The standards issued in this draft of recommendations can be used as models for inspection methods and quality standards.

2. It had conventionally been difficult to estimate the hardening timing for epoxy resin in pre-grouted tendon. The committee originally performed bending and loading tests on pre-stressed concrete beams, sequentially changing the hardening conditions of resin. The concept for designing was provided in the draft of recommendations based on the test results, giving hardening conditions of resin related to strength against bending and loading of pre-stressed concrete beam.

3. The draft of recommendations states that the verification of durability on ECF strand and pre-grouted tendon may be omitted for structures because it was confirmed that it takes more than 100 years for chloride ion to penetrate through the epoxy coatings to the steel.

ECF strand has already been used often in Japan. In many cases, its usage has been as external cable inside pre-stressed concrete box girder. In these cases, standard ECF type is basically used. Bonded-type ECF strand, which has grits on the surface of the epoxy coat, is used for pre-tensioning member and used as internal cable and ground anchorage. PE-coated ECF strand is used for anti-ultraviolet, anti-damage, and multi-layer corrosion protection.

Pre-grouted tendon is a material which can reduce construction term because the grouting operation is eliminated. There are two types, one of which is thermo-hardening type and the other is moisture-hardening type. Pre-grouted tendon has also been used very often in Japan. It is often used for transverse tendon in slab, vertical cable in U shape pre-cast girder and so on.

We expect our social infrastructure will be more durable and have longer life cycles by widely utilizing such forefront materials to pre-stressed concrete structures in the future.