ブックタイトル「近代の文化遺産の保存理念と修復理念」英語版

概要

「近代の文化遺産の保存理念と修復理念」英語版

8for restoring concrete structures as culturalproperties. This is because there are manyobstacles in obeying the rule of “whenrestoration is required, care must be takento retain the original elements and when itcannot be avoided, select reversible method andremovable materials.”　In general repairs of exposed reinforcementbars, first the surrounding concrete is taken off,rust is removed, and the steel surface is treatedwith an anti-corrosive agent. Then finally, theremaining concrete is de-carbonized and newconcrete is poured to enclose the reinforcement.　However, if this method is taken on culturalproperties, it may not be easy to distinguishthe areas which have been replaced withnew concrete and may lead to obscuring thestructure’s history of restoration in later years.(2) Steel StructuresAs is well known, metal corrosion is the majorcause of deterioration in steel structures, andtherefore, surfaces are painted or plated for rustprotection. However, as such finishes do notlast eternally, regular maintenance is essential.If not well taken care of, metal will corrodeand the structure will deteriorate quite rapidly(Photo 2). What methods would be effectiveagainst corrosion of major structural members?In traditional restoration of wooden structures,they can be replaced with replicated elementsusing the same material, species, and processingtechniques. With concrete structures, would thesame concept be applicable? The same kind ofwood is comparatively easy to obtain, but withmetal, its components have changed over theyears and have been transformed into a materialof high strength and specifications. Can thesedifferent types of steel all together be treated asthe same material? Perhaps some will have noobjections to considering them all steel, but thisissue has not yet been seriously discussed.　It maybe possible to reproduce the sameexact steel relying on component analysis ofthe original material, but it is not realisticto employ this method, considering thespecialized manufacturing costs required forlarge-scale modern cultural property structuresusing enormous volumes of steel. From themicroscopic point of view, minute changesin components may cause very small electricpotential differences at the boundaries of theoriginal and new materials, which in turn maycause corrosion when they are welded togetheror tightened with bolts.　Another thing I would like to point outis the fact that in Japan’s modern era (Meijito early Showa era), steel structures were notconstructed by welding, mostly connected withrivets. Today, very few ironworks are capableof executing this construction method andthus the employment of this technique forpreservation is almost impossible. Under suchconditions, how should we undertake suchpreservation projects? This is probably not anew arising problem. Even in the past, theremust have been many cases where substitutematerials and techniques have been employedwhen lost techniques were not available forrestoration. From this aspect, this may not be aproblem at all.(3) Brick StructuresAhe major cause of deterioration of brickstructures is basically salt weathering andfreeze-thaw. Salt weathering occurs when saltsin bricks and soluble salts from rainwater orunderground water from outside crystallize onthe brick surface. As water which permeatedthrough the brick interiors evaporates and salts