（Received July 19, 2021）Abstract2.1 Outline of the experiment(1) Used materials, mix proportion and molding─ 1 ─日本大学生産工学部研究報告Ａ2022年 ６ 月 第 55 巻 第 １ 号＊ Professor, Department of Architecture and Architectural Engineering, College of Industrial Technology, Nihon UniversityHigh-strength concrete buildings with a design strength greater than 60N/mm2 have been constructed since the 1990’s, and the ultra-high-strength concrete with that of 200N/mm2 has now been covering the practical range. The demolition technology capable of demolishing such structures built with high-strength and the ultra-high-strength concrete is needed in the near future.This study examines the effects of loading method on the demolition load of high-strength and the ultra-high-strength concrete structure by the laboratory and full-scale crushing experiments using mock-up beam specimens. It was found that the current breaking demolition method is advantageous even for the ultra-high-strength concrete members on the basis of the tensile mechanism because the increase ratio of tensile strength is smaller than that of compressive strength.Keywords: Demolition, High Strength Concrete, Ultra-high Strength Concrete, Crushing MethodIn June 2014, the business categories in construction Industry Act was revised for the first time in 43 years, and the “demolition industry” was established as a one the of business categories in Japan1).Around 1960, Japan entered the period of high economic growth and many buildings were built. However, the number of cases of demolition work for the buildings around that time has increased in recent years due to deterioration and aesthetic obsolescence. Because of its economic efficiency1)-9), the crushing method has been adopted in many cases. Buildings using high-strength concrete with a design strength over 60N/mm2 have been built since the 1990s, but now ultra-high-strength concrete with a design strength of over 200N/mm2 has been put into practical use10). It is likely that the demolition of the structures using high-strength and ultra-high-strength concrete is needed11)12).However, until now, the emphasis has been placed on research on the “construction” of buildings, so there is little research on “demolition”. There are few papers on the crushing method even at the general strength level, and the demolition technology for high-strength/ultra-high-strength concrete structure has not yet been established10).The purpose of this research is to study the demolition load aiming at developing demolition technology for the high-strength/ultra-high strength concrete structures mainly using the crushing method13). First, the influences of the loading method on the breaking load were clarified by the unreinforced concrete specimens, and then the laboratory and actual crushing experiments were conducted by the mock-up beam member.Based on the mix proportions as shown in Table 1, concretes with water-cement ratio (W/C) of 60%, 40%, 20%, 16%, and 13% were prepared. When the W/C was 40% or ArticlesNoboru YUASA＊1. Introduction2. Experiments on the effects of loading method on the breaking loadApplication of Crushing Method to the Demolition of High-strength and Ultra-high Strength Concrete Structure
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