解体技術情報のグローバル化
Globalization of demolition technology information

湯浅昇Noboru YUASA① 日本における「解体工事業」の成立と展望
ESTABLISHMENT AND PROSPECT OF DEMOLITION BUSINESS IN JAPAN② 日本における解体技術の変遷
THE TRANSITION OF DEMOLITION TECHNIQUES IN JAPAN③ 日本における高層ビルの解体
DEMOLITION OF SKYSCRAPERS IN JAPAN
④ 超高強度コンクリート部材の解体負荷－圧砕工法の適用
APPLICATION OF CRUSHING METHOD TO THE DEMOLITION OF HIGHSTRENGTH AND ULTRA-HIGH STRENGTH CONCRETE STRUCTURES⑤ 再生微粉の有効利用
EFFECTIVE USE OF CONCRETE POWDER BY-PRODUCED FROM RECYCLED
AGGREGATE湯浅 昇
Email: yuasa.noboru@nihon-u.ac.jp
日本大学生産工学部教授・博士（工学）（公社）全国解体工事業連合会理事、日本建築学会解体工事小委員会委員長、日本
非破壊検査協会規格 RC 部門委員長、セメント協会論文審査委員会委員長、日本仕上学会論文審査委員会委員長
2019 年日本建築学会賞（論文）受賞、2009 年日本建築仕上学会論文賞受賞、1998
年セメント協会論文賞、2020 日本コンクリート工学会賞（功労賞）受賞
Noboru YUASA
Email: yuasa.noboru@nihon-u.ac.jp
Professor of College of Industrial Technology, Nihon University
Ph.D. in Engineering
Director of Japan Demolition Contractors Association, Chairman of Demolition
Structure Subcommittee in Architectural Institute of Japan, Chairman of RCDivision of JSNDI Standardization in The Japanese Society for Non-Destructive
Inspection, Chairman of the Paper Review Committee in The Japan Cement
Association, Chairman of the Paper Review Committee in Japan Society for
Finishings Technology
2019 Architectural Institute of Japan Award (Research Paper Division), 2009 Japan
Society for Finishings Technology Research Paper Award, 1998 The Japan Cement
Association Research Paper Award, 2020 Japan Concrete Institute Award(Meritorious Deed Division)日本における「解体工事業」の成立と展望
日本大学教授 湯浅 昇
１．建設業法改正による「解体工事業」の成立
建設業法は、1971 年に建設業を「登録制」
から「許可制」に切り替え、許可業種区分として、総合 2 業種（土木・建築）、専門 26 業種の計 28 業種が規定された。解体工事は「とび・土工工事業」に含まれ、一式工事の土木工事、建築工事、とび・土工工事業の間に埋没したま
ま、43 年という長い月日を費やした。
劣悪な労働環境や労働条件が労働者を危険にさらす最大の弊害となっており、解体工事中の重大事故の発生を防止するうえで、解体業を独立した許可業種として追加することは、解体業界の長年の悲願であり、全国の解体工事業者で構成される全国解体工事業団体連合会（全解工連）が国に何度も訴えかけていた。20 年前の全解工連の発足も、これが契機であった。
そして、2014 年 6 月、改正建設業法が公布され、晴れて解体業が許可業種として独立することが決まった。研究者という第三者の立場で見ても、これは大変喜ばしいことであった。

図 改正建設業法における業種区分の新設

解体工事の業種区分は、それまでの「とび・土工工事業」から分離独立する形で、全体で 29番目（専門業種として 27 番目）の業種として。解体だけを手掛ける専設けられた（図参照）
門の業種であり、土木や建築の全体計画の中で行われる解体工事はそれぞれの「一式工事」区分で対応される。1 件当たり日本円で 500 万円
以上の解体工事を実施する場合は許可取得が必要になった。
その後、解体工事業許可については 2016 年
６月から施行され、施行日時点で「とび・土工
工事業」「コンクリート工事」の許可を受けて解体工事を営んでいた建設業者は、引き続き2019 年 5 月までは、解体工事業の許可を受けずに解体工事を施工できた。その間に順次、解体業としての許可登録を進めていった。
「解体工事業」成立により、解体工事に配置される技術者に求められる、技術・知識を認定する資格制度の確立が必要となり、(1)解体工法の専門知識、技術的知識

(2)安全管理、施工管理能力(3 環境面の課題に対する知識(4)建設廃棄物対策に関する知識(5)関係法令の知識(6)マネジメント能力（現場管理）の観点から議論され、2016 年 6 月技術者要件・資格が発表された。この技術者要件・資格についても、2021 年３月までは、とび・土工工事業の技術者（既存の者に限る。
）も解体工事業の技術者とみなすとされた。

られるように編集されている。非常に優れた資料だと思っている。

３．解体工事の技術開発
さまざまな解体工法がありますが、解体工事業者は多くの種類の資機材を保有していて、対象となる建築物の規模や形状、構造、立地条件などに応じて、どの解体工法を採用するか、受注した解体業者が判断して決定している。
そして、それぞれの資機材や工法において、解体工事業者が日々の解体工事を通して感じ
２．解体工事中の事故を未然に防ぐている技術的な課題についても、改善に向けて
今回、解体業の業種区分が新設されたことで、 地道に活動している。
解体工事の安全管理に対するハードルもさら日本の都市部では、高層建築物の解体に際し、に一段上がった。
油圧ショベルを最上階のスラブ上に設置し、上構造物を「作る」側の安全は確立されている部から順次解体していく「階上工法」が用いらが、「壊す」側の安全はまだ十分とは言えず、れることが多い。油圧ショベルを支持するため
統計的にみると、簡単には比較できないが、解にサポートパイプで上下層スラブを接続し、複体工事は新築工事に比べ事故の発生割合が多数層で支持する方法をとるのが一般的である
いと言える。
が、このサポートパイプの代わりに無筋コンク
事故には、「公衆災害」と「労働災害」があリートを打設しておき、後で床版ごと解体する
りますが、工事当事者以外の第三者に危害が及という方法もある。無筋だから壊しやすいし、
ぶ公衆災害は絶対に起こしてはならない。
価格的にもあうとのことである。
解体工事の事故の原因を探っていくと、その全解工連では、研究助成金を提供して、解体
ほとんどは「管理」の部分で発生している。解技術の進化に向けた取り組みを行っており、年体工事に対する技術的な理解が足りないといに一回、その成果をまとめた研究発表会を開催
うことではなく、「たぶん大丈夫だろう」といしている。この助成金を私の研究室も利用してった、ちょっとした不注意やケアレスミスが大いるが、こうして開発された技術を業界で共有
きな事故につながっている。国土交通省はそこし、共通の技術体系に組み込んでいくことで業を問題にしていて、今回「解体工事業」の業種
界全体のレベルアップが期待されます。
区分を設けることで、事故防止を確立していこ解体工法の研究は、ゼネコンとの共同研究とうとしている。
いう側面もありますが、解体技術そのものは解管理マニュアルは整備されていて、全解工連
体工事業者が保有し蓄積しているものなので、でも、解体工事に関わる事故原因を分析し、そゼネコンとしては、それをシステム化したり、の発生を未然に防ぐべく地道な活動を続けて仕組みを考えたりするということで、お互いのいる。
「解体工事施工技士」（国土交通省令に基役割分担が出来ているように思える。近年、社づく登録資格）の技術講習会や、解体工事施工
会の注目を集めた赤坂プリンスホテルの解体技術講習を実施しているほか、2008 年には「解工事でも、全体のシステムを構築したのはゼネ
体工事 KYT シート集」というビジュアルなテコンですが、破砕したり切断したりする要素技
キストもまとめており、イラストで現場の状況術の部分は解体工事業者が一手に担当していを提示し、その状況において考えられるリスク、 た。
発生するかもしれない事故を予測し、事前にど
現在は、「解体」技術といえば、既存の技術、
ういう配慮をすればよいかを自分の頭で考えとりわけ「圧砕」が最も使われているといえる。

だいたいの建築物は圧砕の技術で、対応可能であり、泥くさいけれども最も効率が良いといえる。圧砕技術によっても太刀打ちできない場合に、別の方法を考慮するという形が多いようである。ワイヤーソーや手こわしなども大事な技術であるが、あくまで補助的な位置づけである。
圧砕に多くの経験値を積み重ねているので、新技術を積極的に採用していくというモチベー
ションは、現在はあまり高くないように思える。
振り返れば、圧砕工法もかつては新技術であり、コンクリートをノミで壊すところから解体
工法ははじまったわけで、それを圧砕に進化させるまでに、大変な進歩があったといえる。これ以上の大幅な進化は、もう望めないかもしれない。

については、特に解体工事用の特殊なものを開発するのではなく、従来の一般的な防音パネル
で十分対応できているようだ。
4.2 高強度化への対応
日本における圧縮強度試験はφ20×100mmの円柱供試体で行うので、以下に示す日本の値
は、100×100×100mm の試験体を使っている国の方にとっては、×1.2 程度を掛けた値で考える必要がある。
さて、一般的な鉄筋コンクリート建築物で使わ れ る コ ン ク リ ー ト の 圧 縮 強 度 は 18 ～36N/mm2 が標準であるが、コンクリート技術の進化とともに、日本では 60N/mm2 クラスの高強度コンクリートが広がり、現在は150N/mm2 を超える超高強度コンクリートも実用化されている。かつて超高層建築は鉄骨造
４．解体工法のこれからの課題についてがメインであったが、コンクリートの高強度
これからの解体工法の課題として、①高層化、 化・超高強度化が進んだことから、とくに集合②高強度化への対応が挙げられる。
住宅などでは、居住性などの点でメリットが大4.1 高層化への対応
きい高強度鉄筋コンクリート造が主流になっ日本の超大手ゼネコンでは、
2010年前後に、ている。
超高層ビルの解体工法を一斉に開発・実用化し鉄骨造であれば、鉄骨部材を切断することでてきた。詳細は別途みていただきたいが、「上解体するが、鉄筋コンクリート造では、鉄筋がから壊す」、「下から壊す」という違いはあれ、 中にあるコンクリートを圧砕して行うのが一全体として共通する部分が感じられる。おそら
般的である。しかし、コンクリートが高強度化
くゼネコン各社は、騒音・振動対策、廃棄物対し、鉄筋も太径化すると、コンクリートの破砕策などを含め、今までの解体工事のままではだ
も鉄筋の切断も困難となる。機械の損耗も早くめだと思っていて、新しい解体工事のあり方・なり、施工効率も落ちる。
戦略を、超高層ビルを題材としてアピールしよ
私の研究室では、150～180N/mm2 クラスの試験体を作製して実験を行っている。結論としうとしたように私は思う。
ただ、これらの工法は鉄骨造を想定しており、 ては、現行の圧砕技術でも対応できる。なぜかというと、圧砕が圧縮力ではなく引張力のメカ
鉄筋コンクリート造や鉄骨鉄筋コンクリート
造の建築物にそのまま適用することは難しい。 ニズムで破壊させる工法であるからである（コンクリートは圧縮強度が高くなっても引張強
都市部の高層建築物は、近隣建築物と近接し度はさほど変わらない）。
ていることが多く、解体工事の施工条件が大変
ただし、圧砕工法の経済活動に見合った、現厳しい。騒音・振動、副産物の搬出などによる実的な採用限度は、設計基準強度 60N/mm2 以
周辺環境への影響を最小限にとどめ、アスベス
下程度までとし、それ以上ではアタッチメント
トやダイオキシンといった有害物質の飛散にに掛かる負荷が大きく、騒音・振動ので難しいも配慮しなければならない。超高層ビルの解体と考える。
工法では、解体階をパネル等で覆って外部へのそこで、設計基準強度 60N/mm2 以下を上回
飛散を防ぎ、閉鎖的な施工環境で解体工事を実る部材では、➀解体現場で、カッタもしくはワ施しているが、最近では中高層の建築物でも同
イヤーソー工法で対象部材をトラックに載せ様の対処が行われるようになった。防音パネル

られる大きさまで切断し、搬出する。
②部材のままリユース or 作業フィールドで圧砕・破砕・分級の上、高級品質のリサイクル材とする。ことを提案する。
超高強度・高強度レベルのコンクリートが使われている部材は、建物全てではなく、下層階の一部に限られることが多い。また、超高強度・高強度レベルのコンクリートは、セメントがリッチであり、リサイクル価値は高いし、高級な再生骨材にもなり得る。
これらを結論づけた研究についてはまたの機会に紹介したい。
5．新設時に解体に配慮した設計を
私はかつて、鉄筋コンクリート造の柱や梁などの部材をそのまま次の構造物に使えないかと、複数の解体工事業者に聞いてみたことがある。しかし彼らの答えは「採算に合わない」「考える余地もない」といったものだった。奇麗に切断して再利用するより、小塊に崩してリサイ
クルしたほうが、今は現実的のようである。解体される建築物は既存不適格の建築物が多く、現行の耐震規定に照らしあわせると転用部材としてそぐわないという点もある。
高強度コンクリートの解体について触れたが、新設構造物において、強度レベルが高くな
ればなるほど、施工管理上、場所打ちよりは
PCa（プレキャスト）部材を現場に搬入して建方する方法が有利といえるが、私は解体もこのことを逆手にとって実施できないだろうかと考えている。昔のものは限界があるが、今現在および将来にわたり、施工される構造部材は十分に転用できるほど、技術レベル・管理レベルは高いと私には思える。また、高強度で壊しにくいほど転用部材としての付加価値は高いともはずである。
設計時に、部材のジョイントを工夫し、施工時と解体時に共用できるようにするのは、それほど困難なことでない。設計時に解体時を想定して工夫を盛り込んでおくことで、解体工事が容易になり、副産物も低減するというメリットを実現できる。
システマチックかつ安全な解体を考慮すべきである。ゼネコンは、絶対にそういう方向で考えているはずである。数年後にはそれを売りにした工法が出てくるかもしれない。
６．解体工事業への期待
1995 年の阪神・淡路大震災でも、2011 年の東日本大震災でも、早期復旧・復興に向けた最大の課題は、がれきの早期処理であった。
解体工事業者は多くの重機を保有し、「どかす技術」を持っている。自治体と協定を締結しており、こうした非常時にはいち早く出動し、がれき処理に尽力してきた。これらの貢献で、全解工連として、国土交通大臣、環境大臣から表彰も受けている。
今回の建設業法改正では、「離職者の増加、若年入職者の減少等による将来の工事の担い手不足が懸念される」ことから、「建設工事の
適正な施工とその担い手の確保が喫緊の課題」と指摘している。今後、解体市場はますます増加する。若く熱意にあふれた技能者入職、熟練工の定着を図るためにも、労働環境や労働条件の改善が図らり、人材の教育を進めて行くことが重要と思える。
今までは土木・建築一式工事の中に含まれていたが、「解体工事業」成立に伴い、今後は解体工事の分離発注が進むことが期待される。それには、多様な建築物に適用できる公的な積算基準を整備し、積算の透明性を高めていくことが必要と思える。ただし、解体工事においては
官庁工事より民間工事が非常に多く、見積り方
式もまだあまり機能していないことや、地域による施工規模や単価の相違があるんで、難しいことと思える。解体工事でも価格だけでなく技術提案も加味して発注を行う、技術提案総合評
価制度の導入も望まれるところである。
今回、国が解体業の許可区分を設けたことについて、ある意味で「パンドラの箱を開けた」
ことになったいわれている。それだけ国土交通省も強い信念・確信をもって決断したわけである。
難しい課題はまだまだあるが、これから各方面で検討を重ね、あるべき解体業の姿を確立していただければと思う次第である。

Establishment and Prospect Of Demolition Business In Japan
Nihon University, Noboru Yuasa
1. Establishment Of “Demolition Work” By Revision of Construction Business
Law

The Construction Industry Law has transformed the construction industry from a“registration system” to a “permit system” in 1971, and the total of 28 industries (including civilengineering and construction) and 26 specialized industries were stipulated as the permitted
industry categories. The demolition work was categorized within “civil engineering/construction
work”, and spent 43 years buried between civil engineering work, construction work, and othersimilar works.
Poor working environment and working conditions are the most harmful factors that
endanger workers. To prevent the occurrence of serious accidents during demolition work, adding
demolition businesses as an independent licensed industry was a long-cherished wish of theindustry. The National Federation of Demolition Works Associations (all federations) which
consisted of worldwide demolishing contractors have repeatedly appealed to the country in order togrant this wish. We can even state that this wish triggered the establishment of the National
Federation of Demolition Works Association 20 years ago.
Finally, in June 2014, the revised Construction Business Law was promulgated, and it was
decided that the demolition business would become an independent licensed business. Even from aperspective of a third party, as a researcher, this is very pleasant to hear. The demolition work
category was set up as the 29th industry (27th as a specialized industry) as a whole, separated fromthe previous categorized businesses (civil engineering/construction work) (See Figure). It is a
specialized industry that deals only with demolition work and the demolition work that is carriedout in the general plan of civil engineering and construction is handled by each "set work" category.

It was necessary to obtain a permit to carry out demolition work of 5 million yen (47,000 USD) or
more per case.
Soon after, the demolition work license came into effect in June 2016, where construction
companies that carried out demolition work with the permit of “civil engineering/construction workbusinesses” and “concrete work” prior to the enforcement date could carry on demolition work until
May of 2019 without the permission of the newly recognized demolition business. During this time,
the license registration for demolition business was promoted.
Along with the establishment of the demolition business, comes a necessity to establish aqualification system that certifies the skills and knowledge required for engineers assigned to thedemolition work: (1) Expertise and technical knowledge of demolition method (2) safety
management and construction management capabilities (3) knowledge of environmental issues (4)knowledge regarding construction waste management (5) knowledge of related laws and regulations(6) perspective of management ability (site management). These necessities were assessed andtechnical requirements/qualifications were announced in June of 2016. Regarding the engineer's
requirements/qualifications, until March of 2021, it is also considered that the civilengineering/construction work’s engineering technicians (limited to existing workers) areconsidered to be the demolition work engineers.

2. Preventing Accidents During Demolition Work

With this opportunity as an independent licensed business, the demolition industry hasraised the hurdle for safety management of demolition work. Although the safety of the "building"side of the structure has been established, the safety of the "demolishing" side is not yet sufficient,and statistically it cannot be easily compared. There are many accidents during demolition workneedless to say that demolition work is more complex than new construction work. Accidents
include "public accidents" and "work accidents", but public accidents that cause harm to a third
party other than the construction party should never occur.
When we investigate further into the cause of the accidents that has occurred during
demolition work, most occurred in the “management". This does not mean that we do not havesufficient technical understanding of the demolition work, but rather a little carelessness andcareless mistakes such as the recurring thought of "maybe it will be all right”, lead to a major
accident. Currently, the Ministry of Land, Infrastructure, Transport and Tourism has addressed thisas a problem, and is trying to establish a guide for prevention by establishing an industry categoryfor "demolition work”.
A management manual has been prepared, and at all demolition work associations, the causeof accidents related to demolition work is being analyzed, and steady efforts are being made toprevent such occurrences. In addition to conducting technical courses for "disassembly work
construction engineers" (registration qualification based on the Ministry of Land, Infrastructure,
Transport and Tourism) and disassembly work construction technology courses, in 2008, the visual
text "Disassembly KYT sheet collection" has also been summarized. This visual text is edited to
predict the accidents that may occur and contains illustrated scenes to asses the possible risks indifferent situations. The reader’s takeaway is to specifically understand the kind of precautions thatneeds to be taken beforehand from one’s perspective. Personally, this is a very good resource foranyone in the field of demolition work.

3. Technology Development for Demolition Work

There are various demolition work methods, but contractors have many kinds of materials
and equipment, and demolition businesses that received order determines which demolition work
method should be adopted according to the scale, shape, structure and location.
With respect to each of the materials and equipment and construction methods, thecontractors are also steadily working towards improvement regarding to the technical problems felt
during demolition work on a daily basis.

In urban areas of Japan, when demolishing high-rise buildings, a hydraulic excavator isoften installed on the slab of the top floor, and is called a “top-down method” in which disassemblyis performed from the top floor. In order to support the hydraulic excavator, it is common toconnect the upper and lower slabs with a support pipe and to support them with multiple layers.
However, instead of this support pipe, there is also a method to place unreinforced concrete in placeof this support pipe and to demolish the floor slab in the end. Since it is straight, it is easy to break
and the prices are reasonable.
The National Federation of Demolition Works Associations provided research grants and is
working on the evolution of demolition technology, and plans to hold a research presentation once a
year that summarizes research results. Although my laboratory also uses this grant, it is expectedthat the level of the industry as a whole will be improved by sharing the technology developed
within the industry and to incorporate it into a common technology system.
Research on demolition method also contains the integrated aspect of joint research withother general contractors, but since demolition technology itself is owned and accumulated by thedemolition business, general contractors will help systematize the demolition technology bythinking about the mechanism. By doing so, it seems that the roles of demolition technology can beshared evenly with each other. Even during the demolition work of the Akasaka Prince Hotel,
which has attracted the attention of society in recent years, it was the general contractor that
constructed the entire system, but the demolishing contractor was in charge of the elemental
technological areas such as crushing and cutting/disconnecting. At present, it has been said that outof all the existing technology, "crushing", is the most used demolition technology. Most of thebuildings can be demolished using the crushing technology and is considered the most efficient outof all existing technologies. However, it seems that there are many cases in which another method isdeemed fit when the crushing technique is not enough. Use of wire saws and manual crushing arealso important techniques, but they are only for auxiliary positions. Since many experiences andknowledge have been accumulated through crushing, the motivation to actively adopt newtechnologies are not at its highest priority at this point.
Looking back, the crushing method was once a new technology, and demolition work
started with the breaking of concrete using chisels, so one can say that great progress has been madesince then. It may not be possible to expect any further evolution from this crushing technology.

4. Future Issues Of Demolition Method

Challenges the current demolition methods will face in the future includes: (1) increasing
the number of layers and (2) measures for higher strength.

4.1 Response To High-rise Buildings (Skyscrapers)

Around the year 2010, major general contractors have simultaneously developed practicaluse of demolition methods for skyscrapers. It is preferred to look at the details separately, but there
are differences between “demolition from above” and “demolition from below”. Nonetheless, there
are correlations when you look as a whole. Perchance, general contractors realized the need fornoise, vibration and waste countermeasures that demolition work up till now has unaddressed. I
presume that general contractors would appeal new strategies of demolition work with the subject
being skyscrapers. However, these construction methods are presumably steel frame construction
and it is difficult to apply them onto reinforced concrete constructions or steel frame reinforced
concrete construction.
High-rise buildings in urban areas are often in close proximity to neighboring buildings, andthe construction conditions for demolition work are very strict. It is necessary to minimize theimpact on the surrounding environment due to noise, vibration, carry-out of by-products, etc., andconsider the scattering of harmful substances such as asbestos and dioxins. In the demolition
method for skyscrapers, panels are used to cover the demolition floor to prevent scattering outside,and the demolition work is performed in a closed construction environment but recently, similar
measures have been taken for high-rise buildings. Regarding soundproof panels, it seems that theconventional general soundproof panels are sufficient, rather than developing special ones fordemolition.

4.2 Measures For Higher Strength

Compressive strength tests in Japan are performed on φ20 × 100 mm cylindrical specimens.
Therefore, for countries using 100×100×100 mm test specimens, the following Japanese values
need to be multiplied by an estimated ×1.2. The standard compressive strength of concrete used ingeneral reinforced concrete buildings ranges from 18-36 N/mm2, but with the evolution of concrete
technology, high-strength concrete of 60 N/mm2 class has spread in Japan, and currently there areultra-high-strength concrete exceeding 150 N/mm2 which has also been put to practical use. In thepast, super-high-rise buildings were mainly made of steel but with the progress of higher strengthand ultra-high strength of concrete, high-strength reinforced concrete construction has become moremainstream. This is due to great merits in terms of habitability, especially in housing complexes.
In the case of a steel frame structure, the steel frame member is disassembled by cutting, but
in the case of a reinforced concrete structure, it is common to crush the concrete with thereinforcing bar inside. However, if the strength of concrete becomes high and the diameter of thereinforcing bar becomes larger, it becomes difficult to crush the concrete and cut the reinforcing
bar. Machines would wear out faster, and construction efficiency will be reduced.
In my laboratory, we make 150-180N/mm2 class specimens to conduct experiments. In
conclusion, the current crushing technology can be used. The reason behind this being, crushing is amethod of breaking not by compressive force but by tensile force (concrete tensile strength does notchange much even if the compressive strength increases).
However, the practical limit of adoption, which commensurate with the economic activity of
the crushing method, is up to a standard strength of 60 N/mm2 or less, and above that, the load on
the attachment would be too large, and there would be difficulties due to noise and vibration.
Therefore, for parts that exceed the standard strength of 60 N/mm2, (1) at the dismantlingsite, use a cutter or wire saw method to cut the target parts into a size that can be placed on a truck
and carried out, (2) reuse or crush/classify the materials in the work field to be used as a highquality recycled material.
In many cases, parts that use ultra-high strength/high strength concrete are often limited toparts of the lower floors rather than the entire building. In addition, ultra-high-strength and highstrength level concrete is rich in cement, has high recycling value, and can be a high-grade recycled
aggregate.
Furthermore, I would like to introduce the research that concludes these points given anotheropportunity.

5. Layout for Disassembly and Demolition When Newly EstablishedI have once asked several demolition contractors whether they could use parts of thereinforced concrete columns and beams for the next planned structure. Their answers didn’t meet
my hopeful expectations and were responded with either “not profitable” or “I have no idea”. It
seems more realistic now to break it down into smaller pieces and recycle, rather than to cut it clean
and reuse it. Many of the buildings that are to be demolished are ineligible existing buildings, andthere is also the point that they will not be suitable as diverted members in light of the current
seismic regulations.
I mentioned the demolition of high-strength concrete, but the higher the strength level of a
new structure, the more convenient the method of bringing in PCa (precast) parts to the site andconstructing them rather than casting-in-place due to construction management. However, I havewondered if demolishing still can be done if we see the light of this unfavorable situation. Although
the old ones have limitations, it seems to me that the technical level and management level are highenough that the constructed structural parts can be diverted enough now into the future. In addition,
the higher the strength and the harder it is to break, the higher the added value as a diversion partshould be.

Perhaps it is not so difficult to devise a joint of parts at the time of design so that it can beused both during construction and demolition. When we incorporate proper measures during thedesigning phase of construction, it is possible to realize the benefits: facilitated demolition andreduced by-products.
A systematic and safe disassembly must be considered and general contractors should
definitely think in that direction. In a few years, there may be new advertisements in this direction.

6. Expectations for the Demolition Work

Both at the Great Hanshin-Awaji Earthquake in 1995 and the Great East Japan Earthquake
in 2011, the biggest issue for early recovery and reconstruction was the early processing/treatment
of debris.
Many demolition contractors own a lot of heavy equipment and has a technology where you
can move/discard debris. There was an agreement with the local government, and in such an
emergency, the contractors dispatched quickly and have devoted their efforts to debris disposal. Allof these contributions have been recognized and they were awarded by the Ministry of Land,
Infrastructure, Transport and Tourism and the Ministry of Environment.
With this recurring revision of the Construction Business Law, there is still a concern that
there will be a shortage of future workers due to an increase in the number of employees leaving theworkforce and a decrease in the number of young employees entering the field. In response to thisissue, proper construction during demolition and security of the people who carry these works need
to be addressed. The market in the demolition business will continue to increase in the future. It is
important to improve the working environment and working conditions and to promote proper
education of human resources in order to recruit young and enthusiastic skilled workers and retain
skilled workers.
Until now, demolition work was included in the civil engineering/set construction work, butwith the establishment of the independent, “demolition work business”, it is expected that a separate
order for demolition work to be proceeded in the future. In order to proceed in that fashion, it isnecessary to establish an official standard calculation applicable to various buildings and to increase
the total transparency of the estimation. However, this can be deemed difficult due to the fact that
demolition work is more of a private construction than a government construction. This entails thatthe estimation method is not yet functioning well, and there are differences in construction scales
and unit prices depending on the region. It is desirable to place an order in consideration oftechnical proposals in addition to price proposals, hence introducing the technical proposal
comprehensive evaluation system.
In a sense, the government setting up a demolition permit category this time was like
opening the Pandora's box. It is evident that the Ministry of Land, Infrastructure, Transport andTourism have made decisions with strong beliefs and convictions of this new industry.
Although there are still many difficult challenges, continuation of studies in various fields
would lead to an establishment of an ideal demolition business.

THE TRANSITION OF DEMOLITION TECHNIQUES IN JAPANNoboru Yuasa
College of Industrial Technology, Nihon University
1. Abstract
When considering the history of demolition, we have to accept that there are very few
written records regarding demolition until about 1965, except for summarized stories of thoseaffiliated with an architectural job. Contrary, there is a long-written history of wooden
construction as well as records of the application of reinforced concrete on newly built
constructions. In addition, it was after 1955 (Showa Year 30) when the full-scale demolition of areinforced concrete construction was carried out.
2. Outline of Demolition During a Reinforced Concrete Structure
The demolition of reinforced concrete structure started with the use of chipping methodin the 1950s. Although demolition of chimneys were carried out during the time of war, thedemolition of reinforced concrete structure started much later than the new constructions thatwere built after World War II. A chipping hammer in Japanese is called, Gen-no which is a large
hammer with both hands that weights from 5 to 20kg (11-44 lbs). The hammer drives an arrow(wedge) into the concrete and breaks it into pieces. During the demolition of the Yurakucho
Pikaderie Theater in 1958, around 50 demolition workers (known as Yamaya: a quarryman)
worked day and night using this method. This method of demolition was utilized in a large-scale
mobilization of labor. The beam was knocked off the stirrup flatly from above, and an arrow was
driven between the axial main bars. Here, the reinforcing bar inside the concrete was taken out
neatly.

Figure 1 Transition in Reinforced Concrete Structure Demolition MethodFigure 1 shows thetransition of the demolition
method for reinforced concrete
structures. After that shows thebreaker method, the wrecking
ball method and the larger
breaker method. These are alltypes of destruction methods
which proceeded but due toenvironmental issues andconcerns, the use of wrecking
ball methods have declined andlarger breaker methods have
Figure 2 Schematic diagram of falling outer wall
gradually changed from pneumaticpressure to hydraulic pressure. When entering
the 1970s, using the cutting method,
disassembly by parts, use of static cracking
agents, electrical indirect crushing methods andjacking methods were tested. Currently, thecrushing method is considered the generalpurpose method, replacing the wrecking ballmethods and larger breaker methods (Figure 1).
It has been said that the speed of progress in themethods of demolition reinforced concrete
structures were fairly slow, and the main reasonsare speculated to be as follows:
Photo 1 Demolition due to a fall (around 1963)
1. Demolition work on reinforced concrete
structure has a short history, and development research on the demolition method started in 1970
or later.
2. In the past, local residents did not often make complaints about the environmental concerns(pollutions, etc.).
3. Demolition using the wrecking ball methods and breaker methods were really efficient.
4. There were many issues with the ordering system of the demolition work. In other words, inorder to receive orders for construction post demolition, it is often the case that the contract’s
highest priority to be extremely lowly budgeted and done in a short duration. Concerns regarding
pollution control was a secondary priority that came after that.
5. Reinforced concrete is a strong material and is hard to demolish due to the following
properties:(a) It is difficult to cut with a normal blade, such as boring (drilling a hole and enlarging an
existing hole).
(b) The mass and volume are very large and it is difficult to handle.
(c) Would not burn and has a high melting point.
(d) Even though acids and other chemicals can be invasive, it is extremely difficult to change theproperties in a short time and the permeability of the liquid is small.
6. The amount of demolished material (by-product) is large and there is a limitation whenreusing the material.

3. Year 1955-1966 (Development of the Era of Hand
Breaker Method)
During this period, the overturn of the structure
was incorporated where the floor sludge and beams weredestroyed and the wall and the columns were pulled down
(Figure 2, Photo 1). At the time, this method was named“overthrow”, where demolition expertise would describe
this as a “man’s flower”, meaning a man’s pride, proving
their spirit and skills. On the other hand, pick hammers
have begun to be used to shave/chip the floating slab
foundations(slab-on-grade) and rooftop cinder concreteslab structures.
After the Korean War, breakers were also used for
demolition work. Initially, the breakers were loaned by the
US military and weighed around 45 kg (100 lbs).
Eventually, the demolition work was finally mechanized.
Prior to then, demolishing one floor took about amonth, which was a slow pace. However, along with thetrend of shortening the duration of construction period,
Photo 2 Demolition due to a wrecking
demolition work gradually moved toward mechanization.
ball (Bank of Japan Head
Picks and breakers during that time seemed to have been
Office around 1970)
used mainly for demolition of foundations, floating slab
foundations(slab-on-grade) and pavements. On the other
hand, attempts were also made to drop the wrecking ball by using a triad(three-pronged)
structure, and it seems that the reinforcing bars in concrete were often collected after separatingconcrete into small blobs. Along with this came the domestic production of picks and breakers
that were light and durable.
4. Year 1965-1980 (From Wrecking Ball Method to Larger Breaker Method, and an Era of
Pollution-Free Demolition Method)
Around 1965, among crane trucks and other large machineries, the use of wrecking balls
as a demolition method has been more so established. In other words, it is a method of hitting thefloor slab from the upper floor in subsequent order, pulling out the beams, cutting the beams, andfinally pulling down the columns and walls.
During the demolition work of the head
office in the Bank of Japan from 1968 to 1969, acrawler crane/truck crane was used to verticallydrop or shake a 1-2.5-ton weight (wrecking ball) to
knock down concrete parts. (Photo 2). In addition,a thick and heavy hose was laid around, andconcrete was broken using many of the hand-heldpneumatic breakers (Photo 3). In this demolition
work, iron mesh concrete in the vault (8 mm wide
and 6 mm thick expanded metal sheets werestacked at intervals of about 25 mm and pea
Photo 3 Demolitions due to a hand breakergravel concrete was poured) were demolished.
(Bank of Japan Head Office around 1970)

Photo 4 Jacking Method

Photo 5 Crushing Method around 1978

Photo 7 Demolition using a large breaker

Photo 6 Parts demolition using a cutter

However, since around 1970, due to the socialchanges accompanied with an increase ofvibration, noise and dust pollution, demolition
methods of reinforced concrete structures using
wrecking balls has become more desirable and fit.
As a result, jacking method using
hydraulic pressure (construction method of
breaking up the beam/slab from below with a
jack: Photo 4), crushing method (Photo 5), andPhoto 8 Current crushing attachment and heavy
cutting each material with a concrete cutter
machine(Photo 6), have been devised and utilized.
However, since these construction methods were slightly expensive in practice and unrealistic,
they were demolished with wrecking balls and large breakers (Photo 7) with soundproofing
measures. During this time period, the Japan Building Industry Association created the"Guideline for Pollution-Fee Destruction of Reinforced Concrete Construction”. Research
related to construction methods using a crusher with slow detonation (slow explosive), methods
using static crushing agents, water jet methods, electric heating methods, wire sawing cutting

methods, has been developed
among with connections to themethod of demolition of thereactor vessel robot.
5. Year 1985- Current (Era of
Crushing Method)
In 1976, when a “nibbler”
was introduced from the UK thatchews down bends, a new
demolishing machine was built
and used by the hands of ademolition specialist/machine
manufacturer. This was partly
Figure 3 Work during ground demolition work
due to the development of thedemolishing method, which had
been led by construction
companies later transferring to
the hands of a demolition
specialist/machine manufacturer.
The crusher, which has relatively
low noise and vibration and ishighly efficient, drives away
wrecking balls and replaces large
breakers to become the mainstream of demolishing machines.
The crushing method is
positioned as the most common
method of demolition leading up
to 2015, today (as seen in Photo8). Depending on the structure,
Figure 4 Work on dismantling upper floors
shape, and location condition of
the model structure, either (1) lift the heavy equipment to the upper floor and demolishes eachfloor from the upper floor, or (2) demolition by a ground demolishing method that demolishes
from the upper floor in subsequent order by heavy equipment placed on the ground. Ground
demolishing method (Figure 3) has been applied to buildings that scale and height from 3rd to
4th floor buildings since about 1980. However, in recent years, a 40-60m class long-reachcrusher boom has been developed, and if there is an open space where a demolition machine canbe moved around the building, it can be demolished from the ground up to a height of about
35m. The operator decides to operate the crusher by looking at the Photo of the camera attachedto the top of the boom.
The top down method (Figure 4) has been used since around 1980, and is currently being
actively applied to the demolition of high-rise buildings in urban areas. With this method, a cranefor hoisting the crusher on the top floor is necessary, and when using a crawler crane, it is limited
to a crusher with a weight corresponding to its lifting performance. In general the limit is about
15 tons.

Photo 9 Bomb dismantling experiment at Takashima company house of Mitsubishi coal mine (1988)

Photo 10 Bomb dismantling experiment at Lakeside Building (1992)

In recent years, in particular cases, it has become difficult to apply the latest technology,
the crushing method, to the construction of new structures. Steel reinforced concrete structure(SRC), concrete filled tube structure (CFT), and reinforced concrete structure (RC) using highstrength and ultra-high-strength concrete are extremely difficult to demolish by the crushingmethod. These are important issues that must be resolved in the near future. The mass demolitionof explosives utilized in the United States can also be seen in Japan as well: it was attempted at
the 1988 Tsukuba Expo Dome, the Mitsubishi coal mine Takashima Company Housing (Photo9), and the 1992 Lake Side Building (Photo 10). However, critics view that the application of theblasting method to buildings in Japan is not simple from the viewpoints of economic efficiency,
safety, economic activity limitation, and crime prevention.
It seems that collective demolition will continue to be difficult in the future, andtechnologies like miniature blasting and micro blasting, which demolishes materials and block
division levels using as few explosives as possible, seem to be useful. There are hopefuladvancements that can be foreseen in the near future in this field.
6. EndingThis article explained the transition of demolition technology in Japan. The demolition
work will be the process of the vacant lot, or the skill of the demolition work: (1) To demolish“safely”, (2) to minimize the damage/trouble for surrounding neighbors in regards to noise,
vibration and dust, (3) with regard to the processing of demolishing materials, the mostimportant evaluation is “to not bring the natural environment into destruction”, (4) cheap, andfinally, (5) speediness of the work. Those five aspects are considered the axis of evaluation. To
put it short, the goal of those involved in the demolition work is to be able to demolish the land
in a clean and tidy manner without stressing everyone involved during the process.

日本における超高層ビルの解体
日本大学教授 湯浅 昇
日本では、現在高さ 100m 以上の超高屈ビルが７００棟以上ある。竣工当初は時代の最先端だった超高屈ビルも 30～40 年も過ぎれば機能・性能は陳腐化し、近年、大地震時の長周期地震動が高層ビルでは問題となることがわかってきた。補強・リニュ
ーアルには限界があり． 今後、超高層建物の建替が増加してくると予想されている。
2012～2013 年、東京の赤坂プリンスホ
テル新館（地上 39 階・塔屋 1 階・地下 2階、高さ 138.9m)が解体され、日本では、
テレビや新聞で大きく取り上げられ、広く一般市民
や国際社会の興味を引くことになった。
高さ 100m を超える超高層ビルの解体は． 従来の解体工法では、解決しなければいけない問題が山積している。超高層ビルは、都市部に立地し、解体工
事上の制約条件が多い。上空の風は地上の数倍にもなり、仮設足場や養生材の設骰・撤去が高所危険作業となることに加え．粉じんの広範囲への飛散． 解
体部材の飛来落下の危険性．騒音・振動の伝播などに、配慇しなければならなく、解決すべき課題多岐にわたる。
日本における５大ゼネコン各社は．超高層ビルの解体を、様々な技術開発を経て提案、先導的に手がけてきた。
各社が、日本建設業連合会において、超高層ビルの解体に関して公開した資料、ホームページでの公開情報に基づき、概要を紹介する。
(1)鹿島渥設「鹿島カットアンドダウン工法」
下層部の各柱位置に設置されたジャッキ
で、建物全体を支持しつ、下階を解体する。
各柱は解体された層ごとに、速やかにジャッキを操作し上階荷重を支え、建物全体の同じ層の解体が終了した時点で、全ジャッキで建物全体をダウンさせる。これを繰り返して解体工事を進める工法である。
従来工法に比し騒音や粉じんの飛散を抑制できる。また．常に地上付近で一定の作業を繰り返して行うため．環境対策設備や施工設備を盛り替える必要がなく．周辺環
境への影響因子について、一定の場所で確

図-1 鹿島カットアンドダウン工法
実に対策でき、高所作業削減による安全性向上に効果がある。
下階に設置されたジャッキにより、上層階の全荷重を支えることになるが、地震対策のため、鉄筋コ
ンクリート造のコアウォールを解体前に設置し、荷重伝達梁による耐震機構により、耐震性を確保していている。
2008 年．鹿島建設旧本社ビル（S 造）解体工事ではじめて適用された。
(2)大成建設「テコレップシステム」
まず、最上階の躯体を壊さずに有効利用して解体を行う閉鎖空間をつくる。 そして、ジャッキを内蔵した仮設の柱を設置し．1 フロアごとにジャッキで解体階を自動降下させていく。解体する空間を閉鎖空間とすることで．部材の飛散・落下．粉じんの飛散、騒音・振動などの問題を大幅に改善できる。
最上階の躯体には水平搬送用のスライド式天井クレーンを、床面開口部には垂直搬送用のテルハを設

図-2 大成テコレップシステム

置し．分解した部材をクレーンで荷降ろしする。また．荷降ろしの際に生じる解体材の自由落下エネル
ギーを利用し発電を行い．徹底したエネルギー削減を図っている。
2011 年東京・大手町フィナンシャルセンター（S造）で初適用し、引き続き 2012 年東京・赤坂プリンスホテル新館（S 造）で適用され、日本では高層ビル解体として大きな話題を振りまいた。その後、鉄筋コンクリート造の超高層建物にも適用可能な「テコレップ‐Light システム」の開発し、2019
年、実構造物に適用した。
(3)清水建設「シミズ・リバース・コンストラクション工法」
同工法はもともと「ブロック解体工法」とネーミングされ、建物をビル上層部から、コンクリートの
スラブはカッターにより切断などしてプロック化した解体部材を．通常では新築工事で使うタワークレーンを使い、地上まで吊り下げて、専用の処理サイ
トで分別処理するシステムである。
信頼性が高く、実績の多い既存技術を巧みに組み合わせ．効率よく作業を繰り返して解体することで、工程を極めてシンプルし、不要な仮設設備の省略につなげている。適用に際し制約がほとんどなく、優れた汎用性を有している。
ここでは、柱・梁の切断作業に必要な一切の機能を集約したアタッチメントの開発も行うなどで更に効率化を図っている。
2008 年、地下 2 階、地上 14 階（2 階～14 階はCFT 柱）の S 造建物に適用された。
(4)大林組「キュープカット工法」
床・梁・柱の構造部材を圧砕せずに、切断してタワークレーンで地上に下ろし、地上で分別処理する

図-4 大林キュープカット工法

図-3 清水リバース・コンストラクション工法
ことで、騒音や振動、粉じんの発生を大幅に低減する。
振動・騒行の小さい機械により切断解体を先行して進め．クレーン作業の効率化を図り．短
工期化を実現する。
同時に．構造図-3 竹中ハットダウン工法
フレームの切断
手順・倒壊防止対策により．解体工事中の地震に対しても切断された部材の安全を確保する仕組みとなっている。
(5)竹中工務店「竹中ハットダウン工法」
ビル上部に周囲を覆った移動式解体工場“ハット”を設置し．下階へ移動させながら順次ビルの解体を行う工法である。
ハット内部には、天井クレーンを含む解体設備が一体設置されており．解体する建物躯体を包みながら隙間なく降下し、解体材も全て建物内部を通して降ろすため、従来工法に比しより安全で環境にやさしい。
ハットの内部でカッターやワイヤーソーを用いてプロック単位に切断するため、粉じんや騒音の拡散を低減できる。解体したプロックは建物内部から天井クレーンで降ろすので周辺への飛来落下の恐れがなく．都心部の工事に有効である。
2012 年、大阪・旧ホテルプラザ（地上 1～4 階Ｓ
ＲＣ造，5～23 階Ｓ造，地下ＲＣ造、高さ 88ｍ）適用させている。高層部が RC 造でも適用とされる。

DEMOLITION OF SKYSCRAPERS IN JAPANNoboru Yuasa
In Japan, there are currently more than 700 ultra-high bending buildings with a heightof 100m (328 ft) or more. The function and performance of the ultra-high bending buildingsthat were at the forefront a couple decades ago at the beginning of construction were obsolete
after 30-40 years. In recent years, it has been discovered that long-period ground motion
during an earthquake is a problem in high-rise buildings. There is a limit to the reinforcement
and renewal, and it is expected that reconstruction of super high-rise buildings will increasein the future.
In 2012-2013, the new building of Akasaka Prince Hotel in Tokyo (39 floors above
ground, 1 floor of penthouse, 2 floors of basement, 138.9m (456ft) in height) was
demolished. In Japan, as well as from the international community, the general public were
intrigued and the news was widely featured on TV and newspapers.
Demolition of a skyscraper that exceeds 100m (328 ft) in height leads to unresolved
issues in the conventional demolition method that needs to be addressed. Skyscrapers aremostly located in urban areas, and there are many restrictions on demolition work comparedto suburban and rural lands. There is a wide variety of issues that must be resolved: the windin the sky being several times higher than that on the ground, the work of installing andremoving temporary scaffolds, curing materials being a dangerous task at high places, dust
being scattered over a wide area, the risk of dismantling members getting injured increasing,noise complaints and the propagation of vibration.
The five major general contracting companies in Japan have been paving the way inproposing the demolition skyscrapers through various technological developments.
The outline of each company will be introduced based on the materials released by
the Japan Construction Federation and the information published on the website regarding thedemolition of skyscrapers.
(1) Kajima Corporation (Kajima Cut and Down Method)
Jacks installed at each pillar position in the lower floor support the entire building anddemolishes the lower floor. For each column, the jack is promptly operated to support theload on the upper floor for each demolished layer, and when the demolishing of the samelayer of the entire building is completed, the entire building is brought down with all jacks.
This is a method of repeating demolition work by repeating this procedure.
With this method, noise and dust scattering can be suppressed compared to theconventional demolition methods. In addition, because constant work is always repeated near
the ground, it is not necessary to refill environmental measures equipment and construction
equipment. Also, the factor s affecting the surrounding environment can be ensured at a
fixed place and can be addressed steadily. Effective measures are taken to improve safety by
reducing work in high places. The jacks installed on the lower floor will support the entire
load of the upper floors, but to prevent earthquakes, a reinforced concrete core wall isinstalled before dismantling and seismic resistance is secured by the seismic mechanism
using load transfer beams. This procedure was first applied in 2008 in the demolition work of
the former Kajima Corporation head office building (Steel structure).

Image１Practical Use of Kajima Cut and Down Method（2008）(2) Taisei Corporation (Taisei Tecolep System)
First, we will create a closed space that can be dismantled by effectively utilizing thestructure on the top floor without breaking it. Then, a temporary pillar with a built-in jack is
installed, and the dismantling floor is automatically lowered by the jack for each floor. By
making the demolishing space a closed space, improvements can be made in terms of
scattering/ falling parts, scattering of dust, noise, and vibration.
A slide type overhead crane for horizontal transportation is installed on the top-floor
frame, and the telpher for vertical transportation is installed on the floor opening, and thedisassembled members are unloaded by the crane. In addition, the free fall energy of thedismantling material that occurs during unloading is used to generate electricity to achieve athorough energy reduction. This method was first applied at the Otemachi Financial Center(Steel structure) in Tokyo in 2011, and subsequently applied at the Akasaka Prince Hotel
New Building (Steel structure) in Tokyo in 2012, which became a sensation in Japan as ademolished skyscraper. It has also been announced that the Taisei Ecological Reproduction
System, known as “Tecolep-Light system” in Japan is applicable to the super high-risebuildings made by reinforced concrete. This “Tecolep-Light system” was applied in 2019.

Image 2 Taisei Tecolep System

Image 3 Shimizu Reverse Construction Method(3) Shimizu Corporation “Shimizu Reverse Construction Method”
This method was originally named as “the block dismantling method”, and thebuilding was demolished from the upper part of the building to ground by using the tower
crane, which is comm only used in newer constructions to dismantle the concrete slab into
blocks by cutting with a cutter. This is a system that suspends and sorts at a dedicatedprocessing site.
By combining skillful existing technologies that are highly reliable and have a proventrack record, and by repeatedly disassembling the work efficiently, this process is extremely
simple and unnecessary temporary equipment can be omitted. There are almost no
restrictions when applied, and has excellent versatility.
Here, we are working to further improve efficiency by developing an attachment that
integrates all the functions required for cutting the pillars and beams.

Image 4 Obayashi Cube-Cut Demolition Method

In 2008, it was applied to an S structural building with 2 basements and 14 floors
above ground (CFT columns from 2nd to 14th floors).
(4) Obayashi Corporation (Obayashi Cube-Cut Demolition Method)
Without crushing the structural members of floors, beams, and pillars, they are cut
and lowered to the ground with a tower crane, sorted and carried forward on the ground to
improve the efficiency of crane work and to implement shorter construction periods. At thesame time, the cutting procedures of the structural frame and the measures that prevents
collapsing ensures the safety of the cut parts against earthquakes during demolition work.
(5) Takenaka Corporation (Takenaka Hat Down Method)
This is a construction method in which a mobile demolition factory “hat” that covers
the surrounding area is installed at the top of the building and the buildings are demolishedsequentially while moving to the lower floor.
Inside the hat, demolishing equipments including an overhead crane is installed
integrally, and it descend s without a
gap while wrapping the building frame
to be demolished. All demolishingmaterials are lowered through the insideof the building. Therefore, it is safer
and more environmentally friendly
compared to the conventional method.
Since the cutter and wire saw
are used to cut into blocks in the hat,
diffusion of dust and noise can also be
reduced. The demolished block is taken
down from inside the building by anoverhead crane, so there is no risk ofparts falling down to the surroundings,
which is effective for construction in
urban centers.
In 2012, this method applied tothe demolition of former hotel plaza inOsaka (1st-4th floor SRC construction,
5th- 23rd floor S construction, RC
construction underground, height 88m(289 ft)). It is a lso applicable when
the high-rise part is made of RC.
Image 4 Obayashi Cube-Cut Demolition Method

高強度・超高強度コンクリート構造物の解体負荷に関する研究
APPLICATION OF CRUSHING METHOD TO THE DEMOLITION
HIGH-STRENGTH AND ULTRA-HIGH STRENGTH CONCRETE STRUCTURES
湯浅 昇※１
Noboru Yuasa

1.はじめに2014 年６月、建設業法が 43 年ぶりに改正され、「解体工事業」が業種として確立した１）。
1960 年頃、我が国は高度経済成長期を迎え、数多くの建築物が建てられた。しかし、その頃の建築物が老朽化や美観性の低下などで解体され、近年解体工事件数は増加している２）。設
計基準強度が 60N/mm²を超える高強度コンク
リートを用いた建築物が 1990 年代から建設されているが、今では設計基準強度が 200N/mm²を超える超高強度コンクリートも実用化されている。今後高強度・超高強度コンクリートを用いた構造物の解体技術が必要になると考えられる２）３）。
しかし、これまでは建物の「建築」に関する研究に重きを置いていたため、「解体」に関する研究は少なく、高強度・超高強度コンクリー
ト構造物解体技術は未だ確立されていない４）。
本研究は、高強度・超高強度コンクリート構
造物解体技術の開発を目的に、高強度・超高強度コンクリート構造物の解体負荷を検討するものである。まず、無筋コンクリート試験体により加圧方法が破壊荷重に及ぼす影響を明らかにし、次に模擬梁部材により圧砕室内実験及び実機圧砕実験を行った。
※１

写真-1 油圧シャベルとアタッチメント

日本大学生産工学部建築工学科 教授・博士（工学）OF表-1 コンクリートの調合及び性状

13

セメント
308
463
775
775
969
969
1192
1192

P

質量(kg/m³)
細骨材
粗骨材
836
939
671
977
647
801
650
798
573
708
575
708
603
603
601
601

150mm

150mm

150mm

P

No.70
(g)
771
-

SP-8N
（g）
1852
-

ssp104
（g）
6200
6200
2960
2960
35770
35770

303A*
（g）
1993
3239
-

150mm

空気量
（％）
4.5
5.1
8.0
9.5
7.5
5.8
5.0
3.8

P

P

25mm 150mm
10mm φ20mm

スランプ値 フロー値
（cm）
(cm)
18.5
23.0
58.0×56.2
46.6×46.0
70.0×68.0
69.0×67.5
67.5×67.0
59.0×58.0

φ100mm

練り温度
（℃）
22.0
22.0
20.0
22.0
21.0
20.5
21.0
21.0 P10mm
φ20mm
φ100mm

φ100mm
10mm
25mm

φ100mmP

PP

図-1 立方供試体加圧試験方法（左から全面加圧、四点半球加圧）P* 100倍希釈
圧縮強度 引張強度(N/mm²)(N/mm²)
31.4
2.98
34.9
3.12
103
5.46
113
5.86
138
4.90
151
3.74
188
5.12
211
4.37

150mm
φ20mm
200mm

16

大井川
大井川
大井川
飯淵
大井川
飯淵
大井川
飯淵

単位水量
(kg/m³)
185
185
155
155
155
155
155
155

200mm

20

骨材

200mm

水セメント比
（％）
60
40

P

図-2 円柱供試体加圧試験方法（左から全面加圧、一点面加圧、一点半球加圧）

2. 加 力 方 法 が 破 壊 荷 重 に 及 ぼ す 影 響に関する実験
2.1 実験概要(1)使用材料、調合および打ち込み
表-1 に示す調合表に基づき、W/C＝60％、40％、20％、16％、13％のコンクリートを練り混ぜた。水セメント比 40％以上では、M 社製普通ポルトランドセメント、大井川水系川砂(表乾密度 2.63g/cm³)、大井川水系川砂利(表乾密
度 2.64g/cm³)、水セメント比 20％以下では、M
社製シリカフュームプレミックスセメント、飯淵産砕石 (表乾密度 2.62g/cm³)、飯淵産砕砂(表乾密度 2.65g/cm³)を使用した。化学混和剤
は、表-1 に従い B 社製 No.70・SP-8N・303A、T
社製 Ssp-104 を使用した。水は習志野市水道水である。150×150×150mm 立方供試体鋼製型枠およびφ100×200mm 円柱供試体型枠に打設した。
(2)養生条件
打ち込み後、材齢 3 日で脱型を行い、その後、60℃の高温室内で封緘養生を行なった。
(3)圧縮強度試験
JIS A 1108「コンクリートの圧縮試験方法」に基づき、材齢 28 日に圧縮強度試験を行なった。その際、150×150×150cm 立方供試体には
図-1 に示す全面加圧および四点半球加圧を、
φ100×200mm 円柱供試体では図-2 に示す全面
加圧、一点面加圧、一点半球加圧を行った。
(4)割裂引張強度試験
JIS A 1113「コンクリートの割裂引張強度試

験方法」に基づき、打ち込みから材齢 28 日後に割裂引張強度試験を行なった。
2.2 結果および考察(1)加圧方法と圧縮荷重の関係
図-3 に 150×150×150cm 立方供試体に対する全面加圧荷重、四点半球加圧荷重、及びφ100
×200mm 円柱供試体に対する全面加圧、一点面
加圧荷重、一点半球加圧荷重を、図-4 に圧縮
強度、割裂引張強度を示す。全面加圧に比し、小さな点で加重すると通常より小さな荷重で破壊できた。
150×150×150mm 立方供試体の場合、四点半
球加圧も、水セメント比が低くなる程、破壊荷重は増加したが、破壊荷重の水セメント比依存性は小さかった。
φ100×200mm 円柱供試体の場合、加圧面積が小さい一点半球加圧に作用した破壊荷重が最も低く、水セメント比が 13％となっても圧縮破壊荷重は 100kN 以下であった。
割裂引張強度は、水セメント比が低くなっても増加は小さく、割裂引張強度は 10N/mm²以下であった。
(2)加圧方法と加圧荷重比率の関係
図-5 は 150×150×150mm 立方供試体および
φ100×200mm 円柱供試体の全面加圧荷重を100％とした時の四点半球加圧荷重、一点面加圧荷重、一点半球加圧荷重の割合を示したものである。150×150×150mm 角柱供試体の場合、四点半球加圧は水セメント比の違いによる差はあまり見られず、常に全面加圧荷重の 10～

全面加圧

1000
1000

500
500

500
500

50

00

00

0

全面加圧に対する圧縮荷重比率（％）

図-3 圧縮破壊荷重

W/C=13％飯淵

W/C=16％飯淵

W/C=13％大井川

W/C=16％大井川

100

図-4 圧縮強度及び引張強度
1点面加圧

4点半球加圧

25

引張強度

150

W/C=13％飯淵

W/C=13％大井川

W/C=16％飯淵

W/C=16％大井川

W/C=20％飯淵

W/C=20％大井川

W/C=40％大井川

W/C=60％大井川

強度（N/mm²）

1000
1000

W/C=13％飯淵

1500
1500

W/C=16％飯淵

1500
1500

W/C=13％大井川

200

W/C=16％大井川

2000
2000

W/C=20％飯淵

2000
2000

W/C=20％大井川

250

W/C=40％大井川

2500
2500

W/C=60％大井川

2500
2500

圧縮強度
φ100円柱供試体

W/C=20％飯淵

150×150×150角柱供試体

圧縮荷重（kN）

300

φ100円柱供試体

W/C=20％大井川

3000
3000

W/C=40％大井川

4点半球加圧W/C=60％大井川

全面加圧

3000
3000

1点面加圧

1点半球加圧

1点半球加圧25
25

W/C=60％試験体に対する圧縮荷重比率（％）

W/C=13％飯淵

W/C=13％大井川

W/C=16％飯淵

W/C=16％大井川

W/C=20％飯淵

W/C=20％大井川

W/C=40％大井川

W/C=60％大井川

W/C=13％飯淵

W/C=13％大井川

W/C=16％飯淵

W/C=16％大井川

W/C=20％飯淵

W/C=20％大井川

W/C=40％大井川

W/C=60％大井川

15％の荷重で破壊した。
150×150×150角柱供試体
φ100円柱供試体
φ100×200mm 円柱供試202020体の場合、一点半球加151515圧および一点面加圧は水セメント比が低くな
101010るにつれて、圧縮破壊
荷重比率は低下してい
5
55
った。
0
00
(3)水セメント比 60％
試験体に対する比率
図-6 は水セメント比60％の四点半球加圧、一点面加圧荷重、一点半球加圧荷重それぞれを
図-5 全面加圧に対する比率100％とした時の比率を400400示したものである。
φ100円柱供試体
150×150×150角柱供試体
350
350
150×150×150mm 角柱供大井川：4点半球加圧
大井川：1面加圧300300
飯淵：1面加圧
飯淵：4点半球加圧
試体の場合、4 点半球加圧
250
250
は、水セメント比 20％以下
200
200
では水セメント比 60％に150
150
比し、圧縮試験結果は 2.5
100
100～4.5 倍であるが、2 倍程度
50
大井川：1点半球加圧
50の破壊荷重であった。
飯淵：1点半球加圧00φ100×200mm 円柱供試
0
10
20
30
40
50
60
0
10
20
30
40
50
60
水セメント比(%)
体の場合、一点面加圧およ水セメント比(%)
図-6 水セメント比 60％試験体に対する比率
び一点半球加圧は、水セメ
ント比 20％以下では水セメント比 60％に比し、圧縮試験結果は 3.5～7
3.模擬部材による圧砕実験倍であるが、2.3～3.7 倍の破壊荷重であった。
3.1 試験体の作製

表-2 コンクリートの調合と性状
W/C
（％）
60
20
16
13

質量(kg/m 3 )

単位
水量

シリカ

(kg/m ) セメント フューム
3

185
157
164
166

308
659
-

116
-

化学混和剤(g/m 3 )シリカ フューム
プ レミックス

細骨材 粗骨材 No.70 SSP104 303A

セメン ト

969
1192

765
630
578
491

1011
780
701
596

770
-

11070
29063
35769

2009
833
-

ｚ試験体は、梁部材を模擬したもの（300×300×900mm）とした。型枠として、鋼製型枠を使用し、鉄筋として、主筋（D19）８本、あばら筋（D10）20 本使用した。配筋は、図-7
示す通りとした。
コンクリートの水セメント比は、60％、20％、16％、13％とした。調合を表-2 に示す。使用材料として、水セメント比 20％において、M社製普通ポルトランドセメントと E 社製シリ
カフュームを使った以外は、2.1(1)記載の通りである。
材齢 28 日及び解体実験時（材齢 161 日）における圧縮試験と引張試験の結果を表-2 に併記した。
表-3 は、それぞれのコンクリートにおける
W/C=60％を基準とした時の圧縮強度比、同一コ
ンクリートにおける引張強度／圧縮強度（％）
、
W/C=60％を基準とした時の引張強度比を示す。
水セメント比を小さくさせることによる圧縮強度の伸びに比し、引張強度の伸びは小さく、圧縮強度が 5.1 倍となっても引張強度は 1.6倍程度でしかなく、超高強度コンクリートの解体では引張荷重をうまく与えることが有利といえる。
3.2 圧砕加圧試験（室内実験）

写真-2 室内圧砕試験状況

スランプ
フロー
（ｃｍ）
19.7(ｽﾗﾝﾌﾟ)72.2×71.4
88.0×86.4
75.8×72.5

圧縮強度(N/mm 2 ) 引張強度(N/mm 2 )空気量 練り温（％）(℃) 材齢２８日 材齢161日 材齢２８日 材齢161日
（解体時）

（解体時）

4.8
8.1
7.4
5.9

20.5
19.5
18.5
19.0

31.5
126.5
113.8
142.2

34.4
128.9
140.6
177.2

2.7
4.8
3.7
3.8

2.9
4.8
5.0
4.8

図-7 配筋表-3

強度比（解体時：材齢 161 日）

W/C
（％）

同一コンク
W/C=60％を リートの引張基準とした時強度/圧縮強の圧縮強度比
度（％）

60.0
20.0
16.0
13.0

1.0
3.7
4.1
5.1

W/C=60％を基準とした時の引張強度比

8.5
3.8
3.6
2.7

1.0
1.7
1.7
1.6

表-4 圧砕荷重

W/C
（％）
60
20
16
13

W/C60％コン
最大圧砕荷重 クリートに対す
る最大圧砕荷
（ｋN)
重比

1706
2395
2280
2452

写真-3 圧砕刃

1.0
1.4
1.3
1.4

写真-4 アタッチメント

写真-5 試験体とアタッチメント

写真-6 コンクリート片の飛散

表-5 実機による最大圧砕荷重

W/C
（％）
60
20
16
13

最大圧砕刃 W/C60％
先端荷重 の荷重に
（ｋN)
対する比
1.00
30.0
780
1.00
30.0
780
0.97
29.0
754
29.5
767
0.98

最大油圧
（MPa）

(1)実験概要
圧砕加圧試験は、最大荷重は 4000kN の試験機で行った。写真-2 は、この圧縮試験機に試験体を設置した状況を示したものである。S 社
製圧砕刃（写真-3）を圧縮試験機の加圧側（写真では上側）に取り付け、下側は固定とし試験体を全面で受ける形とした。圧砕刃を全長900mm の試験体に対し、端から 300mm の梁側面にあたる部分中央にあてて加圧した。
(2)実験結果
表-4 は、各試験体における最大圧砕荷重を示したものである。普通強度コンクリートに比し、超高強度コンクリートの最大圧砕荷重は大きいものの、W/C20％～W/C13％の範囲ではさほど変わらず、W/C13％の超高強度コンクリート
部材で観察された最大圧砕荷重は、普通コンク
リート部材（W/C=60%）における最大圧砕荷重の 1.4 倍程度でしかなかった。
3.3 実機による圧砕実験(1)実験概要
写真-1 に示す最大油圧 30MPa の油圧シャベ
ルを用いた。アタッチメント（大割用圧砕機）
として、S 社製 SDS250-SRC を用いた（写真-4）。
なお、圧砕刃は新品ではなく、使いこなされた
通常の状態のものを使った。30MPa 油圧がかかると刃のおおよそ 800kN の荷重がかかる。

写真-7 W/C13％模擬梁でみられた力不足感（何度もかんだ後の状況）試験体として、室内実験で圧砕試験に供した試験体を使用し、室内実験で圧砕加圧した側の反対の端 300mm の位置の中央部分に対して、梁両側面をアタッチメントでかむ形で行った（写真-5）。
(2)実験結果
普通強度コンクリート（W/C60％）梁試験体
では、アタッチメントでかみ荷重をかけると速やかに刃が梁試験体に入っていき、圧砕解体が容易であったが、超高強度コンクリート梁では、
写真-6 に示すように、①刃がはねる、②細かなコンクリート片が飛び散る等の過程を経て、同じところだけをかみ直すだけではコンクリ
ートの圧縮強度が高いためか油圧不足による力不足を感じた（写真-7）。この油圧不足感は、
水セメント比が低く強度レベルが高いほど顕著であった。
しかしながら、かむ位置を変える、鉄筋位置に刃を当てるなど、圧砕解体過程で通常行うア
タッチメントの操作により、コンクリートの亀裂発生を契機に、一挙にコンクリートが鉄筋から抜けでて圧砕解体が可能であった。破壊されたコンクリート片は、鋭利に角張っていた。
表-5 は、本実験による最大油圧、最大圧砕荷重を示している。普通コンクリートも含めて
油圧ショベルの能力を最大限使っていたこと

がわかる。
3.4 超高強度コンクリート部材圧砕解体に関する総合的知見(1)普通コンクリート試験部材に対する超高強度コンクリート試験部材の破壊倍率
図-8 は、解体時（材齢 161 日）におけるW/C60％の普通コンクリートに対する超高強度
コンクリートの強度（φ10×20cm 円柱供試体
による圧縮強度、引張強度、模擬梁部材における室内実験最大圧砕荷重、実機による最大圧砕荷重）倍率を示したものである。
W/C13％コンクリートの倍率をみると、圧縮強度については 5.1 倍であったが、引張強度は1.6 倍となり、圧砕荷重では室内実験で 1.4 倍、実機による実験では変わらないといえる。超高強度コンクリート部材といえども現在の圧砕解体方法が適用できるとともに、超高強度コン
クリート部材こそ、圧砕による解体工法は、壊し方のメカニズムとして有利であることが明らかになった。
(2)圧砕時の騒音と飛散
超高強度コンクリート部材の圧砕解体では、刃がコンクリートに入りにくく、刃がはねる現象がみられ、爆裂音といえる普通コンクリート
レベルではない高音域の騒音が発生する。
また、φ100×200 圧縮強度試験同様、圧砕解体でも力をため込んで一挙に破壊するため、破壊された破片は普通コンクリートの破片と比べて鋭利であり、飛散力も大きい。
4.まとめ
高強度・超高強度コンクリート構造物の解体
負荷について、加力方法を検討した実験から、(1)全面に圧縮をする場合に比し、点で加重す
ると、通常より小さな荷重で破壊できる。
(2)小さな点として、面で加重する場合に比し、球で加重する方が小さな荷重で破壊できる。
(3)一般的なコンクリート(W/C=60%)に対し超高強度域のコンクリート(W/C=20%以下)の
圧縮強度が 6～7 倍であっても点加重同士での比率は 2 倍程度であった。
(4)超高強度コンクリートは、強度レベルが上
がっても引張強度が伸びないことを確認した。
ことがわかった。

図-8 各試験の W/C=60%コンクリートに対する
超高強度コンクリートの強度倍率
また、圧砕実験から(5)W/C20％から W/C13％の範囲では、強度レ
ベルが上がっても室内実験における最大圧
砕荷重がさほど大きくはならないことを確認した。普通コンクリートに比し、超高強度コンクリートでは、圧砕荷重に対して刃の食い込み量が小さくなることを確認した(6)超高強度コンクリート部材では、圧砕により、高音域の爆裂騒音が発生すること、鋭利なコンクリート片が勢いよく飛散することを確認した。
(7)W/C13％レベルの超高強度コンクリート部
材でも現行の実機による圧砕解体工法・技術により、同じ位置ばかりをかんだのでは
圧縮荷重という意味で力が不足するともいえるが、かみ位置を変えるなどの一般的なアタッチメントの操作の範囲で、解体できることを確認した。
(8)超高強度コンクリート部材の解体は、圧縮強度に比べ引張強度の比が小さいことから、引張のメカニズムにより行うことが有利であるが、現行の圧砕解体工法はこの点で理に適った方法であることが理解できた。
［参考文献］
1) 新時代の「解体工事業」の確立に向けた取り組みと展
望：湯浅昇、積算資料 SUPPORT10 月号解体特集 pp.
特集 22-特集 26、2014.10
2) 山田久司・角一行・末𠮷康一：高強度コンクリートを使用した建築物の解体例、日本コンクリート工学協会、コンクリート工学、29(7)、pp. 77-82、1991.7
3) 長谷部廣行・鈴木信也・半田雅俊・鹿籠泰幸・和田高清：
100 N/mm2 級超高強度コンクリートを使用した RC 構
造物の解体実験、日本建築学会大会学術講演梗概集、pp.1275-1278、2007.8
4) Lauritzen, E. K., (2019). “Construction, demolition anddisaster waste management: an integrated andsustainable approach.” Boca Raton, USA: CRC Press.

APPLICATION OF CRUSHING METHOD TO THE DEMOLITION OF
HIGH-STRENGTH AND ULTRA-HIGH STRENGTH CONCRETESTRUCTURES
Noboru Yuasa
Department of Building Engineering, College of Industrial Technology, Nihon University, Chiba,
Japan, E-mail: yuasa.noboru@nihon-u.ac.jp

Abstract
High-strength concrete buildings with a design strength greater than 60 N/mm2 have been
constructed since the 1990's, and the ultra-high-strength concrete with that of 200 N/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 theultra-high-strength concrete structure by the laboratory and full-scale crushing experiments using
imitated beam specimens. It was found that the current breaking demolition method isadvantageous 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. This paper is an extended version of (Yuasa 2015) published in Japanese.
1. Introduction
In June 2014, the Construction Business Act was revised for the first time in 43 years, and the"demolition industry" was established as a type of business in Japan (Yuasa 2014).
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. Buildings using high-strength
concrete with a design strength over 60 N/mm² have been built since the 1990s, but now ultrahigh-strength concrete with a design strength of over 200 N/mm² has been put into practical use.
It is likely that the demolition of the structures using high-strength and ultra-high-strength concrete
is needed (Yamada et al. 1991; Suzuki et al. 2007).
However, until now, the emphasis has been placed on research on the "construction" of buildings,
so there is little research on "demolition", and the demolition technology for high-strength/ultrahigh-strength concrete structure has not yet been established (Lauritzen 2019).
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. First, the influences of theloading method on the breaking load were clarified by the unreinforced concrete specimens, andthen the laboratory and actual crushing experiments were conducted by the imitated beam member.

Table 1 Mix proportion and properties of concrete for the laboratory experiments.

2. Experiments on the effects of loading method on the breaking load
2.1 Outline of the experiment(1) Materials used, mix proportion and molding
Based on the mix proportions as shown in Table-1, concretes with water-cement ratio (W/C) of 0.6,
0.4, 0.2, 0.16, and 0.13 were prepared. When the W/C was 0.4 or more, the ordinary Portland
cement (company M), river sand of the Oi river system (surface dry density 2.63 g/cm³), river gravelof the Oi river system (surface dry density 2.64 g/cm³) were used, while silica fume premix cement(Company M), Iibuchi crushed stone (surface dry density 2.62 g/cm³), and Iibuchi crushed sand(surface dry density 2.65 g/cm³) were used when W/C was 0.2 or less. As shown in Table 1, thechemical admixture of No. 70/SP-8N/303A by the company B and Ssp-104 by the company T wereused. The mixing water was Narashino City tap water. Concretes were molded both in a
150×150×150 mm cubic specimen steel form and a φ100×200 mm cylindrical specimen form.
(2) Curing conditions
Three days after placing, specimens was removed from the mold, and then sealed and cured in ahigh temperature chamber at 60°C.
(3) Compressive strength test
A compressive strength test was conducted at the material age of 28-day according to JIS A 1108
"Compression test method for concrete". As shown in Fig. 1, the 150×150×150 mm cubic
specimen was subjected to flat head loading and four-point hemispherical head loading, while flathead loading, single-point flat loading and hemispherical loading, as shown in Fig. 2, wereapplied for the φ100×200 mm cylindrical specimen.
(4) Split tensile strength test
Splitting tensile strength test was performed at 28-day after placing according to JIS A 1113 "Testmethod for splitting tensile strength of concrete".
2.2 Results and discussion(1) Relationship between loading method and compression load

P

150mm

150mm

P

150mm

25mm 150mm
10mm φ20mm
150mm

P

P

Fig. 1 Loading method for the cubic specimen. (flat head loading and four-point
hemispherical head loading)

10mm
φ20mm
φ100mm

200mm

200mm

200mm

φ100mmP

P

P

φ100mm
10mm
25mm

φ100mm
P

P

150mm
φ20mm

P

Fig. 2 Loading method for the cylindrical specimen. (flat head loading, single-point flatand single-point hemispherical head loading)Figure 3 shows compressive load applied to the 150 × 150 × 150 mm cubic specimen using theflat head loading and four-point hemispherical head loading, and that applied to the φ100 × 200
mm cylindrical specimen using the flat head loading, single-point flat head loading and one-point
hemisphere head loading. Figure 4 shows compressive strength and split tensile strength.
Compared to the flat head loading, single-point loading wa

s able to break specimens with asmaller load.
In the case of t he 150×150×150 mm cubic specimen subjected to the four-point hemisphericalhead loading, the fracture load increased as the W/C decreased, but the dependency was not
significant.
In the case of φ100×200 mm cylindrical specimen subjected to the single-point hemispherical headloading having a small loading area, the fracture load was the lowest, and the compressive fractureload was 100 kN or less even when the W/C was 0.13.
The splitting tensile strength did not increase much even when the W/C was low, and the splitting
tensile strength was 10 N/mm² or less.

Fig. 3 Compressive fracture load.

Fig. 4 Compressive strength and tensile strength.
(2) Relationship between loading method and compressive load ratio
Figure 5 shows th e compressive load ratio of four-point hemispherical head loading, the singlepoint flat head loading, and the single-point hemispherical head loading normalized with the flathead loading applied to the 150 × 150 × 150 mm cubic specimen and φ100 × 200 mm cylindrical
specimen. In the case of 150 × 150 × 150 mm cubic specimens, the four-point hemispherical headloading did not show much difference by the W/C, and it always broke at a load of 10 to 15% of theflat head loading. In the case of φ100×200mm cylindrical specimens, the compressive fracture load

Fig. 5 Compressive load ratio for the flat head loading.

Fig. 6 Relationship between water-cement ratio and compressive load as compared withthe control specimen.
ratio decreased as the W/C decreased both in the single-point hemisphere loading and the singlepoint flat loading.
(3) Normalization by the specimen with a W/C of 0.6
Figure 6 shows normalized compressive load of specimens subjected to the loading with four-point
hemispherical head, single-point flat head and single-point hemispherical head with respect to thespecimen with a W/C of 0.6.
In the case of 150×150×150 mm cubic specimen with a W/C less than 0.2, compressive strength
obtained with a four-point hemisphere head loading was 2.5 to 4.5 times as much as that with W/C

of 0.6, while fracture load was about twice.
In the case of φ100×200mm cylindrical specimen with a W/C less than 0.2, compressive strength
obtained with the single-point flat head loading and the single-point hemispherical head loading are
3.5~7.0 times as much as with the W/C of 0.6, while fracture load was 2.3 to 3.7 times.
3. Crushing experiment using imitated beam specimens
3.1 Preparation of the specimen
The specimen was an imitated beam member (300×300×900 mm). A steel mold was used and 8
main bars (D19) and 20 stirrup (D10) were used as the reinforcing bars. The bar arrangement isshown in Fig. 7.

Fig. 7 Reinforcing bar arrangement.
Table 2 Mix proportion and properties of concrete for the imitated beam experiments.

Table 3 Relative strength at the age of demolition. (161-day)Fig. 8 Specimen of the laboratory test.
The W/C of the concrete were 0.6, 0.2, 0.16 and 0.13 and the mix proportions are shown in Table2. Materials used are described in the section 2.1(1), except for the Portland cement manufactured
by company M and silica fume manufactured by company E used for the specimen with a W/C of
0.2.
The results of the compressive and tensile strength tests at the material age of 28-day and at thetime of crushing experiment (161-day) are also shown in Table 2.
With respect to the control concrete with a W/C=0.6, the compressive strength ratio of eachconcrete, tensile strength and the tensile strength/compressive strength (%) of the same concrete,
are shown in Table 3.
Compared to the development of compressive strength associated with a decrease in W/C, thedevelopment of tensile strength was small. When the development of compressive strength
became 5.1 times, the tensile strength developed only about 1.6 times. It is therefore advantageous
for the demolition of ultra-high-strength concrete to apply tensile load with ingenuity.
3.2 Crushing loading test (laboratory experiment)(1) Outline of experiment
The crushing test was performed with a tester having the maximum load of 4000 kN. Figure 8

shows the installation of a specimen in the tester. The crushing blade manufactured by company
S (Fig. 9) was attached to the loading side (upper side in the Figure) of the tester, and the lower
side was fixed and supported the entire specimen. The crushing blade was applied to the specimen,with a total length of 900 mm, at the center of a part corresponding to the side surface of the beam
300 mm from the end.
(2) Experimental results
Table 4 shows the maximum crushing load of each specimen. Although the maximum crushing loadof ultra-high-strength concrete was larger than that of normal strength concrete, it did not changemuch in the range of W/C=0.2 to 0. 13, and the maximum observed with W/C=0.13 ultra-highstrength concrete members. The crushing load was only about 1.4 times of the maximum crushingload of the ordinary concrete members (W/C=0.6).

Fig. 9 The crushing blade for loading.
Table 4 Crushing load.

3.3 Crushing experiment with a breaking machine(1) Outline of experiment
A hydraulic shovel with a maximum hydraulic pressure of 30 MPa was used. A jaw crusher
produced by company S (SDS250-SRC) was used as an attachment (Fig. 10), where the blade
was not a new one, but has been used in the normal conditions. When a hydraulic pressure of 30
MPa was applied, the blade was subjected to a load of approximately 800 kN.
The specimens used in the laboratory crushing experiment were reused and subjected to a bitewith both sides of the beam with the attachment to the center part at the horizontal position of 300
mm opposite to the side crushed in the laboratory experiment. (Fig. 11).

Fig. 10 Hydraulic shovel attachment.

Fig. 11 A specimen held with the attachment(2) Experimental results
When a crushing load was applied through the attachment, the blade immediately entered thebeam specimen of the ordinary strength concrete (W/C=0.6), and it was easy to crush and breakit. However, in the ultra-high-strength beam specimen as shown Fig. 12, firstly because thecompressive strength of concrete was so high and secondarily repeated crushing of the same partafter the bounce of the blade and scatter of fine concrete pieces were present (Fig. 13), it seemed
to be in lack of the force due to insufficient hydraulic pressure, which was more remarkable when
the W/C was lower and the strength level was higher.
Nevertheless, when operating attachments as normally performed in the crushing and demolition
process and changing of the biting position and applying the blade to the position of the reinforcing
bar, it was possible for concrete by being pushed out from the reinforcing bar all at once due to theoccurrence of cracks in the concrete. The crushed concrete pieces were sharply angled.
Table-5 shows the maximum hydraulic pressure and maximum crushing load in this experiment. Itwas obvious that the capacity of the hydraulic shovel was used to the maximum, including in thecase of the ordinary concrete.

Fig. 12 Scatter of concrete pieces during crushing

Fig. 13 A beam specimen of W/C=0.13 after repeated crushing loads showing the shortageof the crushing power.
Table 5 Maximum crushing load of shovel crusher.

3.4 Overall look at the crushing demolition of ultra-high-strength concrete members(1) Breaking load ratio of ultra-high-strength concrete specimen (member) to the ordinary concrete
specimen (member)
Figure 14 shows the strength and maximum load ratios of ultra-high-strength concrete against
those of the ordinary concrete with a W/C=0.6 at the time of demolition (age of 161-day). It includes
compressive strength and tensile strength with a cylindrical specimen of φ100 × 200 mm andmaximum crushing loads of imitated beam members both in laboratory and the actual machine
tests.
Looking at the strength ratio of W/C=0.13 concrete, the compressive strength was 5.1 times, but
the tensile strength was 1.6 times, and the crushing load in the laboratory experiment was 1.4 times
and almost no differences was found in the actual machine experiments. It was found that thecurrent crushing demolition method can be applied to ultra-high-strength concrete members, andthat the demolition method by crushing was advantageous as a breaking mechanism for the ultrahigh-strength concrete members.
(2) Noise and particle scattering during crushing
In the crushing of the ultra-high-strength concrete members, it is not easy for the blade to enter theconcrete, and the blade sometimes bounced with explosion noises of high frequency range unlike
the level of the ordinary concrete.
Similar to the compressive strength test of the φ100×200 mm specimen, crushing during demolition
accumulated force and broke members at once, so the broken pieces were sharper and had agreater scattering force than that of the ordinary concrete pieces.

Fig. 14 Strengths of ultra-high-strength concrete normalized with the control with a
W/C=0.6.

4. Conclusions
From the experiment that examined the loading method for the demolition load of high-strengthand ultra-high-strength concrete structures, the followings are obtained.
(1) Compared to the flat head compression loading, the single-point concentrated loading was able
to break specimens at a smaller load.
(2) When the shape of the single-point head was hemispherical, the fracture load was smaller thanloading with a single-point flat head.
(3) The compressive strength of ultra-high-strength concrete (W/C=0.2 or less) was 6 to 7 times
that of the ordinary concrete (W/C=0.6), while the ratio of fracture loads when using point loading
was about twice.
(4) It was confirmed that the tensile strength of ultra-high-strength concrete did not increase unlike
the increase in compressive strength level.
From the crushing experiment,(5) In the range of water to cement ration of 0.2 to 0.13, it was confirmed that the maximum breaking
load in the laboratory experiment did not become so large even if the strength level increased andthat the biting amount of the blade at the breaking load was smaller in ultra-high-strength concrete
than in ordinary concrete.
(6) It was confirmed that breaking of ultra-high-strength concrete members caused explosion noiseof high frequency range associated with vigorous scattering of sharp concrete fragments.
(7) The ultra-high-strength concrete members with a water to cement ratio of 0.13 level can be
demolished using the current actual equipment and the breaking demolition method when the bite
position could be changed within the working range of the currently available attachments, while
the force may be insufficient in terms of compression load if the same position may always be bitten.
(8) Demolition of ultra-high-strength concrete members on the basis of the tensile mechanism isadvantageous because the increase ratio of tensile strength is smaller than that of compressive
strength, and the use of current breaking demolition method makes sense in this respect.
References
Yuasa, N., (2015). “Study on demolition load of reinforced concrete structure using high strengthand ultra-high strength concrete.” In: The 12th Japan･Korea Joint Symposium on Building
Materials & Construction, 105-110. (in Japanese)
Yuasa, N., (2014). “Prospects for establishing the demolition industry of the new era.” Construction
Cost Estimation Support, 10, 22-26. (in Japanese)
Yamada, H., Sumi, K. and Sueyoshi, K., (1991). “Demolition of buildings with a high-strength
concrete.” Concrete Journal, 29(7), 77-82. (in Japanese)
Suzuki, S., Hasebe, H., Handa, M., Shikamori, Y. and Wada, T., (2007). “Demolition experiment of
ultra-high strength concrete with a strength of 100 N/mm2 class.” Preprint of the Annual Meetingof AIJ, Materials and Construction Session, A-1, 1275-1278 (in Japanese)
Lauritzen, E. K., (2019). “Construction, demolition and disaster waste management: an integrated
and sustainable approach.” Boca Raton, USA: CRC Press.

EFFECTIVE USE OF CONCRETE POWDER BY-PRODUCEDFROM RECYCLED AGGREGATE

Noboru YUASA
Department of Architecture and Architectural Engineering
College of Industrial Technology, Nihon University
1-2-1 Izumi-cho, Narashino-shi, Chiba-ken 275-8575, JAPANABSTRACTThis study was carried out for the purpose of effective utilization of concrete
powder which arises in a process of production of recycled aggregate. It was
found that the cement part in the concrete powder which was heated at 600℃
and smashed by a roulette mill contributed to the strength development of mortars
when substituted for cement at approximately 10 percent
Keywords: concrete, by-produced concrete powder, recycled aggregate, inorganic
admixture
INTRODUCTION
When recycled aggregate is produced from demolished concrete rubble, about
one ton of concrete powder arises from ten tons of recycled aggregate. In the
future, recycled aggregates will be used in the general concrete structures andespecially high-quality aggregates will be required. Thus, the processing anddispensing of this fine powder will become a serious problem [1]. Concrete
powder (hereafter referred to as powder) collected by air separator contains
considerable amounts of cement paste which may have been the weakest part in
the original concrete. Thus several experiments have substituted the cement withpowder anticipating the hydration of the unhydrated cement in the powder[2], [3],[4]. However, powder did not show any evidence of hydration and more recently,
applications have focused on segregation resistant admixtures [5], [6], [7], [8].
In this preliminary experiment, a heat-treated powder showed some strength
development. The mortar specimen in this study was prepared by substituting
cement with the heat-treated powder, and with heat-treated and smashed powder(in this paper named smashed powder). These mortar specimens were tested interms of flow, flexural strength and compressive strength.

The powders A and B
collected from a recycled
aggregate plant at different dates
were dried for a half day undersunlight. Table 1 shows thechemical composition of powders
A and B and ordinary Portland
cement. The compositions of thepowdes were almost the same,
except for the amount of ignition
loss and the amount of insolubles.
Powder x-ray diffraction analysis
showed quartz (SiO2), calcite(CaCO3), portlandite (Ca(OH)2) as
common crystallines, while
powder A included pyroxene andmica and B included feldspar.
EXAMINATION ON
HEAT-TREATMENT OF
POWDER
Heat-treatment of powder
If the bound water in the
powder can be removed by theheat-treatment, increase in activityof the powder may be expected.
The powder A was heated to 100,
500, 600, 700, 800, 900 and 1000
℃ and kept for 2 hours, thencooled gradually inside of furnace.
Fig.1 shows relationship between
the heating temperature and thebound water ratio, soluble ratio
and specific gravity.
Quality of the mortar
substituted by heat-treatedpowder for cement
Outline of experiment
The powder was composed of
cement that was dissolved by ten
percent of hydrochloric acid fortwo hours and insoluble part thatcan be regarded as aggregate.
The heat-treated powder A
replacing the ordinary portland

Table 1 Chemical composotion of concrete
powder and cement
Sort of Powder*1

ig.loss
insol.
SiO2
Al203
Fe2O3
CaO
MgO
SO3
Na2O
K2 O
TiO2
MnO
P 2O5
total

Chemical Composition ( ％)CHARACTER OF POWDER

Cl*2
Bonded Water
Ratio (％)
Soluble Ratio (％)
Specific
GravityBlain SpecificSurface (cm2/g)

Concrete Concrete Portland
Powder A Powder B Cement
29.22

25.78

1.5

29.12
9.37
2.81
1.12
25.60
1.55
0.91
0.12
0.11
0.15
0.07
0.09
100.24
0.054

33.44
9.75
2.76
1.32
24.33
0.72
1.00
0.14
0.16
0.10
0.04
0.07
99.61
0.034

－
22.2
5.3
2.5
64.2
1.5
2.0

－
－
－
99.8
0.005

27.5

30.4

－

69.8

65.4

－

2.17

2.15

3.16

1330

1380

3260

0.61

*1 Gauge ig.loss at 1000℃ heating*2 Exclude Cl from total
70

3.0

60

2.8

50
40

2.6

30

2.4

20

E Bonded Water Ratio 2.2
C Soluble Ratio
G Specific Gravity

10
0
0

200
400
600
800
Heating Temperature (℃)

2.0
1000

Fig.1 Relationship between the heating
temperature and the bonded water ratio,
solube ratio and specific gravity

Table 2 Mix-proportion of mortar using heat-treated concrete powder
Heating
Temperature (℃)

Non
Heating

100､500､600､700､
800､900､
1000

SabstituteRatio (％)

W/C
(％)

0
5
10
20
30
5
10
20
30
40

S/C

50

2

50

2

Weight Ratio (Parcentage to Cement (％))
Concrete Powder A
Cement Water Cement Sand Water Sand
Content Content Content
100
100
100
100
100
100
100
100
100
100

50.0
51.6
53.1
57.1
62.1
52.6
55.5
62.5
71.3
83.3

－
5.17
10.9
24.5
42.0
5.28
11.1
25.1
42.9
66.9

－
2.78
5.86
13.2
22.6
2.77
5.84
13.1
22.5
35.1

－
1.25
2.64
5.93
10.2
－
－
－
－
－

200
208
216
237
263
208
216
237
263
298

cement for 5, 10, 20, 30 and 40% and the standard sand (JIS A 5201) were used
to prepare 4× 4×16 cm mortar specimens. The specimens were sealed and cured
in a humidified room at a temperature of 20℃, and thereafter cured in 20℃
water until the age of 28-day. The strength test was done according to JIS A
5201 (The physical test method of cement).
Result and Discussion
Fig.2 shows flow value of each mortar. The flow value decreased with anincrease in the amount of powder. In this mixture proportion, the maximum
amount of powder to substitute cement was 20%, while the effect of heating
temperature of the powder on flow value of mortar was small.
Fig.3 and Fig.4 show the bending strength and compressive strength
260

10

240

9
8

220

7

200
180
160
140
120
100

6

E
C
G
A
S
I
D
2

Non Heating
100℃ Heating
500℃ Heating
600℃ Heating
700℃ Heating
800℃ Heating
900℃ Heating
1000℃ Heating0
5 10 15 20 25 30 35 40
Sabstitute Ratio of Concrete Powder (％)

Fig.2 Relationship between thesabstitute ratio of concrete powder
and the flow

5
4
3
2
1
0

E
C
G
A
S
I
D
2

Non Heating
100℃ Heating
500℃ Heating
600℃ Heating
700℃ Heating
800℃ Heating
900℃ Heating
1000℃ Heating0
5 10 15 20 25 30 35 40
Sabstitute Ratio of Concrete Powder (％)

Fig.3 Relationship between thesabstitute ratio of concrete powder
and the bending strength

70
respectively. The mortar strength
decreased with increasing amount of60
substitution with the powder, and themortar showed large decrease in50
strength when the powder was
non-heated or heated in 100℃ and
40
500℃ . When substituted by the
E Non Heating
powder with little bound water, the30
C 100℃ Heating
strength decrease was small to a 20
G 500℃ Heating
20
percent replacement. However, theA 600℃ Heating
S 700℃ Heating
strength of mortar using the heated
I 800℃ Heating10
powder of 900℃ and 1000℃ were a
D 900℃ Heating
little smaller than that using the
2 1000℃ Heating0
heated powder of 600℃ ～ 800℃.
05 10 15 20 25 30 35 40
This may be attributed to the
Sabstitute Ratio of Concrete Powder (％)
generation of flee-lime by theFig.4 Relationship between theheating over 800℃ .
sabstitute ratio of concrete powder
From the viewpoint of the energy
and the compressive strength
consumption in processing and theeffective use of the powder as a
cement-replacement material, it is desirable that the powder should be heat-tread
at 600℃ and used at a substitution less than 10 percent (where substitution
quantity was the amount of cement part in powder).

EXAMINATION ON THE SMASHING AND PROCESSING OF POWDERSmashing and processing of powder
If the powder is heat-treated and then smashed by roulette mill, it can be
expected that the reactivity and the fluidity of the powder may be improved. The
powder B was heated at 600℃ and then was smashed by the roulette mill for 1,
3, 10 minutes.
Quality of mortar using heat-treated and smashed powder B
Outline of experiment
Materials : The powder B (with a dissolution of 55.7% after heat-treatment at
600℃ ), ordinary portland cement, standard sand specified in JIS R 5201.
Specimen : 4× 4× 16 cm in dimensions with the mixture as shown in Table 3
Table 3 Mix-proportion of mortar using heated and smashed concrete
powder

SabstituteRatio (％)

0
5
10

W/C
(％)

50

S/C

3

Weight Ratio (Parcentage to Cement (％))
Concrete
Powder B
Cement Water
Sand
Cement Sand
Content Content
100
100
100

50.0
52.6
55.6

－
5.20
11.1

－
4.14
8.44

300
311
325

225

9.0

220

8.5

215

8.0

210

7.5

205

7.0

200

6.5

195
190
185
180

E
C
G
A

Non Smashing
1Min.Smashing
3Min.Smashing
10Min.Smashing0 1 2 3 4 5 6 7 8 9 10
Sabstitute Ratio of Concrete Powder (％)

Fig.5 Relationship between thesabstitute ratio of concrete powder
and the flow

was made according to the JIS R
5201. The specimen was sealed andcured in 20℃ room until the age of
1-day, then cured in 20℃ water until
the age of 28-day.

6.0
5.5
5.0

Age Smashing Time (Min.)(Day) Non 1
310
7
E C G A28
J
H B F

0 1 2 3 4 5 6 7 8 9 10
Sabstitute Ratio of Concrete Powder (％)

Fig.6 Relationship between thesabstitute ratio of concrete powder
and the bending strength
55
50
45

Age Smashing Time (Min.)(Day) Non 1
3
10Result and discussion
7
Fig.5 shows the relationship
E
C
G
A
40
28
J
H
B
F
between the flow and the powder
substitution ratio. It was proven that35
the decreasing rate of flow value tosubstitution ratio become small with
the increase in smashing time by30
roulette mill. It was confirmed that0 1 2 3 4 5 6 7 8 9 10
the smashing of the powder
Sabstitute Ratio of Concrete Powder (％)
increased the fluidity of the mortar.
Fig.7 Relationship between theFig.6 and Fig.7 show the bending
sabstitute ratio of concrete powder
strength and compressive strength,
and the compressive strength
respectively. By smashing powder,
the strength development of powder
was improved and even show an increase with the increase in substitution ratio.
This may be attributed that the smashing resulted in finer particle than cement(resulting specific surface area of 10,450 cm2/g in three minutes driving) and theparticle worked as a filler in the mortar.
It is proven that the process of strength development of mortar using smashedpowder was large from 7-day to 28-day compared to non-smashed powder.
With above results, it is desirable for the effective use the powder that itshould be heated at 600℃ , smashed with roulette mill for 3 minutes and used at
10% substitution for cement.

QUALITY OF CONCRETE USING HEAT-TREATED AND SMASHEDPOWDER
Outline of experiment
The reactivity of the powder in concrete using the smashed powder(heat-treated at 600℃and smashed to a specific surface area of 10,450cm2/g), andsubstituted 10% for cement by the smashed powder was examined.
The experiments were consisted of six types of concrete as shown in Table4.
Concrete ① was the ordinary concrete with a slump of 18 cm, an air content
of 4.5% and comprising an ordinary portland cement (specific gravity 3.16), ariver sand (specific gravity 2.62, fineness modulus 2.83), a river gravel (specificgravity 2.66, fineness modulus 6.96) and several chemical admixture.
Concrete ② was almost the same as concrete ① except for 10% substitutionof cement with the smashed powder heat-treated at 600℃ .
Concrete ③ was controlled by the dosage of chemical admixture so as tohave the same slump and air content as that of concrete ①.
Concrete ④ was controlled by the dosage of chemical admixture and the unit
water so as to have the same slump and air content as that of concrete ① .
Concrete ⑤ used the powder which was dried only at 40℃ and wascontrolled by the dosage of chemical admixture so as to have the same slump andair content as that of concrete ① .
Concrete ⑥ used the standard sand instead of the powder and was controlled
by the dosage of chemical admixture so as to have the same slump and aircontent as that of concrete ①.
The size of test specimen was φ10×20 cm cylinder and kept in 20℃ room
under sealed condition until the age of 1, 7, 28, 91 days. The compressive test
specimen was prepared according to JIS A 1108 (Compressive strength test
method).
Workability and dosage of chemical admixture
Concrete ② showed decrease in slump for 4.5 cm and amount of air for 2.7%
compared to concrete ① . Introduction of the heat-treated and smashed powder
decreased the workability and air content.
Concrete ③ required 2.5 times of AE-water decreasing agent and 2 times of
air controlling agent to assure the equivalent slump and air content. Lee, Sakai,
Daimon and Nagataki [4],[8] reported that concrete powder adsorbed larger
Table 4 Mix-proportion of concrete using concrete powder
Unit Weight (kg/m3)
Sand
Concrete
W/C Aggregate
No.
Powder B
Cem
Ratio Water(％)
Sand
ent Cement Sand(％)
Content Content
①
②
③
④
⑤
⑥

48.5
60
46.0

165
165
165
171
165
165

275
247.5
247.5
256.5
247.5
247.5

－
27.5
27.5
28.5
27.5

－
20.5
20.5
21.5
16.5
48

893
873
873
860
831
827

Chemical Admixture (g/m3)
Gra
vel

Tem
Slu
Air
pera
mp
AE- C×％ No. C×％ (％) (cm) ture
(％)
WR
303A
*1

956 688 0.250
956 688 0.250
956 1727 0.628
943 713 0.250
1002 2750 1.00
1002 688 0.250*21145 0.416 4.81145 0.416 2.1
2289 0.832 4.42803 0.980 4.2
67 0.0244 4.4
820 0.298 4.3

18.1 19.0
13.6 19.0
18.3 19.0
18.5 19.0
18.0 23.0
18.0 23.0*1 No.①～④,⑥ used air entraining and water reducing agent admixture (No.70) made by N company
No.⑤ used air entraining and high range water reducing agent admixture (SP-8N) made by N company*2 No.303A：Air entraining agent admixture (No.303A aolution with a concentration of 1/100) made by N company

45

45

E
G
A
S
I

40
35
30

No.①
No.③
No.④
No.⑤
No.⑥

40
35
30

25

25

20

20

15

15

10

10

5

E
C
G
A

No.①
No.②
No.③
No.④

5
0

1

2

3
4
Age (Day)5

6

Fig.8 Relationship between the age andthe compressive strength7

0 10 20 30 40 50 60 70 80 90 100
Age (Day)

Fig.9 Relationship between the age andthe compressive strengthamount of water decreasing agent than unhydrated cement. The shape and specificsurface area of the powder particle were the important factor affecting the above
mentioned phenomena.
Concrete ④ needed an additional 6 kg/m3 of unit amount of water and 2.35
times of the amount of air controlling agent compared to concrete ① .
However, the amount of necessary chemical admixture and unit water content
to have concrete substituted 10% for cement by the heat-treated and smashedpowder are still in the practical range.
Effect of heat-treated and smashed powder
Fig.8 shows the strength development at early ages of concrete ①, ③ , ④ , ⑤
and ⑥ . The concrete ⑥ shows the case of 10% substitution of standard sandfor cement, this means that the standard sand have not effect on strength
development. However the strength of concrete ③ and ④ were a little lager thanthat of concrete ① , the cement part in the heat-treated and smashed powder
worked effectively to develop the strength of concrete. Concrete ⑤ using thepowder which was dried in the oven at 40℃ (the soluble part 62.6%) had larger
strength than concrete ⑥ , though smaller than that of concrete ① .
Fig.9 shows the strength development of concrete ① , ② , ③ and ④ . The
strength of concrete ① , ③ and ④ were almost the same, and the strength of
concrete ② may be due to smaller air content than those of concrete ① , ③ and④.
CONCLUSIONS
Effective utilization of concrete powder by-produced in the recycled aggregate
production process can be summarized as follow.
(1) The concrete powder heated at 600℃ and smashed by roulette mill for 3
minutes (specific surface area 10,450 cm2/g) was able to substitute cement for
10%.
(2) The mortar and concrete using the heat-treated and smashed powder(mentioned in (1)) showed the decrease of workability and entrained air. However
it can be compensated by increasing the amount of admixture or unit water at arealistic range of dosage.
(3) In the mortar and concrete using the heat-treated and smashed powder inthe range of (2), the cement part of the powder contributes to the strength
development in the same way as the original cement.
ACKNOWLEDGEMENT
We thank for the cooperation of Tateishi Construction Industry Conpany andUbe-Mitsubishi Cement Research Laboratory.
REFERENCE
1. Kasai.Y., Barrier to reuse construction by-products and the reuse recycled
aggregate in concrete in Japan, Use of recycled concrete aggregate, Edited by
Rvindra.K.D., et al. 1998 Thomas.T. pp.433-444
2. Kemi.T., Nakata.Y., et al. A study of recrushed concrete powder. Extended
Abstracts ; The 48th Annual meeting of JCA 1994 pp.544-549
3. Kemi.T., Nakata.Y., et al. Characters of concrete including recycled powder.
Extended Abstracts ; The 49th Annual meeting of JCA 1995 pp.406-411
4. Jongu-kyu, Sakai.E., Daimon.M., Nagataki.S., Hydration and adsorption
characteristic of recycled concrete powder. Proceedings of the JCI Vol.21 No.1
pp.193-198
5. Kemi.T., Nakata.Y., et al. Characters of high fluidity concrete used recycled
powder. Summaries of the 50 Annual meeting on Cement Technology 1996
pp.340-341
6. Kemi.T., Nakata.Y., et al. An experiment on concrete placing work for test
wall with high fluidity concrete used recycled concrete powder. Summaries of
the 50 Annual meeting on Cement Technology 1996 pp.342-343
7. Hosino.M., Arashima.T., Some characters of high fluidity concrete usedrecycled concrete powder. AIJ Summaries of technical papers of annual
meeting A-1 1999 pp.163-164
8. Jongu-kyu, Sakai.E., Daimon.M., Nagataki.S., Properties of cement-mortar
containing recycled powder. Proceedings of the JCI Vol.22 No.2 pp.1117-1122