Recycling of Concrete

by T. NAWA

Hokkaido University, Graduated School of Engineering Faculty,

Division of Sustainable Engineering

The Need for Construction and Demolition Waste Minimization

• In 20 century we developed technologies based on an extensive “ use-and-throw-away”philosophy, it has been recognized that we cannot continue this unrestricted use of natural resources and pollution of the world with waste.

• In many countries, construction and demolition waste is considered as harmless, inert waste, which does not give rise to problem.

The Need for Construction and Demolition Waste Minimization (cont.)

• However, construction and demolition waste consists of huge amount of materials that are often deposited without any consideration, causing many problems and encouraging the illegal dumping of other kind of waste.

Construction and Demolition Waste in Japan

In Japan, the annual generation of construction and demolition waste is approximately 80 million tones.

In the European Union (EU), the annual generation of construction and demolition waste is about 200-300 million tones.

In USA, the amount of construction and demolition waste is about 250-300 million tones per year.

Construction and Demolition Waste in Japan

Agriculture90,804

(22.4)

Electric、GasHeat and water

supplier　91,504（22.5）

Construction79,011(19.5)

Pulp, Paper

(6.7)

Steel

Chemical Industry

Mining

Cement, ceramics

Food ProductElectric Machine Product

Theothers

In 2000

Industrial Waste406,037

thousand ton

The amount of demolished concrete in futureThe amount of demolished concrete in future

0

100

200

300

400

500

600

1995 2000 2005 2010 2015 2020 2025

Year

Am

ount

of d

emol

ition

（m

illio

n to

nes）

Road Base materials

Amount of demolished concrete( Infrastructure+Building)

Amount of demolishedconcrete (Building)

Sustainability and green concrete

• Since Agenda 21, the Rio Declaration on Environment and Development, was launched in 1992, sustainable development has been on of the key issues of modern society.

• We should encourage the development and application of environmentally friendly, sustainable concrete materials, design and construction.

Policies and Strategies

• Construction & demolition waste must be considered as a specific individual type of waste associated with the building and construction industry.

• The management and handling of waste is carried out by the industry itself.

• However, the building and construction industry is relatively conservative, and we take a lot of time and need long-term policies and strategies to change in conventional procedures

Policies and Strategies

• Very severe barrier1. Environmental politician in public office intend

to prepare the policies and issue concerning waste recycling and reduction.

2. Building constructor is controlled by law.

Integrate the interests of all parties, it is necessary that long-term polices and strategies should have been prepared and implemented.

Construction Recycle law

• Law to promote effective recycle

• To refer specifically to concrete rubble, asphalt concrete rubble, and construction waste wood

Before: the owner used to submit to the governor a demolition plan, indicating the type of structure and floor area of the building.

Construction Recycle law (cont.)After formulation:

the owner should submit a “notification document ”for any planned generation of waste in the following cases:

1. Demolition of a building with a floor area greater than 80 m2

2. New construction with a floor area than 500 m2

3. Expansion, repair or remolding of building costing more than 100 million yen.

4. Public works projects exceeding a cost of 5 million yen.

Each of the cases of 2,3,4 generates the same amount of waste as the case 1, which is estimated to be about 30 to 40 tons per house.

Construction Recycle law　(cont.)

“Notification Document ”

1. Characteristics of the construction1) the usage2) number of stories3) projected floor area

2. General Contractor’s permit number3. Registration number of the demolition industry association4. Demolition method5. Separation waste material6. Amount of expected waste generation7. Cost of demolition work8. Name of the recycle plant9. Cost of waste recycling

Progress in recycling and reuse of concrete as aggregate

• Fortunately, some Japanese researcher had been investigated recycling of concrete since the early 1970s.

• In 1981, Japanese and European members of RILEM took the initiative to complete the first RILEM technical committee on the demolition and recycling of concrete, including several material research project in this field.

Progress in recycling and reuse of concreteas aggregate (cont.)

In the early 1970　a large number of experimental investigations of the quality of recycled aggregate were performed by Kasai et al.

In 1977, the Japan Building Contractors Society (BCS) published the report, “Proposed Standard of Recycled Aggregate and Recycled Concrete and Commentary”

The first systematic proposal for recycled concrete in the world

Progress in recycling and reuse of concreteas aggregate (cont.)

In 1986 the building Research Institute of the ministry of Construction of Japan issuedthe “Proposal of Quality Standard for Recycled Coarse Aggregate” andthe “Proposed Standard for Recycled Coarse Aggregate Concrete” :the standard of recycled fine aggregate follows the BCE standard of 1977.

Quality Standard of Recycled Aggregate

<12

<5

-<10-<40*<12Loss of soundness

<10<5<7<3<3Water adsorption (%)

2nd

class1st

class3rd

class2nd

class1st

class

Recycled Fine Aggregate

Recycled CoarseAggregate

* In this case, don’t consider freezing and thawing deterioration ** For natural coarse aggregate, <3.0 % of water adsorption and <5.0% loss of soundness; for natural fine aggregate <3.5% of water adsorption

Design Strength of Recycled Concrete

In 1994, the ministry of Construction of Japan published “Tentative Quality Standard Proposal for Concrete”.

-- This formulated the design strength for recycled concrete in which recycled aggregate categories correspond to the quality standard provided in 1986.

<16Recycled aggregate 3rd classIII

Design Strength(MPa)

Fine Aggregate

>16 (Plain)Ordinary aggregate or Recycled aggregate

2nd classII >20 (RC)Ordinary aggregate1st classI

Coarse Aggregate

Class of Recycled Concrete

Example of Structures Using Recycled Concrete(Civil Construction, not Buildings)

3rd class

2nd class

1st class

Coarse Aggregat

e

Concrete sub slab, back fill concrete, non-structural member

Recycled aggregate

Concrete sub slab

III

StructuresFine Aggregate

Concrete block, foundation of road attachment, side drain, gravity bridge basement, wave breaker, and so on

Ordinary aggregate

or Recycled aggregate

Plain C

II

Bridge substructure,Retaining wall, tunnel liner

Ordinary aggregate

RC &Plain C

I

UsageClass of Recycled Concrete

Requests for the Successful Recycling of Demolished Concrete Rubble

1. Selective demolition must be made.

2. Processing plants and depots for recycled materials must be established.

3. Recycled products must be produced and marketed to compare with comparable new raw materials in terms of price and quality.

Selective demolition

Selective demolition is defined as a process in which demolition takes place as ‘reverse construction’.

Different types and fractions of materials are removed from demolished structure and stored at the demolition sites, so that mixing of waste is avoided.

In the process serious attempts are made to separate , store and transport concrete rubble, but this is not always possible.

Processing plants and depots for recycled materials

It is necessary to establish processing plants and depots at strategic locations within a city in order to achieve the flexibility and economy necessary for employing recycled materials.

The right materials must be available in the right quantities, at right place, at the right price , and at the right time.

Economical benefitThe cost of selecting , sorting and processing of

waste is usually higher than the value of comparable new raw materials.

However, recycling of demolition waste can be made economical by imposing a fee on the waste, which is dumped at landfills.

As disposal fees gradually continue to increase, which is in the nature of all taxes and fees, so a level is soon reached where commercial recycling of demolished concrete rubble.

Quality of Recycled Concrete

It is requested that recycled materials either satisfy the requirements of already existing specifications for primary raw materials or the standards to be developed for recycling materials.

Outline of manufacturing process of recycled aggregate

Demolition

Inspection of the building before demolition

by an engineer of processing plant

No

Road base materials Yes

Contract between ConcreteRubble Supplier and Processor

Requirements for Original Concrete for Recycled Aggregate

1. Free from harmful components1) soil2) mud3) asphalt4) ALC

2. Free from harmful substance1) chlorides2) alkali-reactive materials

To guarantee this,inspect signs of corrosion of reinforcing bar due to chlorides,

Inspect cracks caused by alkali-aggregate reaction

Outline of manufacturing process of recycled aggregate (cont.)

Contract between ConcreteRubble Supplier and Processor

Acceptance inspection of concrete rubble(visual inspection)

No

Road base materials Yes

First crushing(rough crushing)

First Crushing of Concrete

First Crushing of Concrete

Outline of manufacturing process of recycled aggregate (cont.)

First crushing(rough crushing)

Vibration screenof 60-70 mm

Road base materials

> 60mm

< 60mm

Removing wood chips andby hands on belt conveyer

Second crushing

Second Crushing of Concrete

Second Crushing of Concrete

Outline of manufacturing process of recycled aggregate (cont.)

Second crushing

Third crushing

Vibration screen

Vibration screen

Air separatorWater washer

Magnetseparator

Magnetseparator

20-5 mm 5-0 mm Powder

Recycled concrete aggregate( inspected at plant site)

Vibration screen

Recycled Coarse and Fine Aggregates

Production of Recycle Aggregate• Rubbing machineMortal adhered to the original aggregate has acute angle,

which should be remove during crushing.

Outside of screw grinding machine

Inside of screw grinding machine

Production data for Recycled coarse aggregate

10 – 20 mg/m3Concentration of dust

50 – 60 dBLevel of loudness50 – 60 dBLevel of vibration

50 - 55%percentage of admitted products

18 kWh/ton (\ 450yens/ton)Power consumption

About 2 days for each processDate for construction and dismantling of plant

4 –5 persons /dayWorkers for manufacturing and quality control

5 – 10 tons/hourManufacturing capacity

DataTerm

Original aggregate: River gravel, 3times grinding

Percentage of admitted products

100%40-0mm

76.7%40-5mm

Pretreatment (0-5mm cut)

1st Screw rubbing

16.7%5-0mm

60.0%40-5mm

2nd Screw rubbing

49.2%40-5mm

23.3+16.7=40.0%

42.3%40-5mm

40.0%40-5mm

10.8%5-0mm

6.9%5-0mm

3rd Screw rubbing

23.3+16.7+10.5=50.8%4th Screw rubbing

57.7%

2.3%5-0mm

60.0%

Problems with Quality of Recycled Aggregate

1．Lower strength

2．Larger shrinkage

3. Low freezing–thawing resistanceRecycled concrete contains the mortar and fine particles.

The freezing-thawing resistance of concrete made with recycledaggregate from non-air-entrained concrete was low. On the other hand, if the original concrete was air-entrained, the frost resistance of recycled concrete were sufficiently good.

Problems with Quality of Recycled AggregateWith 100% recycled coarse and fine aggregate, the strengthAnd durability of concrete are decrease significantly.

4. Mixed use of recycled and regular aggregateSubstituting regular aggregate for recycled aggregate

30% replacement : almost the same strength as that of concretewith regular alone.

In a particular application, there exist suitable combinations of recycled and regular aggregate

Ex.1 100% recycled coarse aggregate with 100% regular sandEx.2 50% replacement of recycled and regular coarse and fine

aggregate

Improvement of Recycled Aggregate

• Heating and grinding Method

Demolished concrete is heated in furnace tower up to 300ºC for 40 to 60 min, which produces fine crack between the cement paste and the aggregate.

Then heated concrete rubble is crushed by a tube mill to abrade the mortar adhered to the original aggregate, and this way we obtained good recycle coarse aggregate and fine aggregate.

Heat treatment Rubbing treatment

Concrete Rubble Weakening Paste due to Heating

Selective removeof Paste

Mechanism to Produce High-quality Recycled Aggregate

DemolishedConcreteRubble

High-quality recycled agrre. Heating Tower

Second Millfor Fine Agg.

Fine powder

Screen

Application to raw of cement

Agg. for normal concrete

First Mill forCoarse Agg.

Outline of Heating and Abrading plant with 3 t/h capacity

Effect of Heat Temperature on Grinding Time Satisfied the Requirement of Dry Density of Aggregate

0

30

60

90

120

150

180

0 100 200 300 400 500

Heat temperature (ºC)

Gri

ndin

g T

ime

(min

)

Dry density：2.5g/cm3

0 100 200 300 400 500

Dry density：2.6g/cm3

●45N/mm2

▲35N/mm2

CompressiveStrength

●45N/mm2

▲35N/mm2

CompressiveStrength

Heat temperature (ºC)

00.51.01.52.02.53.03.54.04.5

2.40 2.45 2.50 2.55 2.60 2.65Dry Density (g/cm3）

Abs

orpt

ion

(%)

Coarse Agg.

Quality Criteria of JIS A 5005

Fine Agg.

Relation between Dry Density and Absorption of AggregateManufactured by Heating and Rubbing Methods

0102030405060708090

100

ConcreteRubble

Heating at300℃

WithoutHeating

Cement PasteFine Agg.Coarse Agg.

3447

33

20 25

31

22

34

44

Com

posi

tion

of C

oncr

ete

(%)

Composition of Original Concrete and Recycled Concrete

Mix Proportion of Recycled Concrete

Properties of Recycled Concrete

Unit Quantity (kg/m3) Kind of

UniConcrete

W/C (%)

s/a(%) Water Cement FA

Fine Agg.

Coarse Agg.

Recycled Concrete

45.6 46.4 152 266 67 832 963

Normal Concrete

48.3 47.3 170 282 70 821 960

Properties of Recycled Concrete

0

10

20

30

40

50

60

70

RecycledAgg.

NormalAgg.

Com

pres

sive

Str

engt

h (M

Pa)

7days28days91days

W/C=60%

W/C=40%

(Normal Agg.: Gravel & Land Sand)

RecycledAgg.

NormalAgg.

Drying Shrinkage

-7

-6

-5

-4

-3

-2

-1

0

0 5 10 15 20 25 30Age (weeks)

Shri

nkag

e St

rain

(×10

-4)

Recycled Agg.Normal Agg.

Properties of Recycled Concrete

Further Problems with Recycling of Concrete

1．Salt within recycled aggregate

2．Alkali-aggregate reaction of recycled aggregate

Recycled concrete contains the mortar and fine particles.

The freezing-thawing resistance of concrete made with recycledaggregate from non-air-entrained concrete was low. On the other hand, if the original concrete was air-entrained, the frost resistance of recycled concrete were sufficiently good.

Education

The most important measures to overcome the barrier toward recycling of concrete, is educations.

It is necessary that the message and understanding of recycling be discussed at technical universities.

Thank You