Application of Conventionally Recycled Coarse Aggregate to Concrete Structure by Surface...

8/13/2019 Application of Conventionally Recycled Coarse Aggregate to Concrete Structure by Surface Modification

1/13

Journal of Advanced Concrete Technology Vol. 5, No. 1, 13-25, February 2007 / Copyright 2007 Japan Concrete Institute 13

Scientific paper

Application of Conventionally Recycled Coarse Aggregate to ConcreteStructure by Surface Modification Treatment

Masato Tsujino1, Takafumi Noguchi2, Masaki Tamura3, Manabu Kanematsu4and Ippei Maruyama5

Received 27 October 2006, accepted 25 January 2007

Abstract

This paper aims to establish a technique for easy concrete recycling as a solution essential for the creation of a closed-

loop recycling society.The technique introduced in this study enables improvement of the recovery rate of original ag-

gregate by enhancing the peeling-off effect of aggregate without any degradation of mechanical properties. The en-

hanced peeling-off effect is realized by applying a surface improving agent to the aggregate.

In this paper, material tests were conducted on recycled aggregates with low quality and middle quality.In the test, twotypes of surface improving agent, an oil-type improving agent and a silane-type improving agent, were used.The test

results have shown that the recycled aggregate finished with silane-type improving agent was greatly improved in re-

covery rate but showed lowered strength.On the other hand, the recycled aggregate finished with oil-type improvingagent was somewhat superior in recovery rate compared with non-finished aggregate. In addition the oil-type im-

proving agent improved hardening properties. Flexural tests of reinforced concrete beams were conducted only for the

oil-type improving agent. Consequently, the possible applicability of recycled aggregate finished with oil-type surface

improving agent was verified.

1. Introduction

The recycling system for concrete is now being signifi-

cantly improved under heightened environmental

awareness and pressing requests for recycling along

with the JIS standardization of high-quality recycled

aggregate for widespread use. On the way to establish-ing a recycling-oriented society, the reverse process,

which requires advanced techniques like heat treatment

and the rubbing method, still faces many hurdles (Shima

et al. 2005, JCI 2005) such as energy-saving, cost-

saving, and the treatment of byproducts such as powder.

The labor-saving design of the reverse process is essen-

tial for the easy attainment of a closed loop. Paying par-

ticular attention to these technical points, this study

aims to establish a technique enabling the easy recycling

of concrete.

The technique introduced to Concrete with Easy-to-

Collect Aggregate (Tamura et al. 1997) in this study is

an easy process that applies surface improving agent to

aggregate. This technique enhances the peeling effect of

aggregate from cement matrix without degrading me-

chanical properties and reduces the high water absorp-

tion of recycle aggregate.

The objectives of this study are to establish the tech-

nique for easy concrete recycling with a surface improv-ing agent and to consider the applicability to architec-

tural structures. Then, following subjects are discussed

in this study:

- clarification of the influence of surface improving

agent on the properties of recycled coarse aggregate,

- investigation of the mechanical properties of concrete

of recycled aggregate finished with a surface improv-ing agent,

- peeling-off effect regarding recovery properties,

- durability of recycled aggregate concrete using a sur-

face improving agent, and

- examination of flexural properties of reinforced con-

crete beams.

2. Characteristics of recycled coarseaggregate

2.1 QualityThe qualities of the recycled coarse aggregate used in

this study are listed in Table 1. The recycled coarse ag-

gregate referred to as middle-quality is screw-ground

with a tertiary crushing after rough crushing with ajaw/cone crusher, and its particle size is adjusted so that

the grain is ranged within the standard particle size

specified in JIS. On the other hand, the recycled coarse

aggregate referred to as low-quality is ground only

without screw grinding and particle size adjustment.

1Graduate Student, Dept. of Architecture, Graduate

School of Engineering, The University of Tokyo, Japan.

E-mail: [email protected] Professor, Dept. of Architecture, Graduate

School of Engineering, The University of Tokyo, Japan.3Research Associate, Dept. of Architecture, Graduate

School of Engineering, Tokyo Metropolitan University,

Japan.4Assistant Professor, Dept. of Architecture, Graduate

School of Engineering, Tokyo University of Science,

Japan.5Associate Professor, Graduate School of Environmental

Studies, Nagoya University, Japan.


2/13

14 M. Tsujino, T. Noguchi, M. Tamura, M. Kanematsu and I. Maruyama / Journal of Advanced Concrete Technology Vol. 5, No. 1, 13-25, 2007

The particle size distribution curves of both types of

recycled aggregate are shown in Fig. 1.

For the test materials, middle-quality recycled aggre-

gate was produced in the laboratory and its mix propor-

tions were known. Waste concrete of unknown mix pro-

portions and for use as sub-grade material was pur-

chased as low-quality recycled aggregate. The mix pro-

portions of the original concrete of the middle-quality

recycled aggregate and the test results of the concrete

are listed in Table 2and Table 3, respectively.

2.2 Content of paste and mortar in recycledcoarse aggregateThe inclusion of a large amount of cement paste in re-

cycled aggregate has been reported to boost water ab-

sorption and negatively affect the properties of hardened

concrete. This is because cement paste is more porous

than aggregate. Consequently, the content of cement

paste is a typical index of the quality of recycled aggre-gate. In this study, the constituents in recycled coarse

aggregate were determined with a chlorine dissolution

process. The results are shown in Fig. 2. The difference

in cement paste content between middle- and low-

quality recycled coarse aggregate is approximately threetimes, and that of mortar content is about two times.About 30% of the total weight in middle-quality aggre-

gate and more than 50% in low-quality aggregate are

mortar. This fact suggests that the grinding effect of

tertiary crushing has reduced the mortar deposit rate of

middle-quality recycled coarse aggregate. By contrast,

in the low-quality recycled coarse aggregate, the mortardeposit rate has not been reduced by rough crushing

only.3. Characteristics of coated recycledcoarse aggregate

3.1 Types of surface improving agentThe surface improving agents used in this study are oil-

and silane-type agents. The silane-type agent is pa-tented (TOYO INK MFG. Co., Ltd. 1995). Table 4lists

their respective applications and main constituents

(Tsuji et al. 2002, Wang 2003). Schematic diagrams of

the effects of surface improving agents are shown in

Figs. 3and 4.

3.2 Water absorption of coated recycled coarseaggregateThe surface improving agent, dispersed in water with a

specific concentration, was applied through repeated

spraying and drying cycles. The number of repetitionsrequired to obtain a stable coating was four times. The

Table 1 Quality of recycled coarse aggregate.

Types of coarse

aggregate Code

Oven-dry

density (g/cm3 )

Surface-dry

density (g/cm3

)

Water

absorption (%)

Material passing

75 m sieve (%)

Mass per unit

volume (kg/L)

Solid content in

aggregate (%)

Fineness

modulus

Middle-quality M 2.36 2.47 4.8 0.64 1.51 64.1 6.51

Low-quality L 2.33 2.46 5.48 2.1 1.41 60.5 6.24

Table 2 Mix proportions of original concrete of middle-

quality recycled coarse aggregate.

Fine Coarse

C1.3% (AE &water reducing agent)

58.0 49.1 180 310 858 909

Unit content (kg/m3

)Admixture

Water Cement Aggregate

W/C

(%)

s/a

(%)

Table 3 Test results original concrete of middle-quality

recycled coarse aggregate.

Air (%)

5.5

Compressive strength at time of crush (N/mm2

)

21.418.0

Slump (cm)

13.6%

17.5%

36.4%

13.6%

0

20

40

60

80

100

Originalcoarse aggregate Middle-quality Low-quality

Mixtureweight(%)

Original coarseaggregate Fine aggregate Paste

Fig. 2 Deposit rate of paste of recycled coarse aggregate.

2.5 5 10 20 250

20

40

60

80

100

Sieve size (mm)

PercentagePassing(%)

Range of std. sizeMiddle-qualityLow-quality

Fig. 1 Grading curves of recycled coarse aggregate.

100%

72.8%

46.1%


3/13

M. Tsujino, T. Noguchi, M. Tamura, M. Kanematsu and I. Maruyama / Journal of Advanced Concrete Technology Vol. 5, No. 1, 13-25, 2007 15

water absorption test was conducted according to JIS A

1110. The test results of water absorption according to

the number of repetitions are shown in Fig. 5. Reduc-

tion of water absorption is not proportional to the num-

ber of repetitions. This may be due to uneven applica-tion over whole recycled coarse aggregate including

paste parts with high water absorption. Ultimate water

absorption is 3.5% for the oil-type agent and 1% for the

silane-type agent, indicating that the reduction effect on

water absorption of the silane-type agent is higher than

that of the oil-type agent.

4. Tests for recycled concrete using coated

recycled coarse aggregate

4.1 Types of concrete and mix proportionsThe types of concretes and mix proportions are listed in

Table 5. Two types of recycled coarse aggregate were

used, i.e., middle- and low-quality recycled coarse ag-

gregate. Three types of surface treatment were applied,

i.e., no treatment (N), oil-type treatment (O), and a si-

lane-type treatment (S). Concrete was made with two

levels of water/cement ratio, i.e., 60% and 40%. Thus,

twelve types of concrete in all were prepared. For the

mechanical properties and peeling-off tests, two types of

aggregate, crushed stone and river gravel, were added

for comparison with ordinary concrete. In addition,crushed stones and river gravel finished with oil-type

agent were also added.

Ordinary Portland cement (density: 3.16 g/cm3) was

used as cement. Oigawa River sand with a surface dry

density of 2.59 g/cm3, water absorption of 0.59% and

fineness modulus of 2.66 was used as fine aggregate.

The mix proportions were selected so that the recycled

concrete using untreated coarse aggregate satisfies the

target properties in a fresh state listed in Table 5. Sup-plemental air-entraining agent was used if the targeted

air volume was not obtained. The aggregates treated

Table 4 Types of surface improving agents.

Type

Application

Mineral oil (Paraffin) 85-95% Silicon analogue 28-32%

Emulsifying agent 1-5% Emulsifying agent Minute quantity

Lanolin fatty acid salt 1-5% Water 68-72%

State Emulsion Emulsion

Oil (O) Silane (S)

Release agent used in wooden form

Mainconstituent

Water-repellent agent with permeability to the concrete surface

Saponification Hydrolysis reaction

Alkali metal salt formationCa2+

Coating formation of alkali metal salt

Calcium ion

== Mineral oil

Application

Drying

RCOOCHRCOOCH22

RRCOOCHCOOCH

RRCOOCHCOOCH22

RCOOCHRCOOCH22

RRCOOCHCOOCH

RRCOOCHCOOCH22

Ca2+ Ca2+

RCOOCaRCOOCa

RRCOOCaCOOCa

RRCOOCaCOOCa

RCOOCaRCOOCa

RRCOOCaCOOCa

RRCOOCaCOOCa

Alkali metal salt film

Surface of aggregate



=Si-OR =Si-OH

1. Fusion

Particles are fused with each other

following water evaporation

from emulsion.

2. Dealcoholization by hydrolysis

Silanol is formed by the reaction

of alkoxyl group, maintained in

polymers, with water.

3. BondingSilanol reacts with hydroxyl

group of silicate contained in cement

to bond to substrate.

Condensation.

Further, after water evaporation,

the silanol reacts with another

Application Mineral oil

Waterevaporation

Approach

between particles

Hydrolysisreaction

Cross-link formation



Reaction Process

Coating formation

Water-repellent coating is formed on the surface of aggregate.

silanol to form siloxane cross-link.

Fig. 3 Schematic diagram of an oil-type

agent for surface improvement.Fig. 4 Schematic drawing of a silane-type surface improv-ing agent (Hasegawa, 1999).

-( ) Aggregate - Surface improving agent ( )- - W/C

Notation used in this paper:

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0 1 2 3 4Number of Applications

WaterAbsorption(%)

Middle-Silane-type

Middle-Oil-type3.78%

Low-Oil-type3.53%

Middle 4.80%

Low 5.48%

Middle-Silane-type

Low-Silane-typeLow-Silane-type

Low-Oil-typeMiddle-Oil-type

1.15%

1.07%

Fig. 5 Reduction of water absorption with improvingagent.


4/13


with surface improving agent were used under air-dry

condition to prevent separation of the agent under water,

especially in the case of the silane-type agent.

4.2 Fresh PropertyThe slump values of concrete are shown in Fig. 6. For

the middle-quality level, the slump values of coated

coarse aggregate are almost similar to those of untreated

coarse aggregate. Accordingly, for the middle-qualitylevel, sufficient fluidity can be achieved by using aggre-

gate finished with surface improvement agent. The flu-

idity obtained without surface drying indicates that an

alkali metallic salt film due to the oil-type agent and a

water repellent coating due to the silane-type agent are

formed to reduce water absorption of aggregate. By

contrast, for low-quality aggregate, the amount of fine

particles of aggregate in itself is more than three times

greater compared with middle-quality aggregate. This

greater amount of fine particles would result in a de-

crease in fluidity, although a film similar to that of mid-

dle-quality aggregate was formed on the aggregate itself.

Thus it is concluded that in the use of low-quality ag-gregate containing an abundant amount of fine particles,

the adjustment of admixture is needed to provide against

the decrease in slump. Compared with the slump values

of untreated aggregate, the decreasing rate of slump

values of aggregates finished with surface improvement

agent shows no significant difference at 30 minutes aftermixing. This may be due to the fact that the water ab-

sorption of treated aggregates is low due to film forma-

tion.

As for the amount of air, as stated in the previous sec-

tion, no significant result was recognized owing to the

mixture of air-entraining agent to obtain the desired

amount of air. The amount of air-entraining agent usedwas the standard level.

4.3 Experiments on mechanical propertiesThe compressive strength test, test for static modulus of

elasticity, and split tensile strength test were conducted

at the age of 28 days according to JIS A 1108, JIS A1149, and JIS A 1113. The compressive strength test and

modulus of static elasticity results are shown in Fig. 7

and the relationship between the compressive strength

and splitting tensile strength test results is shown in Fig.

8.The main concern regarding surface modification

treatment is a significant decrease in strength due to

peeling-off and variations in strength. If decrease and/or

variations in strength occur, it is difficult to apply an

existing structural design. Therefore, a discussion has

been made to investigate if the concrete using coated

recycled coarse aggregate is equal in mechanical prop-

erties compared with normal concrete.

In Fig. 7, compressive strength can be seen to slightly

Table 5 Types of concrete and mix proportions.

Wate r Ceme nt F in e Coarse

No treatment (N) 60 4.0(1) 50.0 175 292 891 925 250ml/c=100kg

(AE & water reducing agent)

Oil (O) 40 2.0(1) 44.0 165 413 790 1004 C0.7%

(Superplasticizer)

No treatment (N) 60 4.0(1) 47.0 165 275 870 982 250ml/c=100kg


Oil (O) 40 2.0(1) 42.0 155 388 772 1067 C0.7%

(Superplasticizer)

Crushed

stone (C) 182

Rivergravel (R)

182

182Oil (O)

40Silane (S)

40

Low-

quality (L)

No treatment (N)60

950

Aggregate

typeUnit content (kg/m

3)

Middle-

quality (M)

No treatment (N)

60182

4.0(1)Oil (O)

906

C0.7%

(Superplasticizer)42.0 175

4.0(1) 826 883 250ml/c=100kg


2.0(1) 438 725

C0.7%

(Superplasticizer)

47.0 185 308

47.0 175 292 844

165 413 743 9812.0(1)Silane (S)

s/a

(%) Admixture

Surface

improving agent

W/C

(%)

Slump

(cm)

Air

(%)

250ml/c=100kg


42.0

Slu

mp

(cm

)

M-60 L-60 M-40 L-40

Oil SilaneNo treatment

0

3

6

9

12

15

18

21

Oil SilaneNo treatment

0 (min)

30 (min)

Fig. 6 Slump values.


5/13


increase in the concrete with a W/C of 60% made using

recycled coarse aggregate treated with the oil-type agent.

This increase may be due to the air-dry condition of the

aggregate. The compressive strength of aggregate fin-

ished with an oil-type agent reaches the level equal tothat of ordinary concrete. Accordingly, it is considered

that the middle-quality aggregate of W/C = 60% is ef-

fective in the increase of strength with no decrease of

fluidity. In addition, Youngs modulus tends also to in-

crease with increased strength. An oil-type agent would

be effective to improve Youngs modulus of recycled

concrete abundant in paste. The above results show that

the structural design similar to existing methods may bepossible for recycled aggregate concrete using the oil-

type improving agent. The strength reduction in the

concrete with W/C of 40% may be due to film forming,

causing a reduction in bond strength between the aggre-

gate and cement matrix. However the strength decreaseis only 10% compared to the untreated specimens. Con-sequently, sufficient strength may be obtained through

the application of the oil-type agent. The strength tends

to decrease if river gravel at W/C = 40%, i.e., an aggre-

gate of high solid volume percentage in the high-

strength area, is used. Caution should be exercised dur-

ing structural design, although no serious problemwould occur because strength of about 40 N/mm

2 is

ensured.

By contrast, in all specimens treated with the silane-

type agent, considerable strength reduction was ob-

served, which may be due to significantly weakened

bonding properties. Calculation of strength by using auniversal estimating equation is difficult. Regarding the

use of aggregate finished with a silane-type agent, re-

consideration based on the collection of additional data

is needed.

In this experiment, three test specimens were tested

for each test level. For R-O-40 only, a test specimen

with compressive strength 5% below the average was

found. The other test levels are likely to present few

quality control problems because the variations in

strength are all limited to within 3%.

Next, the splitting tensile strength of concrete fin-

ished with surface improving agent should be consid-

ered because it may decrease significantly due to peel-ing-off regardless of compressive strength. As shown in

Fig. 8, no test specimen was found to exhibit a signifi-

cant decrease in splitting tensile strength compared with

compressive strength. The splitting tensile strength is

well matched by the existing regression equation (No-guchi et al. 1995). This fact indicates that compressive

and tensile strength are lowered at the same level. Ac-

cordingly, the existing general-purpose equation can

also be applied for surface improvement aggregate. The

above results indicate that the existing equations can be

used to estimate the mechanical properties of aggregatefinished with an oil-type agent and the applicability of

concrete finished with surface improving agent as astructural material.

Finally, a compressive test was conducted for test

samples aged 984 days in water to discuss the decrease

in strength due to the degradation of the surface improv-

ing agent under an alkaline environment over a long

duration. The test results are shown in Fig. 9.

2

Compress

ivestrengthat

28d

ays

(N/

mm

)

0

10

20

30

40

50

60

70

80

M-60 L-60 C-60 R-60 M-40 L-40 C-40 R-400

5

10

15

20

25

30

35

40

Young

'smo

du

lus

kN/

mm

2

Compressive strengthOil SilaneNo treatment

Young's modulusNo treatment Oil Silane

Fig. 7 Test results of compressive strength and Youngs

modulus.

0

1

2

3

4

5

0 10 20 30 40 50 60 70 80Compressive strength at 28 days (N/mm )

2

Sp

littens

ilestrength

N/

mm

2

637.0291.0

Bt =

Recycle (No treatment)

Recycle (Silane)Recycle (Oil)

Normal (No treatment)Normal (Oil)

Fig. 8 Test results of split tensile strength and compres-

sive strength.

M-60 L-60 M-40 L-40

2

C

ompress

ivestrengthat

28d

ays

(N/

mm

)

0

10

20

30

40

50

60

70

80

0

5

10

15

20

25

30

35

40

Young

'smo

du

lus

kN/

mm

2

Compressive strengthOil SilaneNo treatment

Young's modulusNo treatment Oil Silane

Fig. 9 Test results of compressive strength at 984 days.

.


6/13


An increase in strength was recognized for all test

levels and the test results show a behavior similar to that

of ordinary concrete compared with the compressive

strength of 28-day aging. Consequently, the property of

long duration can be evaluated as that of 28-day aging.This fact suggests that the aggregate finished with sur-

face improving agent can be fully used even in a water

environment for a long duration.

In future, the application to an architectural structure

could be established by:

- conducting repeated tests of warm-cool and dry-wet

cycles,

- considering the fire resistance, including mechanicalbehaviors at high temperatures, and

- conducting an exposure test over a long duration of

time.

4.4 Experiments on peeling-off effect (recoveryof original aggregate)The importance of the peeling-off effect lies in, as

shown in Concrete with Easy-to-Collect Aggregate

(Tamura et al. 1997), recycling at low energy and main-

taining aggregate size. In this study, the area of aggre-

gate on the split surface of the specimen was measured

by means of image analysis as proposed by Noguchi et

al. (Noguchi et al. 2001) following execution of a split

tensile strength test to evaluate the peeling-off effect of

surface improving treatment and the recovery of origi-

nal aggregate. The peeling-off effect was determined bythe ratio of the aggregates that are peeled at the coated

surface to total recycled aggregates. To clearly distin-

guish between the peeled aggregates and the crushed

aggregates, specimens were prepared by adding a red

pigment of iron oxide in the amount of 3% of the ce-

ment weight. The results of image analysis on the peel-

ing-off effect in concrete are shown in Fig. 10.

As shown in Fig. 10, the peeling-off of a silane-typeagent is highly effective. This fact suggests that aggre-

gate finished with a silane-type agent can be recycled

with an easy recovery system with low energy require-

ment and maintaining aggregate diameter. Thus, al-

though silane-type agent is considered to be vastly supe-rior in recycling effect, a trade-off relationship exists

between the peeling-off effect and strength, as previ-

ously described. How to balance the peeling-off effect

with strength must be studied by investigating the

amount of application.

By contrast, it is indicated that the use of crushed

Fig. 10 Results of image analysis on peeling-off effect in concrete.

.


7/13


stones of poor grain shape and of acute angle in normal

aggregate treated with the oil-type agent results in low

peeling-off effect, and the use of river gravel of rounded

smooth grain and smooth surface results in high peel-

ing-off effect. River gravel is considered not to hinderthe development of cracks when stress occurs at the

interface part. In this condition, although significant

decrease in split tensile strength is a concern, river

gravel maintains sufficient strength as stated previously.

Thus, the decrease in split tensile strength poses no par-

ticular problem in practical use. In addition, for the

middle-quality recycled aggregate finished with an oil-

type agent, the peeling-off effect is not so effective be-cause the low strength part of old mortar is lower than

the peeling strength. However, the test results obtained

indicate that the peeling-area percentage is higher by

10% compared with non-treated aggregate. Thus it can

be concluded that the application of an oil-type agent iseffective.

The results show that a silane-type agent has suffi-

cient peeling-off effect for low-quality aggregate of rich

paste and, on the other hand, an oil-type agent has high

peeling-off effect for hard aggregate such as river gravel

of rounded smooth grain.

4.5 Resistance to carbonationAn accelerated carbonation test was conducted by using

cylindrical test specimens with a diameter of 100 mm

and a height of 200 mm under the testing and aging

condition specified in JIS A 1153. The carbonation

depth was determined according to JIS A 1152.

Figure 11shows the relationship between the root of

the duration of aging, up to 91 days, and the carbonation

depth determined by an accelerated test. The coefficient

of velocity of carbonation (a value in Fig. 11) wasalso calculated from a regression equation through the

origin on the assumption that linearity exists between

the two axes.

For both W/C = 60% and 40%, the aggregate con-

crete finished with oil-type surface improving agent is

most resistant to carbonation. This phenomenon may be

due to the air-dry condition of the aggregate in the

course of concrete depositing. Accordingly, the actualwater/cement ratio decreases and the effect of increased

resistance of the cement matrix is considered. For mid-

dle-quality aggregate, significantly non-lowered fluidity

of concrete may result in possible improvement of resis-

tance to carbonation of the concrete with recycled ag-gregate treated with the oil-type agent. By contrast, al-though concrete of aggregate finished with a silane-type

surface improving agent uses also the air-dry condition

of the aggregate, carbonation is more developed. In the

case of the silane-type agent, re-emulsifying followed

by dissolution may adversely affect the hydrolysis of

cement. A solution to this problem is needed.

4.6 Experiments on drying shrinkageA drying shrinkage test was conducted according to a

dial gauge method specified in JIS A 1129-3. Specimens

were removed from moulds at the age of one day and

Y = a x

0

4

8

12

16

20

0

1

2

3

4

5

0 1 2 3 4 5 0 1 2 3 4 5Age ( weeks)

3.703.134.75

Y = a x

No treatment

OilSilane

4.063.285.31

Y = a x

No treatment

OilSilane

0.210.110.16

Y = a x

No treatment

OilSilane

0.190.090.19

No treatment

OilSilane

Middle W/C=60 Low W/C=60

Middle W/C=40 Low W/C=40

Deptho

fcarbonation

(mm

)

Deptho

fcarbonation

(mm

)

Fig. 11 Depth of carbonation.


8/13


cured in water up to the age of nine days, followed by

dry condition at 20 degrees and 60% R.H. Figure 12

shows the experimental results of drying shrinkage and

mass change and the predicted values of drying shrink-

age up to the age of 726 days, which are calculated us-ing AIJ equations (AIJ 2006) for natural aggregate con-

crete (hereinafter referred to as ordinary concrete) with

the same mix proportions.

In the case of W/C of 60%, the drying shrinkage of

concrete containing recycled aggregate treated with the

oil-type agent is smaller than that of non-treated aggre-

gate and aggregate finished with a silane-type agent.

The drying shrinkage of middle-quality aggregate issmaller by 10% compared with that of untreated aggre-

gate. The reduction of mass in concrete containing recy-

cled aggregate treated with the oil-type agent is smaller

than that of untreated aggregate and almost equal to that

of ordinary concrete, which may indicate the absence ofany significant problem in practical use. The silane-typeagent was observed to have very little effect on drying

shrinkage and mass change.

In the case of W/C of 40%, the drying shrinkage of

concrete containing recycled aggregate treated with the

oil-type agent is smaller than that of concrete with un-

0

200

400

600

800

1000

1200

91

92

93

94

95

96

97

M-

N-60

M-

O-60

M-

S-6

0

L-

N-6

0

L-

O-6

0

L-

S-6

0

M-

N-40

M-

O-40

M-

S-4

0

L-

N-4

0

L-

O-4

0

L-

S-4

0

Weight rate of change

AIJ shrinkage strain prediction equation(natural aggregate concrete of the same formulation)

Experimental value

We

igh

trateo

fc

hange

(%)

Dry

ings

hrin

kagestra

in(

)

Fig. 12 Drying shrinkage strain at the age of 726 days.

0

25

50

75

100

125

150

175

200

0 100 200 300 400 500 0 100 200 300 400 500 600

0

25

50

75

100

125

150

175

200

0 100 200 300 400 500

Time since loading (days)

0 100 200 300 400 500 600

Time since loading (days)

2

-6

Time since loading (days)Time since loading (days)

Spec

ific

creepstra

in10/(N/

mm

)

Spec

ific

creepstra

in10/(N/

mm

)2

-6

No treatment Oil Silane

AIJ creep strain prediction equation

(natural aggregate concrete of the same formulation)

Fig. 13 Specific creep strain.


9/13


treated aggregate. The oil-type agent is effective in the

reduction of drying shrinkage regardless of the wa-

ter/cement ratio, which gives concrete structures long

service life and leads to sustainability.

4.7 Experiments on creepFigure 13shows the experimental results and predicted

values calculated with an AIJ equation (AIJ 2006) for

the change in specific creep strain in ordinary concrete

with the same mix proportions as those of recycled ag-

gregate. The specific creep strain was calculated so that

both the elastic strain at loading and the drying shrink-

age strain were subtracted from the total strain.The specific creep strain in recycled aggregate con-

crete is greater than that in ordinary concrete regardless

of the water/cement ratio. This phenomenon may be due

to the paste content in concrete made using recycled

aggregate.Concrete with recycled aggregate treated with the oil-

type agent shows nearly the same amount of change in

creep behavior as concrete with untreated aggregate,

which proves that the oil-type surface improving agent

has no significant influence on creep. By contrast, the

creep strain of concrete with recycled aggregate treated

with a silane-type agent is very large. This phenomenonmay be from the result of the decreased bond strength at

the interface between the aggregate and cement paste.

4.8 Experiments on flexural properties of rein-forced concrete beams using aggregate treated

with surface improving agent

4.8.1 OutlineFlexural tests have been conducted in reinforced con-

crete beams made using concrete with aggregate treated

with surface improving agent, except for concrete with

aggregate treated with a silane-type agent, which was

greatly reduced in strength in spite of excellent aggre-

gate recovery, and whose use for structures was consid-ered problematic. The aim of the flexural test is to

evaluate the strength and the cracking resistance of the

concrete with aggregate treated with the oil-type agent,

and to check practical use compared with ordinary con-

crete made using crushed virgin aggregate. The outline

of loading is shown in Fig. 14.

4.8.2 Cracking momentFigure 15shows the experimental results and calculated

values obtained by substituting the mechanical proper-

ties at loading age into the equation. As shown in this

figure, cracking moment in recycled coarse aggregate

concrete is slightly smaller than that in ordinary con-crete. However, no singular point is recognized in theconcrete with recycled coarse aggregate treated with the

oil-type agent, and the experimental results are nearly

equal to the calculated values. Therefore, a conventional

equation for designing can be used to predict a bending

moment causing cracks.

4.8.3 Cracking behaviorRegarding the investigation of the properties of cracks

against long-term allowable stress, Figs. 16 and 17

show the results of cracking properties due to service-

able load when, assuming a RC section, the force ap-

plied on the main reinforcement attains the long-termallowable stress, 215 N/mm

2. In addition, Fig. 18shows

the deflection at the long-term allowable stress.

The maximum crack width did not increase with the

200 600 200 200 600 200

2000

D6@100(SD345)D13(SD345)

20030 140 30

230

30

170

30

Displacement gaugePinRoller bearing

Testing bench

Test piece

Load cell

Loading plate

Pressing head

Cross-section

Fig. 14 Schematic diagram of loading in RC bending test (Unit: mm).


10/13


use of the oil-type agent. This may be considered due to

the fact that the effect of the bond of recycled coarse

aggregate is smaller than that of ordinary aggregate.

However, this should pose no problem in practical use,

because for all the levels, the extent of cracking is sig-

nificantly smaller than 0.3 mm, which is the allowable

crack width to ensure resistance to degradation in a gen-

eral environment as specified in Recommendations for

Practice of Crack Control in Reinforced Concrete Build-

ings (Design and Construction) (AIJ 2006), published

by the Architectural Institute of Japan. In addition, al-

though the maximum crack spacing of recycled coarse

aggregate concrete tends to be small compared with

ordinary concrete, no significant difference is recog-

nized due to the use of the oil-type agent.

Although the recycled coarse aggregate produces lar-ger deflection in RC beams, the extent is not of great

significance for practical use and the low water/cement

ratio may overcome the increase in deflection.

Consequently, in this experiment, as significant deg-

radation of crack behavior due to a surface improving

treatment is not recognized, durability related crackingbehavior need not be given much attention. Recycled

concrete containing the oil-type agent may be applicable

to structural use in combination with a surface finishing

material that can restrain water penetration and follow

the movement of cracks.

4.8.4 Plastic behaviorFigure 19 shows the load-deflection curves of RC

beams. All specimens collapsed due to the failure of

concrete at the ultimate compression fiber.

No significant difference in yielding moment and ul-

timate moment is recognized between recycled coarse

aggregate concrete and ordinary concrete. The load-

deflection curves are similar to those obtained by Sato

(Sato et al. 2000) and Mukai (Mukai et al. 1979) as well

as those of ordinary concrete, and no influence of the

oil-type agent is recognized in any of the specimens.

Further, the observed concrete strains at ultimate com-

pression fiber were constant, nearly 3500 u, in this study.

Figure 20shows a comparison of measured values and

calculated values obtained by using equivalent compres-

M-

N-

60

M-

O-

60

L-

N-

60

L-

O-

60

M-

N-

40

M-

O-

40

L-

N-

40

L-

O-

40

No treatment

Oil

Calculated values

0

5

10

15

stone

Crus

he

d-

60

stone

Crus

he

d-

40B

endin

gmomentcaus

ingcrac

ks

kN

m

Fig. 15 Cracking moment.

0.0

0.1

0.2

0.3No treatment

Oil

M-

60

L-

60

M-

40

L-

40

stone

Crus

he

d-

60

-40

stone

Crus

he

d

Max

imum

crac

kw

idth

mm

Fig. 16 Maximum crack width.

M

-60

L

-60

M

-40

L

-40

stone

Crush

ed

-60

-40

stone

Crush

ed

No treatmentOil

0

100

200

300

Max

imum

crac

kin

terva

l

mm

Fig. 17 Maximum crack spacing.

0

1

2

3No treatment

Oil

M-

60

L-

60

M-

40

L-

40

stone

Crus

he

d-

60

-40

stone

Crus

he

d

De

flection

mm

Fig. 18 Deflection.


11/13


sive stress on Bernoullis Eulers assumption, when the

compressive edge strain reaches 3500 u. First, themeasured values are considered to be almost the same

degree for all levels. No significant difference is found

compared with ordinary concrete. Moreover, the meas-

ured values match the calculated values. Thus the ulti-

mate strength can be assessed for the concrete using an

oil-type agent.

In this experiment, many cracks occurred in the range

from yielding point to ultimate point in the concrete

containing aggregate treated with surface improvingagent. The cracking after the yielding point may be ef-

fective from the viewpoint of aggregate recovery at the

demolition of a structure. However, as this action mayreduce compressive strength under positive-negative

cyclic load conditions, further discussion is warranted.

The shear property of concrete in the reinforced con-

crete is also needed for structural design of RC structure.

Then, the shear property of concrete as well as the test

under positive-negative cyclic load conditions will bediscussed in future.

Based on the above results, it is difficult to consider

that the bending of reinforced concrete beams is prob-

lematic in practical use because the oil-type agent hasefficient performance in strength as well as cracking

resistance. An oil-type agent would be sufficiently ap-

plicable to structural materials if yielding of reinforce-ment were made to occur in advance by making the re-

inforcement ratio less than the balanced steel ratio.

5. Conclusions

The following concluding remarks were obtained

120

0

20

40

60

80

100

120

0 5 10 15 20 25 0 5 10 15 20 25

0 5 10 15 20 25

Deflexion (mm)

0 5 10 15 20 25 30

--60

--60

-60Crushed stone

30

0

20

40

60

80

100

Deflexion (mm)

--60

--60

-60Crushed stone

--60

--60

-40Crushed stone

--60

--60

-40Crushed stone

Loa

d(kN)

Loa

d(kN)

Fig. 19 Load-deflection curves.

0

5

10

15

20

25

30

35

40No treatmentOil

Calculated values

M-

N-

60

M-

O-

60

L-

N-

60

L-

O-

60

M-

N-

40

M-

O-

40

L-

N-

40

L-

O-

40

stone

Crus

he

d-

60

-40

stone

Crus

he

d

Ulti

mate

ben

din

gmoment

kN

m

Fig. 20 Ultimate bending moment.


12/13


through the experiments.

(1) A surface improving agent reduced water absorp-tion of low- and middle-quality recycled aggregate.

(2) For the middle-quality level, sufficient fluidity can

be achieved by using the air-dry condition of ag-gregate finished with surface improving agent. On

the other hand, it is concluded that in the use of

low-quality aggregate containing an abundant

amount of fine particles, adjustment of the admix-

ture is needed to prevent a decrease in fluidity.

(3) As the oil-type agent does not degrade the me-chanical properties of concrete significantly, it can

be used for the surface improvement of recycledaggregate in structural concrete. By contrast, the

silane-type agent decreases the strength signifi-

cantly. The calculation of the strength by using a

universal estimating equation is difficult. To use

aggregate finished with a silane-type agent, recon-sideration based on the collection of additionaldata is needed.

(4) As the peeling-off effect of aggregate treated witha silane-type agent is significantly higher than that

of untreated aggregate, a silane-type agent is very

effective from the viewpoint of aggregate recovery.

On the other hand, an oil-type agent has high peel-ing-off effect for hard aggregate such as river

gravel of rounded smooth grain. The middle-

quality recycled aggregate finished with an oil-

type agent is not so high in the peeling-area per-

centage compared with non-treated aggregate. It is

concluded that an oil-type agent is effective to im-prove the recovery percentage even though the

peeling-off effect is not high for all levels.

(5) For both W/C = 60% and 40%, the aggregate con-crete finished with oil-type surface improving

agent is most resistant to carbonation.

(6) The oil-type agent possibly reduces drying shrink-age of recycled aggregate concrete with W/C of

60% to that of ordinary concrete.

(7) The creep deformation of recycled aggregate con-crete treated with the oil-type agent is not signifi-

cantly different from that of concrete with un-

treated aggregate.

(8) Although the recycled aggregate treated with theoil-type agent reduces the resistance to bending

cracking, the crack width never exceeds 0.3 mm,

which is the threshold limit value from the view-

point of durability. This indicates that recycled ag-

gregate concrete treated with the oil-type agentmay be applicable to structural use combined with

a surface finishing material that can restrain water

penetration and follow the movement of cracks.

(9) The bending strength of RC beams made usingrecycled aggregate treated with the oil-type agent

is comparable to that of ordinary concrete and theload at which cracks occur may be estimated. In

addition, ultimate strength also can be estimatedassuming that the concrete strain at ultimate com-

pression fiber is 3500 u.

(10) It is difficult to consider that the bending of rein-forced concrete beam is problematic in practical

terms because the oil-type agent has efficient per-

formance in strength as well as cracking resistance.An oil-type agent would be sufficiently usable for

structural materials if yielding of reinforcementwere made to occur in advance by making the rein-

forcement ratio less than the balanced steel ratio.

AcknowledgementsThis study was supported by a scientific research grant

on waste disposal sponsored by the Ministry of Envi-ronment for FY2004-2005, Development of the Next-

Generation Recycling Technology of Demolished Con-

crete (Research representative: Dr. Takafumi NOGU-

CHI). Grateful appreciation is extended to all those who

encourage and support this study.

ReferencesAIJ, (2006). Recommendations for Practice of Crack

Control in Reinforced Concrete Buildings. (Design

and Construction) Tokyo: Architectural Institute of

Japan.

Hasegawa, M. (1999). Aqueous silicon analoguecoating agent Silas. Toagosei study annual report

TREND 1999, (2), 45-49. (in Japanese)

JCI, (2005). A proposal toward the spread of concrete

recycling systems. (Activity reports about advanced

use of recycled concrete) Tokyo: Japan Concrete

InstituteMukai, T., Kikuchi, M. and Koizumi, H. (1979). Fun-

damental Study on the Use of Recycled Aggregate

Concrete for Structural Reinforced Concrete Mem-

ber.Review of the 33rd General Meeting (Technical

Session), Japan Cement Association, (33), 120-121.

Noguchi, T. and Tomosawa, F. (1995). Relationship

between Compressive Strength and Various

Mechanical Properties of High-Strength Concrete.

Journal of Structural and Construction Engineering,

(472), 11-16. (in Japanese)

Noguchi, T. and Tamura, M. (2001). Concrete design

towards complete recycling. Structural Concrete

journal of the fib, 2(3), 155-167.Sato, R., Kawai, K. and Baba, Y. (2000). Mechanical

Performance of Reinforced Recycled Concrete

Beams. Proceedings of International Workshop on

Recycled Concrete, 127-146.

Shima, H., Tateyashiki, H., Matsuhashi, R. and Yoshida,Y. (2005). An Advanced Concrete Recycling

Technology and its Applicability Assessment through

Input-Output Analysis. Journal of Advanced

Concrete Technology, 3(1), 53-67.

Tamura, M., Tomosawa, F. and Noguchi, T. (1997).

Recycle-oriented concrete with easy-to-collectaggregate. Cement Science and Concrete Technology,

Japan Cement Association, (51), 494-499. (inJapanese)


13/13


TOYO INK MFG. Co., Ltd., (1995). An aqueous

organo-silicic compound. Japanese patent

application B2 H07-005400.

Tsuji, D., Tamura, M. and Noguchi, T. (2002). Study

on application of improved low-quality recycledaggregate for concrete structure. Proceedings of the

Japan Concrete Institute, 24(1), 1251-1256. (in

Japanese)

Wang, C. H. (2003). The study of the surface

improvement of the low quality recycled aggregate

for structure concrete. Thesis (M.A.). TheUniversity of Tokyo.

Date post:	04-Jun-2018
Category:	Documents
Upload:	krittiya-kaewmanee
View:	218 times
Download:	0 times

Application of Conventionally Recycled Coarse Aggregate to Concrete Structure by Surface...

Documents