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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 Concrete Structure by Surface Modification Treatment Masato Tsujino 1 , Takafumi Noguchi 2 , Masaki Tamura 3 , Manabu Kanematsu 4 and Ippei Maruyama 5 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, two types 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 improving agent 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 coarse aggregate 2.1 Quality The 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 a jaw/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. 1 Graduate Student, Dept. of Architecture, Graduate School of Engineering, The University of Tokyo, Japan. E-mail: [email protected] 2 Associate Professor, Dept. of Architecture, Graduate School of Engineering, The University of Tokyo, Japan. 3 Research Associate, Dept. of Architecture, Graduate School of Engineering, Tokyo Metropolitan University, Japan. 4 Assistant Professor, Dept. of Architecture, Graduate School of Engineering, Tokyo University of Science, Japan. 5 Associate Professor, Graduate School of Environmental Studies, Nagoya University, Japan.
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Page 1: Application of Conventionally Recycled Coarse Aggregate to ...

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 Concrete Structure by Surface Modification Treatment Masato Tsujino1, Takafumi Noguchi2, Masaki Tamura3, Manabu Kanematsu4 and 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, two types 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 improving agent 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 coarse aggregate

2.1 Quality The 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 a jaw/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] 2Associate 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.

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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 2 and Table 3, respectively.

2.2 Content of paste and mortar in recycled coarse aggregate The 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 three times, 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 mortar deposit rate has not been reduced by rough crushing only. 3. Characteristics of coated recycled

coarse aggregate

3.1 Types of surface improving agent The 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 4 lists 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. 3 and 4. 3.2 Water absorption of coated recycled coarse aggregate The surface improving agent, dispersed in water with a specific concentration, was applied through repeated spraying and drying cycles. The number of repetitions required to obtain a stable coating was four times. The

Table 1 Quality of recycled coarse aggregate.

Types of coarseaggregate

CodeOven-dry

density (g/cm3 )

Surface-drydensity (g/cm

3)

Waterabsorption (%)

Material passing75 μm sieve (%)

Mass per unitvolume (kg/L)

Solid content inaggregate (%)

Finenessmodulus

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 CoarseC×1.3% (AE &

water reducing agent)58.0 49.1 180 310 858 909

Unit content (kg/m3)

AdmixtureWater Cement

AggregateW/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/mm 2)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

Mix

ture

wei

ght

(%)

Original coarse aggregate 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)

Per

cent

age

Pas

sing

(%)

Range of std. sizeMiddle-qualityLow-quality

Fig. 1 Grading curves of recycled coarse aggregate.

100%

72.8%

46.1%

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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 proportions The 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

RCOOCHRCOOCH22RR’’COOCHCOOCH

RR””COOCHCOOCH22

RCOOCHRCOOCH22RR’’COOCHCOOCH

RR””COOCHCOOCH22

Ca2+ Ca2+

RCOOCaRCOOCaRR’’COOCaCOOCa

RR””COOCaCOOCa

RCOOCaRCOOCaRR’’COOCaCOOCa

RR””COOCaCOOCa

Alkali metal salt film

Surface of aggregate

Surface of aggregate

Surface of aggregate

= Si-OR =Si-OH

1. FusionParticles are fused with each other

following water evaporationfrom emulsion.

2. Dealcoholization by hydrolysisSilanol is formed by the reactionof alkoxyl group, maintained inpolymers, with water.

3. BondingSilanol reacts with hydroxylgroup of silicate contained in cementto bond to substrate.Condensation.Further, after water evaporation,the silanol reacts with another

Application Mineral oil

Waterevaporation

↓Approach

between particles

Hydrolysisreaction

Cross-link formation

Surface of aggregate

Surface of aggregate

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

Wat

erAbs

orpt

ion

(%)

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 improving agent.

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

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 Property The 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-quality level, 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 after mixing. 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 used was the standard level.

4.3 Experiments on mechanical properties The 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 A 1149, 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.

Water Cement Fine Coarse

No treatment (N) 60 4.0(±1) 50.0 175 292 891 925250ml/c=100kg

(AE & water reducing agent)

Oil (O) 40 2.0(±1) 44.0 165 413 790 1004C×0.7%

(Superplasticizer)

No treatment (N) 60 4.0(±1) 47.0 165 275 870 982250ml/c=100kg

(AE & water reducing agent)

Oil (O) 40 2.0(±1) 42.0 155 388 772 1067C×0.7%

(Superplasticizer)

Crushedstone (C)

18±2

Rivergravel (R)

18±2

18±2Oil (O)

40Silane (S)

40

Low-quality (L)

No treatment (N)60

950

Aggregatetype

Unit content (kg/m3)

Middle-quality (M)

No treatment (N)60

18±2

4.0(±1)

Oil (O)

906

C×0.7%(Superplasticizer)

42.0 175

4.0(±1) 826 883250ml/c=100kg

(AE & water reducing agent)

2.0(±1) 438 725

C×0.7%(Superplasticizer)

47.0 185 308

47.0 175 292 844

165 413 743 9812.0(±1)Silane (S)

s/a(%)

AdmixtureSurface

improving agentW/C(%)

Slump(cm)

Air(%)

250ml/c=100kg(AE & water reducing agent)

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.

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M. Tsujino, T. Noguchi, M. Tamura, M. Kanematsu and I. Maruyama / Journal of Advanced Concrete Technology Vol. 5, No. 1, 13-25, 2007 17

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 to that 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, Young’s modulus tends also to in-crease with increased strength. An oil-type agent would be effective to improve Young’s modulus of recycled concrete abundant in paste. The above results show that the structural design similar to existing methods may be possible 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 decrease is 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 problem would occur because strength of about 40 N/mm2 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 a universal 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 aggregate finished with an oil-type agent and the applicability of concrete finished with surface improving agent as a structural 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.

2C

ompr

essi

vest

reng

that

28da

ys 

(N/m

m)

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

You

ng's

mod

ulus

(kN

/mm

)2

Compressive strengthOil SilaneNo treatment

Young's modulusNo treatment Oil Silane

Fig. 7 Test results of compressive strength and Young’s modulus.

0

1

2

3

4

5

0 10 20 30 40 50 60 70 80Compressive strength at 28 days (N/mm )2

Spl

itte

nsile

stre

ngth

(N/m

m)2

637.0291.0 Bt σσ ×=

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

2C

ompr

essi

vest

reng

that

28da

ys 

(N/m

m)

0

10

20

30

40

50

60

70

80

0

5

10

15

20

25

30

35

40

You

ng's

mod

ulus

(kN

/mm

)2

Compressive strengthOil SilaneNo treatment

Young's modulusNo treatment Oil Silane

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

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

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 mechanical

behaviors at high temperatures, and - conducting an exposure test over a long duration of

time. 4.4 Experiments on peeling-off effect (recovery of 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 by the 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-type agent 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.

.

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M. Tsujino, T. Noguchi, M. Tamura, M. Kanematsu and I. Maruyama / Journal of Advanced Concrete Technology Vol. 5, No. 1, 13-25, 2007 19

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 hinder the 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 is effective.

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 carbonation An 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 11 shows 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) was also 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 actual water/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 shrinkage A 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)

=3.70=3.13=4.75

Y = a xNo treatment

OilSilane

=4.06=3.28=5.31

Y = a xNo treatment

OilSilane

=0.21=0.11=0.16

Y = a xNo treatment

OilSilane

=0.19=0.09=0.19

√No treatment

OilSilane

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

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

Dep

thof

carb

onat

ion

(mm

)D

epth

ofca

rbon

atio

n(m

m)

Fig. 11 Depth of carbonation.

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

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 is smaller 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 of any significant problem in practical use. The silane-type agent 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

-60

L-N

-60

L-O

-60

L-S

-60

M-N

-40

M-O

-40

M-S

-40

L-N

-40

L-O

-40

L-S

-40

Weight rate of change

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

Experimental value

Wei

ght

rate

ofch

ange

(%)

Dry

ing

shrink

age

stra

in(μ

)

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)

Spe

cific

cree

pst

rain

(×10

/(N/m

m))

Spe

cific

cree

pst

rain

(×10

/(N/m

m))

2-6

No treatment Oil Silane

AIJ creep strain prediction equation

(natural aggregate concrete of the same formulation)

Fig. 13 Specific creep strain.

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M. Tsujino, T. Noguchi, M. Tamura, M. Kanematsu and I. Maruyama / Journal of Advanced Concrete Technology Vol. 5, No. 1, 13-25, 2007 21

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 creep Figure 13 shows 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 phenomenon may 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 Outline Flexural 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 moment Figure 15 shows 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 the concrete 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 behavior Regarding 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-term allowable stress, 215 N/mm2. In addition, Fig. 18 shows 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

3017

030

Displacement gaugePin・Roller 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).

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

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 cracking behavior 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 behavior Figure 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 20 shows 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

ston

eC

rush

ed -60

ston

eC

rush

ed -40Ben

ding

mom

ent

caus

ing

crac

ks(kN

・m)

Fig. 15 Cracking moment.

0.0

0.1

0.2

0.3No treatment

Oil

M-60

L-60

M-40

L-4

0

stone

Cru

shed

-60

-40

ston

eC

rush

ed

Max

imum

crac

kw

idth

(mm

Fig. 16 Maximum crack width.

M-60

L-60

M-40

L-4

0

ston

eC

rush

ed -60

-40

ston

eC

rush

ed

No treatment

Oil

0

100

200

300

Max

imum

crac

kin

terv

al(m

m)

Fig. 17 Maximum crack spacing.

0

1

2

3No treatment

Oil

M-60

L-60

M-40

L-4

0

ston

eC

rush

ed -60

-40

ston

eC

rush

ed

Def

lect

ion

(mm

Fig. 18 Deflection.

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sive stress on Bernoulli’s Euler’s assumption, when the compressive edge strain reaches 3500 u. First, the measured 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 improving agent. 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 may reduce 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 be discussed 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 has efficient 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

L-N-60

L-O-60

-60Crushed stone

30

0

20

40

60

80

100

Deflexion (mm)

L-N-60

L-O-60

-60Crushed stone

L-N-60

L-O-60

-40Crushed stone

L-N-60

L-O-60

-40Crushed stone

Loa

d(k

N)

Loa

d(k

N)

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

ston

eC

rush

ed -60

-40

ston

eC

rush

ed

Ultim

ate

bend

ing

mom

ent

(kN

・m)

Fig. 20 Ultimate bending moment.

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

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 recycled aggregate 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 additional data is needed.

(4) As the peeling-off effect of aggregate treated with a 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 the oil-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 agent may 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 using recycled aggregate treated with the oil-type agent is comparable to that of ordinary concrete and the load at which cracks occur may be estimated. In addition, ultimate strength also can be estimated assuming 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 reinforcement were made to occur in advance by making the rein-forcement ratio less than the balanced steel ratio.

Acknowledgements This 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. References AIJ, (2006). “Recommendations for Practice of Crack

Control in Reinforced Concrete Buildings. (Design and Construction)” Tokyo: Architectural Institute of Japan.

Hasegawa, M. (1999). “Aqueous silicon analogue coating 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 Institute

Mukai, 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-collect aggregate.” Cement Science and Concrete Technology, Japan Cement Association, (51), 494-499. (in Japanese)

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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 recycled aggregate 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.). The University of Tokyo.