Properties of concrete pedestrian block mixed with crumb rubber

Construction

Construction and Building Materials 20 (2006) 450–457

and Building

MATERIALSwww.elsevier.com/locate/conbuildmat

Properties of concrete pedestrian block mixed with crumb rubber

Piti Sukontasukkul *, Chalermphol Chaikaew

Department of Civil Engineering, King Mongkut’s Institute of Technology-North Bangkok, 1518 Pibulsongkoram Road, Bangsue,

Bangkok 10800, Thailand

Received 11 August 2004; received in revised form 22 December 2004; accepted 31 January 2005

Available online 21 March 2005

Abstract

Recycling granulated waste tires (crumb rubber) has been widely studied for the last twenty years mostly relating to applications

such as asphalt pavement, waterproofing system, membrane liners, etc. In this study, the use of crumb rubber to replace coarse and

fine aggregates in concrete pedestrian block was studied. It is believed that concrete acting as a binder mixed with crumb rubber can

make concrete blocks more flexible and thus, provide softness to the surface. The crumb rubber block also performed quite well in

both skid and abrasion resistance tests. The production process was economical, due to the simplicity of the manufacturing process.

� 2005 Elsevier Ltd. All rights reserved.

Keywords: Pedestrian block; Rubber crumb; Concrete; Skid resistance

1. Introduction

Worldwide, the use of rubber products increases

every year. In Thailand, the record of the year 2000

alone indicated a consumption of approximately

250,000 metric tonnes of rubber products. About 38%

of this (94,000 metric-tonnes) were vehicle tires. Thesenumbers keep on increasing every year with the numbers

of vehicles, as do the future problems relating to waste

tires.

Generally, the cheapest and easiest way to decompose

waste or used tire is by burning them. However, the pol-

lution and enormous amount of smoke generated by this

method makes burning quite unacceptable and in some

countries it is prohibited by law. Thus, the conventionalsolution is to store them on empty land, which indirectly

creates several other problems because they become fire

hazard or insect and animal habitation (Fig. 1(a)). Some

are moved elsewhere by illegal shipment aboard (as

found in Thailand about two years ago.

0950-0618/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.conbuildmat.2005.01.040

* Corresponding author. Tel.: +66 2 913 2500; fax: +66 2 587 4337.

E-mail address: [email protected] (P. Sukontasukkul).

During the last 20 years, much research has been car-

ried out in an attempt to reuse the abandoned tires by

grinding them into small particles (rubber crumb) and

use in asphalt [1–4], sealants, rubber sheets or in cemen-

titious materials like concrete [5–9].

Several studies indicate that the presence of crumb

rubber in concrete seems to lower the mechanical prop-erties (compressive and flexural strength) as compared

to that of conventional concrete. The lower in strength

is due to the lack of bonding between rubber crumb

and Portland cement. The decrease in strength is found

to be directly proportional to the rubber content. The

size of rubber crumb also appears to have influence on

the strength. The coarse grading of rubber crumbs lower

the compressive strength than the finer grading [5–9].Even though the mechanical properties of concrete

seem to be downgraded by the presence of crumb rub-

ber, there are several other properties of concrete that

are beneficial. For example, concrete mixed with crumb

rubber up to about 30% by cement weight is found to

improve non-structure crack resistance, shock wave

absorption, resistance to acid, and also, lower heat con-

ductivity and noise level reduction. In addition, crumb

mailto:[email protected]

Fig. 1. (a) Piling yard of abandoned tires in Thailand and (b) fire accident due to wasted tires in Stanislaus county, CA.

P. Sukontasukkul, C. Chaikaew / Construction and Building Materials 20 (2006) 450–457 451

rubber concrete also exhibits lighter weight with density

reduced to about 77% and 87% as compared to conven-

tional concrete [9,10].

Thailand, with 10 million cars and the number one

producer of rubber products, is facing the same situa-

tion. The use of recycled tires is growing in Thailand,

although very slowly. A few grinding plants have startedin order to grind used tires into crumb rubber both for

export and local use. Large quantities of crumb rubber

are exported mainly to make rubber tile. The process

of making rubber tile is rather complicated and involves

large amounts of energy and chemical substances, which

make rubber tile expensive.

This study attempts to use crumb rubber as a partial

replacement of aggregate to produce concrete pavingblocks. By using cement as a binder and a conventional

cement block production process, the crumb rubber

concrete block is expected to be more durable, less

expensive (low material cost and easy to manufacture)

and absorb higher energy under impact.

2. Experimental procedure

2.1. Material properties and mix proportions

Materials used in this study consisted of cement

Portland type I, 3/800coarse aggregate, river sand, crumb

rubber (Fig. 2) and water. Two particle sizes of crumb

Fig. 2. Crumb rubber No. 6 and No. 20.

rubber were used: No. 6 (passing ASTM sieve no. 6)

and No. 20 (passing ASTM sieve No. 20), the properties

(specific gravity, fineness modulus and gradation) of

both crumb rubbers are as shown in Table 1 and Fig.

3. As for the mix proportion, the control specimen (no

crumb rubber) was set at 1:0.33:1.5:1.5 (cement: water:

coarse aggregate:fine aggregate).In the case of crumb rubber concrete, Three differ-

ent categories: (1) No. 6, (2) No. 20 and (3) Combined

No. 6 + 20 of crumb rubber were used to replace both

fine and coarse aggregates at equal amount of 10%,

and 20% by weight. Grading curves of the combined

aggregate + Crumb rubber are given in Fig. 4. Details

and assigned designations of each mix are given in

Table 2.As for the water content, because of the low specific

gravity and high specific surface area of rubber crumb,

the water requirement was higher than concrete with-

out rubber. In order to ensure the same consistency,

the water content was varied and controlled by mean

of the Vebe time (using the Vebe test). Using a Vebe

time of 26 ± 2 s for the control mix, the water require-

ment for each concrete–crumb rubber mix is as shownin Table 3.

2.2. Manufacturing concrete block

In this study, conventional block making was selected

as a manufacturing process. The process is quick and

Table 1

Properties of crumb rubber

Categories No. 6 No. 20 No. 6 + 20

Average bulk specific gravity 0.97 0.88

Average bulk specific gravity (SSD) 0.98 0.89

Average apparent specific gravity 0.98 0.89

Average absorption (%) 1.01 1.70

Finess modulus 4.98 2.62 3.77

0

20

40

60

80

100

0.101.0010.00Diameter (mm)

Per

cent

Fin

er B

yW

eigh

t

0

20

40

60

80

100

0.101.0010.00Diameter (mm)

Per

cent

Fin

er B

yW

eigh

t

No. 6 No. 20

0

20

40

60

80

100

0.101.0010.00Diameter (mm)

Per

cent

Fin

er B

yW

eigh

t

No. 6 +20

(a) (b)

(c)

Fig. 3. Gradation of crumb rubber.

452 P. Sukontasukkul, C. Chaikaew / Construction and Building Materials 20 (2006) 450–457

simple, and starts with placing the concrete into the

mold (Fig. 5(a)), compacting it under pressure (Fig.

5(b)), and finally removing the block for air curing (Figs.

5(c) and (d)). All blocks were air cured for 28 days prior

to the tests.

2.3. Testing program

Five different tests were carried out at the Depart-

ment of the Civil Engineering, King Mongkut Institute

of Technology-North Bangkok and consisted of: (1)

dry density test, (2) compression test, (3) flexural test,

(4) skid resistance (ASTM E303-93) and (5) abrasiontest (ASTM C944-95).

3. Experimental results

3.1. Dry density

Results on the dry density of concrete blocks (Fig. 6)indicated that the dry density decreased with the increas-

ing crumb rubber content. The lighter weight of the rub-

ber crumb concrete block was partly due to the lack of

aggregates which were replaced by crumb rubber.

Another reason could be from the flocculation of the

rubber particles during the mix of the concrete with

higher rubber contents. Flocculation was observed

mostly in the mix with 20% replacement, which it cre-

ated large voids inside the block, leading to a higher

porosity.

3.2. Compressive strength

Compressive loading responses of the crumb rubber

concrete blocks compared to the control are given in

Fig. 7. The compressive properties of concrete were af-

fected by both rubber content and crumb size. In terms

of strength and stiffness, both were found to decrease

with increasing crumb rubber content (Table 4 andFig. 7). However, in terms of toughness, the crumb rub-

ber concrete was found to be better than plain concrete

as seen by the larger specific energy density (Table 4)

and the longer post-peak response (Fig. 7). Fracture en-

ergy density (u) is referred to the fracture energy of

material per unit volume, it can be determined by divid-

ing the fracture energy (area under the load deflection

curve up to the point of failure) by the volume of thespecimen.

u ¼R

P ddV

; ð1Þ

where P is the applied load, d is the deformation and V

is the volume of the specimen.

0

20

40

60

80

100

0.1110Diameter (mm)

Per

cent

Fin

er B

yW

eigh

t

0

20

40

60

80

100

0.1110Diameter (mm)

Per

cent

Fin

er B

yW

eigh

t

610 620

0

20

40

60

80

100

0.1110Diameter (mm)

Per

cent

Fin

er B

yW

eigh

t

0

20

40

60

80

100

0.1110Diameter (mm)

Per

cent

Fin

er B

yW

eigh

t

2010 2020

62010 62020

0

20

40

60

80

100

0.1110Diameter (mm)

Per

cent

Fin

er B

yW

eigh

t

0

20

40

60

80

100

0.1110Diameter (mm)

Per

cent

Fin

er B

yW

eigh

t

(a) (b)

(c) (d)

(e) (f)

Fig. 4. Gradation of combined aggregate + crumb rubber at different percentages.

Table 2

Details and assigned designations of crumb rubber mix

Designation Rubber No. and percentage Cement (kg) Fine (kg) Coarse (kg)

#6 [kg (%)] #20 [kg (%)]

Control 0 0 1 1.5 1.5

610 0.075 (10) 0 1 1.425 1.425

620 0.15 (20) 0 1 1.35 1.35

2010 0 0.075 (10) 1 1.425 1.425

2020 0 0.15 (20) 1 1.35 1.35

62,010 0.038 (5) 0.038 (5) 1 1.425 1.425

62,020 0.075 (10) 0.075 (10) 1 1.35 1.35


Table 3

Water requirement for rubber crumb concrete block

Mix % Rubber Vebe times (s) Required w/c

Control 0 26 0.33

610 10 28 0.35

620 20 28 0.39

2010 10 25 0.45

2020 20 26 0.47

62,010 10 27 0.40

62,020 20 26 0.43

Fig. 5. Block making process.

Control10%

20%

0

0.5

1

1.5

2

2.5

Dry

Den

sity

(g

m/c

m3 )

ControlNo.6No.20No.6+20

Fig. 6. Dried density.

-

5

10

15

20

25

30

35

40

0.000 0.010 0.020 0.030 0.040 0.050

Strain

Stre

ss (

MP

a) 0%

10%

20%

#6 Crumb RubberConcrete Block

-

5

10

15

20

25

30

35

40

0.000 0.010 0.020 0.030 0.040 0.050

Strain

Stre

ss (

MP

a)

0%

10%

20%

#20 Crumb RubberConcrete Block

-

5

10

15

20

25

30

35

40

0.000 0.010 0.020 0.030 0.040 0.050

Strain

Stre

ss (

MP

a)

0%

10%20%

#6+20 Crumb Rubber Concrete

Fig. 7. Compressive loading response of crumb rubber concrete blocks.


Control10%

20%

0

1

2

3

4

5

6

7

8

Fra

ctu

re E

ner

gy

(N-m

)


Fig. 9. Fracture energy of crumb rubber blocks.

Table 4

Compressive strength and fracture energy density

Mix Strength (MPa) Fracture energy density (MPa)

Control 36.00 0.25

610 19.96 0.32

620 5.58 0.19

2010 19.08 0.35

2020 5.40 0.21

62,010 23.44 0.39

62,020 7.85 0.24

Control10%

20%

85

90

95

100

10 5

110

115

BP

N


Fig. 10. Skid resistance of rubber crumb concrete block.


It was suspected that by replacing high strength and

stiffness aggregate with a highly elastic material like rub-

ber, the strength of concrete decreased significantly,

while the toughness increased.

Comparing the three crumb rubber mixes, the con-

crete block made from rubber of mixed crumb size

(No. 6 + 20) seemed to perform better than those made

from a single crumb type. This was perhaps due to thebetter grading of the combined rubber which allowed

better compaction and higher density.

3.3. Flexural strength

The flexural responses of concrete block with and

without rubber crumb are given in Fig. 8. Similar to

the case of compressive response, the flexural strengthof crumb rubber concrete blocks was found to be smal-

ler than the plain concrete block. However, the re-

sponses were found to denote greater flexibility and

toughness with larger deflections at peak load, longer

post-peak responses and higher fracture energy.

The fracture toughness calculated from the area un-

der the load-deflection curve up the point of failure is

plotted in Fig. 9. At 10% replacement, the toughnessof crumb rubber concrete was found to be larger than

that of the control, even though the strength was lower.

This was due to the higher post-peak response. At 20%,

0

2

4

6

8

10

12

14

0 1 2 3 0 1

Loa

d (k

N) 0%

10%

20%

No. 6 Rubber Block

0

2

4

6

8

10

12

14

Loa

d (k

N) 0%

No. 20

DeflectiDeflection (mm)

Fig. 8. Flexural responses of

the fracture energy of crumb rubber blocks decreased

significantly due to the decrease in peak load. The larger

fracture toughness of crumb rubber concrete block

indicates that the block was able to absorb larger

2 3

10%

20%

Rubber Block

0

2

4

6

8

10

12

14

0 1 2 3Deflection (mm)on (mm)

Loa

d (k

N) 0%

10%

20%

No. 20 Rubber Block

crumb rubber blocks.

Fig. 11. Test set up for abrasion resistance.


quantities of energy after the peak load and prior to thefinal failure.

3.4. Skid resistance

Skid resistance was measured in accordance to

ASTM E303-93 using the pendulum type apparatus. Re-

sults (Fig. 10) indicated that the crumb rubber concrete

blocks exhibited better skid resistance than the controlblock (except for the blocks made with sieve No. 20

crumb rubber). The highly elastic properties of rubber

allowed the block surface to deform more and create

more friction as the pendulum passed across it. Mixes

with large rubber particle performed better than mixes

containing small particles.

3.5. Abrasion resistance

The abrasion resistance test was carried out in accor-

dance with the ASTM C944-95 method, with the assem-

bling shown in Fig. 11. The test began by setting up the

0

1

2

3

4

5

6

Control 10% 20%

% W

eig

ht

Lo

ss ControlNo.6No.20No.6+20

Fig. 12. Percent weight loss the specimen subjected to abrasion test.

specimen under the cutting roller; the roller was thenlowered down to the specimen surface and spun at the

rate of 200 rpm for 2 min. Abrasion resistance was mea-

sured in term of percent weight loss from the specimen

prior and after testing.

Results in terms of percent weight loss are shown in

Fig. 12. It was found that the rubber crumb concrete

block exhibited less abrasion resistance than the control

block, as indicated by increasing weight loss withincreasing crumb rubber content. Comparison between

the three rubber crumb mixes indicates that the com-

bined mix (No. 6 + 20) seemed to perform better than

the single particle size type. Even though the percent

weight loss of rubber crumb concrete block was higher

than that of concrete, the average percent weight loss

was still low (between 1% and 3% for 62010 and

62020, respectively).

4. Conclusions

� It is possible to manufacture concrete block

containing rubber crumb up to about 20% by

weight using a conventional plain concrete block

manufacturing processes. The resulting blocks,though not as strong as plain concrete block, are

lighter and seem to be more flexible with better

energy absorption.

� The performances of concrete block are affected dif-

ferently depending on the type and content of the

rubber particle. In the case of mechanical properties,

both compressive and flexural strength are found to

decrease with rubber content, while the toughnessincreases.

� Skid resistance increases with rubber content. Large

rubber particles seem to provide better skid resis-

tance. In addition, crumb rubber concrete exhibited

less abrasion resistance that plain concrete.


Acknowledgments

The authors thank the Metal and Material Technol-

ogy Center (MTEC) for providing financial support

and Union Pattanakit Co., Ltd. for providing crumb

rubber.

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Documents

Properties of concrete pedestrian block mixed with crumb rubber