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7th International Conference on Euro Asia Civil Engineering Forum IOP Publishing
IOP Conf. Series: Materials Science and Engineering 615 (2019) 012119 doi:10.1088/1757-899X/615/1/012119

The use of crumb rubber for replacing fine aggregate in cold

mixture asphalt

P S Wulandari1 and D Tjandra2

1,2
Civil Engineering Department, Petra Christian University

E-mail: paravita@petra.ac.id

Abstract. In order to consider the environmental impact, this study investigated the effect of
crumb rubber on the mechanical performance of cold mixture asphalt. Crumb rubber was
obtained from the process of recycling waste tires, which this waste material becomes a major
environmental problem due to the rapid increase in the number of motor vehicles in Indonesia.
Cold mixture asphalt is an environmental friendly option on flexible pavement, which reduces
energy consumption because it does not need heat during the process as in hot mixture asphalt.
In this study, laboratory tests were conducted for Dense Graded Emulsion Mixture Type IV.
The first stage in this study was to perform laboratory experiments on compacted mixture to
determine the optimum residual bitumen content. In the next stage, a series of tests on crumb
rubber mixtures were conducted in the optimum residual bitumen content condition to
investigate the effect of crumb rubber as a partial replacement of fine aggregate. Fine aggregate
in cold mixture asphalt was replaced with 50% of crumb rubber. Three different sizes of crumb
rubber, 20 mesh (0.841 mm), 40 mesh (0.42 mm) and 60 mesh (0.25 mm), were applied in a
series of laboratory experiments. Tests were done using Marshall Test equipment to obtain the
mechanical performance of cold mixture asphalt. The finding indicated that finer crumb rubber
produced higher stability than the larger size of crumb rubber. Even though the use of crumb
rubber decreased stability of mixtures, it still met the minimum specified requirement of cold
mixture asphalt. The stability of the crumb rubber cold mixtures were also comparable to hot
mixture asphalt. Replacement of fine aggregate with crumb rubber on cold mixture asphalt is
expected to overcome the environmental problems by reuse the waste materials to preserve the
natural aggregates.

1. Introduction
In Indonesia, hot mix asphalt (HMA) is the most commonly used as asphalt pavement on new roads,
overlays, and pavement patching. HMA needs high quality of aggregate to produce life-long
pavement, such as tough and abrasion resistant aggregates. In some areas in Indonesia, to produce the
specified HMA, the aggregates are often supplied from other area, which needs more cost and time.
Compared to cold mixture asphalt (CMA), HMA also consumes more energy to heat the mixture. As
the car tyres become a major global waste problem, it needs more attention on the use of recycled car
tyres in the pavement design. The end product of recycled car tyres which is crumb rubber has various
sizes depending on the diameter of the crumbs. Crumb rubber is made from selected waste tire which
no longer be contaminated by steel wire or nylon.
For the environmental impact, the use of CMA, local aggregate and alternative waste material
beside natural aggregate in asphalt mixture could be considered. The use of crumb rubber as waste
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution
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Published under licence by IOP Publishing Ltd 1
7th International Conference on Euro Asia Civil Engineering Forum IOP Publishing
IOP Conf. Series: Materials Science and Engineering 615 (2019) 012119 doi:10.1088/1757-899X/615/1/012119

material tends to increase the strength of asphalt mixture [1]. Volumetric and mechanical properties of
asphalt mixtures were affected by rubber gradation and percentage [2]. The objective of this study was
to investigate the effect of crumb rubber size on performance of cold asphalt mixtures.

2. Materials description and testing procedures

2.1. Materials
CMA in this study used cationic slow setting asphalt emulsion (CSS1-h) produced by Triasindomix
company. Table 1 shows the properties and specifications of asphalt emulsion CSS-1h. The asphalt
content of the emulsion was 63.46%. The aggregate used in this study was supplied from Banyuwangi
quarry, East Java, Indonesia. Several laboratory tests were conducted to determine the properties of
aggregate. Table 2 shows the physical properties and specifications of aggregates and meet the
specifications. Fly ash Type C as filler material was taken from PLTU Paiton. Filler material passed
through a 0.075 mm sieve (No. 200). This study incorporated crumb rubber produced by Pura Agung
Company in three variations of sizes. The higher the mesh size, the smaller the crumb. In this study,
crumb rubber with mesh size #20 (0.841 mm), #40 (0.42 mm), #60 (0.25 mm) were incorporated into
CMA as a replacement material of fine aggregates.

Table 1. Properties and specifications of asphalt emulsion CSS-1h.

Properties Units Method Results Specifications
Test on Emulsions
Viscosity, Saybolt-
second SNI 03-6721 23.275 20-100
Furol at 25° C
Storage stability, 24
% SNI 03-6828 0.33 1 max.
hours
Particle charge - SNI 03-3644 Positive Positive
Sieve test, retained on
% SNI 03-3643 0.00 0.10 max.
No. 20
Distillation
Residue % SNI 03-3642 63.46 57 min.
Test on Residue from Distillation test
Penetration at 25° C, 0.1
SNI 06-2456 51.60 40-90
100g, 5 sec mm
Ductility at 25° C, 5
cm SNI 06-2432 107 40 min.
cm/min
Solubility in
% SNI 06-2438 98.992 97.5 min.
trichloroethylene

2.2. Sample preparations and mix designs

This study was conducted on two stages. First stage performed the mix design to determine optimum
bitumen content. Second stage was to investigate the effect of crumb rubber size on performance of
cold asphalt mixtures.
In this study, one type of aggregate was used as coarse and fine aggregate. The aggregate gradation
for mix design was selected according to Dense Graded Emulsion Mixtures (DGEM) Type IV
Specification. The aggregate gradation is given in table 3 and figure 1 shows that the aggregate
gradation is within the limits according to the specification limits of the Department of Public Works
of Indonesia [3]. In order to improve CMA at the early ages strength of the mixtures, fly ash as filler
material (2% by weight of total aggregates) was used in all mixtures.

2
7th International Conference on Euro Asia Civil Engineering Forum IOP Publishing
IOP Conf. Series: Materials Science and Engineering 615 (2019) 012119 doi:10.1088/1757-899X/615/1/012119

Table 2. Physical properties of aggregates.

Properties Units Results Specifications
Method
F1 F2 F3
Specific gravity, bulk - 2.534 2.772 2.523 -
Specific gravity, SSD - 2.580 2.820 2.548 -
Specific gravity,
- 2.644 2.908 2.587 -
apparent
Water absorption % 1.650 1.680 0.977 3 max.
Los Angeles Abrasion % SNI 2417 36.04 38.66 - 40 max.

Table 3. Aggregate gradations for DGEM type IV.

Coarse Medium Fine
Filler
Aggregate Aggregate Aggregate Combined
Sieve size (Fly Ash Specifications
(F1) (F2) (F3) Aggregate
Type C)
10-15 mm 5-10 mm 0-5 mm
No mm 23% 32% 43% 2% 100% DGEM Type IV
3/4" 19 23.00 32.00 43.00 2.00 100.00 100
1/2" 12.5 14.16 32.00 43.00 2.00 91.16 90-100
4 4.75 0.39 11.73 42.75 2.00 56.88 45-70
8 2.36 0.35 2.68 35.39 2.00 40.43 25-55
50 0.3 0.00 1.56 11.53 2.00 15.09 5-20
200 0.075 0.00 1.09 4.81 2.00 7.90 2-9

Figure 1. Aggregate gradation for design mixtures.

In order to determine the optimum bitumen content (OBC), mix designs were done in various
emulsion content based on calculation as in equation (1) and equation (2) from the Asphalt Institute
[4]. The initial emulsion content was determined as 9% by mass of total mixture.
P = (0.005A+0.1B+0.5C) x 0.7 (1)
where:
P = initial residual asphalt content by mass of total mixture (%)

3
7th International Conference on Euro Asia Civil Engineering Forum IOP Publishing
IOP Conf. Series: Materials Science and Engineering 615 (2019) 012119 doi:10.1088/1757-899X/615/1/012119

A = percentage of aggregate retained on the 2.36 mm (No. 8) sieve

B = percentage of aggregate passing the 2.36 mm (No. 8) sieve and retained on the 0.075 mm
(No. 200) sieve
C = percentage of aggregate passing the 0.075 mm (No. 200) sieve
IEC = (P/X) (2)
where:
IEC = initial emulsion content by mass of total mixture (%)
X= percentage of bitumen content in the emulsion

The mixing process was conducted as following procedures. Prepare the oven-dried proportioned
aggregate as in table 3. The dried aggregate then was pre-wetted with 2% water at the beginning of the
mixing process. Five different bitumen emulsion content were determined as 8%, 8.5%, 9%, 9.5%,
and 10% by mass of total mixture. The determined emulsion content was then added to the aggregates.
Compactions of the DGEMs were done by applying 75 blows to each end using Marshall Compactor.
The DGEMs then cured in oven at 40°C for 24 hours. Then, Marshall Test was conducted to
determine the optimum bitumen content and Marshall properties.

3. Results and discussion

Table 4 shows the Marshall, stability and flow test results of fifteen specimens, three specimens were
prepared at each bitumen content. The OBC was chosen as the percentage of bitumen content at which
the CMA properties meet the specifications of DGEM Type IV as shown in table 4. The OBC was
determined considering the maximum soaked stability mixture which was at 8% by mass of total
mixture [5], as shown in figure 2. The values of VMA and VFB in all mixtures also meet the general
requirements as in specification of HMA, although VMA and VFB are not specified in CMA.

Table 4. Properties of the DGEM Type IV.

Bitumen content (%)
Properties Units Specifications
8 8.5 9 9.5 10
Soaked Stability kg 1294.045 1109.841 1155.202 1153.555 1070.673 300 min.
Void in Mixture
% 6.810 6.724 7.411 8.022 7.141 5 – 10
(VIM)
Void in Mineral
% 22.402 23.286 24.786 26.199 26.406 -
Aggregate (VMA)
Void Filled with
% 69.646 71.213 70.387 69.448 73.165 -
Bitumen (VFB)
Asphalt Film
µm 15.757 16.931 18.118 19.318 20.532 8 min.
Thickness (AFT)

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7th International Conference on Euro Asia Civil Engineering Forum IOP Publishing
IOP Conf. Series: Materials Science and Engineering 615 (2019) 012119 doi:10.1088/1757-899X/615/1/012119

(a) (b)
Figure 2. Relationships of stability (a) and VIM (b) with variation of bitumen content.

Crumb rubber asphalt mixtures were prepared at optimum bitumen content. In order to incorporate
crumb rubber into the CMA, a 50% by weight of fine aggregate was replaced with an equal volume of
each size of crumb rubber. All factors in mixtures were keeping constant.

(a) (b)
Figure 3. Effect of curing time on soaked stability (a) and VIM (b) of crumb rubber asphalt mixtures.

The stability increased with an increase in curing time, as shown in figure 3 because CMA required
longer curing times. Although the use of recycled crumb rubber reduced the stability of CMA, but still
met the minimum requirement as in standard specification. The finer crumb rubber in the CMA
mixtures produced the higher stability. The finer crumb rubber (#60) in CMA also produced the
required value of Void in Mixture (VIM) as in standard specification. In this study showed that the
finer crumb rubber produced less void in mixtures, which is closely related to durability of mixtures.
In general, the finer crumb rubber as fine aggregate replacement in CMA had better properties than
the larger sized crumb rubber. Also, the mixtures had a good comparison to HMA specification, as
HRS-A and AC-WC, as shown in table 5. Therefore, crumb rubber modified CMA can be used as
flexible pavement, which does not need heat during the process and the use of recycling of waste tires,
also give contribution to the protection of environment.

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7th International Conference on Euro Asia Civil Engineering Forum IOP Publishing
IOP Conf. Series: Materials Science and Engineering 615 (2019) 012119 doi:10.1088/1757-899X/615/1/012119

Table 5. Comparison of mixtures to HMA specifications.

7 days of curing Specifications
Properties DGEM
NO CR #20 #40 #60 HRS-A1 AC-WC2
Type IV
Soaked Stability (kg) 1277.211 522.832 654.568 903.820 300 min. 450 min. 800 min.
VIM (%) 6.917 10.906 11.957 8.220 5 - 10 4-6 3-5
VMA (%) 22.484 25.806 26.681 23.569 - 18 min. 15 min.
VFB (%) 69.282 57.785 55.219 65.124 - 68 min. 65 min.
Flow (mm) 4.572 8.213 7.281 8.043 - 3 min. 2-4
Retained Stability
90.347 91.439 79.874 89.189 50 min. 75 min. 75 min.
(%)
Note: 1Hot Rolled Sheet Wearing Course (HRS-A); 2Asphalt Concrete Wearing Course (AC-WC)

4. Conclusions
From this study, it can be recommended that crumb rubber can be incorporated into CMA as a
replacement material of fine aggregates. It has been shown that at 50% crumb rubber replacement, the
CMA with crumb rubber had stability that meet the standard specification. The finer crumb rubber in
the CMA mixtures produced the higher stability. The finer crumb rubber (#60) in CMA also produced
the required Void in Mixture (VIM) as in standard specification. Replacement of fine aggregate with
crumb rubber on CMA is expected to overcome the environmental problems by reuse the waste
materials to preserve the natural aggregates.

Acknowledgement
The authors gratefully acknowledge the laboratory works and data collection performed by Kevin
Ronaldo Gotama and Yoel Wuisan.

References
[1] Wulandari P S and Tjandra D 2017 Use of Crumb Rubber AS An Additive in Asphalt Concrete
Mixture Proc. Engineering vol 171 pp 1384 – 1389
[2] Pettinari M and Simone 2015 A Effect of crumb rubber gradation on a rubberized cold recycled
mixture for road pavements Materials & Design 85 598 – 606
[3] Directorate Generals of Highways 1991 Specifications of Cold Asphalt Emulsion Mixtures
(Public Works Department Jakarta)
[4] Asphalt Institute 1989 Asphalt Cold Mix Manual (MS – 14) Third Edition (USA: Lexington)
[5] Thanaya INA 2007 Review and Recommendation of Cold Asphalt Emulsion Mixtures (CAEMs)
Design Civil Engineering Dimension 9(1) 49 – 56