International Journal of Scientific & Engineering Research, Volume 6, Issue 4, April-2015 39
ISSN 2229-5518
Improvement of Mechanical Properties of Asphalt Concrete Surface Course Mixtures Using Yellow Sulfur
Nibras A. Hussain AL-Sahaf
Index Terms— Marshall Stability, Hot mix asphalt, yellow sulfur, and Asphalt concrete.
—————————— ——————————
PECIFIC requirements are needed to control the quality of highway pavement materials to improve its durability es- pecially for the roads suffer from heavy trafficked, high temperatures and water damages. It is worthy to say that in Iraq, the main deterioration in roads happens because of very high temperatures and extreme lack of solar isolation during
summer.[1]
Generally, Sulfur is added to asphalt cement as a replacement of the weight of the later to generate the new binder which is called asphalt cement-sulfur. The aim of this study is to inves- tigate the performance of asphalt concrete mixtures produced by using asphalt cement-sulfur binder.
Asphalt cement is a widely used binding material for roads construction. Many materials such as polymers, carbon black and sulfur used to be blended with asphalt cement to improve certain properties of the pure asphalt cement as well as the produced asphalt concrete mixture. One of the main challenge when adopting asphalt cement-sulfur binder is the increment of the total cost of the final product, therefore an economic analysis is required before commercial use becomes a reality. Block styrene-butadiene elastomer, known as block SB rubber and block SBS rubber as well, is utilized to improve the prop- erties of asphalt cement and asphalt concrete treated mixtures. The treated mixtures generally display better physical proper- ties in comparison with untreated mixtures. The main re- striction to use the block SB elastomer in paving applications is the high cost. Therefore, sulfur is recommended to modify asphalt cement as an economic option which is traditionally
prepared from a comparatively inexpensive sulfur.[2]
The aggregate, asphalt cement, Portland cement (as min- eral filler) used in current study were conventionally used in roads paving materials in Iraq. Furthermore, yellow sulfur is utilized as replacement of asphalt cement with different per- centages by weight of asphalt cement.
The aggregate used in this study was crushed aggregate. The aggregate was divided into coarse aggregate ranges from (25.4mm) to (4.75mm) while fine aggregate ranges between (4.75mm) to (0.075mm) according to S.O.R.B specification [R9]. Table (1) shows the physical properties of aggregate while Table (2) presents the gradation of the aggregate which is cor- responding to the limits of grading requirements for asphalt mixtures that is used in the surface coarse construction accord- ing to S.O.R.B. specification.
Portland cement was used in this study as filler. Table (3)
shows the physical properties of the Portland cement.
The asphalt cement used in this study was of grade (40-
50) Penetration brought from Al-Nasiriya refinery. Table (4)
presents the physical properties and the tests of the asphalt cement.
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Sulfur forms polyatomic molecules with different chemical formulas, with the best-known allotrope being octasulfur, cy-
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International Journal of Scientific & Engineering Research, Volume 6, Issue 4, April-2015 40
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clo-S8. Octasulfur is a soft, bright-yellow solid with only a faint odor, similar to that of matches. It is melting point and boiling point are 115.21 °C and 444.6 °C, respectively and sub- limes easily. Between its melting and boiling temperatures, octasulfur changes its allotrope again, turning from β- octasulfur to γ-sulfur, again accompanied by a lower density but increased viscosity because of the formation of polymers.
The bulk density is determined in accordance with the method described in ASTM D2726 [8] . The weight of the spec- imen is measured in air, in water at 25°oC and in condition of saturated surface dry condition (SSD). The bulk density in (g/cm3) is the calculated as follows:
At even higher temperatures, however, the viscosity decreases
as de-polymerization occurs. Molten sulfur assumes a dark
red color above 200 °C. The density of sulfur is about 2 g.cm-3, depending on the allotrope; all of its stable allotropes are ex- cellent electrical insulators.[3] Eight percentages were used in
Gmb = WA
WB − WC
where:
..............(1)
preparing modified binder as a replacement of the asphalt
cement i.e. 5, 10, 15, 20, 25, 30, 35 and 40% by weight of asphalt
cement.
The amount of sulfur was determined by multiplying it's percent by the total weight of asphalt cement. As mentioned previously, eight percentages of sulfur were added to prepare the hot mixtures. The asphalt cement with the required weight was heated in an oven at 150 oC, then the required amount of sulfur was added as quickly as possible i.e. 10 sec. then, they were mixed thoroughly
Gmb = Bulk density of the compacted specimen.
WA = Weight of specimen in air (gm).
WB = Weight of saturated surface dry (SSD) specimen (gm).
WC = Weight of specimen in water (gm).
The percentage of Air voids and maximum specific gravity were performed in accordance with standard test method of ASTM D204[8]. The maximum specific gravity and air voids can be calculated as follows:
keeping the temperature constant at 150 oC. After that the required amount of modified asphalt cement was added to the preheated
Max. S.G. at 25°C=
WA
W − W
..............(2)
aggregate and filler in the mixing bowl. The materials were mixed comprehensively within the required limits i.e. 145-155 oC until all aggregates and filler particles were completely coated with modi- fied binder. Each asphalt mixture was placed in the preheated mold and then spaded vigorously with the preheated spatula 15
VTM (%) =
where:
A
S.G. − Gmb
S.G.
C
*100
..............(3)
times around the perimeter and 10 times in the interior. Then 75
blows on the top and bottom of the specimen were applied with
the standard compaction hammer. The specimens were left in mold to be cooled at room temperature for 24 hours and then it was extruded from the mold. Three Marshall specimens were pre- pared at each asphalt content. Therefore, 15 specimens were pre-
pared for each control and modified mixtures.
Marshall Specimens were prepared with various asphalt ce- ment content i.e. 4-6% and tested to determine Marshall and
Gmb = Bulk density of the compacted specimen (gm/cm3). WA = Weight of specimen in air (gm).
WC = Weight of specimen in water at 25oC (gm). S.G. = Maximum specific gravity.
VTM = Voids in total mix.
The percentage of the Voids Filled with Asphalt VFA char- acterizes the effective asphalt cement in compacted mixtures as percent of the Voids in Mineral Aggregate VMA. It can be calculated as below:
VMA(%) − VTM (%)
volumetric Properties. The procedure used for determining
these properties are as follows:
VFA(%) =
where:
VMA(%)
*100
..................(4)
Marshall Stability and flow test is performed on each speci- men in accordance with the procedure described by ASTM D
1559[8]. Marshall Stability represents the resistance to the plas- tic flow of bituminous mixture using Marshall apparatus with Electronic recording system. The specimen is placed in water bath at 60 °C for (30-40) min. The Marshall Stability value is the maximum load in (KN), while the Marshall flow is the to- tal displacement or strain corresponding's to the maximum load during the stability test.
VTM = voids in total mix.
VMA = voids in meniral aggregate.
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The optimum asphalt content of the various mixtures was determined from Marshall property curves (stability, bulk density, and air voids in total mix). It represents the numerical average of the percentages of binder content corresponding to the maximum Marshall stability, maximum bulk density, and medium range of voids in total mix. The Asphalt Institute [9] recommends this procedure
Marshall stability (MS) of control and modified mixtures with different percentages of sulfur and different asphalt ce- ment contents are shown in Figure (1). It is clearly shown that the stability values for different mixtures are following the typical trend in their relation with different asphalt cement content i.e. MS values increase with asphalt cement content increment until reaching a maximum value then MS trends to decrease.
On the other hand, MS for the same asphalt cement content and with different modified binder is higher than those pre- pared with untreated binder. In addition, it can be indicated that MS values increased with sulfur content increased until
30% after this point MS values decreased slightly. The largest MS value was occurred for mixtures with 5% binder content and 30% sulfur (12.85 KN) which represents almost 52% more than those for untreated mixtures (8.5 KN).
Generally, MS of a mixture depends on internal friction and
cohesion. Inter particle friction i.e. internal friction among the
aggregate particles based on the characteristics of aggregate
such as surface texture and shape. While cohesion is related to the bending ability of the binder[10]. Therefore MS increase for the modified asphalt concrete mixtures can be contributed to improve the workability of the mixture with sulfur particles addition as well as increase the cohesion between the aggre- gate and the modified binder. Kam [3] reported that MS of the comparative paving mix compounds had almost 10,000 KN when 6% by weight of asphalt cement was added in the mix. Accordingly and depending on the improvement in MS value due to yellow sulfur addition it can be reported that adopting the modified binder should provide paving compositions hav- ing a reduced tendency to become rutted.
Figure (2) shows the influence of addition of sulfur on Mar- shall flow with different asphalt cement contents. It is clearly shown that Marshall flow for the control and modified mix- tures increased with asphalt cement content increment. Fur- thermore, modified mixtures i.e. asphalt mixtures prepared with asphalt cement sulfur binder, exhibited lower Marshall flow values in comparison with control mixtures. Finally, Marshall flow decreased when sulfur content increased.
The relationship between the bulk density values of different asphalt concrete mixtures i.e. control and modified mixtures and binder content is shown in Figure (3). It is clearly shown
that the trend of the modified mixtures is similar to those of the control mixtures as the bulk density increased with binder content increment until reached the maximum value, 5%, after which the bulk density decreased. On the other hand and for the same binder content, the bulk density for the control mix- tures is higher than those for the modified mixtures. This re- duction of the bulk density of the modified mixtures can be contributed to the low specific gravity of the yellow sulfur.
The relationship between voids in total mix and binder con-
tent for treated and control mixtures is presented in figure (4). The VTM percentage decreased with binder content increase which is common in asphalt concrete mixtures. In addition, it can be reported that the VTM percentage for modified mix- tures is lower than those of untreated mixtures for different asphalt cement content. Generally, mixtures' workability and compaction efficiency increased due to addition of sulfur for modified mixtures, therefore the VTM percentages increased.
Figure (5) illustrates the relationship between voids filled with asphalt (VFA) percentage and binder content for control and modified mixtures. Generally, it can be reported that VFA percentage increased with the increase of binder content. For the same asphalt cement content, VFA percentage of modified mixtures is more than those of control mixtures. The high VFA percentage can be explained as the modified mixtures have high VTM percentage in comparison with untreated mixtures. As for the same asphalt cement content, VTM percentage de- crease leads to increase of VFA percentage.
The optimum binder content for control mixtures is 5.0%
while for the modified mixtures are 5.15, 5.12, 5.11, 5.08, 5.06,
5.04, 5.01 and 5.0% for asphalt concrete mixtures with 5, 10, 15,
20, 25, 30, 35 and 40% sulfur (by weight of asphalt cement), respectively. There is a small difference in the optimum binder content between untreated and treated mixtures. This differ- ence is within S.O.R.B tolerance (±0.15%). Therefore, it can be considered that the optimums binder content for modified mixtures is 5.0%.
Figure (6) shows the effect of sulfur content percent on Mar- shall stability at optimum binder content for control and mod- ified mixtures. MS values increased with sulfur content in- crease until 30% addition of sulfur then MS values decreased. From this Figure, it can be reported that Marshall stability for different mixtures are above the requirement adopted by S.O.R.B specification for asphalt concrete mixtures for surface course (8.4 KN).
On the other hand, Figure (7) illustrates the influence of addi- tion of sulfur on Marshall flow at optimum binder content for treated and untreated mixtures. It can be stated that Marshall flow values for different mixtures are within the range speci- fied by S.O.R.B. specification for the asphalt concrete mixtures suitable for surface course (2-4mm). In addition, all treated mixtures exhibit low values of Marshall flow when compared with untreated mixtures.
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International Journal of Scientific & Engineering Research, Volume 6, Issue 4, April-2015 42
ISSN 2229-5518
Firstly, Figure (8) illustrates the influence of sulfur content
on VTM at the optimum binder content i.e. 5%. Generally, it can state that VTM values for all mixtures are within the re- quirement that specified by S.O.R.B. for surface course asphalt concrete mixtures (3-6%). In addition, it is clearly shown that VTM percentage decreased with sulfur content increase that can be contributed to the role of sulfur to fill the voids in the mixtures.
Secondly, the effect of sulfur addition on the VFA at optimum binder content is shown in Figure (9). From this Figure, VFA percentage for the modified mixtures increased with increas- ing of sulfur content and all the results of modified mixtures are within the specification adopted by S.O.R.B for surface course mixtures (65-85%).
The main conclusions from these laboratory studies can be listed as below:
• Addition of yellow sulfur to the asphalt cement increase mixture workability and compaction efficiency for modi- fied mixtures.
• The same behavior of Marshal properties for modified mix- tures in comparison with untreated mixtures is revealed.
• There is no significant difference in optimum binder con- tent between control and modified mixtures.
• Marshall properties i.e. MS, Marshall flow, and volumetric properties i.e. bulk density, VTM and VFA for modified mixtures comply with the S.O.R.B requirements for surface course mixtures.
• By means of MS, adding 30% of sulfur leads to maximum improvement in MS values. While, Marshall flow and VTM decrease with increasing yellow sulfur percentage.
[1] Salim J. Sulaiman, Emad A. Ismail., Nagham N.AL-Zadi ''Improving Bitumen Properties by the Use of Scrap Tires Rubber'', Journal of Engineering and Devel- opment, volume IV-No.1, March 2000.
[2] Moran, U.S. Patent, 4, 863, 233, September 1989.
[3] Kam, Zanzotto, and Ludo, U.S. Patent, 5, 302, 638, April 12, 1994.
[4] Goodrich J.L., Statz R.J., U.S. Patent, 5, 306, 750, April 26, 1994.
[5] Gorbaty, MartinL, Nahas, and Nicholas, 5, 336, 705, Agust 9, 1994.
[6] State Organization of Roads and Bridges (SORB),'' Standard Specification for
Roads and Bridges'', Republic of Iraq, Ministry of Housing and Construction, De- partment of Design and Studies, Baghdad, 1983.Addendum No.1,1984, Ad- dendum No. 2, 1989.
[7] State Organization of Roads and Bridges (SORB),'' Standard Specification for
Roads and Bridges'', Republic of Iraq, Ministry of Housing and Construction, De-
partment of Design and Studies, Baghdad, 2003.
[8] ASTM Standard,''Road and Paving Materials; Traveled surface Characteristics'',
Annual Book of American Society for Testing and Materials Standard, Section 4, Vol.
0403, 2003.
[9] The Asphalt Institute,'' Mix Design Method for Asphalt Concrete and Other Hot
Mix Types'', Manual Series, No.2 (MS.2), U.S.A, May 1984.
[10] Heukelom, W.,'' A Bitumen Test Data Chart for Showing the Effect of Tempera-
ture on the Mechanical Behavior of Asphaltic Bitumen's,'' Journal of Institute of
Petroleum, Vol. 55, No. 546, 1969.
TABLE 1
PHYSICAL PROPERTIES OF AGGREGATE
Property | Coarse aggregate | Fine ag- gregate |
Bulk specific gravity (ASTM C127&C128) | 2.646 | 2.63 |
Apparent specific gravi- ty(ASTM C127&C128) | 2.656 | 2.667 |
Percent water absorption (ASTM C127&C128) | 0.14 | 0.523 |
TABLE 2
AGGREGATE GRADATION FOR SURFACE LAYER ACCORDING TO
S.O.R.B [7]
Sieve size(mm) | Passing% |
19.0 (3/4 in) | 100 |
12.5 (1/2 in) | 90 - 100 |
9.5 (3/8 in) | 76 - 90 |
4.75 (No. 4) | 44 - 74 |
2.36 (No. 8) | 28 - 58 |
0.3 (No. 50) | 5 - 21 |
0.075 (No. 200) | 4 - 10 |
TABLE 3
PHYSICAL PROPERTIES OF FILLERS
Property | Portland Cement |
Passing sieve No. 200, (%) | 94.76 |
Specific gravity (ASTMC188-95) | 3.05 |
TABLE 4
PHYSICAL PROPERTIES OF THE SELECTED ASPHALT CEMENT
TABLE 5
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PHYSICAL PROPERTIES OF YELLOW SULFUR
Property Yellow sulfur Phase Solid, powder Density Alpha 2.07 gm/cm3
Density Beta 1.96 gm/cm3
Density Gamma 1.92 gm/cm3
Liquid density 1.819 gm/cm3
Melting point 388.36 K, 115.21 Co, 239.38 oF Boiling point 717.8 K, 444.6 Co, 832.3 oF Critical point 1314 K, 20.7 MPa
Heat of fusion (mono) 1.727 kJ/mol Heat of vaporization (mono) 45 kJ/mol Molar heat capacity 22.75 J/mol.K
Vapor
pressure
P
(Pa) 1
At T
(oC) 101.8
Bulk modulus
Fig. 1. Marshal Stability curves for control mixes and modified mixes
Fig. 2. Marshal Flow curves for control mixes and modified mixes
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Fig. 3. Bulk Density curves for control mixes and
modified mixes
Fig. 4. Voids in total mix curves for control mixes and modified mixes
Fig. 5. Voids Filled with asphalt curves for control mixes and modified mixes
Fig. 6. The relationship between Stability and yellow sulfur percent
Fig. 7. The relationship between Flow and yellow
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sulfur percent
Fig. 8. The relationship between %voids in total mix and yel- low sulfur percent
Fig. 9. The relationship between %voids filled with asphalt and yellow sulfur percent
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