mechanical properties of modified asphalt concrete

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), INTERNATIONAL JOURNAL OF CIVIL ENGINEERING ISSN 0976 – 6316(Online), Volume 5, Issue 5, May (2014), pp. 61-68 © IAEME AND TECHNOLOGY (IJCIET) ISSN 0976 – 6308 (Print) ISSN 0976 – 6316(Online) Volume 5, Issue 5, May (2014), pp. 61-68 © IAEME: www.iaeme.com/ijciet.asp Journal Impact Factor (2014): 7.9290 (Calculated by GISI) www.jifactor.com

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MECHANICAL PROPERTIES OF MODIFIED ASPHALT CONCRETE MIXTURES USING CA(OH)2 NANOPARTICLES Farag Khodary*1,

M.S. Abd El-sadek2,

H.S. El-Sheshtawy3

1

3

Civil Engineering Department, Faculty of Engineering, South Valley University, Qena, Egypt Nanomaterials Lab., Physics Department, Faculty of Science, South Valley University, Qena, Egypt 2 Chemistry Department, Faculty of Science, South Valley University, Qena, Egypt

ABSTRACT Increasing the traffic volume and the tire pressure raise the need to use new bitumen blend to pave the roads in heavy traffic area. Conventional bitumen has a limited capacity under wide range of loads and temperatures, which occur over the life of the pavement. Therefore, conventional bitumen needs to be modified to face the heavy loads and weather change. Nanomaterial, which have high surface to volume ratio, is recently used as bitumen modifier. Here, conventional bitumen were used with AC (60/70) penetration grade, modified by Ca(OH)2 nanoparticles at five different modification percentage namely 1%, 2%, 3% 4%, and 5%. Penetration, viscosity, softening point, indirect tensile strength and compressive strength tests were performed. The physical and mechanical properties of Ca(OH)2 modified bitumen were successfully enhanced, in particular 5% Ca(OH)2 nanoparticles was the optimum percentage. The 5% Ca(OH)2 modified bitumen decrease the tensile strength and increases the compressive strength for all asphaltic mixtures. Keywords: Asphalt Modifier, CA(OH)2 Nanoparticles, Highway Construction, Sol-Gel Method, Physical and Mechanical Properties. 1. INTRODUCTION Bitumen is refined from crude oil and has to meet certain specifications for pavement and industrial purposes [1]. Bitumen is a visco-elastic material, where temperature and rate of load application have a great influence on the performance. The visco-elastic behaviour of asphalt leads to pavement distress. For example, at high temperatures and traffic loading asphalt is not able to maintain its original shape. This process leads to permanent deformation (Rutting). On the other hand, at low temperatures asphalt gets brittle and tends to crack as a result of the stiff structure. Unmodified bitumen lacks the balance between the visco-elastic and the increase of the traffic volume. In addition, over the life of a pavement unmodified bitumen has limited capacity at wide 61

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 5, May (2014), pp. 61-68 © IAEME

range of loads and temperature [2]. Therefore, binders were modified to face the load and weather challenges. Modified bitumen introduces real some advantages to the field of highway construction, by improving pavement performance as well as extent the pavement life [3,4]. Recently, nanomaterials are widely used in the filed of highway construction as modifiers. Using nano-size bypass was used as asphalt modifier, which found to increase compressive strength, penetration, and softening point and decreases the tensile strength [5]. The 5% styrene butadiene styrene (SBS) and 2% SiO2 nanopowder can increase the physical and mechanical properties of asphalt binder and mixtures [6-9]. On the other hand, the small amounts of nano-clay enhance stiffness, tensile strength, tensile modulus, flexural strength and modulus thermal stability. The elasticity of the nano-clay modified bitumen is much higher than unmodified bitumen [10,11]. In the present work, we extended our previous study [12] and used Ca(OH)2 nanoparticles as bitumen modifier. Different tests for the prepared bitumen Ca(OH)2 blend were measured. These tests include both the physical and the mechanical properties of the modified bitumen and mixtures. 2. MATERIALS AND METHODS All materials used in this work include aggregate, sand, mineral filler; bituminous materials were used without further purifications. The used bitumen was Asphalt Cement (60/70) penetration grade and obtained from Suez Refinery Company, Egypt. Ca(OH)2 nanoparticles were prepared by the addition of 1 M NaOH to CaCl2.2H2O (20 gm) under vigorous steering for 2 h at 90 °C. The obtained white precipitate was washed several times with distillated water and kept in the oven for 2 h at 120 °C. Then the material was grounded in a mortar machine. The following blending protocol was used to modify bitumen materials with Ca(OH)2 nanoparticles [13]. The unmodified bitumen was heated in an oven at a temperature of at least 140 °C and five different modification levels namely 1%, 2%, 3% 4% and 5% by weight of the bitumen were added to the unmodified bitumen. More than 5% of Ca(OH)2 nanoparticles produce heterogeneous phase. Low shear mixer was used to prepare homogeneous modified bitumen. The asphalt concrete mixtures were prepared using Marshall mix design method for both modified and unmodified bitumen. The morphology and structural of the prepared materials were investigated by transmission electron microscope (TEM, JEOL JEM-1230 with accelerating voltage of 120 kV) and X-ray detraction (XRD), scan electron microscope (SEM, JEOL 5500 LV). The properties of the used asphalt binder AC 60/70 penetration grade according to the certificate authority form Suez Refinery CompanyEgypt, Table (1). Table (1): Properties of asphalt binder AC (60/70) Test Results Specifications o Penetration at 25 C. 67 60-70 Kinematics Viscosity (centistokes at 135 oC) 280 320 Ring and Ball softening point 51.5 oC 45-55 Specific gravity 1.03 1-1.1 Flash point 245 oC 250 3. RESULTS AND DISCUSSION 3.1 Structural and Morphology Analysis Fig. (1) shows X-ray diffraction pattern of Ca(OH)2 nanoparticles. The prepared Ca(OH)2 nanoparticles precipitate in hexagonal phase, which was in consistence with the standard structure of Ca(OH)2 (Portlandite, JCPDS card No.004-0733). 62


Fig. (1): X-ray diffraction patterns of Ca(OH)2 nanoparticles Scherrer′s equation (eq.1) has been used to calculate the mean crystalline size of Ca(OH)2 nanoparticles: D = 0.9λ/βcosθ(1) Where D is the mean crystalline size (nm), λ is the wavelength of Cu Kα (0.154), β is the full width at half maximum intensity (FWHM) in radian and θ is the Bragg angle. The mean crystalline size of the Ca(OH)2 calculated to be in the range from 25-35 nm. The morphology of Ca(OH)2 nanoparticles was analyzed using transmission electron microscope (TEM) and scanning electron microscope (SEM). Figure 2 shows the homogeneity phase of (Ca(OH)2 nanoparticles. Upon addition of different percentage of the modifier (Ca(OH)2 nanoparticles), the homogeneity of the mixtures were increased until the 5%. Figure 3 shows the SEM pictures of the modified bitumen with the 5% Ca(OH)2 nanoparticles. Generally, the structure morphology of the resulting mixture depends on the the ratio of the additives [14]. The modified bitumen, 5% Ca(OH)2, forms strong reinforcing network structure, which have positive effect on asphalt concrete mixture properties. While on using more than 5% Ca(OH)2, the sample was unhomogenous and the binder was separated on the surface of the mixture.

Fig. (2): TEM micrograph of Ca(OH)2 nanoparticles

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Fig.(3): SEM micrograph of bitumen modified with 5% Ca(OH)2 nanoparticles 3.2 Mechanical Properties of Asphalt Mixtures 3.2.1

Penetration Test, Softening Point and Viscosity Test Figure (4) shows the result of the penetration test for the modified and unmodified bitumen. In general, the penetration grade decreases with the increase of Ca(OH)2 nanoparticles ratio. The addition of 5% Ca(OH)2 nanoparticles decreases the penetration grade of the blend by nearly 30 %. The significant decrease of the mixture penetration reduces the chance of rutting process. This result is important for the roads pavement in the hot climate area [15].

P enetration (1/10 m m )

80 70 60 50 40 30 20 10 0 0%

1%

2%

3%

4%

5%

Percentage (wt)

Fig. (4): Penetration test result for modified and unmodified bitumen On the other hand, the addition of 5% Ca(OH)2 nanoparticle to the unmodified bitumen increase the softening point by 15 °C (45 %). This result is in consistence with the decrease in the penetration grade and support the potential use of the blend (biutame-5% Ca(OH)2) for using in high temperature area and for heavy traffic load [16].

64


S oftening point (Tem p.)

60 50 40 30 20 10 0 0%

1%

2%

3%

4%

5%

Percentage (wt)

Fig. (5): softening point test result for modified and unmodified bitumen

Kinematics Viscosity (cSt)

Fig. (6) present the modified bitumen with 5% Ca(OH)2 nanoparticles has a lower viscosity that means the modified bitumen less sensitive to temperature. When the bitumen is less sensitive to temperatures that mean this bitumen is useful to use to resist rutting and heavy loads from traffic [16].

285 280 275 270 265 260 255 250 0%

1%

2%

3%

4%

5%

Percentage (wt)

Fig. (6): viscosity test result for modified and unmodified bitumen 3.2.2

Tensile Strength and Compressive Strength Test Two types of testes were investigated to characterize the properties of modified and unmodified asphalt concrete mixtures. The first test was indirect tensile strength using the following equation (2) [17,18]: ITS = 2Pmax/ (πd*h) (2) Where, Pmax represents the maximum applied breaking load (Newton) of the specimens under diametric compression, d and h are average values of the diameter (mm) and height (m) of the 65


ITS (Kn/cm2)

Marshall specimens, respectively. Values of load at failure and indirect tensile strength for modified and unmodified asphalt concrete mixtures are calculated based on Equation (2) and shown in fig (7). Figure (7) presents the results of indirect tensile strength for both modified and unmodified mixtures. It can be seen that the unmodified specimens had the lowest value of indirect tensile strength, while Ca(OH)2 nanoparticles modified asphalt concrete mixtures has the highest value of indirect tensile strength at modification level 4%. Higher tensile strength means that asphalt pavement can tolerate higher strains before cracking. It is clear that from Fig. 7, adding Ca(OH)2 nanopaerticles to the unmodified bitumen increase the tensile strength for asphalt concrete mixtures with small rate and this improvement stop with increasing the percentage of modifier [19]. 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 0%

1%

2%

3%

4%

5%

Percentage (wt)

Fig. 7: Indirect tensile test result for modified and unmodified asphalt concrete mixtures The second test was compressive strength to evaluate modified and unmodified mixtures using the following equation (3) [20]:

σ

c

=

4 P max

π

D

2

Compressive Strength (MPa)

Where σc is the unconfined compressive strength, Pmax is the maximum applied compressive load, and D is the specimen diameter. 4 3.5 3 2.5 2 1.5 1 0.5 0 0%

1%

2%

3%

4%

5%

Percentage(w)

Fig. 8: compressive strength for modified and unmodified asphalt concrete mixtures 66


The average unconfined compressive strength for unmodified and modified mixtures is calculated based on Equation (3) at the optimum asphalt content for each mixture and presented on Fig. (8). Figure (8) indicate that the increase of compressive strength with increasing the modification level that means high resistance for rutting [18]. The modification level with 5% Ca(OH)2 nanoparticles was more than two times of compressive strength which used in high traffic area. 4. CONCLUSION Ca(OH)2 nanoparticles were synthesized by sol.gel method and analyzed by XRD and TEM. The effect of Ca(OH)2 nanoparticles on the mechanical properties of unmodified and modified asphalt concrete mixtures were investigated. The results showed significant improvement on both physical and mechanical properties of modified asphalt concrete mixtures. The addition of 5% Ca(OH)2 nanoparticals decreases the penetration grade of the blend by nearly 30 %. Softening point was increase by 15 °C (45 %) and the viscosity was decreases by 7%. Unmodified specimens had the lowest value of indirect tensile strength, while Ca(OH)2 nanoparticles modified asphalt concrete mixtures has the highest value of indirect tensile strength specially at modification level 4%. The modified asphalt concrete mixtures with 5% have a higher increase of compressive strength. Finally the modified asphalt concrete mixtures with Ca(OH)2 is preferable to be used in hot climate as well as heavy traffic load area. From the results of various test using Ca(OH)2 nanoparticles can improve road mechanical properties, including rutting resistance and enhance bitumen performance to resist high traffic loads. ACKNOWLEDGEMENTS The authors sincerely thank central Lab., South Valley University, Qena, Egypt for TEM and SEM measurements. 5. REFERENCES [1] [2] [3]

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