The Effect of Aggregate Packing Interlocking on the Performance of Bituminous Mixtures

Transcription

1 The Effect of Aggregate Packing Interlocking on the Performance of Bituminous Mixtures YASREEN GASM ELKHALIG, MADZLAN B. NAPIAH, IBRAHIM KAMARUDDIN Civil Engineering Department, Universiti Teknologi PETRONAS Seri Iskandar, 31750, Tronoh, Perak MALAYSIA Abstract: - The purpose of this paper is to look at some aspects of the effects of aggregate packing interlocking mechanism on the rutting and fatigue behavior of hot mix asphaltic concrete (HMA). Coarse aggregate with a good particles packing can bring the particles closer, and thus decreasing the space between them which consequently gives the interlocking necessary to improve the mixture resistance. In this study, different sizes of coarse aggregate retain on 20mm, 14mm, 10mm, and 5mm are vibrated through the packing test to identify their corresponding optimal proportion in bituminous mixture. The proportions for the developed mixture are obtained and compared with the proportions of the conventional mixture (JKR) through the packing theory and the theoretical density of aggregate. The performance characteristics for the developed and the conventional mixtures are evaluated using dynamic creep test, wheel tracking test, and beam fatigue test. According to the performance characteristics results, developed mixture is presented higher resistance to rutting and fatigue compared to the conventional one. This is due to the optimal distribution of the big and small particles that makes the developed mixture more homogenous in size distribution providing a good interlocking mechanism. Key-Words: - coarse aggregate, packing density, dynamic creep test, wheel tracking test, beam fatigue test. 1 Introduction The frequent problems associated with road pavements like rutting, abrasion, fatigue cracking, thermal cracking, aging and stripping cause the roads to wear away or fail [1, 2]. Among these road related problems, rutting and fatigue are considered to be the main problems in highway pavements. Rutting occurs only on flexible pavements as indicated by the permanent deformation or rut depth along the wheel paths. Earlier studies have identified that rutting occurs as a result of accumulated plastic deformation due to high traffic loads and high temperatures [3]. Another study was considered rutting as a longitudinal subsidence localized in the wheel tracks caused by vehicles loads. The second form of the pavement distress is cracking. It is considered as one of the primary reasons for failure of structural components of the pavement. When a bituminous pavement is loaded, tensile stresses and strains are induced at the underside of the bitumen bound layer. If the structure is inadequate for imposed load or if the characteristics of the sub grade change through ingress of water, the tensile strength of the material will be exceeded and crack at the bottom of the bituminous layer will result. Repeated loads inducing tensile stresses above the tensile strength of the mix, this leads the crack to propagate upwards towards the road surface [4, 5]. A number of research have been carried out on modifying the bituminous mixtures to bring real benefits to highway performance in terms of better and longer lasting roads and savings in vehicle operating cost. Materials proportions such as composition of aggregate also have a great effect on pavement performance. Therefore a good quality properly blended mix can reduce or eliminate the rutting and fatigue failure in the pavement. The packing mechanism (interlocking) of the aggregate is the one possible solution that may help to give the optimum aggregate proportions. Packing is the way of an arrangement of solids in a given volume. When mixing granular materials with bonding agents (e.g. aggregate with cement), it is critical to achieve the highest possible particle packing. The highest particles packing is because of different proportions of the aggregates which has greatest density when blended dry. Obtaining the highest particles packing can significantly improves ISBN:

2 the strength of bonded materials and reduces the amount of binder required for bounding mixtures [6]. The packing of particles has attracted the interest of many researchers since it is an important factor governing the properties of materials in different industries. As asphalt concrete mixtures are also composed of particles including coarse, fine, and filler, the packing plays an important role in their behaviour. In mixture, poor packing or interlock between the particles leads to permanent deformation. Hence, optimizing the particles packing when combining aggregate with binder can radically increase the strength of the composite material and decrease the distress [6]. There are many factors that can affect the packing characteristics, one of them is the physical properties of particles which are discussed in detail as follows: 1.1 The physical properties of the particles: The physical properties that affect the particles packing density and consequently the performance of the pavement are; particles size distribution, grading zone, and particles density. Shen et al. [7] studied the effect of size on permanent deformation. The authors found that large-size, angular and rough textured aggregates improved the rutting resistance and minimized plastic flow. Airey et al. [8] investigated continuously graded and gap-graded mixture to study the effect of different packing characteristics on the degradation of aggregate under compaction. Their results showed that, gap-graded asphalt mixture experienced a greater amount of aggregate degradation after compaction compared to the continuously graded mixture. This is due to the lack of any cushioning or interacting between the aggregate for the gap-graded mixture. Shen et al. [7] found that aggregate gradation (distribution of particle sizes) is one of the most important factors to resist pavement distress. This is also confirmed by Asi [9] when he studied the effect of aggregate interlocking on the fatigue life. The author found that, stone matrix asphalt mixture has lower fatigue life compared to the control mixture. This is because the gap graded stone matrix asphalt mixture lacks mechanical interlocking of the aggregate. 2 Problem Formulation Conventional mixture often results in low density which is not optimum in term of performance characteristics, because of the poorer interlock between the aggregate particles i.e. lack of the mechanical interlocking of the aggregate. Therefore, optimizing the interlocking mechanism of aggregate by using aggregate packing theory is considered necessary for resistance the distress. 3 Problem Solution The main objective of this study is to determine the optimum proportions of aggregate to be used in general framework with especial data, and to investigate the effects of these optimum proportions on the performance characteristics of developed bituminous mixture and compare it with conventional bituminous mixture (JKR). 4 Methodology The function of coarse aggregate in the mix is to provide stability to the pavement due to the interlocking behavior between the coarse particles. Roque et al. [10] found that the gradation characteristics of the coarse aggregate fraction had the strongest effect on mixture shear resistance. The methodology of this study is discussed in detail as follows: 4.1 Prepare the coarse aggregate To achieve the objectives of this study coarse aggregate, granite, was washed, dried, and sieved to the single size. The sieved aggregate are kept in containers, each containing different sizes that are; retain on 20mm, 14mm, 10mm and 5mm. 4.2 Packing test Based on the lees` rational method (as cited in [11]), different sizes larger than 20mm, 14mm, 10mm and 5mm with random packing are vibrated in metal mould. The mould has specific size with defined dimension which are mm in the diameter and 176mm in the length while others used different moulds with different dimensions. Waddah et al. [12] used 152mm 2 mold with an inside height of 155mm and plate weight of 1,920 g and vibration duration of 8 minutes, Takemi et al. [13] used 2 liters steal while in Kansas Test Method [14] the capacity of the mould is 0.014m 3, inside diameter 254mm, inside height 280mm and the wall thickness of measure bottom 5.0mm, side 3.0mm, and top rim 5.0mm. In this study, the shaker machine is used to allow the possibility for the particles to find the best arrangement. ISBN:

3 The three kilograms of coarse aggregate retain on 20 mm sieve size (A) are measured and transferred into the mould. The surface of the aggregate in the mould is leveled using slit plate and the height and the gage reading are recorded. Initially, the mould is vibrated by the shaker machine for 2.5 minutes and then the height and the gage reading are recorded very carefully. The vibration process was applied continually for every 2.5 minutes until constant height and gage reading are obtained. The vibration time that gave the constant height and gage reading is 35 minutes. The 2.7 kilograms of coarse aggregate retain on 20 mm sieve size (A) and 0.3 kilogram from coarse aggregate retain on 14 mm sieve size (B) are measured and put on the clean tray. Both of the two sizes are mixed well and transferred to the mould. The mould is vibrated by the shaker machine for 35 minutes and then the height and the gage reading are recorded. The steps will be applied for 80% from A and 20% from B respectively until 0% from A mixed with 100% from B as shown in the Table I. All the previous steps are applied again for coarse aggregate retain on 10mm (C) sieve size and retain on 5 mm (D) sieve size. Taken into account that A and B are considered as one aggregate size (A+B) (after mixing optimum percentage (OP) of A with optimum percentage of B that gave the maximum density). The previous steps for the percentages and vibration are repeated with the A+B and C. The optimum percentage of (A+B) is mixed well with optimum percentage of C (after the maximum density obtained). Aggregate after mixing is considered as one aggregate (A+B+C). The A+B+C is vibrated with D (retain on 5mm sieve size) and the same previous steps for the percentages and vibrations are applied to get the optimum proportions for them. 4.3 Sieve Analysis Test Sieve analysis test is conducted for the conventional mixture aggregate using the Malaysian standard specification Jabatan Kerja Raya (JKR) [15].The proportions for the conventional mixture are 45% for coarse aggregate, 50% for fine aggregate, and 5% for filler. 4.4 Specific Gravity Test Specific gravity test is conducted for the four different sizes coarse aggregate of developed mixture, and for conventional mixture aggregate, sand, filler. The results of the specific gravity are , , , , , , for the coarse aggregate 20mm, 14mm, 10mm, 5mm, coarse aggregate (JKR), fine aggregate and filler correspondingly. 4.5 Marshall Test Marshall Test is an empirical test used to measure the stability and flow of cylindrical specimens of bituminous mixtures [16]. The optimum binder content is calculated as the average of asphalt contents that meets the maximum stability, maximum unit weight, minimum voids in mineral aggregate and bitumen content that meets 80% of voids filled with bitumen. The result of optimum bitumen content for developed is 4%, and for conventional bituminous mixtures is 5%. 4.6 Dynamic creep test A total of 6 specimens were prepared to conduct dynamic creep test at 40 0 C by using the Universal Testing Machine (UTM) A repeated pulsed uniaxial stress was applied to a mixture specimen and the resulting deformations in the same axis were measured using Linear Variable Displacement Transducers (LVDTs) [17]. 4.7 Wheel tracking test The wheel tracking test was conducted at 40 0 C. An actual wheel of 200 mm diameter and 50 mm width with a total wheel load of 520 N was applied on the square specimen for 46 minutes loading. The total rut depth was determined and recorded by the Wessex software. The testing procedures conform to the specification of BS : 1998 [18]. 4.8 Beam fatigue test Fatigue test was performed using the MATTA apparatus. The test temperature 20 0 C was chosen since the effect of air void content on fatigue life is more pronounced than at lower temperatures [19]. A thin pavement with thickness of less than 60 mm is suggested for use in the control strain mode, because failure will be more noticeable in this mode [20]. The number of load repetitions at which the current stiffness decreases to 50% of the initial value is defined as the fatigue life of the specimen. 5 Results and discussions 5.1 Dynamic creep The results of creep test are obtained from three specimens for each developed and conventional mixture. Fig. 1 showed typical graphical plot of mixture stiffness (S mix ) versus bitumen stiffness (S bit ) in a double logarithmic graph. Mixture stiffness was measured by universal testing machine at 40 0 C for 1 hour loading time period and the corresponding ISBN:

4 bitumen stiffness S bit was calculated by using Van Der Poel s nomograph [21]. The resistances to permanent deformation from the creep test were determined using the slope from the log-log relationship of mixture stiffness versus binder stiffness. Mixture stiffness corresponds to a fixed loading time, or the time to reach a critical strain level. This manner of characterization in the mix is based on the fact that more resistant mixtures have stiffness that are greater and decrease less rapidly with increasing time. The developed mixture has higher mix stiffness compared to the conventional one. The result pointed out that developed mixture is less susceptible to loading time in comparison to the conventional mixture. This is refers to the fact that developed mixture grading is much coarser and more continuous grading resulted in better interlocking properties which helps to increase the mix stiffness. high significant correlation exists between estimated rut depth and number of standard axle repetitions. The estimated rut depth of the developed mixture is lower than the estimated rut depth of conventional mixture. This is because the developed mixture has a higher resistance to rutting compared to the conventional one. This is due to the interlocking effects of the smaller size particles within the large size particles for developed mixture results in continues grading which increase the strength for the developed mixture to resist the rutting. This observation agrees well with previous work (as cited in [6]). They found that the aggregate interlocking characteristic has important roles in resisting permanent deformation. Rut depth(mm) E+07 1E Number of standard axle repetitions Dev Mix 1 Dev Mix 2 Dev Mix 3 JKR 1 JKR 2 JKR 3 Power (Dev Mix 1) Power (Dev Mix 2) Power (Dev Mix 3) Power (JKR 1) Power (JKR 2) Power (JKR 3) Figure 2. Rut depth estimation related to the number of standard axle repetitions for developed and conventional mixtures Figure 1. Rut depth estimation related to the number of standard axle repetitions for developed and conventional mixtures. The formula which was used to calculate the rut depth of the pavement from laboratory creep test results was initially proposed by Hills et al. and Van Der Loo (as cited in [17]). R d = Cm H σ av / S mix. creep (1) Where: R d - calculated rut depth of pavement, C m - correlation factor for dynamic effect varying between 1.0 and 2.0, H- pavement layer thickness, σ av - average stress in pavement related to wheel loading and stress distribution, S mix - stiffness of design mixture derived from creep test at a certain value of stiffness related to the viscous part of bitumen. The results of rut depth estimation are shown in Fig. 2 and are presented in relation to the number of standard axle repetitions. The results indicate that a Fig. 3 shows the estimated number of cycle at maximum rut depth allowable in the pavement, which is 25mm. It can be seen that developed bitumen mixtures are able to take more number of cycles than the conventional mixtures. This is due to developed mixture has continues grading coming from the good particles interlocking which increase the strength to be able to carry the load for long time. Figure 3. Number of cycles at maximum Rd allowable in the pavement 5.2 Wheel tracking A total of 6 samples were tested for the permanent deformation using Wessex machine. The rut depth was therefore obtained after 1932 cycles. The wheel tracking test results are shown in the Fig. 4. ISBN:

5 Figure 4. Rut depth estimation related to the number of cycles for developed and conventional mixtures. From the figure it can be noted that developed mixture exhibited higher resistance to rutting compared to the conventional mixture. This is because of developed mixture has the least rut depth as compared to the conventional mixture. This behavior has similar trend as the interlocking properties and as other researchers have obtained that the aggregate interlocking could improve the rutting resistance. Because poor interlock between the particles leads to permanent deformation [6]. 5.3 Beam fatigue The result of the beam fatigue test are expressed as the numbers of loading cycles required to initiate a fatigue crack as a function of both the constant load applied to the beam and the maximum initial tensile bending stress. In a plot relating tensile stress and number of cycles, a linear part of the curve which represents an initial period of large stress and a part of it represents a constant rate of stress amplitude were extrapolated. The stress value corresponding to the intersection point (x) of these two extrapolations is defined as the initial stress. The same principle was applied in determining the number of cycles to failure. Fig.5 shows the procedure adopted to determine the initial stress and the number of cycles to failure on each beam. In this study, the beam fatigue test results were analyzed based on the number of cycles (fatigue life). The result showed that developed mixture has number of fatigue life, while conventional one has number of fatigue life. It can be noted that developed mixture is observed to have higher fatigue life (cycles) compared to the conventional mixture. This demonstrates that developed mixture has a better fatigue resistance than conventional mixture. This is due to the optimal distribution of large and small particles (gradation) vary from developed aggregate grading to conventional aggregate grading. Because the developed mixture has optimal aggregate proportions, which make the grading much coarser and more continuous grading resulted in better interlocking properties. This agrees with earlier study carried by Kim et al. [22]. The larger particles resist compressive stress better than the smaller particles. More over to get better resistance to fatigue deformation good distribution of particles is required. This is because inhomogeneous distribution reduces adhesion by fines leading to less fatigue resistant. Figure 5. Determination of initial stress and number of cycles to failure 6 Conclusions According to the maximum density obtained from the packing test, the optimum proportions for the developed mixture is found to be 8.64%, 12.96%, 14.4%, 24%, 32%, and 8%for coarse aggregate retain on 20mm, 14mm, 10mm, 5mm, fine aggregate, and filler respectively. The developed mixture has lower OBC (4%) compared to the conventional mixture (5%). This because the JKR mixture has a higher percentage of fine aggregate which is 50%, while the developed mixture has a fewer amounts of finer which is 32%. The more finer or small particles means large or more surface area which requires more amount of binder to cover the particles. Moreover the aggregate grading for developed mixture is much coarser and more continuous than for the conventional one. This is resulted in better aggregate interlocking mechanism for developed mixture, which decreases the voids between the particles, there for it required less bitumen. Rutting results from the dynamic creep test and wheel tracking test showed that developed mixture which has much coarser and more continuous grading contributes to increase the rutting resistance of hot mixture asphalt. The developed mixture exhibits highest rutting resistance compared to the conventional mixture. The conventional mixtures has a maximum deformation of about 4.5 mm while ISBN:

6 the developed mixture has deformations of 2.1 mm lesser than the conventional mixture, indicating that developed mixture is more resistant to permanent deformation. Particles size and good distribution of particles could also contribute to the mixture strength that is reflected in better fatigue resistance. A developed mixture exhibited better fatigue performance as compared to conventional mixture. References: [1] Navarro, F.J., Partal, P., Martinez-Boza, F., Valencia, C. and Gallegos, C., Rheological Characteristics of Ground Tire Rubber- Modified Bitumens, Chemical Engineering Journal, Vol.89, 2002, pp [2] Lu, X. and Isacsson, U., Rheological Characterization of Styrene-Butadiene -Styrene Copolymer Modified Bitumens, Science Direct Journal of Construction and Building Materials, Vol.11, 1997, pp [3] Navarro, F.J., Partal, P., Garcıa-Morales, M., Martinez-Boza, F.J. and Gallegos, C., Bitumen Modification With A low-molecular-weight Reactive Isocyanate-Terminated Polymer, Science Direct Journal of Fuel, 2007, pp [4] Peattie, K.R., The Analytical Design of Flexible Pavements, Lecture Notes, Department of Civil Engineering Symposium, University of Glasgow, Apr [5] Whiteoak, D., The Shell Bitumen Handbook, Published By Shell Bitumen U.K, First Edition, [6] Best Practices in Glass Recycling, Simple Particle Packing, Material Recycled Glass, CWC, Product Manufacturing Fusing, Nov 1996, pp. 1-2 [7] H. D. Shen, F. M. Kuo and C. J. Du, Properties of Gap- Aggregate Gradation Asphalt Mixture and Permanent Deformation, Science Direct Journal of Construction and Building Materials, Vol. 19, 2005, pp [8] G. D. Airey, A. E. Hunter and A.C. Collop, The Effect of Asphalt Mixture Gradation and Compaction Energy on Aggregate Degradation, Science Direct, Construction and Building Materials, Vol. 22, 2008, pp [9] M. I. Asi, Performance Evaluation of Superpave and Marshall Asphalt Mix Designs to Suite Jordan Climatic and Traffic Conditions, Science Direct Journal of Construction and Building Materials, Vol. 21, 2007, pp [10] R. Roque, S. Huang, and E. B. Ruth, Maximizing shear resistance of asphalt mixtures by proper selection of aggregate gradation, 8th International Society for Asphalt Pavements, Seattle, 1997, pp [11] Y. Abdel-Jawad, and S. W. Abdullah, Design of Maximum Density Aggregate Grading, Construction and Building Materials, Vol. 16, 2002, pp [12] S. W. Abdullah, T. M. Obaidat, M. N. Abu- Sa da, Influence of Aggregate type and Gradation on Voids of Asphalt Concrete Pavements, ASCE J Mater Eng Div 1998; Vol.10, 1998, pp [13] I. Takemi, G. Yasuo, A. Hirokazu, Rational Design Method of Hot Mix Asphalt Based on Calculated VMA, 3rd Eurasphalt and Eurobitume Congress Vienna, 2004, pp [14] Unit Weight of Aggregate, Kansas Test Method KT-5, AASHTO T KT-05. pp [15] Flexible Pavement, Standard Specification for Road Works, Malaysia: Jabatan Kerja Raya, 1988, pp [16] P. Ahmedzade, and M. Yilmaz, Effect of Polyester Resin Additive on the Properties of Asphalt Binders and Mixtures, Science Direct Journal of Construction and Building Materials, 2007, pp [17] Cabrera, J.G. and Nikolaides, A. F., Creep Performance of Cold Dense Bituminous Mixtures, Journal of the Institution of Highways and Transportation, Oct 1988, pp [18] British Standard 1998: Part , Method of Test For The Determination of Wheel- Tracking Rate and Depth, Sampling and Examination of Bituminous Mixtures for Roads and Other Paved Areas. [19] Kim, Y.R., Khosla, N.P. and Kim, N., Effect of Temperature and Mixture Variable on Fatigue Life Predicted By Diametral Fatigue Testing, Journal of Transportation Research Record, 1317, 1991, pp [20] Doan, Mechanical Test for Bituminous Materials, Fatigue of bituminous mixture, RILEM Interlaboratory Test, [21] Pell, P.S., The Analytical Design of Flexible Pavements, Lecture Notes, Department of Civil Engineering Symposium, University of Glasgow, Apr [22] Kim, K.W., Doh, Y.S. and Lim, S., Mode 1 Reflection Cracking Resistance of Strengthened Asphalt Concretes, Science Direct Journal of Construction and Building Materials, Vol. 13, 1999, pp ISBN: