Al-Qadisiya Journal For Engineering Sciences Vol. 4 No. 1 Year 2011 548 EFFECT OF AGGREGATE PROPERTIES ON HOT MIX ASPHALT PERFORMANCE Romel Nano Yaqob University of Kirkuk/Civil Engineering Department E-Mail: eldadoner@yahoo.com ABSTRACT Mineral aggregates make up 90 to 95% of a HMA mix by weight or approximately 75 to 85% by volume. The properties of the mineral aggregates have significant affects in performance of our local roadways which offers the possibility of investment in these properties towards resisting different ranges of external applied loads and environmental conditions. For this reason, the performance properties susceptibility due to aggregate properties (Consensus and Source) is going to be evaluated with a wide range of blends, fine, medium and coarse gradation mixtures. The selected source property in this study was toughness (% abrasion), and the consensus property used in this study was angularity (% crushed). Results show that the medium graded mixtures were more susceptible in terms of Marshall Stability due to the change in % abrasion and % crushed aggregate, while the coarse graded mixtures were more susceptible in terms of Marshall Flow due to the change in % abrasion and % crushed aggregate. Keywords: % Los Angeles abrasion, %Crushed, Marshall Stability, Marshall Flow, Air Voids تأثير خواص الركام على اداء الخلطة االسفلتية الحارة روميل ننو يعقوب قسم الهندسة المدنية\كركوك جامعة الخالصة ونوعية الركام . من وزن الخلطة % 95 الى 90من حجم الخلطة االسفلتية الحارة و % 85الى % 75يشكل الركام حوالي وى ، والذي يوفر امكانية استثمار هذه الخواص باتجاه مقاومة مختلف مديات القالمعدني له تاثير كبير على اداء طرقنا المحلية لهذا السبب اصبح من الضروري تقييم تأثرية الخواص االدائية للخلطة االسفلتية نتيجة . المسلطة الخارجية والظروف البيئية باستعمال مجال واسع من التدرجات الناعمة ) الخواص المصدرية والخواص المتفق عليها( التغيير في خواص الركام وفي هذه الدراسة تم تقييم خاصية المصدر باالعتماد على خاصية القساوة وتقييم .والخشنة) الكثيفة( والمتوسطة النعومة mailto:eldadoner@yahoo.com Al-Qadisiya Journal For Engineering Sciences Vol. 4 No. 1 Year 2011 549 اظهرت نتائج الدراسة بان الخلطة االسفاتية ذات التدرج الكثيف تتأثر بشكل اكبر . خاصية الركام المتفق عليها وهي التزاوي ت التدرج الخشن فقد اظهرت تاثرية اكبر عند تغيير اما الخلطة االسفلتية ذا. بتغيير خواص الركام من ناحية ثباتية مارشال . خواص الركام من ناحية جريان مارشال INTRUDUCTION Asphalt concrete (AC) is a heterogeneous material that consists of asphalt cement, natural or artificial aggregate, mineral filler, additives and air voids. Aggregate comprise the vast bulk of paving mixture and therefore, exert significant influence on the resulting engineering properties of the structure. The fundamental measurements of aggregate morphological properties (angularity, shape, surface texture and toughness) are essential for good quality control of aggregates and for understanding the influence of these properties on the behavior of asphalt (Khandhal and Parker, 1998). In ASTM D8 ( ASTM 2003), aggregate is defined as " a granular material of mineral composition such as sand, gravel, shell, slag, or crushed stone, used with cementing medium to form mortars or concrete or alone as in base course, railroad ballasts, etc." (Fwa, 2006). OBJECTIVE AND TEST PLAN The objective of this study was to evaluate the effect of aggregate properties (Toughness and Angularity) on Marshall Properties for HMA mixture (stability, flow, and air voids). To accomplish this, various mixtures were compacted with optimum asphalt content and three different gradation types. Variable values of percent Los Angeles Abrasion (Source Property) were used throughout this study which refers to the different quarry in Iraq. Different percentages of crushed aggregate (consensus property) were also used for all three gradation types. The same compactive effort 50 blows/face was used to determine their volumetric and performance-related properties. In order to consider a range of mixtures, three blends of fine, medium and coarse gradations limited by the ASTM specification for gradation were used and shown in Figure 1. Three source of aggregates from Al-Nebaey, daqooq, and Al-Akhaither were used and their determined properties were shown in Table 1, and one grade (40-50) penetration graded of asphalt cement were utilized from daurah refinery, and its properties were shown in Table 2. Coarse Aggregate Properties: Coarse aggregate is the material, which is substantially retained on No. 4 sieve (2.365 mm). Generally, the asphalt concrete mixture contains from 35-65 percent of coarse aggregate for a nominal maximum size of 19.0 mm. This content normally gives a suitable texture for a heavily trafficked road (ASTM, 2003). The most significant properties of graded coarse aggregate to be used in the manufacture of asphaltic mixtures are: (Superpave, 1994) A. Consensus properties which are critical properties required to develop a desirable HMA mix. These properties are: - Flat and Elongated Particles Al-Qadisiya Journal For Engineering Sciences Vol. 4 No. 1 Year 2011 550 - Aggregate Angularity ( Coarse and Fine) - Clay content B. Source properties, which are critical also, including: - Effective Specific Gravity and Asphalt Absorption. - Toughness - Soundness - Deleterious materials - Mineral Composition Two significant important properties were considered as factors affecting the performance of HMA mix. Coarse Aggregate Angularity Coarse aggregate angularity is defined as the percent by weight of aggregate retained on the No.4 (4.75 mm) sieve with one or more fractured face. This property is determined using ASTM D5821 "Standard Test Method for Determining the Percentage of fractured Particles in Coarse Aggregate" (ASTM, 2003). This property ensures a high degree of aggregate internal friction and rutting resistance. The HMA mixtures containing different aggregates types were evaluated by Ishai and Gelber for Marshall Stability and flow, resilient modulus, and split tension strength. The results showed that there was a significant increase in the stability with the increase in the geometric irregularities of the aggregates. There was no correlation between geometric irregularities and resilient modulus or split tension strength of the HMA mixtures. (Ishai and Gelber, 1982) In 1962, Huang developed the particle index test for evaluating particle shape and surface texture. Particle index is determined by rodding aggregate in a mold and determining the voids. The particle index is then derived as follows: (Huang, 1962) Ia = 1.25 V10 -0.25 V50 – 32% (1) Where; Ia= the particle index value V10= % voids in the aggregate sample compacted with 10 blows per layer V50= % voids in the aggregate sample compacted with 50 blows per layer The results indicate that the test method is capable of distinguishing the difference between natural rounded and rough angular aggregate by increasing particle index value. This test has been standardized as ASTM D3398, index of aggregate particle shape and texture. Al-Qadisiya Journal For Engineering Sciences Vol. 4 No. 1 Year 2011 551 Toughness (% L.A. Abrasion) Toughness is the percent of material from an aggregate blend during the Los Angeles abrasion test. This property is determined using (ASTM C131) "standard Method of Test for Resistance to Degradation of Small-size Coarse aggregate by Abrasion and Impact in the Los Angeles Machine". This test provides some indication of the aggregate's ability to resist degradation from processes that it would encounter through its life as an aggregate in HMA. HMA aggregates can be degraded during stockpiling, processing (through a HMA plant), placing, compacting, and may due to traffic loads. Aggregate which lack adequate toughness and abrasion resistance may cause construction and performance problems. Degradation occurring during production can affect the overall gradation, and thus, widen gap between properties of the laboratory designed mix and field production [Yiping, et.al, 1998]. RESULTS OF EXPERIMENTAL WORK The optimum asphalt content by the Marshall Mix design method for three blend mixtures, and designations for each mixture used in the remaining discussion are provided in Table 3. Effect of Los angeles Abrasion of Aggregate Mixture performance to percent of wear variation is illustrated in Figures (2,3,4) for the three target mixtures considered (fine, medium, and coarse). Over an increase of percent Los Angeles Abrasion from (12.1-to-20.1-to-26.5), the medium gradation mixture was more susceptible to increase in percent Los Angeles Abrasion of aggregate. Changing the percent Los Angeles Abrasion from 12.1 to 26.5 revealed a decrease in Marshall Stability by 1.88 kN, whereas, the coarse gradation shows less susceptibility and reveals less decrease in Marshall Stability by 0.93 kN, as shown in Figure 2. Figure 3 shows that the increase of percent Los Angeles Abrasion of aggregate will decrease the Marshall Flow for all gradation mixtures used in this study. The medium gradation mixture revealed less decrease in Marshall Flow (about 0.26 mm) than do the coarse gradation mixture which decreased by 0.428 mm. Figure 4 shows the effect of Percent Los Angeles Abrasion of aggregate to % air voids. In this figure the fine gradation mixture revealed less decrease in % air voids and the variance was 0.15 % , while the coarse and medium gradation show more variation in % air voids, which revealed as twice as the fine gradation reveals. Al-Qadisiya Journal For Engineering Sciences Vol. 4 No. 1 Year 2011 552 Effect of Crushed of Aggregate Mixture performance to percent of crushed aggregate variation is illustrated in Figures (5,6,7) for the three target mixtures considered (fine, medium, and coarse) gradations. Figure 5 shows that the an increase of percent crushed in aggregate from 0 % -to- 20 % - to – 40 % will increase the Marshall stability for the three gradation mixtures, and the medium gradation mixture was more influenced by the increase in % crushed, and the variance was 1.4 kN. While the coarse graded mixture shows less influencing to the increase in % crushed, and the variance was 0.72 kN Figure 6 shows that the increase of %percent crushed in aggregate from 0 % - 20 % - to – 40 % will decrease the Marshall flow for all gradation mixtures used. Fine and medium graded mixtures show less susceptibility to the change in percent crushed and the decrease was about 0.22 mm as average, while the coarse graded mixture was more susceptible to the increase in percent crushed in aggregate, and the change in Marshall Flow was 0.42 mm. Figure 7 shows that the increase of percent crushed in aggregate from 0 % - 20 % - to – 40 % will decrease the percent air voids for all gradation mixtures used in this study. The results show that the fine graded mixture was more susceptible to the change in percent crushed of aggregate, and the decrease value was 0.96 %, while the coarse graded mixture shows less susceptibility to the change of % crushed and the value of the decrease was 0.68 % CONCLUSION Within the limitations of materials and test used in this study the following conclusions are drawn: 1- The medium graded mixtures were more susceptible to the increase of percent Los Angeles Abrasion, measured by the Marshall stability. 2- The course graded mixtures evaluated were more susceptible to the increase of percent Los Angeles Abrasion, measured by the Marshall Flow and percent Air Voids. 3- The medium graded mixtures were more susceptible to the increase in percent crushed aggregate, measured by the Marshall stability. 4- The coarse graded mixtures were more susceptible to the increase of percent crushed, as measured by the Marshall flow. 5- The fine graded mixture was more susceptible to the increase in percent crushed aggregate, measured by the percent Air Voids. REFERENCES 1- ASTM, 2003. Annual Book of ASTM Standards. Volume 04.03 2- Huang, E. Y. "A Test for Evaluating the geometric Characteristics of coarse Aggregate Particles" Proceeding American Society of Test and Material, 62:1223-1242, 1962. Al-Qadisiya Journal For Engineering Sciences Vol. 4 No. 1 Year 2011 553 3- Iraqi Standard Specification for Road and Bridges, Republic of Iraq, Ministry of Housing and Construction, state Commission of Roads and Bridges, Department of Planning and Studies, 2003. 4- Ishai, I. and Gelber, H. “Effect of Geometric Irregularity of Aggregates on the Properties and Behavior of Asphalt Concrete,” Association of Asphalt Paving Technologists, Vol. 51. 1982 . 5- Khandhal, P. S. and Parker, F. Jr. (1998) " aggregate Tests Related to Asphalt Concrete Performance in Pavement Program", Transportation Research Board, NCHRP Report 405. 6- Standard Specification for Roads and Bridges, State Organization of Roads and Bridges, Republic of Iraq, Ministry of Housing and Construction, Revised Edition (2003). 7- Superpave Asphalt Mixture Design & Analysis. National Asphalt Training Center Demonstration Project 101. federal Highway Administration office of technology Application, Washington, DC, 1994. 8- T. F. Fwa, "The Handbook of Highway Engineering", Taylor and Francis Group, 2006. CRS Press in an Imprint of Taylor & Francis Group, 6000 Broken Sound Parkway NW, Suite 300, USA. 9- Yaqob. R. N., "Influence of Avoiding the Superpave Restricted Zone on Asphalt Concrete Performance", M.Sc., Thesis, University of Baghdad, Baghdad, 2004. 10- Yiping, Wu, Parker, F. and Kandhal, K. "Aggregate Toughness/Abrasion Resistance and Durability/ Soundness Test Related to asphalt Concrete Performance in Pavements", Transportation Research Board, TRB, National Research Council, Washington, 1998. Table 1: Physical Properties of Aggregate. *: Iraqi Standard Specification for Roads and Bridges Table 2: Physical properties of asphalt cement (Yaqob, 2004) Test Unit ASTM Results D(40-50) Penetration 250 C, 100 gm, 5 sec. 1/10 mm D 5 42 Absolute Viscosity at 60 0 C Poise D 2171 3068 Kinematic Viscosity at 135 0 C C St. D 2170 373 Ductility (25 0 C, 5 cm/min.) Cm D 113 > 100 Softening point (Ring & Ball) C0 D 36 51.0 properties ASTM SORB* Al- Akhaither Nebaey Daqooq Bulk Specific Gravity C 127 2.639 2.568 2.614 % Wear ( L.A. Abrasion) C 131 <=35 12.1 26.5 20.1 Al-Qadisiya Journal For Engineering Sciences Vol. 4 No. 1 Year 2011 554 6 7 8 9 10 11 12 10 12 14 16 18 20 22 24 26 28 Percent Los Angeles Abrasion M ar sh al l S ta b ili ty , k N fine gradation medium gradation coarse gradation Specific gravity at 250 C ……. D 70 1.04 Flash point ( Cleveland Open Cup) C0 D 92 332 After Thin- Film Oven Test Penetration of Residue 1/10 mm D 5 39 Ductility of Residue Cm D 113 82 Loss on Heat at 1350C, 50 gm, 5 hrs % D 1754 0.82 Table 3: Type of Aggregate Gradation and Optimum Asphalt Content for Mixtures Gradation Type (SORB) Optimum AC (%) Designation Lower Limit ( Coarse) 4.6 Coarse Average Limit (Medium) 4.9 Medium Upper Limit (Fine) 5.2 Fine Figure 2: Marshall Stability Variation due to changes in Percent Los Angeles Abrasion Al-Qadisiya Journal For Engineering Sciences Vol. 4 No. 1 Year 2011 555 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 10 12 14 16 18 20 22 24 26 28 Percent Los angeles Abrasion M ar sh al l F lo w , m m fine gradation medium gradation coarse gradation 3 3.2 3.4 3.6 3.8 4 4.2 10 12 14 16 18 20 22 24 26 28 Percent Los Angeles Abrasion P er ce nt A ir V oi ds fine gradation medium gradation coarse gradation Figure 3: Marshall Flow Variation due to changes in Percent Los Angeles Abrasion Figure 4: Percent air Voids Variation due to changes in Percent Los Angeles Abrasion Al-Qadisiya Journal For Engineering Sciences Vol. 4 No. 1 Year 2011 556 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 0 5 10 15 20 25 30 35 40 45 Percent Crushed (2 Face or More) M ar sh al l S ta bi lit y, k N fine gradation medium gradation coarse gradation 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 0 5 10 15 20 25 30 35 40 45 Percent Crushed ( 2 Face or More) M ar sh al l F lo w , m m fine gradation medium gradation coarse gradation Figure 5: Marshall Stability Variation due to changes in Percent Crushed of Aggregate Figure 6: Marshall Flow Variation due to changes in Percent Crushed of Aggregate Al-Qadisiya Journal For Engineering Sciences Vol. 4 No. 1 Year 2011 557 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 0 5 10 15 20 25 30 35 40 45 Percent Crushed (2 Face or More) P er ce nt A ir v oi ds fine gradation medium gradation coarse gradation Figure 7: Percent Air Voids Variation due to changes in Percent Crushed of Aggregate