STIFFNESS MODULUS of ASPHALTIC CONCRETE WEARING COURSE (AC-WC) MIX CONTAINING RETONA BLEND 55 : Theoretical and Experimental Analysis

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1 STIFFNESS MODULUS of ASPHALTIC CONCRETE WEARING COURSE (AC-WC) MIX CONTAINING RETONA BLEND 55 : Theoretical and Experimental Analysis Bambang S.SUBAGIO Harmein RAHMAN Professor Assistant Professor Civil Engineering Dept. Civil Engineering Dept.. Institute of Technology Bandung Institute of Technology Bandung Bandung-Indonesia Bandung-Indonesia Fax: Fax: bsugengs@si.itb.ac.id office@trans.si.itb.ac.id Sri HENDARTO Associate Professor Civil Engineering Dept. Institute of Technology Bandung Bandung-Indonesia Fax: stjr@trans.si.itb.ac.id Freddy John PHILIPS Graduate Student Highway Engineering Master s Program. Institute of Technology Bandung Bandung-Indonesia Fax: stjr@trans.si.itb.ac.id Abstract: This paper described an experimental and theoretical analysis of Asphaltic Concrete Wearing Courses (AC-WC) mixes; based on the Indonesian Specification for Hot Mix Asphalt, containing the RETONA (Buton Rock Asphalt) as an asphalt additive. The main laboratory works were: Resilient Modulus Test, Marshall Standard dan Marshall Immersion test. The results of Marshall test showed that the OAC and Marshall Stability of AC-WC mix using Retona were higher than the AC-WC mix using conventional bitumen ( Pen 60/70). The results of Immersion Test indicated that in general, the IRS value was higher than 95%, showing the high resistance to water. The results of Resilient Modulus test showed that the AC-WC mixes using Retona Asbuton have the highest Resilient Modulus and give the better resistance also to high temperature. While the comparison of the UMATTA results to the theoretical calculation showed that the Ullidtz-Nottingham s equation give the better approach to the experimental results than the Ullidtz-Shell s equation. Key Words: AC-WC mix, Asbuton Retona, Resilient Modulus, Nottingham s formula 1. INTRODUCTION Rock asphalt deposits exist in large quantities in Buton Island, South-East Sulawesi, Indonesia, and is named locally as Aspal Buton or ASBUTON. Since the deposits are widely variable in both composition and properties, then the production of a consistently uniform material, whose its performance can be predicted with reasonable confidence is really difficult (McElvaney,1986). When installed under carefully controlled conditions, pavement materials incorporating Asbuton, have performed well, but in general, its performance on a wider scale, has been disappointing. In particular, when used as a road surfacing material or overlay, the life of that material was not

2 equal to that achieved by using conventional refinery bitumen, regardless the type of mix considered. On the other hand, extensive maintenance and betterment of the Indonesian road network, involves the use of very large quantities of bitumen-bound materials. Given the relatively high cost of refinery bitumen, much of which is imported from another country, and the existence within the country of large resources of rock asphalt, the outcome of the research of natural rock asphalt becomes significantly important. There are many types of Asbuton Bitumen, such as : Micro Asbuton, Mastic Asbuton, Buton Granular Asphalt, Retona, Retona Blend etc., which was produced by many agencies. Retona Blend 55 is one type of Asbuton bitumen, produced by one agency, named PT Olah Bumi Mandiri, and was firstly introduced in the beginning The advantage of this type of Asbuton is the highly content of bitumen content, when it was compared to the others. Pursuing our previous research on Asbuton bitumen (Subagio, 2005), (Subagio, 2007), this study focuses on the measurement of Resilient Modulus of Asphaltic Concrete Wearing Courses (AC- WC) mixes using Retona Asbuton as an asphalt additive, and then compared to the theoretical calculation of Resilient Modulus, using Ullidtz Nottingham s formula. The laboratory works were conducted at Highway Engineering Laboratory, Institute of Technology Bandung (ITB), while the UMATTA Resilient Modulus Test was conducted at the Center for Research & Development for Highway and Bridges, Department of Public Works, Bandung. 3. PRELIMINARY LABORATORY TESTS The standard method used in this study is the New Indonesian specification for Hot-mix Asphalt Mixture containing Asbuton (Dept.PU, 2007), as shown in Table 1. Another standard methods, for example, British Standard, ASTM and AASHTO were used when appropriate. 2.1 Bitumen Properties Petroleum asphalt (Pen 60/70) was used in the AC-WC mixture, as an ordinary binder material. The laboratory tests performed to evaluate the bitumen properties were: Penetration, Softening Point, Ductility, Flash Point, Solubility, Specific Gravity, Thin-film Oven Test (TFOT) and Viscosity. The results of those tests were presented in Table 2, and the specification used was the Indonesia Specification for Hot-mix Asphalt Asbuton Properties The specification for Retona Blend 55, an extracted Asbuton asphalt from Lawele, Buton Island, was given in Table 3. It is shown that the bitumen content of Retona Blend was very high (90%) and its bitumen properties was relatively hard (Pen 40 ~ 50). 2

3 No Table 3 Specification of Retona Blend 55 Types of test Test Results 1 Softening Point ( o C) Min 55ºC 2 Penetration (0,1 mm) Specific Gravity Bitumen Content (%) Min 90% 5 Mineral Content (%) Maks. 10% 6 Ductility > 50 cm The mineral grading of Retona Blend 55 was shown in Table 4. Considering of their mineral size, Asbuton affects the total aggregate grading on sieve size no.50 and 200, as fine aggregate and filler. The calculation of design mix for each AC-WC mixture has to take into account the percentage (by weight) of the Retona s mineral. Sieve size ASTM Table 4 Mineral Grading of Retona Blend 55 Passing ( by weight, grams) Asbuton s mineral Passing ( % ) Asbuton s mineral No , No Filler Aggregate Properties The coarse and fine aggregates used were crushed rock and the filler used were Asbuton and stone-dust. The laboratory tests performed to evaluate the properties of coarse aggregates were: Specific Gravity, LA Abrasion, Water Absorption, Soundness, Flakiness, Elongation and Angularity. The tests for fine aggregates were: Specific Gravity, Sand equivalent and Water Absorption, while for filler was Specific Gravity only. The specification adopted and results of these laboratory tests are given in Table Aggregate Grading The aggregate grading used in this study was the aggregate grading for Indonesian s Asphaltic Concrete Wearing Course (AC-WC), as shown in Table 6 and Figure 1. The grading curve was started from the upper side, crossed the Euler s curve and then was laid at the bottom side, as shown in Figure 2. 3

4 Table 6. Aggregate Grading for Indonesian Wearing Course (AC-WC) Sieve size ( ASTM ) Specification ( % passing ) Design Grading ( % passing ) Final Grading ( % retained ) ¾ ½ / No No No No No No Pan Figure - 1 The curve of aggregate grading for AC-WC Mixture 4

5 2.5 Design Mix of Hot Rolled Sheet The principle design of bituminous mixtures is to choose the aggregate type, aggregate grading, bitumen grade, bitumen modifier (if necessary), and to determine the bitumen content that will optimize its engineering properties in relation with the in-service behavior during pavement life (TAI, 1993). In this research, mix design was prepared for 4 (four) types of mixture,namely RFA-mix with 6% Retona and Fly-ash filler, RPC-mix with 6% Retona and Portland Cement-filler, AFA-mix with Asphalt Pen 60/70 and Fly-ash filler, and AFC-mix with Asphalt Pen 60/70 and Portland Cement filler. 3. TEST RESULTS AND DISCUSSIONS 3.1 Marshall Test In order to determine the Optimum Asphalt Content (OAC) of AC-WC mixture, the New Indonesian Specification ( Dept. PU, 2007 ) required 7(seven) parameters to be considered, namely Marshall Stability, Marshall Flow, Marshall Quotient (MQ), VIM, VIM Refusal, VMA and VFB. The specimens for Standard Marshall Test were prepared at asphalt content ranging from 4.5% to 6.5% by weight, at 0.5% increment. The weight of each specimen was 1030 grams in average, compacted by 2x75 blows, and three specimens were tested for each asphalt-content. The total specimens prepared for this test were 5x5x3 = 75 samples. The results of Standard Marshall Test were presented in Table 7 ( Philips, 2007). As mentioned previously, 4(four) mix types were prepared namely RFA (6% Retona, fly-ash), RFC (6% Retona, cement), AFA (0% Retona,fly-ash) and AFC (0% Retona, cement). The results showed that the OAC of AC-WC mix using Retona was higher than the AC-WC mix using conventional bitumen ( Pen 60/70). The similar result was obtained for the Marshall Stability. Obviously, the Cement filler could give the higher Stability compared to the fly-ash filler. Table - 7 Marshall Test results of Wearing Course (AC-WC) Mix OAC VIM VMA VFA Stability Flow MQ types (%) (%) (%) (%) (kg) (mm) (kg/mm) RFA RFC AFA AFC Specification(*) - 3.5%~5.5% >15% >65% > 800 Kg > 3 mm >250 Kg/mm (*) : Dept. PU,

6 3.2 Marshall Immersion Test The Marshall Immersion test was conducted for specimens prepared at optimum bitumen content. The objective of this test was to measure its durability or its water resistance after an immersion test for 24 hours at 60 o C. The specimens prepared for this test were 4x3x1 = 12 samples. The results of calculated IRS (Index of Retained Stability) were presented in Figure 2 and all values were higher than minimum value, tnamely, 75% ( Dept.PU, 2007 ). It is shown also that the value of IRS for each mix type, was significantly high, for example : 96.41% for AFA-mix, 96.03% for AFC-mix, 98.05% for RFA-mix, and 97.38% for RFC-mix. The maximum durability, therefore, obtained for RFA-mix. 3.3 Resilient Modulus Test Figure 2 Index of Retained Stability for AC-WC mixes The Resilient Modulus of all specimens, prepared at OAC, was measured by UMATTA test (Philips, 2008), for 2(two) temperatures i.e. 35 C and 45 o C. The total specimens for this test were 2x4x1 = 8 samples. The results of Resilient Modulus test were presented in Table 8 and Figure 3. It is shown that the highest Resilient Modulus at 35⁰C was obtained by RFA-mix, followed by RFC-mix. It means that the Asphalt mix (AC-WC) using Asbuton Retona could give the high strength. The similar results were obtained also at higher temperature ( 45ºC), showing that the Asbuton Retona give the better resistance to high temperature. 6

7 Table - 8 Results of Resilient Modulus test by UMATTA Temperature ( o C) AFA-mix AFC-mix RFA-mix RFC-mix Figure - 3 Resilient Modulus UMATTA versus Temperature 4. RESILIENT MODULUS : THEORY vs. EXPERIMENT Resilient or Stiffness Modulus of bituminous mix is defined as the ratio of stress to strain under given conditions of loading time and temperature ( McElvaney, 1988 ) Some formula was proposed in order to predict the Bitumen Stiffness, as well as the Mix Stiffness. Considering some bitumen characteristics i.e. loading time (t) and temperature difference (T-T 800 Pen ), the Van der Poel s nomograph can be used to predict the Bitumen Stiffness. Alternatively, a formula proposed by Ullidtz ( Shell, 1990 ) could be used to simplify the use of Van der Poel s nomograph, i.e. S bit = x 10-7 x t x exp -PIr x ( SP r T ) 5 ( MPa )... (1) where : PI r : Recovered Penetration Index SP r : Recovered Softening Point ( o C ) T : Bitumen Temperature ( o C ) t : time of loading ( second ) Before using that formula, some requirements should be accomplished i.e. 7

8 SP r T = 20 o C to 60 o C t = 0.01 second to 0.1 second PI r = -1 to +1 Following the simplified Ullidtz s formula, Brown et al. ( McElvaney,1988 ) proposed one formula to predict the Mix Stiffness i.e x VMA S mix = S bit [ ] n (2) n x ( VMA 3 ) 4 x 10 5 where : n = 0.83 x log [ ]... (3) S bit And : VMA : Voids in the mixed aggregate ( 12% VMA 30% ) In this study, those formulas were used to calculate the Bitumen Stiffness and Mix Stiffness of AC-WC mixes containing Asbuton Retona namely,. RFC-mix, RFA-mix, AFC-mix and AFAmix, at 2(two) temperatures i.e. 35 o C and 45 o C. The result was presented in Table 9 and Figure 4 and 5. It is shown that the Ratio of 2(two) Mix Modulus i.e. Stiffness Modulus measured by UMATTA to the Stiffness Modulus calculated by Shell s or Nottingham s formula, exclude the Stiffness Modulus of AFA mix at 35ºC, was different, for example 2.11 using the Shell s formula and 1.36 using Nottingham s formula. It is obvious that the Nottingham s formula give the relatively small different with the experimental results. Table 9 : Calculation of Mix Modulus (S mix ) using Shell s and Nottingham s Formula RFA RFC AFA AFC Temp ( o C) UMATTA Resilient Modulus ( MPa ) SHELL s formula Nottingham s formula UMATTA/ SHELL Ratio UMATTA/ Nottingham (*) 2.90(**) (*) 3.12(**) Note : (*) : Ratio is greater than 4.0 (**) : Ratio is greater than 2.0 8

9 It was shown also that the ratio was not depending on the temperature. This results was relatively different with the previous research for HRS-WC mixes using Asbuton Lawelle (Subagio, 2007), where the Ratio was depending on the temperatures. Figure 4 Ratio of Resilient Modulus measured by UMATTA vs calculated by Shell s equation at 35⁰C Figure 5 Ratio of Resilient Modulus measured by UMATTA vs calculated by Shell s equation at 45⁰C 9

10 5. RESILIENT MODULUS OF ASBUTON MIXES Comparing the Ratio of Resilient Modulus for Hot-Rolled Sheet (HRS) mixes (Subagio, 2007), (Fitriadi, 2006), with that for Asphaltic Concrete (AC-WC) mixes (Philips,2008), it was found that the results was relatively different, as shown by the figure 6 below. Its Ratio for HRS mixes was relatively constant at 35⁰C, while the Ratio for AC-WC mixes was nearly the same trend, only for RFA and RFC mixes. In contrary, its Ratio for AC-WC mixes at 45⁰C was relatively constant, while the Ratio for HRS mixes was significantly high. Those results are the subject for the future research on Asbuton mixes. Figure 6 Comparison of Ratio of Resilient Modulus between AC-WC mix versus HRS-WC mix 6. CONCLUSIONS Referring to the results of laboratory test and data analysis, some conclusions could be drawn: a. The AC-WC mixes using Retona Blend 55 have the better Marshall Characteristics than that using Petroleum asphalt Pen 60/70, showing by the high Stability, but those mixes need the higher asphalt content. b. The Water Resistance, represented by the IRS value, of all AC-WC mixes was significantly higher, namely greater than 95%, while the IRS value of AC-WC mix containing Asbuton Retona was higher than that using conventional bitumen. It means that the AC-WC mix containing Asbuton Retona gave the better resistance against water immersion. 10

11 c. The results of UMATTA test showed that the Resilient Modulus of AC-WC mix containing Asbuton Retona was greater than the AC-WC mix using conventional bitumen and the Asbuton Retona could increase also the mix resistance to high temperature. d. The Ratio between the experimental results to the theoretical calculation showed that its value was varied, from 1.15 to 5.09, meaning that no consistency was obtained. In effect, these Ratio calculated using Ullidtz-Nottingham s formula has little difference with the experimental results, compared to the Ratio calculated using Ullidtz-Shell s formula. REFERENCES McElvaney, J. (1986), Characteristics of Asbuton and Asbuton-Aggregate Mixtures, Pasca Sarjana Workshop, Bandung, Indonesia. McElvaney, J. (1988), Layered Elastic Analysis and the Structural Design of Flexible Pavements, Seminar on Road Pavement Design & Evaluation, University of Hongkong. Fitriadi, H., (2006), Evaluation of Resilient Modulus of Hot Rolled Sheet (HRS-WC) mixture containing Lawele s Asbuton ( in Indonesian ), Master s Thesis, STJR-ITB, Bandung, Indonesia. Dept.PU, (2007), Hot Mix Asphalt Mixture, 5 th volume: Specification, ( in Indonesian ), Jakarta, Indonesia. Kusnianti, N., (2003), Laboratory Assessment of the characteristics of Lawele s Asbuton in the Asphalt Concrete Mix ( in Indonesian ), Master s Thesis, STJR-ITB, Bandung, Indonesia. Lusyana, (2006), Assessment of Deformation and Dynamic Stability of Hot Rolled Sheet (HRS-WC) mixture containing Lawele s Asbuton ( in Indonesian ), Master s Thesis, STJR- ITB, Bandung, Indonesia. Subagio, B.S., et al. (2005), Fatigue Performance of Hot Rolled Asphalt and Superpave mixes using Asbuton as fine aggregates and filler, Journal of the 6 th International Conference of EASTS, Bangkok, Thailand. Subagio, B.S., et al. (2007), Plastic Deformation characteristics and Stiffness Modulus characteristics of Hot-Rolled Sheet (HRS) containing Buton Asphalt, Journal of the 7 th International Conference of EASTS, Dalian, China. The Asphalt Institute (1993), Mix Design Method for Asphalt Concrete and other Plant Mix Types, Manual Series No.2 (MS-2), 6 th Edition. SHELL Bitumen (1990), SHELL Bitumen Handbook, United Kingdom. 11

12 Table 1 Specifications for Asphaltic Concrete Wearing Course (AC-WC) Mix Characteristics Minimum Maximum Asphalt Absorption Compaction Number ( each surface ) 75 - Voids in Mix (VIM) (%) Voids in Mix Aggregates (VMA) (%) 18 - Voids filled with Asphalt (VFA) (%) 68 - Marshall Stability (kg) Flow (mm) Marshall Quotient (kg/mm) Index of Marshall Immersion (%) ( 24 hours, 60 ºC ) 75 - Voids in Mix Refusal (%) (VIM-R) Source : Dept. PU, 2007 Table - 2 Specification and test result for Bitumen Properties No Laboratory Test Unit Result Indonesian Specification Minimum Maximum 1 Penetration 0.1 mm Softening Point ºC Burning Point ºC Ductility cm > Solubility % Specific Gravity Loss on Heating (TFOT) % Penetration after TFOT % Viscosity (Saybolt Furol ) 120 o C cst ºC cst ºC cst ºC cst Source : Dept. PU,

13 Table - 5 Specification and test results for Aggregate Properties No Laboratory Test Unit Results Specification Min Max Coarse Aggregates 1 Bulk Specific Gravity SSD Specific Gravity Apparent Specific Gravity Water Absorption % Los Angeles Abrasion test value % 21, Angularity % >95 95/90 7 Flakiness Index % Elongation Index % Fine Aggregates 1 Bulk Specific Gravity SSD Specific Gravity Apparent Specific Gravity Water Absorption % Sand Equivalent % Filler 1 Specific Gravity ( fly-ash ) Specific Gravity ( Asbuton ) Source : Dept. PU,