THE STRENGTH AND STIFFNESS MODULUS OF THIN LAYER HOT MIX ASPHALT CONCRETE AT VARIOUS TEMPERATURE

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1 THE STRENGTH AND STIFFNESS MODULUS OF THIN LAYER HOT MIX ASPHALT CONCRETE AT VARIOUS TEMPERATURE Abdulhakim Mustafa Elshawesh 1), Ary Setyawan 2), Sholihin As ad 3) Post Graduate Civil Engineering ProgramsUniversitas Sebelas Maret ( ), Jl. Ir. Sutamai 36A, Surakarta 57126; Telp Abstract Stiffness modulus of asphalt concrete mixture is one of the most important parameters for the flexible pavement design that is very susceptible from temperature and time loading. The stiffness modulus here may be defined as a measure of the load spreading ability of material. The stiffness of asphalt mixture can be measured through various laboratory researches and empirical methods. Various laboratory researches have been employed to measure this property of asphalt such as indirect tensile modulus test, ITSM. The aims of this research were to achieve the viability of using asphalt 60/70 pen with different temperature on strength and stiffness modulus on thin layer HMA (4 cm) compared to Asphalt Concrete Wearing Course (6.8 cm). The other purpose is to get to know the effect of the using thin layer HMA (4 cm) in different climate region. All of the asphalt concrete mixtures of thin layer HMA and AC-WC which were used in this research based on Marshall Mix design according to Indonesian standard (Bina Marga 2010). The laboratories tests which have been conducted in this research were: indirect tensile strength (ITS), unconfined compressive strength (UCS) and indirect tensile stiffness modulus (ITSM) at temperature 10 C, 20 C, 40 C and 60 C. In comparison with the results of indirect tensile strength test, indirect tensile stiffness modulus test and unconfined compressive strength test, it is noticed that the strength and stiffness modulus of thin layer hot mix asphalt was affected by the temperature which the temperature degree might increase to decrease or the way around. From the results of ITSM test for HMA and AC-WC showed that starting from the temperature 20 C to 60 C there is no significant value of stiffness behavior at them. However, there is slight different value at temperature 10 C mixture respectively. Keywords: Thin layer, AC-WC, Asphalt 60/70 pen, ITS test, UCS test & ITSM (10 ºC, 20 ºC, 40 ºC, 60 ºC). I. Introduction Pavement materials should be designed to achieve a certain level of performance and the performance should be maintained during the service life. In order to provide a comfortable ride and withstand the effects arising from traffic loading and climate, asphalt concrete is the most commonly used material in pavement because of its superior service performance in providing driving comfort, stability (Ahmedzade, 2009). Asphalt concrete or as it is more commonly called hot mix asphalt (HMA) pavement, refers to the bound layers of a flexible pavement structure. For most applications, HMA is placed and compacted at elevated temperatures, hence the name. The temperature changes play a dominant role as a crack development factor. Therefore, studies have shown that the effect of the temperature shrinkage on the crack of the asphalt pavement is identical to that of the traffic loading. Temperature fatigue is one of the main failure modes of pavement structures, which results in degradation of the pavement materials and finally degradation of pavement structure (Ahmedzade, 2009). 1

2 Thin Hot Mix Asphalt Concrete Overlays are comprised of a thin less than one inch hot mix asphalt concrete layer and a binder material/tack coat. The binder material/tack coat is an asphalt emulsion modified to provide excellent adhesion of the hot mix asphalt concrete to the surface being overlaid. THMACO s are placed in a single lift at 3/8 to ¾ thick, making it an ultrathin overlay. THMACO s can be used as preventative maintenance on a roadway or as a new surface during construction. Several usages for this material are to improve ride quality, to restore skid resistance to seal the pavement surface, and to extend the pavement structure s life. Stiffness modulus of asphalt concrete mixture is one of the most important and necessary of parameters for flexible pavement design that it is very susceptible from temperature and time loading. Stiffness may be defined as a measure of the load spreading ability of a material and applies whether it is granular, asphaltic or cementations. It is a fundamental and important parameter that must be fully understood by the pavement Engineer. Libya is arid country where the temperature ranges from 11 O C-57.8 O C. This temperature variation can affect much on the property of thin layer asphalt. The current research study is focused on the effect of temperature variation on strength and stiffness modulus of thin layer hot mix asphalt concrete. The primary objectives of this study are: 1. To analyze the effects of temperature on strength and stiffness of thin layer hot mix asphalt; 2. To study the stiffness behavior of hot mix asphalt for thin layer and AC-WC with variations temperature (10 o C,20 o C, 40 o C, 60 o C); 3. To investigate the correlation between the ITS, UCS and ITSM). II. The Method In this study, the laboratory works can be divided into three stages: The First Stage: make tests in the laboratory on the following Aggregate materials, to know the physical properties and the possibility of their use in the mixture. The Second Stage: make test in the laboratory on the following bituminous material on Asphalt 60/70 pen, to know their physical properties and specifications. The Third Stage: a total of 102 samples prepared from Asphalt (60/70 pen) by Thin layer and AC-WC all of them separately. Including Marshall Stability Test (MS) to get OBC, (UCS), (ITS) and (ITSM) with at (10ºC, 20ºC, 40ºC, 60ºC). The objective of that is a comparing the results of laboratory tests to know the effects of temperature on strength and stiffness of thin layer hot mix asphalt. a) Sample preparation (for 1st stage): Preparing the Aggregate Samples: Aggregates used in this study consist of coarse aggregate, fine aggregate and filler. Coarse aggregate is defined as the aggregate retains on sieve size 4.75 mm (No.4) while fine aggregate is defined as the aggregate passing sieve size 4.75 mm (No.4) and retains on sieve size 75 μm (No.200). 1) 2 sample of Aggregate (Impact test); 2) 2 sample of Aggregate Specific Gravity and Absorption of Aggregates. 3) Aggregate Gradation The percentages of aggregates required for every sieve size were determined according to the Indonesian standards. Then the samples retained were calculated using the percent passing for every sample size. Table 1 below summaries the upper and lower limit According to Indonesian standards. Table: 2.1: Gradation limits for Wearing Course in Sieve size mm Upper Limit specs. Lower Limit specs. 3/4"

3 1/2" /8" # # # # # # # Pan (Source: Indonesian standards, 2010) b) Sample preparation (for 2nd stage): Preparing the bitumen samples in this study will use the type of bitumen asphalt 60/70 pen. The bitumen contents for these samples were ranged as (5 to 7) % of the total weight according to ASTM It has been made the tests for bitumen to know the physical properties of bitumen. c) Sample preparation (for 3rd stage): 1- Samples for Marshall Stability Test (M.S) The numbers of samples required are: 3 Samples for each percentage of bitumen and 15 samples for all percentages, according to Table 3.2. Table 3.2: Shows the distribution and number of samples of Marshall testing for each Percentage. 1- Sample Testing for Indirect Tensile Strength (ITS) at OBC. The numbers of sample required are: 3 samples of each type of thickness: Thin layer and AC-WC at each different temperature (10 C, 20 C, 40 C, 60 C) at OBC; Total of samples = 3 x 2 x 4 = Sample Testing for Unconfined Compressive Strength (UCS) at OBC. The numbers of sample required are: 3 samples of each type of thickness: Thin layer and AC-WC at each different temperature (10 C, 20 C, 40 C, 60 C) at OBC. Total of samples = 3 x 2 x 4 = Sample Testing For Indirect Tensile Stiffness Modulus (ITSM) At OBC The numbers of samples required are: 2 samples of each type of thickness: Thin layer and AC-WC at each different temperature (10 C, 20 C, 40 C, 60 C) at OBC. Total of samples = 2 x 2 x 4 = 16. III. Results and Discussions The aim of this study was to achieve the viability of using asphalt 60/70 pen with deferent temperature on strengths and stiffness modulus on thin layer HMA compared with AC-WC. To know the influence of used thin layer HMA at different climate region. All of the asphalt concrete mixtures thin layer HMA and AC- WC were prepared based on Marshall mix design. In comparison between the two types of thickness properties in terms of Marshall stability test (MS) to get optimum bitumen content, "Indirect Tensile Strength Test (ITS) and Unconfined Compressive Strength Test (UCS) and Indirect Tensile Stiffness Modulus (ITSM)" in different temperatures (10 C, 20 C, 40 C, 60 C). A- Aggregate Tests 1- Sieve Analysis and Aggregates Distribution. In this study, sieve analysis was conducted to separate the aggregate according to the sieve size. Asphalt concrete mixtures specifications require aggregate particles to be within a certain range of sizes and for 3

4 each size of particle to be presented in a certain proportion. Based on the Indonesian National Standards, the aggregates were blended as in Fig 4.1 and sieved. The aggregate samples passing from each sieve size were collected based on the percentage of the weigh. Fig 4.1: Grading chart for aggregates sieve analysis 2- Aggregate Impact Value Impact test was conducted to determine the validity of the use of aggregates in asphalt concrete mixture, the asphalt concrete mixture has been designed according to Indonesian national standards for the paving wearing course. the result was indicated to the good quality of strength of Aggregate Impact Value is 26.92%, where the Aggregate impact value must be Less than 30% (according to ASTM D Standard Test Method for Determination of the Impact Value). 3- Specific Gravity and Water Absorption. Aggregate size above 4.75 mm is defined as coarse aggregate and the specific gravity and absorption were analyzed according to Bina Marga, The results shown in Table 4.3 were indicated to the good quality of strength of aggregate. Table 4.3: Specific Gravity of Aggregate. Size of Aggreg ate Coarse Aggreg ate (%) % Bul k Specific Gravity gr/cm Appar ent Absorpt ion % % Fine Aggreg ate 33.6% 55 B- Asphalt Tests % Result of Penetration & Softening point Tests. The penetration test is an empirical test that measures the consistency (hardness) of asphalt. This test was conducted according to Indonesian National Standards (Bina Marga, 2010). Softening point test measures the temperature in which the asphalt reaches certain softness at the softening point temperature of asphalt. This test was conducted according to Indonesian National Standards (Bina Marga, 2010), where table 4.4 presents the results of penetration test & softening point value. Table 4.4: Results of Penetration & Softening point. 2- Maximum Specific Gravity of AC (Gmm) Maximum Specific Gravity of AC (Gmm) was important to use in Marshall Mix design control and carried out using 6.25% of bitumen by weight of sample. This test was conducted according to (ASTM D2041), to estimate the bitumen ratio (Pb) depending on the aggregate gradation in the Table 4.5 before by the following equation 4

5 Pb = A B C + K Where: A = Aggregate passed of Sieve 3/4 "and reserved on sieve 8 #. B = Aggregate passed of Sieve 8 # and reserved on sieve 200 #. C = Aggregate passed of Sieve 200 #. K = constant (0.5 to 1). Pb= x7+1 =5.901%. Table 4.5 shows the result of the Maximum Specific Gravity test of Asphalt concrete. 2- Indirect Tensile Strength Test (ITS) Indirect tensile strength testing under hot and low conditions was performed both on samples of thin layer HMA and AC-WC. Three samples for each type of tests were conducted at a temperature of 10ºC, 20ºC, 40ºC and 60ºC, the results can be seen in Table 4.7 and Figure 4.2. Table 4.7 Indirect tensile strength test results at various temperatures C- Asphalt Mixtures Tests 1- Marshall Mix Design The blend was prepared of asphalt 60/70 pen for two thicknesses of samples. Marshall Specimens were conducted according to (ASTM D 1559); specimens were prepared for each bitumen contents within the range given (5%, 5.5%, 6%, 6.5% and 7%). The optimum bitumen content has been determined in this study based on the maximum Stability according to the Marshall Stability (MS). Table 4.6 shows some properties of OBC that obtained from mix design. Figure 4.2: ITS results for each type of Asphalt cement mixes. From Figure 4.2 it is clear that ITS value decrease following the increase temperature for both of thin layer hot mixture and AC- WC. The different between them decreases with the increase the degree of temperature. The max different was at lowest temperature of 10 o C and minimum different was at highest temperature of 60 o C. The reason of these phenomena is cohesion (bonding) 5

6 between aggregate and asphalt bitumen decreases by increase of temperature. This relationship agrees with many literatures (Setyawan, 2003 & Anderton 2000). Where this bonding reduce by temperature especially when the temperature nearest to the softening point of asphalt bitumen (60/70) (48 o C). This bonding increases at the lower temperature and from the figure it s shown that the ITS AC-WC is higher than thin layer HMA in average (19.62%) for each temperature. 3- Unconfined Compressive Strength Test (UCS) This test used to determine the permanent deformation of normal and modified asphalt mixtures. Unconfined compressive strength was performed both on samples of thin layer HMA and AC-WC. They are used to determine the resistance to permanent deformation of bituminous mixtures at (10 C, 20 C, 40 C and 60 C) and loads. UCS was conducted by applying a static load to a specimen using OBC and then measuring the maximum load. It noticed that the permanent deformation of the asphalt mixtures correlated with the rutting potential. Figure 4.3 and Table 4.8 shows the summarized results for the Unconfined Compressive Strength Test (UCS) for each type of asphalt cement at OBC. Table 4.8 : Results of UCS Test at OBC. Figure 4.3: Results of UCS test for each type of asphalt cement mixers at OBC. Through a review of the results of UCS test in Table 4.8 and Figure 4.3 it can stated that: a) The unconfined compressive strength is affected by temperature From the Figure 4.3 It is clear that there are differences on unconfined compressive strength between thin layer hot mixture and AC-WC. The thin layer hot mixture for unconfined compressive strength is higher than AC-WC for all degrees of temperature and the unconfined compressive strength increase as the temperature decrease. This relationship agrees with the research by Mater (2014). b) The unconfined compressive strength is affected by thickness The unconfined compressive strength is affected by thickness and the compressive strength increased by decrease thickness of sample and from the figure it is shown that the UCS of thin layer HMA is higher than AC-WC in average (49.81%) for each temperature. 4- Indirect tensile strength modulus (ITSM) Resilient modulus testing was performed both on samples of thin layer HMA and AC- WC using UMMATTA. Tests were conducted at a temperature of 10ºC, 20ºC, 40ºC and 60ºC and the results can be seen in Table 4.9 and Figure 4.4. Table 4.9 Resilient modulus test results at various temperatures. 6

7 Figure 4.4 and Table 4.9 shows the summarized results for the Test for each type of asphalt cement at OBC. From the fig 4.4 it is clear that temperature 20 o C to 60 o C there are no differences on indirect tensile stiffness modulus and only small different recorded at temperature10 o C. The stiffness modulus decreases following the increase the degree of temperature. This relationship agrees with many literatures (Setyawan, 2003 & Anderton, 2000). It is shown that temperatures from 40 o C to 60 o C the result is not good however, this is normal because the temperature of the softening point of asphalt bitumen 60/70 is 48 o C. 5- The correlation between the ITS and ITSM for thin layer Resilient modulus and indirect tensile stiffness testing was performed on samples of thin layer. Tests were conducted at a temperature of 10ºC, 20ºC; 40ºC and 60ºC, and the results can be seen in Table 4.10 and Figure 4.5. Table 4.10 the ITSM and ITS tests results at various temperatures. Figure 4.5 The correlation between the ITS and ITSM for thin layer From figure 4.5 it is shown that the result is good as the (R 2 =0.992) and almost to one. It is clear that there is correlation between ITS and ITSM. The following equation to calculate ITSM at specified temperature ITSM = * ITS with R 2 can be used. 6- The correlation between the ITS and ITSM for AC-WC Resilient modulus and Indirect tensile stiffness testing was performed on samples of AC-WC. Tests were conducted at a temperature of 10ºC, 20ºC; 40ºC and 60ºC, and the results can be seen in Table 4.11 and Figure 4.6. Table 4.11 the ITSM and ITS tests results at various temperatures Figure 4.6 The correlation between the ITS and ITSM for AC-WC From figure 4.6 it is shown that the result is good as the (R 2 =0.986) and almost one. It is 7

8 clear that there is correlation between ITS and ITSM. The following equation to calculate ITSM at specified temperature ITSM = * ITS with R 2 can by used. Table 4.13 the ITSM and UCS tests results at various temperatures 7- The correlation between the UCS and ITSM for thin layer Resilient modulus and unconfined compressive strength testing was performed on samples of thin layer. Tests were conducted at a temperature of 10ºC, 20ºC; 40ºC and 60ºC, and the results can be seen in Table 4.12 and Figure 4.7. Table 4.12 the ITSM and UCS tests results at various temperatures Figure 4.8 The correlation between the UCS and ITSM for AC-WC From figure 4.8 it is shown that the result is good as the (R 2 =0.996) and almost one. It is clear that there is correlation between UCS and ITSM. The following equation to calculate ITSM at specified temperature ITSM = * UCS with R 2 can by used. CONCLUSIONS Figure 4.7 The correlation between the UCS and ITSM for thin layer From figure 4.7 It is clear that there is correlation between UCS and ITSM as the result (R 2 =0.772), it is nearest to one. The following equation to calculate ITSM at specified temperature ITSM = * UCS with R 2 can by used. 8- The correlation between the UCS and ITSM for AC-WC Resilient modulus and unconfined compressive strength testing was performed on samples of AC-WC. Tests were conducted at a temperature of 10ºC, 20ºC; 40ºC and 60ºC and the results can be seen in Table 4.13 and Figure Conclusion a) The effect of temperature on the strength and stiffness modulus decrease with increase the degree of temperature and increase with decrease the degree of temperature and this relationship agrees with many literatures (Setyawan, 2003 & Anderton, 2000 & Matar, 2014). b) The results of ITSM test for thin layer and AC-WC shows that temperature 20 o C to 60 o C there are no differences values of stiffness behavior between thin layer and AC-WC. There is small different at temperature 10 o C mixtures respectively. c) From the result of ITS, UCS and ITSM for thin layer and AC-WC it is clear there is correlation between ITS, UCS and ITSM.it can be using the following 8

9 equation calculate ITSM at specified temperature for thin layer and AC-WC: 1) The equation of AC-WC is ITSM = * ITS with R 2. 2) The equation of thin layer is ITSM = * ITS with R 2. 3) The equation of AC-WC is ITSM = * UCS with R 2. 4) The equation of thin layer is ITSM = * UCS with R 2. IV. REFERENCES Ahmedzade P, Sengoz B Evaluation of Steel Slag Coarse Aggregat in Hot Mix Asphalt Concrete, 165: Matar. M., The Application of Asbuton and Polymer Modified Bitumen for Pavement Mixture Design at Arid Region. Repulik Indonesia, Kementerian Pekrjaan Umum Direktorat Jenderal Bima Marga Setyawan A, 2002, Development of Semi- Flexible Heavy-Duty Pavements. 9