Testing and appraisal of Lucobit polymer effect as an additive on asphalt mixture performance

Transcription

1 Abstract Testing and appraisal of polymer effect as an additive on asphalt mixture performance Hamid Sabbagh mollahosseini*,golazin Yadollahi**, Ershad Amoosoltani*** *, ***Executive of Engineering and civil organization of Tehran municipality **MS of Civil Engineering Corresponding author's & During two last decades intensive investigations have been performed on polymer modified asphalts. Polymers have acceptable effects on asphalt mixes in low and high temperature, by increasing fatigue cracking resistance, rutting and thermal cracking. In the majority of investigations which have ever done, only performance properties of polymer modified asphalts have been compared with other mixes. Optimum polymer content in binder due to volumetric and performance properties of asphalt mixtures must be considered in polymer modified asphalt mix design, which is the most important factor in mix design. Since fatigue and rutting of asphalt mixtures depend on structural properties of used binder, so it's necessary to perform different tests on binder specimens. Although many types of polymer modified binders have been used in Iran up to now, unfortunately particular performance tests were not performed on using binder for determining their optimum properties. In addition to all mentioned factors, other common tests such as fatigue and rutting tests were not performed on polymer modified binders. This essay tries to introduce a type of polymer additives named lucobit for using in asphalt mixtures and evaluating its effect on mixture performance properties, which is important in comparison with traditional asphalt mixtures, after determining optimum polymer content. The results depicted that lucobit could better achieve mixture performance like rutting and fatigue and moisture susceptibility than other polymer such as. These results in combination with the ease of using this kind of additive can lead us to a better system for producing asphalt mixture. 1 Introduction For Assessing and identifying the pavement problems, it's necessary to recognize the conditions which are exerted to pavement during time periods, and also attention to these problems in test process. Among these parameters, we can mention internal factors (mechanic of material, time intervals and material properties), pavement structure, construction process (production and construction, compaction process, climate conditions) external factors (temperature and moisture, bearing capacity and traffic volume).

2 Pavement failures such as fatigue cracks usually occur in places which pavement subjected to maximum tension stresses and also due to combination of effect of load, temperature and traffic. This is a long lasting process and propagates due to time passing. As the process of fatigue cracking propagation is slow, so modified asphalt mixture and pavement structural analysis can be use to eliminate this process. Permanent deflection as rutting usually occurs under pressure and shear stress and some parameters such as temperature and traffic jam effect intensively. Since the deflection propagation usually occurs gradually, but during hot season and under heavy traffic load, deflections reach to critical point. Rutting usually decrease with aging. The affected region is located in upper layer and it demonstrates that the problem is not solvable with design type only. Therefore the suitable asphalt mixture design and improvement of asphalt properties are the only way for rutting prevention. Using binder additives has an important effect on fatigue cracks and rutting prevention. In this article we try to evaluate the effectiveness of some polymeric additives such as on asphalt properties by using performance test. 2 polymeric binder production With considering the particle dimensions and for distributing them in the form of micro particles in binder, a high shear mixer was used. Polymeric mixtures were fabricated using 3,5,7,9 percent of and ; and added to binder during 5 minutes and in 160 º C. Mixing procedure were began with high shear speed about 4000 (rpm) and after a short while it increased to 5500 (rpm) and last about one hour and 30 seconds. During this procedure, the mixing temperature was controlled with thermometer in 190 º C. The flexibility of binder was saved in low temperature simultaneously by increasing of stability (Asphalt mixture tests such as flow and resilient modulus confirmed this idea) and it relates to performance of plastic grid and elastomeric part. The viscosity of modified binder is higher in 60 º C and this high viscosity is the main reason for improving binder and asphalt mixture properties. The relationship between viscosity and temperature for modified and original binder have illustrated in figure 1.

3 Viscosity Binder Polymeric binder 70 C 30 C Tempreature Figure1: Typical viscosity changes versus temperatures for original and polymer modified binder Simultaneously with increasing the percent of polymer, softening point is increased and binder reaches to viscous form later. Both of modified binders with and have increased flash point. In the other word the higher flash point prepared more safety factors during working with binder. 21 Binder tests The increasing stability and promoting pavement performance are the main purpose for adding polymeric additives in binder. The effects of these additives on pavement performance are not clear in short time. However the technical tests usually take a long time, but they are necessary. In this way the following tests were performed on modified binder: Penetration test (ASTM D5), softening point (ASTM D3676), Tension test (ASTM D113), kinematics viscosity test in 135 o c (ASTM D2170), specific gravity in 25 oc (ASTM D70) and flash point (ASTM D92). The results of tests have been demonstrated in table Binder test results analysis The results depicted that polymer modified mixtures had less specific gravity due to expansion and propagation of polymer in binder. Penetration test results showed that in modified binder severely reduction in penetration value occurred by increasing the polymer content. It means that the higher stability obtained in medium and high temperatures and also rutting decrease in tropical regions.

4 Table 1: Binder test results for and additives Binder type Asphalt Cement 3% 3% 5% 5% 7% 7% 9% 9% Specific gravity in 25 oc Tension test (cm) > Penetration test in 25 oc (dmm) Softening point ( o c) kinematics viscosity in 135 oc (cst) Flash point ( o c) Aggregates The specific gravity of coarse and fine aggregate and also filler and aggregate mixture obtained according to tables 2 and 3. As polymeric asphalt usually use in top coat, so the production of samples accomplished according to the middle grading limits of SP2 standard. Table 2: specific gravity of aggregates Aggregates type Filler Fine aggregate Coarse mixture Apparent specific gravity Bulk specific gravity Table 3: selected grading Sieve No. (mm) Passing percent (middle curve)

5 4 Asphalt tests results In general, the asphalt tests usually have 2 purposes. First, receive to an optimum asphalt mixture design (estimating the polymer and optimum binder content) respect to available aggregates. Second, forecasting the performance of asphalt mixtures in term of aging. After analyzing the binder results, asphalt samples prepared with different percent of binder and polymer. The results have been demonstrated in table 4 and figures 2 and 3. Table 4: Volumetric properties of polymer modified asphalt mixtures Binder type Asphalt Cement 3% 3% 5% 5% 7% 7% 9% 9% Maximum apparent specific gravity in 25 oc Air void Void in mineral aggregate (VMA) Void fill with asphalt (VFA) Marshal stability Optimum binder content In order to produce an asphalt mixture with polymer modified binder, two polymer modified binders with 5% & were used. For assessing the moisture susceptibility of mixtures, two tests include, immersion marshal, and, moisture effect on asphalt mixture, were carried out. Furthermore, the elasticity properties were controlled with resilient modulus test. Specific Gravity Binder content Figure2: specific gravity curves of asphalt mixtures (a)

6 Binder content Figure2: specific gravity curves of asphalt mixtures (b) Marshal Stability (Kg) Binder Content Marshal Stability (Kg) Specific Gravity Binder Content Figure3: Stability changes of asphalt mixture

7 5 Asphalt Performance Test 51 Indirect Tensile Test Modified and ordinary samples prepared in optimum binder percent and laid in specific test mold according to AASHTO T283. This mold has 2 loading frames with 12.7 (mm) width and a radius curve equal to the radius of samples. A compressive load was applied by marshal apparatus with the speed of 50.8 mm/min. The tensile stability (St) was calculated according to following equation. 2 p S t = (1) π Dt t: Sample thickness D: Diameter P: Failure force kg kg The average of tensile stress is 7.55 ( ) 2 for 3 ordinary samples and ( 2 ) for 3 cm cm kg modified samples with and ( ) for Lcobit. 2 cm 52 Marshal Immersion Test The 6 marshal asphalt samples prepared with pure binder and 6 additional samples prepared with modified binder at optimum binder content. 50% of samples placed in 60 o c water bath about 24 hours and the remained samples leaved in room temperature and in dry condition. Finally all samples loaded with marshal apparatus. The stripping damage index is the ratio of compressive stability after moisture conditioning to compressive stability in dry condition. The results summary has been shown in table 5. Table 5: Marshal Immersion Test Results Type of samples ordinary Modified Modified With With condition wet dry wet dry wet dry The average of marshal stability (kg) Marshal stability ratio (%)

8 53 Predicting the Moisture Resistance of Asphalt Mixture This test was done according to ASTM D4867. The specific property of this test is 7.0±0.5 percent air void. Moisture susceptibility index which is called TSR is the ratio of average tensile stability of samples in wet conditions to dry conditions. The abstract of results have been demonstrated in table 6. Table 6: moisture susceptibility test results Type of samples ordinary Modified With Modified With Condition wet dry wet dry wet dry Indirect Tensile Strength (Kpa) Tensile Strength Ratio (%) Resilient Modulus Test This test was done using UTM apparatus according to ASTM D4123 in 3 temperature include 5, 25, 40 o c and under 1300 (N) load pressure, 1(Hz) frequency, 0.1 sec loading time. This load was frequently applied in vertical diagonal direction. The horizontal elastic deformation measured with two sensors which had attached to the samples oppositely. The resilient modulus was calculated by assuming υ= Results have been demonstrated in table 7. Table 7: Resilient Modulus in different temperatures (Mpa) Temperature ( oc ) ordinary samples Modified samples Modified samples Creep Test This test was used for determining asphalt mixture deformation. The deformations of cylindrical samples evaluate under static loads and in different times. We can use this test for estimating a long lasting permanent deformation of asphalt mixtures.

9 This test was performed in 40 o c. Specimens were preloaded for 2 minutes under 20 KPa static pressure. More over specimens were loaded under 100 kpa load about 3600 sec. Creep test results have been shown in figure 7. Time (ms) Cumulative Strain (micro) Cumulative Strain (micro) Time (ms) Figure 7: Cumulative Strain of different asphalt mixtures 6 Asphalt mixture tests analysis The maximum apparent specific gravity is lower in polymer modified asphalt mixture and it relates to the lower specific gravity of binder. Simultaneously with decreasing binder specific gravity and effective specific gravity of aggregates in polymer modified asphalt mixture, we face with deduction of aggregates binder absorption percent and it prove that in the same amount of asphalt content in these mixtures, more effective binder is available.

10 The bulk specific gravity of modified binder mixture is a bit higher than ordinary samples. Compressive stabilities (marshal stability) of modified samples in all binder contents are higher than normal samples (Figure 3). Furthermore the higher flow values relate to the higher diagonal deformation in failure time and also the better flexibility. Since insufficient tensile strain resistance caused by repeated traffic loading, temperature deduction and shrinkage of asphalt mixture, is one of the main reasons for pavement cracks, [4,1], therefore 35 percent increase in tensile stability is entirely satisfactory for polymer modified asphalt mixtures with modifier. Table 5 and 6 illustrate that the modified mixtures are more durable due to the same value of indirect tensile strength in wet and dry conditions. According to the resilient modulus test results (table 7), polymer modified samples reveals better elastic behavior against fatigue. The higher amount of resilient modulus shows the better resistance against frequently loading and delay in fatigue cracking. Figure 3 shows the higher resistance against permanent deformations in asphalt mixtures with modified binder. 7 Conclusion It seems to be satisfying to mix binder with 46 percent of or modifiers. In lower percent, modification and improvement of binder's performance is so insignificant and higher percent more than 6 is not recommended due to high viscosity of binder. The assessment of results for two different asphalt mixture designs shows that deduction of air void, results the difficulty of water and air penetration and also higher durability in polymer modified asphalt without any increase in binder percent and stability decrease. It seems to be satisfying using modified binder with polymer in regions which have hot summer and cold winter and high difference between day and night temperatures. Increase of binder penetration with high stability of mixtures in hot weather can be a reason for high bearing capacity of pavement without any rutting. An excellent tensile strength, higher flow and resilient modulus of asphalt mixture and elastic properties of binder create a suitable flexibility which makes proper and durable mixture for using in cold weather. Despite of higher initial production costs for this type of modified binder, it is economical due to the high durability, long life period time and cost effectiveness in periodic maintenance programs and rehabilitations.

11 8 References 1. Massenza. S.r.l., Technical Aspect of PMBs, November The Asphalt Institute, Durability of Asphalt Mixtures, MS2, Section 3, Page Hunter. H, Asphalt in Road Construction, Annual book of ASTM standards, Volume 0403, Xiaohu. Lu, Isacsson Ulf, Chemical & Rheological Characteristics of PMB, TRR, Paper No Grunfelder. T, Asphalt Modified by Triblock Copolymer Polymer engineering & science, No 12, Vol. 36, June Behbahani Hamid, Ziari Hassan, Noubakhat Shams." The Use of Polymer Modification of Binder for Durant Hot Asphalt Mixtures" Journal of Applied Sciences Research, 4(1): , , INSInet Publication 8. Baha Vural KÖK, Necati KULOĞLU. " INVESTIGATION OF MECHANICAL PROPERTIES OF ASPHALT CONCRETE CONTAINING STYRENE BUTADIENE STYRENE" Journal of Engineering and Natural Science Mühendislik ve Fen Bilimleri Dergisi