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Influence of using nonmaterial to reduce the moisture susceptibility of hot mix asphalt
Construction and Building Materials 31 (2012) 384–388
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Influence of using nonmaterial to reduce the moisture susceptibility of hot mix asphalt F. Moghadas Nejad a,⇑, A.R. Azarhoosh b, GH.H. Hamedi a, M.J. Azarhoosh c a
Department of Civil & Environmental Engineering, Amirkabir University of Technology, Tehran 15875, Iran Department of Civil Engineering, University of Guilan, Rasht, Iran c Department of Chemical Engineering, Amirkabir University of Technology, Tehran, Iran b
a r t i c l e
i n f o
Article history: Received 1 October 2011 Received in revised form 30 November 2011 Accepted 11 January 2012 Available online 8 February 2012 Keywords: Moisture damage Zycosoil Indirect tensile-strength Fatigue Silanol group Siloxane bond
a b s t r a c t Moisture damage in an asphalt mixture can be defined as the loss of strength, stiffness and durability due to the presence of moisture leading to adhesive failure at the binder–aggregate interface and/or cohesive failure within the binder or binder–filler mastic. In order to improve adhesion and reduce moisture sensitivity in asphalt mixtures, two different approaches have become apparent. One approach suggests that the aggregate surface be coated by a suitable agent that will reverse the predominant electrical charges at the surface and thus reduce the surface energy of the aggregate. In this study, the effects of nanomaterial, namely Zycosoil, on the moisture damage of asphalt mixtures were studied. Two types of aggregates that represent a considerable range in mineralogy, limestone and granite, were evaluated during the course of this study. To assess the impact of Zycosoil on moisture damage of hot mix Asphalt, control mixes (without Zycosoil) and mixes containing Zycosoil in dry and wet conditions were tested using indirect tensile-strength (ITS) and indirect tensile fatigue (ITF) tests. The results showed that limestone has less moisture damage potential compared to granite. The ratio of wet/dry values of ITST and ITFT for mixes containing Zycosoil was higher than the control mix for two types of aggregate. However, in mixtures made of granite aggregate, using Zycosoil is more effective. As the density of silanol groups is more in its surface, these groups are hydrophilic, and Zycosoil migrates to the polar water-loving surface, reacts with the silanol groups and forms siloxane bond, the strongest bond in nature, and creates a molecular level hydrophobic zone. Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved.
1. Introduction Moisture damage in asphalt pavements has been considered a widespread problem in the world. Water that infiltrates the pavement structure may cause premature failure of hot-mix asphalt layers. Moisture damage can generally be classified in two mechanisms: (a) loss of adhesion and (b) loss of cohesion. The loss of adhesion is due to water getting between the asphalt binder and the aggregate and stripping away the asphalt film. The loss of cohesion is due to the softening of asphalt concrete mastic. The two mechanisms being interrelated, a moisture damaged pavement may be a result of both mechanisms combined [1]. Moisture damage is a function of several factors. These factors include asphalt mixture characteristics, environmental factors, construction practices, etc. [2]. Moisture damage has caused many pavement failures. Moisture reduces the internal strength of the HMA mix, the stresses generated by traffic loads increase significantly and lead to fatigue cracking or rutting of the HMA layer. In general, susceptibility of HMA to ⇑ Corresponding author. Tel.: +98 (21) 64543004; fax: +98 (21) 66414231. E-mail address: [email protected] (F. Moghadas Nejad).
fatigue and rutting caused by moisture damage are determined by tensile strength test. The use of antistrip agents (ASA) is the most common method of improving the moisture susceptibility of asphalt mixes. The primary goal of an antistrip additive is to eliminate the moisture sensitivity of the HMA mixture by improving the bond between the asphalt binder and the aggregate. Typical antistrip agents used today are fatty amines and fatty amido-amines. It should be noted that an effective additive must improve both the unconditioned and moisture conditioned properties in order to ensure good long-term performance, which antistrip agents often fail to do [3]. 1.1. Literature review A study of the impact of lime and liquid additives on the moisture susceptibility of HMA mixtures from eight Texas districts in 1991 was conducted by Kennedy and Ping. The tensile strength ratio (TSR) of the laboratory mixtures indicate that lime treatment is consistently highly effective in reducing moisture damage of the Texas HMA mixtures from all eight districts. The TSR values of the lime-treated mixtures are significantly higher than those values for all liquid additives from all eight districts [4]. In another
0950-0618/$ - see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2012.01.004
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F. Moghadas Nejad et al. / Construction and Building Materials 31 (2012) 384–388
study conducted by Pickering et al. [5], the objective of the research was to compare the effectiveness of lime and two liquid additives in reducing the moisture damage of HMA mixtures. The research program measured the resilient modulus (Mr) and tensile strength (TS) properties of the HMA mixtures before and after moisture conditioning. The resilient modulus and tensile strength data indicate that the lime treatment of the two aggregate sources resulted in significant improvements of the unconditioned and moisture conditioned properties. In the case of the two liquid additives, the improvements in the Mr and TS properties were insignificant and inconsistent. In most cases the liquid additives showed an improvement in the unconditioned property but they did not maintain the improvement after moisture conditioning and vice versa. Sebaaly et al. [6] examined the resilient modulus and tensile strength properties of the field mixed-laboratory compacted samples measured at both unconditioned and conditioned stages, and showed that the mixtures treated with hydrated lime on both projects (SD-314 and US-14) exhibited better moisture resistance than the control, UP5000 (a latex polymer additive) and liquid antistrip mixtures. The superior performance of the mixtures treated with hydrated lime was shown by higher retained strength after the moisture conditioning process. Lu and Harvey evaluated the resistance to moisture damage of an HMA mix manufactured with a California aggregate that is known to have poor compatibility with asphalt binder. They used fatigue and tensile strength tests to evaluate the resistance to moisture damage of mixes. The tensile strength properties of the evaluated mixture showed that hydrated lime improves the tensile values at both un-conditioned and moisture-conditioned stages. They show that the tensile ratios of the lime-treated mixture are significantly higher than the control and liquid A-treated mixtures. In addition, fatigue properties indicated that the lime-treated mixture started with higher fatigue life than the control and the two liquid-treated mixtures, and maintained higher fatigue life after moisture damage [7]. In this study, the effect of moisture damages on HMA was evaluated using indirect tensile strength (ITS) and indirect tensile fatigue (ITF) tests. The ITS test examines the strength loss of asphalt mixes due to moisture, whereas the ITF test examines the moisture effect on the fatigue response of asphalt mixes. Zycosoil was used as an antistrip agent. 2. The statement and objectives of the present study Opposed to the typical antistrip agents (amines), Zycosoil nanotechnology produces a hydrophobic nano layer on aggregates since it converts the hydrophilic silanol groups to hydrophobic siloxane groups. Although both Zycosoil and amines reduce the moisture damage, the key difference between Zycosoil and amines is that Zycosoil eliminates water sensitive surface permanently and makes it oil-loving, whereas amines can only moisturize, and do not chemically modify the surface. Instead, it always remain hydrophilic, which leads to moisture susceptibility. In order to avoid stripping in HMA, antistrip agents modifying the aggregate surface can be used. In this study, nanotechnology is investigated as a new antistrip agent. Considering the fact that fatigue damage is one of the most common failures in asphalt pavement, indirect tensile fatigue test is used. The indirect tensile strength test was also utilized to consider the effect of moisture on strength of asphalt mixtures. The specific objectives of this study are: To evaluate the effect of Zycosoil as an additive on the asphalt mixes. Evaluating the behavior of asphalt concrete mixes under ITS and ITF tests in dry and wet conditions with and without Zycosoil treated aggregates.
To provide fatigue models for mixtures with and without Zycosoil treated aggregates. 3. Materials 3.1. Aggregate and asphalt binder Two types of aggregates were evaluated in the study. The two aggregates (limestone and granite) represent a considerable range in mineralogy and associated degree of stripping with them. The chemical compositions of the aggregates are listed in Table 1. The physical properties of the two types of aggregates are given in Table 2. To characterize the properties of the base asphalt binder, conventional test methods, such as the penetration test, softening point test and ductility were performed. The engineering properties of the asphalt binder are presented in Table 3. The gradation of the aggregates used in the study (mean limits of ASTM specifications for dense aggregate gradation) is given in Table 4. The nominal size of this gradation was 19.0 mm. 3.2. Additive Zycosoil (Zy) is a water soluble reactive organo-silicon component that is specially designed to improve the adhesion between bitumen and aggregates in hot mix asphalt. The dosage of this antistrip additive is normally between 1% and 1.6% by weight of the aggregate. Physical and chemical properties of Zycosoil are given in Table 5. 4. Experimental setup and procedure 4.1. Mix design Initially, the Zycosoil solution is sprayed on the aggregates and is then exposed to air to dry after being mixed with the aggregates. Then, aggregates are heated to 160–170 °C for 24 h and are combined with the asphalt binder at 165 °C. Finally, the asphalt mixtures were designed using standard marshal mix design. Two series of marshall specimens were fabricated. The first series of the specimens contained several of binder contents to determine the optimal binder content. The second
Table 1 Chemical composition of the two types of aggregates. Properties
Limestone
Granite
pH Silicon dioxide, SiO2 (%) R2O3 (Al2O3 + Fe2O3) (%) Aluminum oxide, Al2O3 (%) Ferric oxide, Fe2O3 (%) Magnesium oxide, MgO (%) Calcium oxide, CaO (%)
8.8 3.8 18 1 0.4 1.2 51.3
7.1 68.1 16.2 14.8 1.4 0.8 2.4
Table 2 Physical properties of the aggregate. Test
Standard
Specific gravity (coarse agg.) Bulk SSD Apparent Specific gravity (fine agg.) Bulk SSD Apparent Specific gravity (filler)
ASTM C 127
Los angeles abrasion (%) Flat and elongated particles (%) Sodium sulfate soundness (%) Fine aggregate angularity
Limestone
Granite
Specification limit
2.612 2.643 2.659
2.654 2.667 2.692
– – –
2.618 2.633 2.651 2.640
2.659 2.661 2.688 2.656
– – – –
C
25.6
19
Max 45
D
9.2
6.5
Max 10
C
2.56
1.5
Max 10–20
C
46.65
56.3
Min 40
ASTM C 128
ASTM D854 ASTM 131 ASTM 4791 ASTM 88 ASTM 1252
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Table 3 Results of the experiments conducted on 60/70 penetration grade asphalt binder. Test
Standard
Result
Penetration (100 g, 5 s, 25 °C), 0.1 mm Penetration (200 g, 60 s, 4 °C), 0.1 mm Penetration ratio Ductility (25 °C, 5 cm/min), cm Solubility in trichloroethylene (%) Softening point (°C) Flash point (°C) Loss of heating (%) Properties of the TFOT Residue Penetration (100 g, 5 s, 25 °C), 0.1 mm Specific gravity at 25 °C (g/cm3) Viscosity at 135 °C, cSt
ASTM ASTM ASTM ASTM ASTM ASTM ASTM ASTM
64 23 0.36 112 98.9 51 262 0.75
D5-73 D5-73 D5-73 D113-79 D2042-76 D36-76 D92-78 D1754-78
19 100 100
12.5 90– 100 88
4.75 44– 74 75
60 1.020 158.5
2.36 28– 58 56
0.3 5– 21 40
0.25 2– 10 20
0.106 7–18
0.075 4–10
9
6
series were at the optimal binder content to evaluate the HMA mechanistic properties. For each aggregate blend and asphalt binder content, at least three samples were produced to determine the reproducibility of the results [8]. The optimum binder content for the mix design was determined by taking the average values of the following three bitumen contents: (1) Binder content corresponding to maximum stability. (2) Binder content corresponding to maximum bulk specific gravity. (3) Binder content corresponding to the median of designed limits of percent air voids in the total mix. The stability value, flow value, and voids filled with bitumen (VFB) are checked with the marshall mix design specification. The optimum asphalt binder contents were found to be 5.6% and 5.1% for limestone and granite aggregates, respectively. Tests are conducted on samples in dry and wet conditions. Wet conditions were created by placing the samples in water of 60 °C for 24 h.
4.2. Indirect tensile-strength test (ITST)
where ITS is the indirect tensile stress (kPa), F is the failure load (kN), t is the sample thickness (m), and d is the sample diameter (m). The indirect tensile strength ratio (TSR) was determined by the following equation:
TSR ¼ 100ðF cond =F uncond Þ
ð2Þ
where Fcond is the indirect tensile strength of the wet specimens, Funcond is the indirect tensile strength of the dry specimens.
Fatigue cracking is one of the three major distresses (fatigue cracking, low-temperature cracking and rutting) of flexible pavements. Fatigue cracking is primarily caused by repeated traffic loading leading to significant reduction in the serviceability of flexible pavements. The cracking resistance of hot-mix asphalt (HMA) mixtures is directly related to the fatigue performance of flexible pavements. Therefore, the fatigue behavior of HMA mixtures has been intensively studied for many years [12]. The fatigue process occurs in three distinct stages: (1) crack initiation: development of microcracks, (2) crack propagation: development of macrocracks out of microcracks resulting in stable crack growth and, (3) disintegration: collapse and final failure of the materid due to unstable crack growth [13]. Numerous models of varying sophistication have been developed to predict the fatigue behavior of asphalt concrete including elastic, viscoelastic, elastoplastic, viscoplastic, and crack models that are developed by using different laboratory testing modes. The most common methods for characterizing the fatigue behavior of asphalt mixtures are the Wohler approach, dissipated energy method and fracture mechanics approach [14]. Several factors can be effective on fatigue behavior of asphalt mixtures, which are included: asphalt layer thickness; type of loading (controlled strain and controlled stress); shape, frequency and rest period in loading; properties of asphalt mixtures (asphalt content; air void; type, shape and gradation aggregates) and environmental conditions (temperature changes, wet and freezing) [15–17]. The indirect tensile fatigue test is able to characterize the fatigue behavior of the mixture. Fatigue tests were carried out in both controlled strain mode and controlled stress mode. In controlled strain mode, the strain was maintained by reducing the stress on the sample. In controlled stress mode, the stress was held constant to increase the strain within the sample [18]. The relationship between tensile strain and number of cycles to failure for each material was established. A linear relationship was recorded when strain is plotted against the numbered cycles to failure in logarithmic scale and the fatigue life prediction equations were developed [14]. Using a regression analysis, the fatigue equations were developed, which are in the form of Wohler’s fatigue prediction model (Eq. (3)).
Nf ¼ K 1
The stripping resistance (water susceptibility) of asphalt mixtures was evaluated by the decrease in the loss of the indirect tensile strength (ITS) after immersion in water for 24 h in temperature 60 °C, according to AASHTO T-283 test procedure [9]. The tensile strength of an HMA mix is generated by the cohesive strength of the asphalt binder and the bond strength at the binder-aggregate interface. The tensile strength is calculated from the maximum load the sample can undergo prior to cracking. A mix with higher tensile strength provides better resistance to fatigue and thermal cracking [10]. Therefore, any additives that can generate a higher tensile strength in the HMA mix in the dry and moisture-conditioned stages will improve the long-term performance of an HMA pavement. This test involves loading a cylindrical specimen with vertical compressive loads; this generates a relatively uniform tensile stress along the vertical diametrical plane. Failure usually occurs in the form of splitting along this loaded plane [11]. Six samples from each mix (dry and wet) prepared and compacted. The compacted specimens should have air void contents between 6.5% and 7.5%. Half of the compacted specimens are conditioned. First, vacuum is applied to partially saturate specimens to a level between 55% and 80%. Vacuum-saturated samples are kept in a 60 °C water bath for 24 h. After this period the specimens are considered conditioned. The other three samples remain unconditioned. The failure load for each sample was recorded at 25 °C. The ITS for each sample was calculated using the following formula: Table 5 Properties of the Zycosoil. Properties Form Color Flash point Viscosity (at 25 °C)
ð1Þ
4.3. Indirect tensile fatigue test (ITFT) ASTM D5-73 ASTM D70-76 ASTM D2170-85
Table 4 Gradation of the aggregates used in the study. Sieve (mm) Lower–upper limits Passing (%)
ITS ¼ 2F=tpd
Zycosoil Solid Colorless – pale yellow 80 °C 0.2–0.8 Pa s
K 2 1
et
ð3Þ
In Eq. (3), Nf is the number of cycles to failure of specimen, et is the applied strain and k1 and k2 are the coefficients related to mixture properties. The fatigue life of the specimens was measured using a Nottingham asphalt tester (NAT) in constant stress mode by applying repeated loads with fixed amplitude along the diametrical axis of the specimen. The repeated load consisted of 0.1 s loading time followed by a 0.4 s of rest time. Cylindrical specimens with a diameter, height and air void content of 101.6 mm, 40 mm and 4% were tested in 25 °C, respectively.
5. Results and discussion 5.1. Indirect tensile-strength test (ITS) Figs. 1 and 2 show that the unconditioned and moisture conditioned tensile strength (TS) and TSR properties of the HMA mixtures for two types of aggregates. TSR of the control mixtures (without Zy) containing limestone is greater than control mixtures containing granite, which leads to better resistance against moisture damage. Since limestone has less SiO2 compared to granite, this causes a reduction in the bond between asphalt and aggregate. The data also show that the unconditioned and conditioned tensile strength are significantly improved with the addition of Zycosoil for both aggregates. All of the TSR values of the Zycosoiltreated mixtures are well above 80%. The addition of Zycosoil in mixtures containing limestone and granite resulted in an increase in TSR of 3% and 14%, respectively, compared to the control samples.
F. Moghadas Nejad et al. / Construction and Building Materials 31 (2012) 384–388
Unconditioned
14000
Tensile Stress (KPa)
387
Condition
12000 10000 8000 6000 4000 2000 0 Granite
Granite+Zy
Limestone
Limestone+Zy
Mixtures Fig. 1. Tensile stress of dry and conditioned specimens (AASHTO T-283).
100 Fig. 4. Comparison of fatigue behavior of the mixes containing granite at 25 °C.
TSR %
80 60 40 20 0 Granite
Granite + Zy
Limestone
Limestone+Zy
Mixtures Fig. 2. Tensile stress ratio results.
Therefore, in mixtures containing granite aggregate, using Zycosoil is more effective. Zycosoil migrates to the polar water-loving surface, reacts with the silanol groups and forms Si–O–Si siloxane bond (the strongest bond in the nature) and creates molecular level hydrophobic zone (water repellent). This process is shown in Fig 3. Fig. 5. Comparison of fatigue behavior of the mixes containing limestone at 25 °C.
5.2. Indirect tensile fatigue tests (ITFT) The results of the indirect tensile fatigue test are given in Figs. 4 and 5. In these figures, regression lines were drawn through the mean results of each sample at each strain level. The results show the usual linear relationship between the logarithm of the applied initial tensile strain and the logarithm of fatigue life (number of applied load repetitions until failure). The fatigue equations and fatigue life ratio are shown in Table 6 for every type of the aggregate in dry and wet conditions. Analysis of the obtained fatigue test results showed fatigue life of the granite mixes is higher, because granite, due to its stiffness and greater angularity, improved the fatigue properties of the asphalt concrete mixes. Also, using Zycosoil in asphalt mixtures increases their fatigue life for two reasons. First, aggregate being covered with
Zycosoil may increase the amount of filler and decrease the air void in asphalt mixtures. Second, Zycosoil modify aggregate surface and causes a better compaction of asphalt mixtures. The use of Zycosoil in mixtures containing limestone and granite aggregates resulted in increasing fatigue life ratio of 6% and 25%, respectively. Due to chemical composition of granite (68.1% SiO2), the fatigue life of samples containing granite aggregate is 19% higher.
6. Conclusions This research focused on the effect of using Zycosoil in the asphalt mixes. Behavior of asphalt concrete mixes with and without
Fig. 3. Aggregate surface structure: (a) before Zycosoil reaction and (b) after Zycosoil reaction.
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Table 6 Fatigue prediction equations of HMA. Condition
Aggregate type
R2
Fatigue equation 4
Wet
Granite
0.956
N f ¼ 4:6 10
Dry
Granite
0.912
N f ¼ 3:2 104
Wet
Granite + Zy
0.932
Nf
Dry
Granite + Zy
0.924
Nf
Wet
Limestone
0.944
Nf
Dry
Limestone
0.936
Nf
Wet
Limestone + Zy
0.958
Nf
Dry
Limestone + Zy
0.965
Nf
Zycosoil treated aggregates in dry and wet conditions were investigated with ITS and ITF tests. The following conclusions have been drawn from this study: Due to density of silanol groups being higher and converting granite aggregate to hydrophobic siloxane groups, in mixtures having granite aggregate, Zycosoil is more effective. The addition of Zycosoil in mixtures containing limestone and granite cause TSR to increase to 3% and 14%, respectively, compared to the control samples. Due to stiffness and greater angularity of granite aggregates, mixtures containing granite have more fatigue life. Using Zycosoil in asphalt mixtures increases their fatigue life for two reasons. First, aggregate coverage with Zycosoil may increase the amount of filler and decrease the air void in asphalt mixtures. Secondly, Zycosoil modified the aggregate surface and caused a better compaction of asphalt mixtures. Because of formation of a hydrophobic nano layer on aggregates, use of Zycosoil in mixtures containing limestone and granite aggregates lead to increase of fatigue life of 6% and 25%, respectively.
References [1] Lottman RP. Predicting moisture-induced damage to asphaltic concrete. NCHRP report 192. Washington, DC: Transportation Research Board; 2001. [2] Hicks RG. Moisture damage in asphalt concrete. NCHRP report 175. Washington, DC: Transportation Research Board; 1991. [3] Peter E, Sebaaly PE. Comparison of lime and liquid additives on the moisture damage of hot mix asphalt mixtures. USA: Prepared for the National Lime Association; 2007.
0:78
e e0:59 ¼ 4:3 104 e0:67 ¼ 2:9 104 e0:55 ¼ 4:9 104 e0:76 ¼ 3 104 e 0:62 ¼ 4:5 104 e0:71 ¼ 2:7 104 e0:57
Fatigue life ratio (%) 57 82 84 90
[4] Kennedy T, Ping WV. An evaluation of effectiveness of antistripping additives in protecting asphalt mixtures from moisture damage. J Assoc Asphalt Paving Technol 1991;60:1991. [5] Pickering K, Sebaaly PE, Stroup-Gardiner M, Epps JA. Evaluation of New Generation of Antistripping Additives. Transportation Research Record 1342, Transportation Research Board, Washington, DC; 1992. [6] Sebaaly PE, Tohme P, Hajj EY, Johnston D. Effectiveness of antistrip additives for bituminous mixtures. Int J Pavements 2004;3(1–2). [7] Lu Q, Harvey JT. Laboratory evaluation of long-term effectiveness of antistripping additives. The 85th Annual Meeting of the Transportation Research Board CD-ROM, Washington DC; 2006. [8] ASTM D4123. Annual book of ASTM standards. Road and paving materials. 04.03: 2000. [9] Yongjie X, Haobo H, Shujing Z, Jin Z. Utilization of municipal solid waste incineration ash in stone mastic asphalt mixture: pavement performance and environmental impact. Construct Build Mater 2009;23:989–96. [10] Huang B, Li G, Mohammed NL. Analytical modeling and experimental study of tensile strength of asphalt concrete composite at low temperatures. Composites: Part B 2003;34:705–14. [11] Aksoy A, Samlioglu K, Tayfur S, Ozen H. Effect of various additives on moisture damage sensitivity of asphalt mixtures. Construct Build Mater 2005;19:11–8. [12] Shu X, Huang B, Vukosavljevic D. Laboratory evaluation of fatigue characteristics of recycled asphalt mixture. Construct Build Mater 2008;22:1323–30. [13] Jacobs MMJ. Crack growth in asphaltic mixes. The Netherlands: Thesis Delft University of Technology; 1995. [14] Moghadas Nejad F, Aflaki E, Mohammadi MA. Fatigue behavior of SMA and HMA mixtures. Construct Build Mater 2010;24:1158–65. [15] Hafiang Wen. Fatigue performance evaluation of westrack asphalt mixtures based on viscoelastic analysis of indirect tensile test. Department of Civil Engineering: North Carolina State University; 2001. [16] NCHRP APPENDIX II-1. Calibration of fatigue cracking models for flexible pavements. 2004. [17] SHRP A-404. Fatigue response of asphalt – aggregate mixer. In: Strategic highway research program. National Research Council; 1994. [18] Arabani M, Mirabdolazimi SM, Sasani AR. The effect of waste tire thread mesh on the dynamic behavior of asphalt mixtures. Construct Build Mater 2010;24:1060–8.
Contents lists available at SciVerse ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Influence of using nonmaterial to reduce the moisture susceptibility of hot mix asphalt F. Moghadas Nejad a,⇑, A.R. Azarhoosh b, GH.H. Hamedi a, M.J. Azarhoosh c a
Department of Civil & Environmental Engineering, Amirkabir University of Technology, Tehran 15875, Iran Department of Civil Engineering, University of Guilan, Rasht, Iran c Department of Chemical Engineering, Amirkabir University of Technology, Tehran, Iran b
a r t i c l e
i n f o
Article history: Received 1 October 2011 Received in revised form 30 November 2011 Accepted 11 January 2012 Available online 8 February 2012 Keywords: Moisture damage Zycosoil Indirect tensile-strength Fatigue Silanol group Siloxane bond
a b s t r a c t Moisture damage in an asphalt mixture can be defined as the loss of strength, stiffness and durability due to the presence of moisture leading to adhesive failure at the binder–aggregate interface and/or cohesive failure within the binder or binder–filler mastic. In order to improve adhesion and reduce moisture sensitivity in asphalt mixtures, two different approaches have become apparent. One approach suggests that the aggregate surface be coated by a suitable agent that will reverse the predominant electrical charges at the surface and thus reduce the surface energy of the aggregate. In this study, the effects of nanomaterial, namely Zycosoil, on the moisture damage of asphalt mixtures were studied. Two types of aggregates that represent a considerable range in mineralogy, limestone and granite, were evaluated during the course of this study. To assess the impact of Zycosoil on moisture damage of hot mix Asphalt, control mixes (without Zycosoil) and mixes containing Zycosoil in dry and wet conditions were tested using indirect tensile-strength (ITS) and indirect tensile fatigue (ITF) tests. The results showed that limestone has less moisture damage potential compared to granite. The ratio of wet/dry values of ITST and ITFT for mixes containing Zycosoil was higher than the control mix for two types of aggregate. However, in mixtures made of granite aggregate, using Zycosoil is more effective. As the density of silanol groups is more in its surface, these groups are hydrophilic, and Zycosoil migrates to the polar water-loving surface, reacts with the silanol groups and forms siloxane bond, the strongest bond in nature, and creates a molecular level hydrophobic zone. Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved.
1. Introduction Moisture damage in asphalt pavements has been considered a widespread problem in the world. Water that infiltrates the pavement structure may cause premature failure of hot-mix asphalt layers. Moisture damage can generally be classified in two mechanisms: (a) loss of adhesion and (b) loss of cohesion. The loss of adhesion is due to water getting between the asphalt binder and the aggregate and stripping away the asphalt film. The loss of cohesion is due to the softening of asphalt concrete mastic. The two mechanisms being interrelated, a moisture damaged pavement may be a result of both mechanisms combined [1]. Moisture damage is a function of several factors. These factors include asphalt mixture characteristics, environmental factors, construction practices, etc. [2]. Moisture damage has caused many pavement failures. Moisture reduces the internal strength of the HMA mix, the stresses generated by traffic loads increase significantly and lead to fatigue cracking or rutting of the HMA layer. In general, susceptibility of HMA to ⇑ Corresponding author. Tel.: +98 (21) 64543004; fax: +98 (21) 66414231. E-mail address: [email protected] (F. Moghadas Nejad).
fatigue and rutting caused by moisture damage are determined by tensile strength test. The use of antistrip agents (ASA) is the most common method of improving the moisture susceptibility of asphalt mixes. The primary goal of an antistrip additive is to eliminate the moisture sensitivity of the HMA mixture by improving the bond between the asphalt binder and the aggregate. Typical antistrip agents used today are fatty amines and fatty amido-amines. It should be noted that an effective additive must improve both the unconditioned and moisture conditioned properties in order to ensure good long-term performance, which antistrip agents often fail to do [3]. 1.1. Literature review A study of the impact of lime and liquid additives on the moisture susceptibility of HMA mixtures from eight Texas districts in 1991 was conducted by Kennedy and Ping. The tensile strength ratio (TSR) of the laboratory mixtures indicate that lime treatment is consistently highly effective in reducing moisture damage of the Texas HMA mixtures from all eight districts. The TSR values of the lime-treated mixtures are significantly higher than those values for all liquid additives from all eight districts [4]. In another
0950-0618/$ - see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2012.01.004
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F. Moghadas Nejad et al. / Construction and Building Materials 31 (2012) 384–388
study conducted by Pickering et al. [5], the objective of the research was to compare the effectiveness of lime and two liquid additives in reducing the moisture damage of HMA mixtures. The research program measured the resilient modulus (Mr) and tensile strength (TS) properties of the HMA mixtures before and after moisture conditioning. The resilient modulus and tensile strength data indicate that the lime treatment of the two aggregate sources resulted in significant improvements of the unconditioned and moisture conditioned properties. In the case of the two liquid additives, the improvements in the Mr and TS properties were insignificant and inconsistent. In most cases the liquid additives showed an improvement in the unconditioned property but they did not maintain the improvement after moisture conditioning and vice versa. Sebaaly et al. [6] examined the resilient modulus and tensile strength properties of the field mixed-laboratory compacted samples measured at both unconditioned and conditioned stages, and showed that the mixtures treated with hydrated lime on both projects (SD-314 and US-14) exhibited better moisture resistance than the control, UP5000 (a latex polymer additive) and liquid antistrip mixtures. The superior performance of the mixtures treated with hydrated lime was shown by higher retained strength after the moisture conditioning process. Lu and Harvey evaluated the resistance to moisture damage of an HMA mix manufactured with a California aggregate that is known to have poor compatibility with asphalt binder. They used fatigue and tensile strength tests to evaluate the resistance to moisture damage of mixes. The tensile strength properties of the evaluated mixture showed that hydrated lime improves the tensile values at both un-conditioned and moisture-conditioned stages. They show that the tensile ratios of the lime-treated mixture are significantly higher than the control and liquid A-treated mixtures. In addition, fatigue properties indicated that the lime-treated mixture started with higher fatigue life than the control and the two liquid-treated mixtures, and maintained higher fatigue life after moisture damage [7]. In this study, the effect of moisture damages on HMA was evaluated using indirect tensile strength (ITS) and indirect tensile fatigue (ITF) tests. The ITS test examines the strength loss of asphalt mixes due to moisture, whereas the ITF test examines the moisture effect on the fatigue response of asphalt mixes. Zycosoil was used as an antistrip agent. 2. The statement and objectives of the present study Opposed to the typical antistrip agents (amines), Zycosoil nanotechnology produces a hydrophobic nano layer on aggregates since it converts the hydrophilic silanol groups to hydrophobic siloxane groups. Although both Zycosoil and amines reduce the moisture damage, the key difference between Zycosoil and amines is that Zycosoil eliminates water sensitive surface permanently and makes it oil-loving, whereas amines can only moisturize, and do not chemically modify the surface. Instead, it always remain hydrophilic, which leads to moisture susceptibility. In order to avoid stripping in HMA, antistrip agents modifying the aggregate surface can be used. In this study, nanotechnology is investigated as a new antistrip agent. Considering the fact that fatigue damage is one of the most common failures in asphalt pavement, indirect tensile fatigue test is used. The indirect tensile strength test was also utilized to consider the effect of moisture on strength of asphalt mixtures. The specific objectives of this study are: To evaluate the effect of Zycosoil as an additive on the asphalt mixes. Evaluating the behavior of asphalt concrete mixes under ITS and ITF tests in dry and wet conditions with and without Zycosoil treated aggregates.
To provide fatigue models for mixtures with and without Zycosoil treated aggregates. 3. Materials 3.1. Aggregate and asphalt binder Two types of aggregates were evaluated in the study. The two aggregates (limestone and granite) represent a considerable range in mineralogy and associated degree of stripping with them. The chemical compositions of the aggregates are listed in Table 1. The physical properties of the two types of aggregates are given in Table 2. To characterize the properties of the base asphalt binder, conventional test methods, such as the penetration test, softening point test and ductility were performed. The engineering properties of the asphalt binder are presented in Table 3. The gradation of the aggregates used in the study (mean limits of ASTM specifications for dense aggregate gradation) is given in Table 4. The nominal size of this gradation was 19.0 mm. 3.2. Additive Zycosoil (Zy) is a water soluble reactive organo-silicon component that is specially designed to improve the adhesion between bitumen and aggregates in hot mix asphalt. The dosage of this antistrip additive is normally between 1% and 1.6% by weight of the aggregate. Physical and chemical properties of Zycosoil are given in Table 5. 4. Experimental setup and procedure 4.1. Mix design Initially, the Zycosoil solution is sprayed on the aggregates and is then exposed to air to dry after being mixed with the aggregates. Then, aggregates are heated to 160–170 °C for 24 h and are combined with the asphalt binder at 165 °C. Finally, the asphalt mixtures were designed using standard marshal mix design. Two series of marshall specimens were fabricated. The first series of the specimens contained several of binder contents to determine the optimal binder content. The second
Table 1 Chemical composition of the two types of aggregates. Properties
Limestone
Granite
pH Silicon dioxide, SiO2 (%) R2O3 (Al2O3 + Fe2O3) (%) Aluminum oxide, Al2O3 (%) Ferric oxide, Fe2O3 (%) Magnesium oxide, MgO (%) Calcium oxide, CaO (%)
8.8 3.8 18 1 0.4 1.2 51.3
7.1 68.1 16.2 14.8 1.4 0.8 2.4
Table 2 Physical properties of the aggregate. Test
Standard
Specific gravity (coarse agg.) Bulk SSD Apparent Specific gravity (fine agg.) Bulk SSD Apparent Specific gravity (filler)
ASTM C 127
Los angeles abrasion (%) Flat and elongated particles (%) Sodium sulfate soundness (%) Fine aggregate angularity
Limestone
Granite
Specification limit
2.612 2.643 2.659
2.654 2.667 2.692
– – –
2.618 2.633 2.651 2.640
2.659 2.661 2.688 2.656
– – – –
C
25.6
19
Max 45
D
9.2
6.5
Max 10
C
2.56
1.5
Max 10–20
C
46.65
56.3
Min 40
ASTM C 128
ASTM D854 ASTM 131 ASTM 4791 ASTM 88 ASTM 1252
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Table 3 Results of the experiments conducted on 60/70 penetration grade asphalt binder. Test
Standard
Result
Penetration (100 g, 5 s, 25 °C), 0.1 mm Penetration (200 g, 60 s, 4 °C), 0.1 mm Penetration ratio Ductility (25 °C, 5 cm/min), cm Solubility in trichloroethylene (%) Softening point (°C) Flash point (°C) Loss of heating (%) Properties of the TFOT Residue Penetration (100 g, 5 s, 25 °C), 0.1 mm Specific gravity at 25 °C (g/cm3) Viscosity at 135 °C, cSt
ASTM ASTM ASTM ASTM ASTM ASTM ASTM ASTM
64 23 0.36 112 98.9 51 262 0.75
D5-73 D5-73 D5-73 D113-79 D2042-76 D36-76 D92-78 D1754-78
19 100 100
12.5 90– 100 88
4.75 44– 74 75
60 1.020 158.5
2.36 28– 58 56
0.3 5– 21 40
0.25 2– 10 20
0.106 7–18
0.075 4–10
9
6
series were at the optimal binder content to evaluate the HMA mechanistic properties. For each aggregate blend and asphalt binder content, at least three samples were produced to determine the reproducibility of the results [8]. The optimum binder content for the mix design was determined by taking the average values of the following three bitumen contents: (1) Binder content corresponding to maximum stability. (2) Binder content corresponding to maximum bulk specific gravity. (3) Binder content corresponding to the median of designed limits of percent air voids in the total mix. The stability value, flow value, and voids filled with bitumen (VFB) are checked with the marshall mix design specification. The optimum asphalt binder contents were found to be 5.6% and 5.1% for limestone and granite aggregates, respectively. Tests are conducted on samples in dry and wet conditions. Wet conditions were created by placing the samples in water of 60 °C for 24 h.
4.2. Indirect tensile-strength test (ITST)
where ITS is the indirect tensile stress (kPa), F is the failure load (kN), t is the sample thickness (m), and d is the sample diameter (m). The indirect tensile strength ratio (TSR) was determined by the following equation:
TSR ¼ 100ðF cond =F uncond Þ
ð2Þ
where Fcond is the indirect tensile strength of the wet specimens, Funcond is the indirect tensile strength of the dry specimens.
Fatigue cracking is one of the three major distresses (fatigue cracking, low-temperature cracking and rutting) of flexible pavements. Fatigue cracking is primarily caused by repeated traffic loading leading to significant reduction in the serviceability of flexible pavements. The cracking resistance of hot-mix asphalt (HMA) mixtures is directly related to the fatigue performance of flexible pavements. Therefore, the fatigue behavior of HMA mixtures has been intensively studied for many years [12]. The fatigue process occurs in three distinct stages: (1) crack initiation: development of microcracks, (2) crack propagation: development of macrocracks out of microcracks resulting in stable crack growth and, (3) disintegration: collapse and final failure of the materid due to unstable crack growth [13]. Numerous models of varying sophistication have been developed to predict the fatigue behavior of asphalt concrete including elastic, viscoelastic, elastoplastic, viscoplastic, and crack models that are developed by using different laboratory testing modes. The most common methods for characterizing the fatigue behavior of asphalt mixtures are the Wohler approach, dissipated energy method and fracture mechanics approach [14]. Several factors can be effective on fatigue behavior of asphalt mixtures, which are included: asphalt layer thickness; type of loading (controlled strain and controlled stress); shape, frequency and rest period in loading; properties of asphalt mixtures (asphalt content; air void; type, shape and gradation aggregates) and environmental conditions (temperature changes, wet and freezing) [15–17]. The indirect tensile fatigue test is able to characterize the fatigue behavior of the mixture. Fatigue tests were carried out in both controlled strain mode and controlled stress mode. In controlled strain mode, the strain was maintained by reducing the stress on the sample. In controlled stress mode, the stress was held constant to increase the strain within the sample [18]. The relationship between tensile strain and number of cycles to failure for each material was established. A linear relationship was recorded when strain is plotted against the numbered cycles to failure in logarithmic scale and the fatigue life prediction equations were developed [14]. Using a regression analysis, the fatigue equations were developed, which are in the form of Wohler’s fatigue prediction model (Eq. (3)).
Nf ¼ K 1
The stripping resistance (water susceptibility) of asphalt mixtures was evaluated by the decrease in the loss of the indirect tensile strength (ITS) after immersion in water for 24 h in temperature 60 °C, according to AASHTO T-283 test procedure [9]. The tensile strength of an HMA mix is generated by the cohesive strength of the asphalt binder and the bond strength at the binder-aggregate interface. The tensile strength is calculated from the maximum load the sample can undergo prior to cracking. A mix with higher tensile strength provides better resistance to fatigue and thermal cracking [10]. Therefore, any additives that can generate a higher tensile strength in the HMA mix in the dry and moisture-conditioned stages will improve the long-term performance of an HMA pavement. This test involves loading a cylindrical specimen with vertical compressive loads; this generates a relatively uniform tensile stress along the vertical diametrical plane. Failure usually occurs in the form of splitting along this loaded plane [11]. Six samples from each mix (dry and wet) prepared and compacted. The compacted specimens should have air void contents between 6.5% and 7.5%. Half of the compacted specimens are conditioned. First, vacuum is applied to partially saturate specimens to a level between 55% and 80%. Vacuum-saturated samples are kept in a 60 °C water bath for 24 h. After this period the specimens are considered conditioned. The other three samples remain unconditioned. The failure load for each sample was recorded at 25 °C. The ITS for each sample was calculated using the following formula: Table 5 Properties of the Zycosoil. Properties Form Color Flash point Viscosity (at 25 °C)
ð1Þ
4.3. Indirect tensile fatigue test (ITFT) ASTM D5-73 ASTM D70-76 ASTM D2170-85
Table 4 Gradation of the aggregates used in the study. Sieve (mm) Lower–upper limits Passing (%)
ITS ¼ 2F=tpd
Zycosoil Solid Colorless – pale yellow 80 °C 0.2–0.8 Pa s
K 2 1
et
ð3Þ
In Eq. (3), Nf is the number of cycles to failure of specimen, et is the applied strain and k1 and k2 are the coefficients related to mixture properties. The fatigue life of the specimens was measured using a Nottingham asphalt tester (NAT) in constant stress mode by applying repeated loads with fixed amplitude along the diametrical axis of the specimen. The repeated load consisted of 0.1 s loading time followed by a 0.4 s of rest time. Cylindrical specimens with a diameter, height and air void content of 101.6 mm, 40 mm and 4% were tested in 25 °C, respectively.
5. Results and discussion 5.1. Indirect tensile-strength test (ITS) Figs. 1 and 2 show that the unconditioned and moisture conditioned tensile strength (TS) and TSR properties of the HMA mixtures for two types of aggregates. TSR of the control mixtures (without Zy) containing limestone is greater than control mixtures containing granite, which leads to better resistance against moisture damage. Since limestone has less SiO2 compared to granite, this causes a reduction in the bond between asphalt and aggregate. The data also show that the unconditioned and conditioned tensile strength are significantly improved with the addition of Zycosoil for both aggregates. All of the TSR values of the Zycosoiltreated mixtures are well above 80%. The addition of Zycosoil in mixtures containing limestone and granite resulted in an increase in TSR of 3% and 14%, respectively, compared to the control samples.
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Unconditioned
14000
Tensile Stress (KPa)
387
Condition
12000 10000 8000 6000 4000 2000 0 Granite
Granite+Zy
Limestone
Limestone+Zy
Mixtures Fig. 1. Tensile stress of dry and conditioned specimens (AASHTO T-283).
100 Fig. 4. Comparison of fatigue behavior of the mixes containing granite at 25 °C.
TSR %
80 60 40 20 0 Granite
Granite + Zy
Limestone
Limestone+Zy
Mixtures Fig. 2. Tensile stress ratio results.
Therefore, in mixtures containing granite aggregate, using Zycosoil is more effective. Zycosoil migrates to the polar water-loving surface, reacts with the silanol groups and forms Si–O–Si siloxane bond (the strongest bond in the nature) and creates molecular level hydrophobic zone (water repellent). This process is shown in Fig 3. Fig. 5. Comparison of fatigue behavior of the mixes containing limestone at 25 °C.
5.2. Indirect tensile fatigue tests (ITFT) The results of the indirect tensile fatigue test are given in Figs. 4 and 5. In these figures, regression lines were drawn through the mean results of each sample at each strain level. The results show the usual linear relationship between the logarithm of the applied initial tensile strain and the logarithm of fatigue life (number of applied load repetitions until failure). The fatigue equations and fatigue life ratio are shown in Table 6 for every type of the aggregate in dry and wet conditions. Analysis of the obtained fatigue test results showed fatigue life of the granite mixes is higher, because granite, due to its stiffness and greater angularity, improved the fatigue properties of the asphalt concrete mixes. Also, using Zycosoil in asphalt mixtures increases their fatigue life for two reasons. First, aggregate being covered with
Zycosoil may increase the amount of filler and decrease the air void in asphalt mixtures. Second, Zycosoil modify aggregate surface and causes a better compaction of asphalt mixtures. The use of Zycosoil in mixtures containing limestone and granite aggregates resulted in increasing fatigue life ratio of 6% and 25%, respectively. Due to chemical composition of granite (68.1% SiO2), the fatigue life of samples containing granite aggregate is 19% higher.
6. Conclusions This research focused on the effect of using Zycosoil in the asphalt mixes. Behavior of asphalt concrete mixes with and without
Fig. 3. Aggregate surface structure: (a) before Zycosoil reaction and (b) after Zycosoil reaction.
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Table 6 Fatigue prediction equations of HMA. Condition
Aggregate type
R2
Fatigue equation 4
Wet
Granite
0.956
N f ¼ 4:6 10
Dry
Granite
0.912
N f ¼ 3:2 104
Wet
Granite + Zy
0.932
Nf
Dry
Granite + Zy
0.924
Nf
Wet
Limestone
0.944
Nf
Dry
Limestone
0.936
Nf
Wet
Limestone + Zy
0.958
Nf
Dry
Limestone + Zy
0.965
Nf
Zycosoil treated aggregates in dry and wet conditions were investigated with ITS and ITF tests. The following conclusions have been drawn from this study: Due to density of silanol groups being higher and converting granite aggregate to hydrophobic siloxane groups, in mixtures having granite aggregate, Zycosoil is more effective. The addition of Zycosoil in mixtures containing limestone and granite cause TSR to increase to 3% and 14%, respectively, compared to the control samples. Due to stiffness and greater angularity of granite aggregates, mixtures containing granite have more fatigue life. Using Zycosoil in asphalt mixtures increases their fatigue life for two reasons. First, aggregate coverage with Zycosoil may increase the amount of filler and decrease the air void in asphalt mixtures. Secondly, Zycosoil modified the aggregate surface and caused a better compaction of asphalt mixtures. Because of formation of a hydrophobic nano layer on aggregates, use of Zycosoil in mixtures containing limestone and granite aggregates lead to increase of fatigue life of 6% and 25%, respectively.
References [1] Lottman RP. Predicting moisture-induced damage to asphaltic concrete. NCHRP report 192. Washington, DC: Transportation Research Board; 2001. [2] Hicks RG. Moisture damage in asphalt concrete. NCHRP report 175. Washington, DC: Transportation Research Board; 1991. [3] Peter E, Sebaaly PE. Comparison of lime and liquid additives on the moisture damage of hot mix asphalt mixtures. USA: Prepared for the National Lime Association; 2007.
0:78
e e0:59 ¼ 4:3 104 e0:67 ¼ 2:9 104 e0:55 ¼ 4:9 104 e0:76 ¼ 3 104 e 0:62 ¼ 4:5 104 e0:71 ¼ 2:7 104 e0:57
Fatigue life ratio (%) 57 82 84 90
[4] Kennedy T, Ping WV. An evaluation of effectiveness of antistripping additives in protecting asphalt mixtures from moisture damage. J Assoc Asphalt Paving Technol 1991;60:1991. [5] Pickering K, Sebaaly PE, Stroup-Gardiner M, Epps JA. Evaluation of New Generation of Antistripping Additives. Transportation Research Record 1342, Transportation Research Board, Washington, DC; 1992. [6] Sebaaly PE, Tohme P, Hajj EY, Johnston D. Effectiveness of antistrip additives for bituminous mixtures. Int J Pavements 2004;3(1–2). [7] Lu Q, Harvey JT. Laboratory evaluation of long-term effectiveness of antistripping additives. The 85th Annual Meeting of the Transportation Research Board CD-ROM, Washington DC; 2006. [8] ASTM D4123. Annual book of ASTM standards. Road and paving materials. 04.03: 2000. [9] Yongjie X, Haobo H, Shujing Z, Jin Z. Utilization of municipal solid waste incineration ash in stone mastic asphalt mixture: pavement performance and environmental impact. Construct Build Mater 2009;23:989–96. [10] Huang B, Li G, Mohammed NL. Analytical modeling and experimental study of tensile strength of asphalt concrete composite at low temperatures. Composites: Part B 2003;34:705–14. [11] Aksoy A, Samlioglu K, Tayfur S, Ozen H. Effect of various additives on moisture damage sensitivity of asphalt mixtures. Construct Build Mater 2005;19:11–8. [12] Shu X, Huang B, Vukosavljevic D. Laboratory evaluation of fatigue characteristics of recycled asphalt mixture. Construct Build Mater 2008;22:1323–30. [13] Jacobs MMJ. Crack growth in asphaltic mixes. The Netherlands: Thesis Delft University of Technology; 1995. [14] Moghadas Nejad F, Aflaki E, Mohammadi MA. Fatigue behavior of SMA and HMA mixtures. Construct Build Mater 2010;24:1158–65. [15] Hafiang Wen. Fatigue performance evaluation of westrack asphalt mixtures based on viscoelastic analysis of indirect tensile test. Department of Civil Engineering: North Carolina State University; 2001. [16] NCHRP APPENDIX II-1. Calibration of fatigue cracking models for flexible pavements. 2004. [17] SHRP A-404. Fatigue response of asphalt – aggregate mixer. In: Strategic highway research program. National Research Council; 1994. [18] Arabani M, Mirabdolazimi SM, Sasani AR. The effect of waste tire thread mesh on the dynamic behavior of asphalt mixtures. Construct Build Mater 2010;24:1060–8.