Laboratory Assessment of Deteriorating Performance of Nano Hydrophobic Silane Silica Modified Asphalt
3. Characterization and Performance Testing 1. Freeze-thaw Aging Procedure
Figure 5.Nanosilica and nano hydrophobic silane silica (NHSS) particle size distribution statistics. (a) Nanosilica; (b) NHSS.
2.3. Asphalt Sample Preparation
In the previous study, the incorporation method of nano hydrophobic silane silica was discussed in detail [25]. A high shear mixer with the speed of 2000 rpm was used for incorporating the nano hydrophobic silane silica into the base asphalt. Mixing percentages of nano hydrophobic silane silica were 3 wt% of the base asphalt and the mixing temperature was kept at 140◦C. The mixing time was about 60 min to ensure homogeneous blending. The asphalt modified by nano hydrophobic silane silica was denoted by NHSSMA. Moreover, as a comparison, carbon black was selected for its unique physiochemical properties and wide application. Carbon black possesses many unique properties that distinguish it from other conventional modified: it has a large specific surface area, irregular shapes and various functional groups. Related research has proved that carbon black had good compatibility and a reinforcement effect on asphalt binders, and decreased the resistivity of asphalt [26]. In this paper, carbon black was obtained from Jiangxi black cat carbon black Co, Ltd. (Jiangxi, China). The technical information about carbon black is listed in Table3. Thus, 3 wt% carbon black modified asphalt and base asphalt were prepared for comparison, base asphalt and carbon black modified asphalt were denoted by BA and CBMA.
Table 3.Technical parameters of carbon black.
Technical Parameters Unit Value
Iodine absorption g/kg 43±5
DPB absorption 10−5m3/kg 121±7
DPB absorption of the compressed sample 10−5m3/kg 80~90
PH value - 8±2.0
CTAB surface area 103m2/kg 36~48
Ash content % ≤0.7
45-μm sieve residue mg/kg ≤1000
3. Characterization and Performance Testing
First, base asphalt and modified asphalt binders were heated to a fluid state and poured into a fixed-size plate to ensure the dimensions of asphalt binder samples is approximately 6×250×250 mm.
The purpose of this was to ensure that the moisture could completely penetrate the asphalt and the preparation conditions of all samples were consistent.
Then, the base asphalt and modified asphalt samples were submerged in a container containing water, and the container with specimens were placed in the precision temp-enclosure at−15◦C and frozen for 10 h.
Finally, the base asphalt and modified asphalt samples were soaked in water at 15◦C for 16 h through adjusting the temperature controller.
As per the method described above, a complete freeze-thaw aging cycle was completed. Then, after 10, 20 and 30 freeze-thaw aging cycles, damaged samples were collected for physicochemical property test to explore the effect of NHSS modifier on the characteristics of asphalt under the freeze-thaw aging process. The photos of fresh and weathered specimen are shown in Figure6.
Figure 6.The photos of fresh and weathered specimen.
3.2. Property Test of the Asphalt
In order to investigate the deteriorating properties of nano hydrophobic silane silica modified asphalt under freeze-thaw aging process systematically, the penetration, softening points, ductility test, rotational viscosity test, DSR, FTIR and TGA test was employed in this paper. The penetration, softening points, ductility test and rotational viscosity test are conventional physical property tests to explore the deteriorating properties of asphalt from the perspective of physical properties, and the DSR FTIR and TGA test was applied from the perspective of rheological properties, chemical properties and thermal properties, respectively.
3.2.1. Physical Property Tests
The basic properties of the asphalt sample, including penetration, softening points and ductility, were tested according to Chinese standards GB/T4507-2010, GB/4508-2010, and GB/T4509-2010, respectively. Moreover, rotational viscosity test at 135◦C was performed according to Chinese standards GB/T0625-2011. The intercept (K) along with slope (A) were obtained to calculate Penetration Index (PI) through linearly regressing the logarithm of Penetration (P) against temperature (T).
PI= 30
1+50A−10 (1)
The DV-Шviscometer was used to measure the 135◦C rotational viscosity for evaluating the pumping ability and aging resistance of asphalt binder during F-T cycles. The aging index calculation formula based on the rotational viscosity test is as follows.
C=lglg ηa∗103
−lglg η0∗103
(2) where C is the aging index of the specimens,η0is the rotational viscosity of the specimens before freeze-thaw aging procedure, andηais the rotational viscosity of the specimens after different F-T cycles. The aging index reflects the upward deviation of the viscosity curve before and after freeze-thaw aging procedure. The larger the aging index value, the lesser the anti-aging ability of the asphalt.
In order to ensure the repeatability of the results, three specimens were tested for each material.
3.2.2. Dynamic Shear Rheometer Test (DSR)
In order to characterize the fundamental rheological properties of asphalt film after different F-T cycles, the dynamic shear rheometer test was performed according to ASTM-D7175 standard test method. The DSR test can properly describe the elastic and viscous behaviors of asphalt film after different F-T cycles. In this paper, a Bohlin automatic dynamic shear (ADS) rheometer (DSRII, Malvern, United Kingdom) was used to investigate the rheological properties of the modified asphalt binder under freeze-thaw aging procedure. Complex shear modulus (G*) and phase angle (δ) were measured at temperatures ranging from 58◦C to 76◦C at 6◦C increments for both asphalt binders, while the frequency equaled 1.59 Hz. The parameter G* provides information about the resistance of asphalt sample to deformation when it is subjected to shear loading. The parameter (δ) shows time lag between the applied shear stresses and shear strain responses. The parameter G*/Sinδwhich is called the rut factor represents the rutting resistance of asphalt sample under a freeze-thaw aging procedure.
3.2.3. Fourier Transform Infrared Spectroscopy Test (FTIR)
Fourier Transform Infrared Spectroscopy test was used to analyze the functional groups of BA, CBMA and NHSSMA under F-T aging procedure from chemical characteristics. A Vertex 70 Fourier Transform Infrared Spectroscope (Bruker Optics .co, Changchun, China) was employed with wavelength ranging from 40 cm−1to 4000 cm−1[27]. From the peak position and size, the chemical bonds and the functional groups of the materials in the asphalt can be determined. Based on the previous research, waves of representative chemical bonds are obtained. The results are shown in Table4.
Table 4.Featured chemical bonds of asphalt binder.
Wave Number (cm−1) Chemical Bonds
3676 Intermolecular hydrogen bond (O–H) vibration
2924 The antisymmetric stretching vibration absorption band of the alkyl (C–H)
2852 The symmetric stretching vibration absorption band of the alkyl (C–H)
1607 Conjugated double bonds (C=C) stretching vibration in aromatics
1456 The C–H asymmetric deformations in CH2and CH3vibrations
1377 The C–H symmetric deformation in CH3vibrations
1250 The C–O stretching vibration in saturated alcohols
1031 The sulfoxide group (S=O) stretching vibration
966 The C–H out-plane bending vibrations in unsaturated hydrocarbons
747 Bending vibration of aromatic branches
3.2.4. Thermogravimetric Analysis (TGA)
TGA simultaneous thermal analyzer (Netzsch .co, Bolin, Germany) was employed to measure the thermal behavior and stability properties of BA, CBMA and NHSSMA under a freeze-thaw aging procedure. The temperature range of the test was from room temperature to 900◦C, and the heating rate was controlled at 20◦C/min.
4. Results and Discussion