Laboratory Assessment of Deteriorating Performance of Nano Hydrophobic Silane Silica Modified Asphalt
2. Materials 1. Asphalt
We selected 90# asphalt binder produced by Panjin Northern Asphalt Co., Ltd. for base asphalt.
The asphalt binder is the most common paving grade binder used in Jilin province. The technical parameters of the asphalt used in this study are summarized in Table1.
Table 1.Technical parameters of asphalt.
Technical Parameters
Penetration 25◦C
Ductility
Softening
Point Density Wax Content
Flash Point 15◦C 25◦C 30◦C
Units 0.1 mm cm ◦C g·cm−3 % ◦C
Test results 25.3 86.9 142.4 >130 44.6 1.003 18 340
2.2. Nano Hydrophobic Silane Silica
Nanosilica is one of the nano-materials that have been extensively used in asphalt mixtures.
However, nanosilica as a kind of inorganic non-metallic nanomaterial that is very prone to agglomeration.
In addition, the asphalt binder is an organic cementitious material formed by high molecular hydrocarbons and non-metallic derivatives of these hydrocarbons, which makes nanosilica in asphalt binder have poor dispersibility and compatibility. In order to improve the dispersion of nanosilica in organic solvents and enhance their interaction with the medium, and to broaden the application field of nanosilica, the commonly used method is to physically or chemically react the surface of the nanosilica with the surface modifier through a certain process. The nano hydrophobic silane silica is obtained by grafting the silane coupling agent onto the surface of the nanosilica to carry out surface modification.
The silane coupling agent has two groups with different properties, and the chemical formula is R-Si-X.
X represents hydrolysable groups such as methoxy group (CH3O-) or ethoxy group (C2H5O-), which can be condensed with a hydroxyl group on the surface of nanosilica to form a siloxane bond and to be bonded to the R group. The R group can react strongly with different matrix resins or organic materials, such as vinyl, epoxy, sulfhydryl, amino, etc. [24,25].
Nano hydrophobic silane silica remains amorphous and the crystal form does not change.
The coupling agent grafts the organic group to the surface of the nanoparticle by chemical action, and the bonding ability is strong, and the modification effect more obvious. The nanosilica, after surface modification, have relatively uniform particle size and when the nanosilica changes from hydrophilic to hydrophobic, the oil absorption value of nanoparticles is increased, the agglomeration phenomenon between the nanoparticles is greatly improved, and the nanoparticles are more evenly dispersed in the organic system.
The nano hydrophobic silane silica material was obtained from Changtai Weina Chemical Co., Ltd. (Shouguang, Shandong province, China). The technical properties of nano hydrophobic silane silica material have been presented in Table2.
Table 2.Technical parameters of nano hydrophobic silane silica.
Technical Parameters
Water
Characteristics BET (m2/g) Loss on Drying (105◦C, 2 h, wt%)
Average Particle
Size (nm) pH Value SiO2
Content (%)
Test results Hydrophilia 125±20 ≤0.5 12 5.0–8.0 ≥99.8
Standard values __ 130±30 ≤3.0 ≤20 3.7–6.5 ≥99.8
The microstructure of nanosilica and NHSS were examined by SU8000 electronic microscopy (Tianmei.co, in Japan). The scanning electron micrographs of nanosilica and NHSS observed at magnifying power of×1000,×10,000 and×100,000, which are shown in Figures2–4. (a and b).
Figure 2.SEM images of nanosilica and nano hydrophobic silane silica (NHSS) at magnifications of
×1000. (a) nanosilica; (b) NHSS.
Figure 3.SEM images of nanosilica and NHSS at magnifications of×10,000. (a) nanosilica; (b) NHSS.
Figure 4.SEM images of nanosilica and NHSS at magnifications of×100,000. (a) nanosilica; (b) NHSS.
The shape of nanosilica and NHSS is evident from Figure4, and the difference between nanosilica and NHSS is more obvious. From the physical structural characteristics, the NHSS particle can better connect to asphalt. From the chemical linking characteristics, the surface modified nanosilica can form a stable chemical bond with asphalt at the interface to enhance the overall strength and toughness of the modified asphalt system.
After obtaining SEM images with different magnifications, the distribution of particle size of nanosilica and NHSS was statistically analyzed using Nano Measurer 1.2 software. The statistical results are shown in Figure5.
The diameters of 200 particles in the nanosilica and NHSS SEM images were randomly counted.
Among them, the minimum particle size of nanosilica is 28 nm, the maximum particle size is 93nm, the average particle size is 52 nm, and 91% of the particle size distribution is concentrated between 35 nm and 70 nm. NHSS has a minimum particle diameter of 15 nm, a maximum particle diameter of 82 nm, and an average particle diameter of 46 nm, 90% of the particle size distribution is concentrated in the 28 nm~69 nm range.
The dispersion of nano-scale modifiers in asphalt is an important factor limiting the development of nano-scale modified asphalt. According to Figures4and5, it can be clearly concluded that the nanosilica particles are smooth, have a larger size, and are more likely to be agglomerated. This agglomeration phenomenon is mainly attributed to Van der Waals gravity and Ostwald ripening. After the surface modification of nanosilica, the particle size is slightly reduced, the surface roughness is increased, and the physical attraction between the particles is reduced, which is beneficial to improve the dispersion and fusion of NHSS particles in the asphalt, and to improve the nanosilica being easy to agglomerate.
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