<p>Moisture from surface runoff significantly accelerates fatigue cracking in asphalt by damaging bitumen cohesion and its bond with aggregates. This effect is worsened when surface contaminants like dust and soot change the pH of the runoff water. Accordingly, the influence of pH on fatigue cracking in asphalt mixtures was investigated using two aggregate types, two performance grade bitumen types, and nano-hydrated lime (NHL) at two dosage levels as a bitumen modifier. For this purpose, mechanical evaluations were conducted at intermediate temperatures, including Dynamic Shear Rheometer (DSR) tests on bitumen and Semi-Circular Bending (SCB) tests on HMA samples. Furthermore, surface free energy (SFE) tests, such as Wilhelmy plate (WP) and Universal Sorption Device (USD), were conducted to determine the thermodynamic interactions between bitumen, aggregate, modifier, and acidic/basic runoff. Results showed that applying environmental conditions, particularly acidic conditions, lowered the debonding energy of bitumen-aggregate samples by an average of 10%. This phenomenon was more evident in the mixture’s performance, which showed an average 20% reduction in fracture toughness (FT) under acidic/basic wet conditions. This was attributed to diminished bitumen-aggregate adhesion, which reduces resistance to crack growth in the presence of moisture. Acidic and basic conditions increased bitumen’s complex modulus and phase angle, raising the fatigue parameter (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\:{G}^{}\times\:\text{sin}\delta\:\)</EquationSource> </InlineEquation>) and cracking probability. Consequently, the fracture energy (FE) of the HMAs under acidic/basic moisture conditions decreased by an average of 17%. In contrast, the application of NHL was found to increase the basic elements while reducing the acidic elements of bitumen’s SFE. According to SFE theory, this resulted in stronger intrinsic bitumen-aggregate adhesion, which was reflected in the mixture as a 24% increase in FT. NHL also improved the nonpolar elements of SFE, positively affecting both cohesive and adhesive strength. The influence of this factor on the performance of the bitumen and mixture also included a reduction in the <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\:{G}^{}\times\:\text{sin}\delta\:\)</EquationSource> </InlineEquation> and an increase in FE. For instance, the PG 58 − 22 bitumen modified with 0.4% NHL exhibited a fatigue parameter of 1078 kPa under acidic conditions (pH = 5), which was even lower than that of the base bitumen. Overall, the combination of PG 58 − 22 modified with 0.4% NHL and limestone demonstrated the greatest resistance to fatigue under acidic/basic moisture conditions.</p>

Investigating the effect of runoff characteristics on fatigue cracking in HMA modified with nano-hydrated lime using mechanical and thermodynamic approaches

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2025年12月29日

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Zahra Rasouli,
Mehdi Mehdinazar,
Gholam Hossein Hamedi

摘要

Moisture from surface runoff significantly accelerates fatigue cracking in asphalt by damaging bitumen cohesion and its bond with aggregates. This effect is worsened when surface contaminants like dust and soot change the pH of the runoff water. Accordingly, the influence of pH on fatigue cracking in asphalt mixtures was investigated using two aggregate types, two performance grade bitumen types, and nano-hydrated lime (NHL) at two dosage levels as a bitumen modifier. For this purpose, mechanical evaluations were conducted at intermediate temperatures, including Dynamic Shear Rheometer (DSR) tests on bitumen and Semi-Circular Bending (SCB) tests on HMA samples. Furthermore, surface free energy (SFE) tests, such as Wilhelmy plate (WP) and Universal Sorption Device (USD), were conducted to determine the thermodynamic interactions between bitumen, aggregate, modifier, and acidic/basic runoff. Results showed that applying environmental conditions, particularly acidic conditions, lowered the debonding energy of bitumen-aggregate samples by an average of 10%. This phenomenon was more evident in the mixture’s performance, which showed an average 20% reduction in fracture toughness (FT) under acidic/basic wet conditions. This was attributed to diminished bitumen-aggregate adhesion, which reduces resistance to crack growth in the presence of moisture. Acidic and basic conditions increased bitumen’s complex modulus and phase angle, raising the fatigue parameter ( \(\:{G}^{*}\times\:\text{sin}\delta\:\) ) and cracking probability. Consequently, the fracture energy (FE) of the HMAs under acidic/basic moisture conditions decreased by an average of 17%. In contrast, the application of NHL was found to increase the basic elements while reducing the acidic elements of bitumen’s SFE. According to SFE theory, this resulted in stronger intrinsic bitumen-aggregate adhesion, which was reflected in the mixture as a 24% increase in FT. NHL also improved the nonpolar elements of SFE, positively affecting both cohesive and adhesive strength. The influence of this factor on the performance of the bitumen and mixture also included a reduction in the \(\:{G}^{*}\times\:\text{sin}\delta\:\) and an increase in FE. For instance, the PG 58 − 22 bitumen modified with 0.4% NHL exhibited a fatigue parameter of 1078 kPa under acidic conditions (pH = 5), which was even lower than that of the base bitumen. Overall, the combination of PG 58 − 22 modified with 0.4% NHL and limestone demonstrated the greatest resistance to fatigue under acidic/basic moisture conditions.