Enhancing the fracture stiffness of bituminous mixtures before cracking is essential to resist elastic deformations. Fibers have proven effective in enhancing the fracture properties of mixtures before cracking. This research aims to assess the effects of the mixing process of polypropylene fibers on the pre-cracking behavior of asphalt mixtures by analyzing pre-peak fracture energy index (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">${\text{G}f}^{pre-peak}$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mtext>G</mtext> <mi>f</mi> </mrow> <mrow> <mi>p</mi> <mi>r</mi> <mi>e</mi> <mo>-</mo> <mi>p</mi> <mi>e</mi> <mi>a</mi> <mi>k</mi> </mrow> </msup> </math></EquationSource> </InlineEquation>), Tensile Strength Index (TSI), and Tensile Strength (TS) at temperatures of – 18 °C and + 25 °C (under Modes I and II). In this research, three groups of asphalt mixtures were strengthened by polypropylene fibers, with the reinforcement ratios of 0.5, 1.0% and 1.5% (based on aggregate weight). The resulting mixtures underwent testing using the Short Beam Bending (SBB) geometry. The results demonstrated an improvement in the elastic deformation resistance of bituminous mixtures, when polypropylene fibers were added using both the Sequential Mixing Process (SMP) and the Traditional Dry Mixing Process (TDMP), based on <InlineEquation ID="IEq2"> <EquationSource Format="TEX">${\text{G}f}^{pre-peak}$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mtext>G</mtext> <mi>f</mi> </mrow> <mrow> <mi>p</mi> <mi>r</mi> <mi>e</mi> <mo>-</mo> <mi>p</mi> <mi>e</mi> <mi>a</mi> <mi>k</mi> </mrow> </msup> </math></EquationSource> </InlineEquation>, TSI, and TS. The statistical analysis indicated a significant correlation between the TSI and TS values with <InlineEquation ID="IEq3"> <EquationSource Format="TEX">${\text{G}f}^{pre-peak}$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mtext>G</mtext> <mi>f</mi> </mrow> <mrow> <mi>p</mi> <mi>r</mi> <mi>e</mi> <mo>-</mo> <mi>p</mi> <mi>e</mi> <mi>a</mi> <mi>k</mi> </mrow> </msup> </math></EquationSource> </InlineEquation> indicator, highlighting a relationship between the <InlineEquation ID="IEq4"> <EquationSource Format="TEX">${\text{G}f}^{pre-peak}$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mtext>G</mtext> <mi>f</mi> </mrow> <mrow> <mi>p</mi> <mi>r</mi> <mi>e</mi> <mo>-</mo> <mi>p</mi> <mi>e</mi> <mi>a</mi> <mi>k</mi> </mrow> </msup> </math></EquationSource> </InlineEquation> indicator and fracture stiffness (elastic deformation resistance). In the SMP technique, the PP-1.5 mixture demonstrated the peak <InlineEquation ID="IEq5"> <EquationSource Format="TEX">${\text{G}f}^{pre-peak}$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mtext>G</mtext> <mi>f</mi> </mrow> <mrow> <mi>p</mi> <mi>r</mi> <mi>e</mi> <mo>-</mo> <mi>p</mi> <mi>e</mi> <mi>a</mi> <mi>k</mi> </mrow> </msup> </math></EquationSource> </InlineEquation> values under most testing conditions, with increases of 120% and 107% under Mode I and 22% and 96% under Mode II at − 18 °C and + 25 °C, respectively, compared to the base mixture findings. In contrast, in the TDMP technique, the PP-1 mixture enhanced <InlineEquation ID="IEq6"> <EquationSource Format="TEX">${\text{G}f}^{pre-peak}$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mtext>G</mtext> <mi>f</mi> </mrow> <mrow> <mi>p</mi> <mi>r</mi> <mi>e</mi> <mo>-</mo> <mi>p</mi> <mi>e</mi> <mi>a</mi> <mi>k</mi> </mrow> </msup> </math></EquationSource> </InlineEquation> with 160% and 163% under Mode I and with 91% and 100% under Mode II. Regarding fracture stiffness indexes, TSI and TS, a 1% fiber content exhibited peak findings in both SMP and TDMP mixtures under most testing conditions. Regression models with high R2 values at + 25 °C indicated that fracture stiffness could be assessed using the fracture curve slope in SBB geometry. Asphalt mixtures reinforced with 1% polypropylene fibers through the SMP method showed high deformation resistance pre-and post-cracking under different loading conditions, making it the optimal approach. Graphical Abstract

Investigating Fracture Stiffness of Fiber Asphalt Mixtures with Various Mixing Processes Under Modes I/II using SBB Geometry at Low and Intermediate Temperatures

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发表日期：

2025年7月16日

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Hesham Akram,
Hozayen A. Hozayen,
Akmal Abdelfatah,
Farag Khodary

摘要

Enhancing the fracture stiffness of bituminous mixtures before cracking is essential to resist elastic deformations. Fibers have proven effective in enhancing the fracture properties of mixtures before cracking. This research aims to assess the effects of the mixing process of polypropylene fibers on the pre-cracking behavior of asphalt mixtures by analyzing pre-peak fracture energy index ( ${\text{G}f}^{pre-peak}$ ${G f}^{p r e - p e a k}$ ), Tensile Strength Index (TSI), and Tensile Strength (TS) at temperatures of – 18 °C and + 25 °C (under Modes I and II). In this research, three groups of asphalt mixtures were strengthened by polypropylene fibers, with the reinforcement ratios of 0.5, 1.0% and 1.5% (based on aggregate weight). The resulting mixtures underwent testing using the Short Beam Bending (SBB) geometry. The results demonstrated an improvement in the elastic deformation resistance of bituminous mixtures, when polypropylene fibers were added using both the Sequential Mixing Process (SMP) and the Traditional Dry Mixing Process (TDMP), based on ${\text{G}f}^{pre-peak}$ ${G f}^{p r e - p e a k}$ , TSI, and TS. The statistical analysis indicated a significant correlation between the TSI and TS values with ${\text{G}f}^{pre-peak}$ ${G f}^{p r e - p e a k}$ indicator, highlighting a relationship between the ${\text{G}f}^{pre-peak}$ ${G f}^{p r e - p e a k}$ indicator and fracture stiffness (elastic deformation resistance). In the SMP technique, the PP-1.5 mixture demonstrated the peak ${\text{G}f}^{pre-peak}$ ${G f}^{p r e - p e a k}$ values under most testing conditions, with increases of 120% and 107% under Mode I and 22% and 96% under Mode II at − 18 °C and + 25 °C, respectively, compared to the base mixture findings. In contrast, in the TDMP technique, the PP-1 mixture enhanced ${\text{G}f}^{pre-peak}$ ${G f}^{p r e - p e a k}$ with 160% and 163% under Mode I and with 91% and 100% under Mode II. Regarding fracture stiffness indexes, TSI and TS, a 1% fiber content exhibited peak findings in both SMP and TDMP mixtures under most testing conditions. Regression models with high R² values at + 25 °C indicated that fracture stiffness could be assessed using the fracture curve slope in SBB geometry. Asphalt mixtures reinforced with 1% polypropylene fibers through the SMP method showed high deformation resistance pre-and post-cracking under different loading conditions, making it the optimal approach.

Graphical Abstract