Development and Road Performance Verification of Aggregate Gradation for Large Stone Asphalt Mixture

Area of Science:

• Civil Engineering
• Materials Science
• Pavement Engineering

Background:

• Pavement base and subbase structures require high bearing capacity, traditionally achieved with conventional asphalt mixtures.
• Large Stone Asphalt Mixtures (LSAM-50) with a 50 mm nominal maximum particle size lack established mineral gradations for optimal performance.
• The strength of LSAM-50 relies heavily on mineral gradation due to the large aggregate size and lower asphalt binder content.

Purpose of the Study:

• To enhance the road performance of LSAM-50 by optimizing its mineral gradation.
• To investigate the impact of coarse aggregate size distribution on void ratios within the aggregate skeleton.
• To examine the influence of fine aggregate gradation on asphalt mortar strength and the coarse-to-fine aggregate ratio on overall mechanical strength.

Main Methods:

• Investigated void ratios in coarse aggregate skeletons using varying proportions of 37.5-53 mm (D1), 19-37.5 mm (D2), and 9.5-19 mm (D3) aggregates.
• Analyzed the effect of fine aggregate gradation on asphalt mortar strength and the coarse-to-fine aggregate ratio on LSAM-50 mechanical strength.
• Proposed and verified a densely graded LSAM-50 structure with strong interlocking.

Main Results:

• The optimal ratio of D1:D2:D3 aggregates for minimizing coarse aggregate void ratio was determined to be 5:2:3.
• Maximum compressive and splitting strengths of the asphalt mortar were achieved at a decrement factor (i) of 0.75.
• The proposed LSAM-50 gradation demonstrated a 400% increase in dynamic stability, 3% improvement in low-temperature bending strain, 47% higher SCB bending strength, and 90% greater residual SCB strength compared to ATB-30.

Conclusions:

• A specific mineral gradation (5:2:3 for D1:D2:D3 aggregates) significantly optimizes the coarse aggregate skeleton void ratio in LSAM-50.
• Optimized fine aggregate gradation and coarse-to-fine aggregate ratios are crucial for maximizing LSAM-50 strength.
• The developed LSAM-50 with the proposed gradation offers substantially superior road performance, including enhanced stability and strength, over conventional mixtures.