Abstract
Top-down cracking (TDC) alongside the wheel path is one of the commonly seen distress types on asphalt pavements, especially on heavy-duty asphalt pavements. It has been believed that TDC is caused by either tension stress or shear stress in the top asphalt layer(s). In this paper, new initiation and propagation mechanisms of TDC are proposed and validated through both accelerated pavement testing in the field and uniaxial repeated loading penetration tests in the laboratory at different temperatures. The test results clearly show that the uniaxial repeated loading penetration test can simulate both initiation and propagation processes of TDC very closely. Based on these test results, the mechanisms for crack initiation and propagation are further investigated with the finite element (FE) program. The FE analysis results show that under repeated loading, shear damage will occur first in the asphalt layer, then extend horizontally and consequently result in a shear-damaged layer. The damaged layer then led to higher tensile strain in the upper mixture which caused tension cracks and finally propagated upwards to the pavement surface. The whole process of TDC initiation and propagation can be described as “shear damage, then tension propagation”, which is the new mechanism proposed in this paper.
Highlights
Cracking alongside the wheel path is one of the common distress types seen on asphalt pavements, especially on heavy-duty ones
Some researchers believe that Top-down cracking (TDC) is caused by the tensile stress/strain initiated at the surface of the pavement
CIRCLY(a computer program for mechanistic pavement design and analysis) elastic analysis program to analyze the effects of the lateral and vertical contact stresses within the pavement and stresses of the tyre on the pavement within the asphalt layers, and concluded that the surface tensile stress at the tyre edge was the cause for top-down cracking
Summary
Cracking alongside the wheel path is one of the common distress types seen on asphalt pavements, especially on heavy-duty ones. Some researchers believe that TDC is caused by the tensile stress/strain initiated at the surface of the pavement. Kim and Roque et al [9] later developed the models for TDC initiation and propagation based on the “tension cracking mechanism assumption”. By using the FE method to analyze the pavement stress/strain distributions under tyre loads, Bensalem [10] found that traffic-induced shear strain on the vertical plane at tyre edge was much larger than the lateral tensile strain at same position. The results indicated that the crack was initiated at a depth of 25 mm, and obvious plastic deformation was observed below the cracking zone He believed that the crack was caused by the shear stress.
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