Low temperature tensile strength and fracture toughness of asphalt concrete determined from small notched 3-P-B samples

Abstract

Cracking in asphalt concrete at low temperatures and relevant brittleness and toughness properties are primary concerns, considering the long-term complex road service conditions and economic impacts due to costly maintenance. In this study, we examine a simple closed-form solution for tensile strength ft and fracture toughness KIC measurements as the key cracking property characteristics of asphalt concrete. Although the limited size or thickness of real asphalt concrete structures invalidates the application of LEFM and fracture toughness KIC criterion, a Boundary Effect Model (BEM) for quasi-brittle fracture of heterogeneous solids considering the combined effects of ft and KIC [11-13] overcomes the problem. Asphalt concrete AC-13 is chosen in this study, small notched three-point-bending (3-p-b) samples are tested at -10°C. The 3-p-b samples have width (or size) W = 35 mm, span S = 88 mm, and thickness B = 30 mm. Two different notch lengths of 7 and 10 mm (or -ratio = a0/W = 0.2 and 0.3) are selected for Group A and B samples to induce different notch and sample boundary interactions. The average aggregate size (or grain size) G of the asphalt concrete is around 5 mm, i.e. the a0/G ratio is only between 1.4 and 2, making the samples highly heterogeneous. BEM analyses of test results show the relative error between the two groups for strength and toughness is less than 13%. If all tests are grouped together, the relative errors of Group A and B in comparison to the strength (ft = 7.23 MPa) and toughness (KIC = 1.81 MPam) of the total sample population are halved to 6%. These preliminary results show that the simple closed-form solution potentially can provide a reliable method for determination of low temperature fracture properties of asphalt concrete for optimization of materials mix for higher cracking resistance.

A strength criterion for size effect on quasi-brittle fracture with and without notch

“…(3) can be used to analyse quasi-brittle fracture of rocks. Asphalt concrete results with the average aggregate size around 5 mm can be found in [15]. Concrete results with the maximum aggregate dmax from 10 to 40 mm can be found in [10].…”