Development and Verification of CTIndex Correction Methods to Normalize Air Void Content and Thickness of Field Cores

Abstract

The IDEAL cracking test (IDEAL-CT) (ASTM D8225) provides a fracture mechanics-based parameter: cracking tolerance index or CTIndex which is sensitive to specimen thickness and air void (AV) content. The CTIndex of field cores with variable thicknesses and AV contents are not comparable to those of laboratory-compacted specimens prepared at specified values. This study analyzed the CTIndex sensitivity to these features by preparing reheated plant-mixed laboratory-compacted (RPMLC) specimens with variable thickness and AV content and developing thickness and AV content correction factors. The correction factors were obtained using trendline equations from the relationships between CTIndex and varying thickness and CTIndex and varying AV content. The correction factors were then applied to RPMLC specimens fabricated with variable thickness and AV content and compared with RPMLC specimens prepared at 62 ± 1 mm and 7 ± 0.5% AV. CTIndex results were comparable, and one correction method was proposed. This method was applied to replicate field cores of 22 independent mixtures and compared with RPMLC specimens fabricated at 62 ± 1 mm and 7 ± 0.5% AV. CTIndex results of field cores and the RPMLC specimens still showed differences after applying the correction method, suggesting the need for a different (larger) CTIndex threshold for field cores. Finally, more data are required to improve the proposed correction methods and more mixtures need to be evaluated to consider a wider range of thickness, AV, component materials, and aging conditions.