Development and Verification of CT Index 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 CT_Index which is sensitive to specimen thickness and air void (AV) content. The CT_Index 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 CT_Index 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 CT_Index and varying thickness and CT_Index 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. CT_Index 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. CT_Index results of field cores and the RPMLC specimens still showed differences after applying the correction method, suggesting the need for a different (larger) CT_Index 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.