Adequate initial compaction is critical in a cold mix repair, as its mechanical properties improve with time due to curing. The objective of this investigation was to develop a test methodology to assess the stability of uncured bituminous cold mixtures under repeated loading, potentially usable in the field as a compaction quality control method. The methodology was developed by identifying the relationships between parameters from a Laboratory Stability Test (LST), and the penetration rate from a lighter version of the Dynamic Cone Penetrometer (identified herein as NPR) at various densification levels. The LST is a modified version of the laboratory uniaxial repeated loading test, and uses the power model [commonly used to evaluate permanent deformation characteristics in Hot Mix Asphalt (HMA)] to account for the initial instability present in non-cured asphalt cold mixes. Multiple Linear Regression Analysis (MLRA) was used to develop equations to estimate the slope of the secondary stage of deformation during the LST (identified herein as b) and the number of load cycles to flow failure (also known as the flow number, and identified herein as Cf) as a function of NPR and other mixture properties. The equations presented are based on laboratory data from mixes commonly used by utility companies in their pavement repair operations. To cover the range of possible stability levels expected in materials of this type, mixes with different characteristics were included. Based on the laboratory results, limiting values for b and Cf to separate acceptable from unacceptable stability levels are suggested.
Samenvatting