Sensitivity to Laboratory Sample Fabrication Procedures for Cold In-Place Recycling Mixtures

Abstract: While cold in-place recycling (CIR) has both cost and environmental benefits, widespread use has been limited, in part, by uncertainty regarding laboratory design procedures which mimic construction practices in the field, specifically mixing, compaction, and curing conditions. These stages of construction can be related to properties of workability, compactability, and cohesion gain, which have unique considerations for asphalt emulsion CIR as compared to traditional asphalt paving. Reviewing literature, six different sample fabrication procedures believed to affect each of these properties were identified as having ambiguous guidance on best practices for asphalt emulsion CIR sample fabrication in the laboratory. For workability and compactability, the same factors apply and include 1) use of cement; 2) disturbance or re-mixing of a loose sample after pre-compaction curing; 3) mixing temperature; 4) humidity control; 5) curing time; and 6) curing temperature. The factors identified for cohesion gain include 1) use of cement; 2) testing temperature (i.e., whether a sample is allowed to cool to room temperature prior to testing or tested at curing temperature); 3) mixing temperature; 4) humidity control; 5) curing time; and 6) curing temperature. Each of these factors was evaluated for the effect on test results using a Plackett-Burman experimental design developed according to ASTM E1169. Superpave gyratory compaction metrics, Dongre workability test, and a loose mixture triaxial test were used to assess workability and compactability. Cohesion gain was measured using the raveling test and a direct shear test. Overall, pre-compaction curing temperature significantly influenced workability and compactability; while cohesion gain was significantly influenced by sample temperature at time of testing and mixing temperature. In general, the majority of factors evaluated did not yield statistically significant differences in test results, which indicates the ambiguity in guidance may be acceptable and gives an appropriate degree of flexibility to designers.