Date of this Version
Nsengiyumva, G. (2015). Development of Semi-Circular Bending (SCB) Fracture Test for Bituminous Mixtures. Civil Engineering. Lincoln, University of Nebraska. Master's.
Granted that most distresses in asphalt (flexible) concrete (AC) pavements are directly related to fracture, it becomes clear that identifying and characterizing fracture properties of AC mixtures is a critical step towards a better pavement design. This thesis examines the testing variables of a reliable and practical semicircular bending (SCB) test for evaluating the fracture characteristics of asphalt concrete mixtures at intermediate service temperature conditions. The first part of this thesis investigates the repeatability of the SCB fracture test method by integrating a statistical-experimental approach to identify testing variables of the SCB test that result in repeatable test results. Toward this end, five testing variables (the number of testing specimens, specimen thickness, notch length, loading rate, and testing temperature) of the SCB test were investigated due to their significant effects on mixture fracture characteristics. After statistical analysis of 18 specimens tested a typical testing variables, approximately, five to six specimens/replicates were found to be a reasonable sample size that could properly represent asphalt concrete fracture behavior using the SCB test method. The coefficient of variation (COV) of the mixture fracture energy was used to evaluate the effect of each variable on the repeatability of test results. A range of 1 mm/min. to 5 mm/min. for the loading rate, a notch length from 5 mm to 25 mm, and a specimen thickness of 40 mm to 60 mm and a testing temperature of 15-40°C showed the lowest variation of fracture energy. The second part of this work is to investigate the sensitivity of the SCB test using the previously determined testing variables. Fourteen different asphalt concrete (AC) mixtures collected from 12 field construction projects in Nebraska were used in this task. The ANOVA test showed statistically significant differences between mixtures at a 95% confidence level. Tukey’s HSD multiple-comparison analysis found similarities within mixtures of same types and significant difference between mixtures types. In addition, the fracture energy of bituminous mixtures increased with increasing amount of virgin asphalt content in mixture. Overall, the SCB test method developed herein proved to be repeatable and sensitive to changes in mixtures, and thus a promising tool for evaluating the fatigue fracture resistance of AC mixtures.
Adviser: Yong-Rak Kim