Evaluation of stiffness to predict rutting resistance of hot-mix asphalt: a Canadian case study

This paper investigates the relationship between the stiffness and rutting resistance of hot-mix asphalt. Ten different types of hot-mix asphalt were examined. The Superpave mix design method was utilized to produce nine mixes; the remaining mix was designed using the Marshall method. The asphalt mixes were tested for stiffness and rutting resistance under the Centre for Pavement and Transportation Technology research program at the University of Waterloo. The stiffness was determined by the laboratory resilient and dynamic moduli tests. The dynamic modulus test was conducted at six different loading frequencies and five different temperatures. The rutting test was executed by the Hamburg Wheel Rut Tester and the French Laboratory Rutting Tester to obtain rutting depth. The regression analysis was performed to examine the relationships of resilient and dynamic moduli with rutting depth. The results of the regression analysis revealed that resilient modulus did not correlate well with rutting depth. In contrast, dynamic modulus showed strong correlation with rutting depth for a number of loading frequencies and temperatures. The strong relationship was observed at the higher temperatures of +46.1 oC and +54.4 oC. Moreover, the relationship between dynamic modulus and rutting depth was better for lower loading cycles/wheel passes applied in the rutting test. It was also noticed that dynamic modulus exhibited a better relationship with rutting depth obtained from the French Laboratory Rutting Tester. The overall findings indicate that the dynamic moduli obtained at 0.1–1.0 Hz and +46.1–(+54.4) oC are useful to predict the rutting resistance of hot-mix asphalt.

French Laboratory Proficiency Testing Program for Food Microbiology

The proficiency testing program in food microbiology (Réseau d' Analyses et d'Echanges en Microbiologie des Aliments; RAEMA), created in 1988, currently includes 440 participating laboratories. The program establishes proficiency in detection of Salmonella and Listeria monocytogenes, as well as quantitation of aerobic microorganisms, Enterobacteriaceae, coliforms, Escherichia coli, Clostridium perfringens, coagulase-positive Staphylococcus, and Listeria monocytogenes. Twice a year, 5 test samples are sent to participants to assess their precision and trueness for enumeration and detection of microorganisms. Results show an increasing involvement of food microbiology laboratories in quality assurance programs and use of standard and validated analytical methods. However, the percentage of laboratories obtaining questionable and unsatisfactory microbiological results remains relatively onstant.