Effects of diurnal temperature dynamics on curing of cold-emulsion reclaimed asphalt pavements

Abstract

Strength development in Cold-Emulsion Reclaimed Asphalt Pavements is gradual and largely dependent on the rate at which curing proceeds. Its early life strength is therefore low and presents a major challenge in material specification for mechanistic pavement design. The solution has been to subject a sample of the mixture to be used in the pavement to accelerated laboratory curing to the attainment of Equilibrium Moisture Content (EMC) condition. Fatigue and Stiffness parameters of the mix along with the chemical properties of the binder can be determined from the cured samples and results incorporated into the pavement design process. The emphasis is in the choice of a laboratory curing protocol that adequately simulates expected curing trends in the field. Protocols in popular use employ steady state curing temperatures to predict long term behaviour of Reclaimed Asphalt Pavements. This project set out to investigate the likely effects of seasonal variations and diurnal cycles in ambient temperatures on the engineering properties of Reclaimed Asphalt and the incorporated binders. To simulate the above phenomena, a predictive model was adopted in computation of high and low temperature peaks that can be expected in two pavements, one in the tropics and the other in a temperate region. The resulting sets of temperatures were used to cyclically cure Reclaimed Asphalt Pavement cores that were manufactured by artificially aging Dense Bitumen Macadam (DBM) in the laboratory and mixing it with a cationic bitumen emulsion. Another set of cores were subjected to steady temperatures as is the current practice. This acted as a control for the two cyclic temperatures under study. Use was made of a suite of tests available in the Nottingham Asphalt Tester (NAT) to determine stiffness and fatigue properties of the mix under the three treatments. Bitumen binders recovered at the end of curing was tested for penetration, softening point temperatures and percentage of Asphaltenes. The findings pointed at a likelihood of severe treatment of asphalt samples by the existing laboratory curing protocols. Curing at a steady temperature led to a lower fatigue life, over estimation of early life strength and underestimation of long term strength of the cold asphalt. Low penetration values, high softening point temperatures and high percentages of Asphaltenes in bitumen from the cured samples attest to severe aging of the samples