Influence of curing on cold mix mechanical performance

Abstract

Cold mixes are evolutive materials, especially in their early life. Their initial cohesion is low and builds up gradually. The materials characteristics have to be evaluated at different states: fresh, mature, aged. An evaluation method is already available for fresh cold mixes. Ageing issues have been addressed elsewhere and are not dealt with here. Different curing procedures have been assessed and compared. Their goals are: laboratory curing must be related to field curing, the binder film must not be brought to an artificial state, no binder ageing must be caused by curing. Diverse curing sequences have been applied to grave-emulsion and dense wearing course mix. The effects of temperature, relative humidity and time have been evaluated. During each curing span, the mix moisture content has been monitored. The mechanical behaviour has been characterized by compressive strength and stiffness modulus (measured by indirect tensile testing). At the end of the varied curing periods, the bitumen was extracted and characterized. Special care has been taken in selecting the extraction method, to prevent any alteration of the bitumen. To establish a relationship between laboratory and field, the above results have been compared to those obtained on cores taken from similar mixes laid on roads. Finally, a new curing method has been selected and is proposed to road engineers.