Influence of Test Specimen Compaction and Curing Condition for Pavement Cold Recycled Mixtures

Presently in most European countries the quality of cold recycling mixtures in pavement rehabilitation is proven by achieving required strength values (indirect tensile strength or compressive strength) and eventually by values of stiffness modulus (IT-CY test method). This empirical approach of quality assessment is quite simple, relatively fast in performance and set in the long term. On the other hand this kind of assessment is characterized by distinctive weaknesses. Foremost strong dependence of magnitude of received strength values on various factors, whereas one of the most important is the way how test specimens are prepared and compacted. Second important parameter is influence of test specimen curing procedure for given conditions. Technical specifications in various European countries specify specimen preparation by using different laboratory equipment, which compact the test specimen by static pressure, dynamic hits or gyratory motion. In case of gyratory compactor further difference is also in the magnitude of used compaction pressure, number of applied gyrations etc. These parameters influence the resulting mix voids content as well as the resulting strength and stiffness modulus. Curing of test specimens is influenced by used binders (bituminous emulsion, cement, special hydraulic binders, bitumen foam etc.), which have different principles of hardening. Other factors are time and surrounding conditions (temperature, humidity). Presently there are in national specifications different conditions for curing. Usually common is the effort with respect to practical needs and condition to reduce the curing and testing periods by introducing e.g. accelerated curing procedures. Objective of this paper is to investigate impact of specimen preparation and lastly the curing procedure by using different conditions on the quality characteristics of the cold recycled mixes. This should set necessary fundaments for unification of technical specifications. Testing was done on specimens prepared by static compacting machine, impact compactor and gyratory compactor (following SUPERPAVE standards. Testing was executed on specimens where reclaimed asphalt material has been used in cold recycling technique by applying combined binder of cement and bituminous emulsion or foam bitumen.