Comparative evaluation and modification of laboratory compaction methods of road base mixtures manufactured in low-emission CIR technology with foamed bitumen and bitumen emulsion

Abstract

The paper evaluates the influence of laboratory compaction methods on the properties of recycled mixtures with foamed bitumen (Foam-Mix) and bitumen emulsion (Emulsion-Mix). In Poland, the requirements concerning the design of recycled mixtures and quality control of the cold in-place recycled base course layers specify two laboratory methods of sample preparation: static compaction in a hydraulic press and impact compaction with the use of Marshall hammer. The statistical analysis (Student t-test) indicates that the compaction method has a significant effect on physical and mechanical characteristics of the recycled mixtures. The method of sample preparation has been found to affect the arrangement of aggregate grains in the compacted material. The hydraulic press method over-compacted the samples from both mixtures, crushing the grains. The samples compacted in the hydraulic press had better strength parameters and resistance to water, which was undoubtedly related to the lower air void content, regardless of the asphalt binder used. Static compaction, which according to the Polish guidelines is conducted under pressure of 100kN maintained for 5 minutes, in many cases (depending on the grading of the recycled mixture or amount of binding materials) produces mixtures with excessive bulk density being inadequate to real conditions and difficult to attain in the field. This paper proposes the technique for the calibration of compaction methodology for foamed and emulsion mixture samples in the hydraulic press against the Marshall method.