Retained compressive strength index test

The retained compressive strength index test is conducted in accordance with ASTM D 1075 (2011). The determination of the impact of water on the bituminous mixture cohesion is expressed as the percentage of the retained compressive strength. 

The test requires cylindrical specimens of usually 101.6 mm in diameter and 101.6  

5 mm height to be produced. Specimens are produced and tested on compressive strength according to the standard ASTM D 1074 (2009) (AASHTO T 167 2010). The compaction is carried out with a compression testing machine, which applies an initial compressive load of 1 MPa (150 psi) to the bituminous mixture for a few seconds and then a full load of 20.7 MPa (3000 psi) for 2 min. 

If the specimens are required to be compacted at a certain void percentage, usually 6%, the abovementioned full compressive load varies accordingly. 

The specimens are extracted from the moulds and left to room temperature for 24 h. Once bulk specific gravity is determined, half of them (at least three specimens) are tested in axial compression, without lateral support, at a uniform rate of vertical deformation (5.08 mm/ min for the 101.6 mm specimen) until crushing. 

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In the second category, fracture tests on specimens after immersing them into water are used for the determination of (a) the ratio of indirect tensile strength (ITSR) (CEN EN 12697-12 2008) or (b) the index of the retained compressive strength (ASTM D 1075 2011) and (c) the ratio of retained Marshall stability. 

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