Study of moisture damage (by water immersion and freeze thawing conditioning) in warm asphalt recycling

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Environmental factors and traffic load contribute to early failures in bituminous pavements. Moisture is a key element in the deterioration of the asphalt mix. It can degrade the integrity of pavement by loss of cohesion (strength) and stiffness of the asphalt film, failure of the adhesion between the aggregate and asphalt (stripping) and degradation or fracture of the aggregate, particularly when the mix is subjected to freezing.

This work studies moisture damage (by water immersion and freeze-thaw conditioning) in asphalt pavements. The methodology used is well known among engineering pavement experts, however, this is a case of a novelty research work, since the study is about water sensitivity and freeze-thaw damage of warm recycled bituminous mixtures.

Water Sensitivity was studied according to European Standards EN 12697-12:2003 and EN 12697-23:2003 by measuring the indirect tensile strength of bituminous specimens, as well by Immersion-Compression Test carried out according to the Spanish Standard NLT-162/00.

The resistance to moisture damage by freeze-thawing conditioning was also determined by ASTHO T283.

A new method based on ultrasonic accelerated moisture conditioning was also proposed, demonstrating to be as well as effective to evaluate the moisture sensitivity, having the advantage of being executed in a shorter period of time.

Tests were carried out in laboratory compacted specimens and taken of Portuguese roadway EN244, section between PONTE DE SÔR and the proximity of the GAVIÃO. This is a case of a Portuguese roadway rehabilitation using a new technology designated by WARM ASPHALT RECYCLING. The technology consists of removing the existing pavement structure, in a 7cm depth, by a ripping/crushing operation and producing a recycled mix in central plant consisting of 98% of reclaimed asphalt pavement and 2% of a cold emulsion. This recycled bituminous mix is produced at 130ºC, placed again in the roadway as replacement of the existing old pavement, and compacted at 90ºC. The reason this methodology is designated warm asphalt recycling is that temperatures used in process are lower than those used in hot asphalt recycling. The method was proposed by CEPSA and the work in EN244 roadway is being carried out by JJR Construções Lda, being follow up and developed by CMADE researchers and LNEC.

Results obtained have shown that warm asphalt recycled pavement has a very good resistance to water damage, when submitted to water sensitivity tests used in this research work.

Master dissertation in Civil Engineering of Maria João Torres, 2009.

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