Developments in asphalt pavement compaction by variable tire pressure rollers.

Pavements are currently compacted in the field in two stages. The first stage consists of rolling at high temperatures during construction, and it may be continued for an hour or two after the mix leaves the spreader. The second stage is compaction by traffic, which takes place at normal service temperatures, and it ordinarily continues from two to four years to achieve ultimate density, which corresponds to 100% of laboratory compacted density. Poor compaction by rolling during construction leaves a pavement with a high air voids content. The higher this content, the faster the asphalt cement in the pavement hardens, and the shorter is the pavement's service life. Consequently, there is a need to combine this two-stage pavement compaction into a single stage. This means that pavements should be rolled during construction to 100% of laboratory compacted density. Experience shows that rolling to 100% of laboratory compacted density cannot be achieved by steel wheel rollers. It could probably be attained by the proper use of pneumatic-tire rollers equipped for rapid change of tire inflation pressure. Some improvements in the latter type that are needed to accelerate this development are reviewed. Compacting pavements during construction to 100% of laboratory compacted density would retard the rate of hardening of the asphalt cement in the pavement, thereby substantially lengthening pavement service life, and it would greatly increase the load carring capacity of binder and surface courses, and particularly of asphalt base courses, per inch of thickness. Low viscosity asphalt cements, because of their low viscosities at high temperature, provide paving mixtures with much less resistance to compaction by rolling, and this would be highly advantageous for: (1) assisting properly operated pneumatic-tire rollers with rapidly adjustable tire pressure to attain 100% of laboratory compacted density by rolling during construction, (2) achieving much faster compaction by traffic to 100% of laboratory compacted density, where this is not attained by rolling, and (3) achieving compaction to much higher density by rolling during cold weather construction. /author/.