An alternative technology using microwaves for dry back process of unbound granular pavements during construction – A review

Field compaction practice and (or) weather conditions could lead to excessively wet unbound granular pavement materials (UGMs) or pavement layers that are problematic for the construction of durable pavements. Such excessive wet conditions with high degrees of saturation can cause undesirable delays in road construction schedule, as the materials need to be dried back to a low moisture content or degree of saturation (DoS). Hence, a feasible method to achieve accelerated drying of wet UGMs or pavement layers is crucial. Microwave drying technology is considered to be a viable solution due to its rapid drying rate with short drying time. However, there is a lack of knowledge regarding the applicability of microwave energy for accelerated dry back of wet UGMs and pavement layers. This paper identifies the key parameters that may affect the microwave drying process of wet UGMs and pavement layers. Further, the paper discusses how the dielectric properties of soil and UGMs vary with changes in moisture content and temperature, and the impact that these properties have on microwave drying. Finally, a practical method is proposed for utilising microwave technology to efficiently dry back the wet UGMs and compacted unbound granular pavements during the road construction process.