Laboratory and field performance of recycled aggregate base in a seasonally cold region

The objective of this project was to characterize the freeze-thaw properties of recycled concrete(RCA)and asphalt(RAP)as unbound base and to assess how they behaved in the field for nearly 8 years.This paper includes an examination of existing information,laboratory studies of freeze-thaw behavior,and evaluation of data from Mn ROAD field-test sections in a seasonally cold region,i.e.,in Minnesota,USA.Test sections were constructed using recycled materials in the granular base layers at the Mn ROAD test facility.One test section included 100%RAP,another 100%RCA,a third one a 50/50blend of RCA/natural aggregate,and a fourth one only natural aggregate(Class 5)as a control.The stiffness(i.e.,elastic modulus)was monitored during construction and throughout the pavement life by the Minnesota Department of Transportation,along with the variation of temperatures and moisture regimes in the pavement to determine their effects on pavement performance.The resilient modulus of each material was determined by bench-scale testing in accordance with NCHRP 1-28a,as well as by field-scale tests incorporating a falling-weight deflectometer.Specimens were subjected to as many as 20 cycles of freeze-thaw in the laboratory,and the change in their resilient modulus was measured.In the field-test sections constructed with the same materials as the base course,temperature,moisture,and field modulus(from fallingweight deflectometer tests)were monitored seasonally for nearly 8 years.From the temperatures in the base course layer,the number of freeze-thaw cycles experienced in the field was determined for each test section.Inferences were made relative to modulus change versus freeze-thaw cycles.Conclusions were drawn for long-term field performances of the recycled base(RAB)in comparison to natural aggregate.

Freeze-thaw performance of chemically stabilized natural and recycled highway materials

This article provides an overview of several previous studies that investigated the stiffness and strength performance of chemically stabilized roadway materials under winter conditions （freeze-thaw cycling）. The objective of this research was to understand the behavior of different materials stabilized with different type of binders when they were subjected to freeze-thaw cycling. Nine different materials including natural soils （organic soil, clay, silt, sand, and road surface gravel）, reclaimed pavement material, and recycled asphalt pavement stabilized with nine different binders （five different fly ashes, lime, cement, lime kiln dust, cement kiln dust） were discussed. This article investigated how the volume, resilient modulus and unconfined compressive strength of soils/materials stabilized with different binders change in response to freeze-thaw cycling. Overall, the review results indicate that the stiffness and strength of all stabilized materials decrease somewhat with freeze-thaw cycling. However, the reduced strength and stiffness of stabilized materials after freeze-thaw cycling was still higher than that of unstabilized-unfrozen original soils and materials. In addition, materials stabilized with cement kiln dust provided the best performance against freeze-thaw cycling.