Performance evaluation of unconventional aggregates from primary and recycled sources for construction platform and low volume road applications

Unbound granular layer;aggregate;low volume roads;accelerated pavement testing;rutting;falling weight deflectometer;large-scale triaxial testing

Kazmee, Hasan

关键词: Unbound granular layer;    aggregate;    low volume roads;    accelerated pavement testing;    rutting;    falling weight deflectometer;    large-scale triaxial testing;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/101130/KAZMEE-DISSERTATION-2018.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Unbound aggregate layers are frequently used as remedial alternatives for weak subgrade soils. With the recent focus on sustainable construction practices, ever-increasing transportation cost, and scarcity of natural resources, nontraditional and locally available recycled materials have become viable for the construction of unsurfaced and low volume roads. Although large-size unconventional virgin aggregates (also referred to as ‘rock cap’, ‘primary crusher run’ and ‘macadam stone base’) have been successfully used by several transportation agencies previously, performances of recycled materials, e.g. reclaimed asphalt pavement (RAP) and recycled concrete aggregate (RCA) with possible large particle sizes, are not readily available in current engineering literature. The main objective of this research study was to evaluate engineering applications and field performances of unconventional aggregates from virgin and recycled sources used in both construction platform type pavement foundation and low volume road applications.A total of seven different aggregate materials varying in particle size distributions and material compositions were selected for this study. Since conventional laboratory testing could not accommodate engineering property characterizations and performance evaluations of large size unconventional aggregates, a field evaluation study was essentially undertaken involving accelerated pavement testing of twelve full-scale working platform and twelve asphalt concrete surfaced low volume road test sections constructed with the aforementioned materials. Regular base course type virgin crushed dolomite and 100% reclaimed asphalt pavement (RAP) materials were used as a thin capping layer to limit the movement of large particles over weak subgrade condition. Among the 24 test sections, 16 test sections comprising of large rocks were constructed over an engineered subgrade with a California bearing ratio (CBR) of 1%; meanwhile, the remaining 8 test sections were built with regular size dense-graded base course aggregates over a modified subgrade with a design strength of CBR = 3%. Considering the dimension-specific requirements of standardized test protocols, limited laboratory characterization tests could be conducted to evaluate the physical and mechanical properties of selected aggregate materials. A state of the art field imaging technique was adopted to measure the size and shape properties of these large size, so-called ‘aggregate subgrade’ materials. For the virgin aggregates, imaging-based angularity and surface texture indices were found to increase when particles sizes were mechanically reduced through the aggregate crushing effort from primary to tertiary stage quarry processes. Conversely, RAP materials had comparatively lower angularity and surface texture owing to the presence of asphalt binder coating around those particles. Visual observations and laboratory test results indicated that uniformly graded large size aggregates underwent significant particle reorientation during the monotonic triaxial strength testing. Despite exhibiting higher modulus values, 100% RAP accumulated higher permanent deformation compared to the virgin crushed dolomite.Quality control tests conducted with nuclear density gauge during the construction of full-scale test sections indicated, in general, lower than desired density levels achieved in the constructed aggregate layers. Non-nuclear tests conducted on those unbound granular layers, with lightweight deflectometer and GeoGauge, exhibited higher modulus values in test sections containing 100% RAP capping/subbase layers. After construction, the test sections were subjected to accelerated pavement testing with a moving wheel load of 44.5 kN at a constant speed of 8 km/h exerting an approximate tire pressure of 758 kPa. Periodic rut measurements were carried out on pavement surfaces throughout the accelerated loading process. Observed rutting trends in unsurfaced and low volume road test sections were weighed against as-constructed layer thicknesses, penetration-based strength indices, and hot-mix asphalt bulk specific gravities. Within the current design framework of Illinois Subgrade Stability manual, aggregate subgrade layers with unconventional large rocks constructed over weak subgrade with a controlled strength of CBR = 1%, performed satisfactorily accumulating a minimal amount of rutting. Among the different field applications, the 60–40% blend of recycled concrete aggregate and RAP materials performed the most satisfactorily as an improved subgrade. Despite exhibiting better relative compaction and higher in situ modulus values, unbound granular layers consisting of 100% RAP were found to be quite susceptible to large deformations during paving as well as wheel–load rutting during trafficking.