Investigating the Relationship Between Moisture Content and Dry Density on Different Gradations for Road Base Granular Materials

Abstract

California Bearing Ratio (CBR)in granular materials is the key technical characteristic of layers in flexible pavement. The CBR value is a way to measure the material stiffness used in the pavement design procedure for the road base layer depending on the aggregate types. Road base layers’ ultimate role in the flexible pavement is to spread loading evenly over the sub-grade from the loading of vehicles throughout the design life. Among the factors affecting the material's bearing capacity, aggregate gradations are one of the most important parameters that give a considerable result. This study was carried to evaluate the effects of different aggregate gradations using granite, basalt, and quartzite aggregates on the bearing capacity of the granular materials. Further analysis on the base course layer’s upper and lower gradation limit were conducted to identify the bearing capacity of the layer, through a series of aggregates physical tests and strength tests. The results indicated that physical properties of the selected aggregates complied to the Public Works Department (PWD) Specifications (2008) for soaked and un-soaked condition. For both soaked and un-soaked conditions, the samples with lower limit gradations showed higher stress values compared to upper limit gradations for all three types of aggregates. Granite showed higher CBR values for both, soaked, and un-soaked conditions, followed by basalt and quartzite at upper and lower limit gradation. Un-soaked granite samples with lower limit gradation showed 60.5% increment in strength compared to un-soaked upper limit gradation, followed by quartzite 53.6% and basalt 9.94% respectively. The results indicated that strength is highest in the lower limit gradations where the use of coarse-grained aggregates could significantly increase the strength.