# Evaluation of the Impact of Fines on the Performance of Sub-Base Materials
###### Abstract  
The study aims to evaluate the change in the behavior of sub-base materials being used in road pavements through blending fines of different types in different amounts. Fines are added in aggregate samples as part of gradations proposed by the American Association for State and Highway Transportation Official (AASHTO). Composite samples conforming to AASHTO gradations B and C were prepared by mixing coarse aggregates in varying proportions, ranging from 0 to 15%. Laboratory tests--including aggregate quality tests (abrasion test, flakiness index and elongation Index), physical tests (particle size analysis and specific gravity), and strength test (modified Proctor, California bearing ratio, and permeability test)--were performed on the control as well as the modified samples. It was observed that the material with 0% fines yielded the highest CBR values (greater than 98%) and coefficient of permeability of 4.4 \(\times\) 10\({}^{-4}\) cm/s. However, with the increasing of the fines up to 15%, a substantial reduction in CBR value up to 10% and coefficient of permeability to 1.62 \(\times\) 10\({}^{-7}\) cm/s was noticed. Based on these results, the modulus of rigidity (M\({}_{\text{R}}\)) and the corresponding structural numbers were determined for each layer. Conclusively, the required thickness of the base course was increased from 11 cm for the samples with 0% fines to 24 cm (118%) for the samples with the addition of 15% fines according to the AASHTO Design method. gradition; sub-base; fines; pavement; structural number +
Footnote †: journal: Applied  
and concluded that the frost susceptibility of aggregates depends on their mineralogical composition, quantity of fine particles, and hydraulic conductivity. [PERSON] et al. [3] reported that the deformation behavior of unbound aggregates under repeated traffic loading can be interpreted through their resilient response and availability of fines up to specific limit. However, these fines will have little effect on performance if the drainage conditions are excellent. [PERSON] et al. [4] determined the resilient modulus (M\({}_{\text{R}}\)) for base materials by selecting finer, medium, and coarser gradation limits as specified by the Oklahoma Department of Transportation. In their study, three varying moisture contents, namely, optimum moisture content (OMC, 2% below and 2% above the OMC), were considered. The reported variability in M\({}_{\text{R}}\) values ranged between 10 and 50% for three different gradations, and between 10 and 20% for three different moisture contents. Additionally, they proposed a predictive model for M\({}_{\text{R}}\) values based upon multiple linear regression. [PERSON] et al. [5] conducted research on an unbound granular base using eight different grain size distributions to identify a free draining material to dissipate excess pore water pressure quickly and reduce pumping, and that had a high in situ stiffness and adequate resistance to permanent deformation. [PERSON] et al. [6] compared the effect of fines on the dynamic response for open and dense graded base courses and observed that, under saturated conditions, the damage probability for the pavement with open graded aggregates is lesser. This is owing to fact that they offer more resistance to pore pressure build-up than dense-graded aggregates. [PERSON] and [PERSON] [7] conducted a series of repeated load triaxial tests on aggregates by varying the gradation, degree of compaction, and moisture contents and concluded that, with the increase in moisture content, the elastic stiffness decreases slightly in the case of broadly graded materials. They also observed a reduction in stiffness with the increase in the fine proportion. [PERSON] and [PERSON] [8] studied the influence of density, gradation, and degree of saturation on the modulus of resilience and concluded that the value of the resilient modulus was directly proportional to the confining pressure, whereas a variation in resilience modulus was insignificant with an increase in axial stress.