Effect of Fine Clay Particles on the Strength Characterization of Cement Treated Flex-Base Materials

摘要

The recycled materials such as recycled crushed concrete aggregates (RCCA) and reclaimed asphalt pavement (RAP) treated with cement have been widely used as an alternative granular base in pavement construction in different states throughout USA. In the flexible pavement systems, the base layer contributes to the structural capacity, so, the quality performance of this layer is essential. However, presence and migration of fines from the subgrade into granular base may affect the strength and stiffness of flex-base. As such, the main purpose of this study was to examine the effect of fine contents in granular base materials in terms of strength and stiffness. For this study, RAP and RCCA were mixed in different proportions from 0% to 100% with different amount of soil intrusion varying between 0% and 24% with cement content ranging between 0% and 6% at 2% interval. An experimental program was designed and conducted to determine the optimum moisture content (OMC), maximum dry density (MDD), unconfined compressive strength (UCS), and resilient modulus (M_r) of the mixes of RAP, RCCA, soil, and ordinary Portland cement (Type Ⅰ/Ⅱ). Based on the experimental results, it was found that with the intrusion of fines in cement treated as well as untreated recycled granular bases, both the strength and stiffness decreased as compared with the same specimens without fine particles. With the addition of 12% and 24% of soil in the combination of 30% RAP + 70% RCCA and 50% RAP + 50% RCCA, the value of resilient modulus decreased in the range of 30-55% in the cement stabilized as well as natural forms. For example, the Mr value of (30/70) RAP/RCCA with 2% cement ranged between 69 MPa (10,000 psi) and 310 MPa (45,000 psi); it was reduced to a range of 69-207 MPa (10,000-30,000 psi) with 12% soil intrusion. Similarly, at 6% cement content, the highest value of M_r of (30/70) RAP/RCCA was observed as 517 MPa (75,000 psi) whereas with the 12% soil, the moduli value was reduced to 262 MPa (38,000 psi) at the maximum confining pressure of 0.14 MPa (20 psi).