Saturated and unsaturated properties of recycled concrete aggregate for sustainable pavement design

Abstract

Pavement base layers are constructed to specified quality standard to distribute traffic loads and drain excess water from the pavement structure. The use of recycled concrete aggregates (RCAs) as base material has become increasingly common due to their mechanical properties and sustainability benefits. However, poor drainage and the presence of unhydrated cement in RCAs can lead to pavement saturation, adversely affecting their performance. Therefore, it is essential to thoroughly evaluate the physical, mechanical, and hydraulic properties that may impact the pavements’ performance. In this research, twelve RCA base materials, including three Open-Graded Drainage Courses (OGDC), a blended mix, and five natural aggregates (GMs) were evaluated for index properties, hydraulic properties, and stiffness (resilient modulus, M_R). Using the FHWA Drainage Requirement in Pavements (DRIP) software and the laboratory test results, the time required to drain 50 % of the saturated layer was also evaluate. The GMs, with M_R ranging from 114 to 513 MPa, had higher density but exhibited “poor” to “very poor” drainage quality. In contrast, the coarse gradation of RCAs, with M_R varying from 162 to 730 MPa, led to higher stiffness and better drainage. However, coarse RCAs exhibited 4 to 6 times higher moisture absorption, while the sand fraction had 3 to 5 times higher absorption, causing RCAs to retain moisture longer than GMs. No material exhibited “excellent” drainage quality, not even the OGDCs. Furthermore, increasing the layer thickness had minimal impact on improving drainage quality, highlighting the importance of considering alternative pavement drainage solutions for effective pavement drainage.