Effects of fines content and maximum particle size on mechanical properties and saturated hydraulic conductivity of recycled concrete aggregates for unbound roadbed materials in Vietnam

Road base layers play an important role in bearing, transmitting, and distributing part of the load to the underground. Unbound aggregates crushed from natural rock are the most popular materials used to construct the base layers of the pavements. However, nowadays the sources of natural materials have been increasingly exhausted and the pollution from construction and demolition waste (CDW) is a big problem in Vietnam. Therefore, the utilization of CDW for recycling is a crucial issue to reduce the generation amount of CDW and consumption of natural resources. With regards to the applicability of recycled concrete aggregates (RCA) to unbound roadbed materials, many studies have been done to investigate the effect of grading of particles on mechanical properties. However, the effect of other factors such as maximum particle size (Dmax) and fines content (Fc in wt.%; typically, with particle size less than 0.075 mm) have not been fully understood. In this study, concrete waste taken from a CDW landfill in Vietnam and was crushed and sieved to prepare graded RCA samples for a series of laboratory tests to characterize mechanical properties such as compaction, bearing capacity, and saturated hydraulic conductivity. The graded RCA samples with two different Dmax, 25 and 37.5 mm, and four different Fc values ranging from 0 to 20 %, were prepared. This study showed that maximum dry density (MDD) and CBR value of graded aggregates with Dmax = 25 and 37.5 mm reached the highest values at Fc = 5%. Except for the sample with Fc = 20 % and Dmax = 25 mm, the measured CBR values of tested samples satisfied the technical requirements of Vietnamese and Japanese standards. Besides, the particle breakage of aggregates and saturated hydraulic conductivity were highly controlled by Fc and both values decreased with increasing in Fc.