The Use of Recycled Aggregates in Continuously Reinforced Concrete Pavements (CRCP)

Abstract

The use of recycled aggregates in concrete has increased in recent decades. Increasing scarcity of natural aggregates and the growing ecological importance promote this evolution. The first test section in Belgium of a two-layer continuously reinforced concrete pavement (CRCP) with recycled aggregates in the substrate layer was built on the highway E34/N49 in 2007. Horizontal cracking at the level of the reinforcement showed up after only a few years. This is a problem which was never seen before in CRCP and was probably due to the use of recycled aggregates. Therefore it is important to understand the impact of recycled aggregates on concrete. Recycled aggregates are a two-component material consisting of natural aggregates and adhering mortar. The adhering mortar is more porous than the rock particles which insures a higher water absorption and lower density. In addition, they have a lower abrasion loss in the Los Angeles-test and less resistance against weather and temperature changes. This is due to, respectively, the less strong mortar content, and the large pores of recycled granulates. A first cause of horizontal cracking can be found in the results of high drying shrinkage, high creep and low modulus of elasticity. These properties insure larger tensions in the concrete layer. In combination with a lower tensile strength it is a possible cause for the horizontal cracking. In addition, the paper reports on laboratory testing concerning the properties of concrete with recycled aggregates and discusses an alternative method to determine the concrete mixture which takes the influence of the adhering mortar into account.