Strength Development and Microfabric Structure of Construction and Demolition Aggregates Stabilized with Fly Ash–Based Geopolymers

Abstract

The reuse of recycled construction and demolition (C&D) aggregates in civil engineering infrastructure applications has been considered a low-carbon solution to replace conventional pavement aggregates. Evaluating the strength development mechanism and interparticle flow of forces in geopolymer stabilized C&D aggregates will provide fundamental understanding of the behavior of stabilized C&D aggregates. The C&D aggregates studied are reclaimed asphalt pavement (RAP), recycled concrete aggregate (RCA), and crushed brick (CB). The performance of alkali-activated fly ash (geopolymer) on the stabilization of C&D aggregates, under different curing conditions and sample preparation methods were studied. Fly ash was used as the precursor for the alkali-activated binder that was used to stabilize the C&D aggregates. The effect of low and high content of fly ash–based geopolymers on strength development of recycled materials is investigated for the first time. Sodium silicate and sodium hydroxide were used, with different ratios, to intensify the alkaline environment for fly ash to accelerate the strength development of the mixture. The effect of static and dynamic compaction on the density and strength development was investigated for both low-content fly ash and high-content fly ash. Temperature treatment of geopolymer stabilized C&D aggregates up to 40°C and humidity curing in the moisture chamber for 7 days indicated improvement of the strength development of the mixture. The results of unconfined compressive strength (UCS) and resilient modulus testing of geopolymer-stabilized C&D aggregates indicate that alkali-activated fly ash is a viable binder for the stabilization of C&D aggregates.