CONSTRUCTION AND DEMOLITION WASTE FINE AGGREGATE FOR SUSTAINABLE 3D PRINTABLE CONCRETE: RHEOLOGICAL AND MECHANICAL PERFORMANCE

Abstract

This study investigates the feasibility of incorporating locally sourced construction and demolition waste (CDW) as fine aggregate replacements in 3D concrete printing (3DCP) mixes. Three mortar mixes were developed: a 100% natural sand reference mix, and two recycled mixes replacing natural sand with processed CDW at substitution levels of 25% and 50% by weight. Fresh-state properties, including initial setting time, flow diameter, and rotational rheometry, were evaluated to map the fresh matrix performance. The 28-day compressive strength was assessed to evaluate mechanical performance of the printable mixes. Results indicate that CDW mixes accelerated early structural build-up, peaking at a static yield stress of 2854.0 Pa for 50% replacement compared to 1235.5 Pa for the reference mix. Furthermore, the addition of CDW altered the plastic viscosity, which rose from a reference baseline of 1.8 Pa·s to 3.14 Pa·s at 25% replacement due to grain angularity, but dropped to 1.94 Pa·s at 50% replacement because of high superplasticizer lubrication. Testing on the layered specimens revealed a clear directional compressive strength hierarchy of x > z > y. This study shows the potential success of a practical blueprint for adopting local construction waste in structural 3DCP applications.