Sustainable recycling of asphalt mixing plant dust in ultra-high performance concrete: Effects on engineering performances and microstructure

Asphalt mixing plant dust (AMPD), a fine particulate solid waste collected during asphalt mixture production, was systematically evaluated as sustainable supplementary cementitious materials (SCMs) in ultra-high performance concrete (UHPC). This investigation employed AMPD replacements of 10 %, 20 %, and 30 % (by mass) for Portland cement (PC) to assess the effects on engineering performances and microstructure evolution. The results showed that the proper content of 20 % AMPD addition achieved optimal mechanical properties of comparable 28-day compressive/flexural/tensile strengths (138.8/29.1/9.8 MPa) to the control AMPD-free mixture (139.2/29.9/10.4 MPa). Concurrently, the fresh-state fluidity was enhanced, and the 72-h drying shrinkage was mitigated. The low pozzolanic reactivity of AMPD contributed to reduced early-age hydration heat release. The synergistic improvements in bound water content of main hydration products, portlandite formation and proportion of gel pores indicated that the filler effect of AMPD enhanced the hydration degree of PC per unit mass in UHPC. Nanoindentation analysis also confirmed that AMPD addition elevated proportion of C-S-H gel phase, and meanwhile incorporated high-stiff remnants in UHPC to increase the elastic modulus. This work highlighted the technical advantages of AMPD addition in UHPC. • Feasibility of recycling asphalt mixing plant dust in ultra-high performance concrete was investigated. • Proper 20 % dust addition achieved optimal 28-day cured mechanical properties. • Fresh-state fluidity was enhanced, and 72-h drying shrinkage was mitigated. • Filler effect of dust enhanced hydration degree of cement. • Nanoindentation test exhibited elevated elastic modulus.