The objective of this study is to use electro mechanical impedance (EMI) based Structural Health Monitoring (SHM) to monitor the early age strength development of concrete with refuse derived fuel (RDF) ash used as a sustainable supplementary cementitious material. The global construction trend of a circular economy and low-carbon materials has already begun to deliver the double advantage of waste reduction and resource recovery by incorporating municipal solid waste by-products like RDF ash into concrete. In the current study, 30% of ordinary portland cement (OPC) was replaced with retrieved RDF ash and the hydration process was monitored by embedding piezo (PZT) sensor into samples. Conductance signatures (100–400 kHz) and the root mean square deviation (RMSD), mean absolute percentage deviation (MAPD) indices were evaluated in order to assess microstructural changes over a 90-day curing period. Results show progressions in conductance signatures that appear to have a significance as curing continues. During the early hydration stages (Days 1–10), rise of conductance magnitude was gradual, which we associate with the formation of calcium silicate hydrate (C-S-H) gel. Between Day 11 and Day 28 there was a concomitant increase of frequencies along with pronounced sharp peaks which signified secondary hydration reactions producing a more well-defined, denser stiffer concrete matrix. After the 28 days, signatures stabilized as pozzolanic activity plateaued. From the quantitative point of view, the increase in the RMSD index at early ages (10–28 days) goes from about 20–25% to approximately 55–75%, indicating a continuous swelling of compressive strength from 25 MPa to 40 MPa at 28-day age. The significative positive relation between the mechanical performance and RMSD strongly validates the non-destructive, real-time applicability of EMI-based SHM technique for high-fidelity monitoring of RDF ash concrete. These results promote the idea of coupling smart monitoring systems with sustainable infrastructure to maintain structural health while leveraging industrial by products.