## 2 EMM-ARM in the Literature  
EMM-ARM is a non-destructive technique that indirectly measures the early age evolution of the Young's modulus of cementitious materials since casting through the solution of an inverse problem. This requires the identification of the fundamental frequency of a properly designed beam from its ambient vibration response. More details about the theoretical background of the method and the experimental testing procedure are provided in Section 3.2; herein, an extensive literature review about relevant applications of the methodology is reported to point out established outcomes and less investigated threads. The review is presented according to chronological order, whereas Table 1 summarizes the main outcomes of the literature review in terms of (i) tested materials, (ii) cement typology, (iii) curing conditions (temperature and/or relative humidity, RH), and (iv) investigated experimental variables. The EMM-ARM method was originally proposed by [PERSON] et al. [9] for continuous monitoring of concrete E-modulus evolution since casting. The results were validated by comparison with those obtained from ordinary compression tests carried out after setting time (typically at 3, 7, 14, and 28 days after casting). A different experimental setup was proposed later to characterize cement pastes and mixtures with retarding and accelerating additives [12]. The influence of the composition of cement pastes on the evolution of the E modulus was investigated by EMM-ARM in [18]. In particular, the study focused on the influence of different water-to-cement (w/c) ratios and contents of limestone filler, fly ash, silica fume, and metakaolin. The procedure was able to continuously catch the performance changes due to the variation in the composition; w/c ratio and filler typology strongly affected stiffness evolution over time. A case study aimed at assessing the reliability of the methodology for in situ applications was discussed in [19]. The Authors tried to adapt the setup used in a laboratory environment to field conditions, but some problems were revealed. The use of multiple accelerometers was proposed, and Stochastic Subspace Identification (SSI) [20] was used to estimate the fundamental natural frequency. [PERSON] et al. [21] investigated the extension of the EMM-ARM to sand-cement samples extracted by stabilized soils; in particular, the study faced the problem of mold geometry and sampling techniques. A good match with the results of cyclic compression tests was found. A detailed and extensive study [22] compared the results obtained using EMM-ARM with those provided by other conventional non-destructive and destructive techniques in the presence of different temperatures during the test, as well as various constituent materials. An in-situ application of EMM-ARM to stabilized soils is reported in [PERSON] et al. [23], where an assessment of the influence of mold geometry and different mixes of cement was carried out. The results of a round-robin test involving three independent laboratories are presented in [13]: the experimental program encompassed eight different automatic destructive and non-destructive techniques to evaluate the evolution of stiffness in concrete at early ages. Evidence of a good agreement among the estimates provided by the different techniques is documented. [PERSON] et al. proposed some improvements to the conventional test setup to simplify in situ applications [24]. The influence of biomass ashes on the evolution of concrete early-age Young's modulus was studied through the EMM-ARM. In particular, cement was partially replaced by biomass ash, which reduced the stiffness within the first 28 h and also largely increased the electrical conductivity of the mix [25]. The influences of recycled aggregates and curing temperature on the evolution of the Young's modulus of concrete at early ages were investigated in [26] through EMM-ARM and other non-destructive techniques, obtaining results in good agreement with each other.