###### Abstract  
The effects of uncontrolled storage and curing temperature on the early-age mechanical behavior of cement are under-investigated issues, and the few available studies in the literature analyze their influence mainly from a chemical-physical point of view. The present study, on the contrary, aims at studying the effects of temperature and, above all, cement prehydration due to uncontrolled storage from a phenomenological perspective through the application of the EMM-ARM method. In particular, the influence of those factors on the early-age evolution of the Young's modulus of cement pastes produced from Portland as well as pozzolanic cement is experimentally assessed. The obtained results confirm the possibility of exploiting the EMM-ARM method to characterize those effects on a phenomenological basis, sorting back to the comparison of the curves of prehydrated cement with reference ones in controlled storage conditions. As a result, the methodology shows promising applicative perspectives for acceptance checks of the materials before use. cement paste; pozzolanic cement; Portland cement; early-age elastic modulus; storage conditions; EMM-ARM +
Footnote †: journal: Applied  
The evolution of the stiffness of the cementitious materials may play a key role in many retrofit and upgrading structural interventions: the assessment of the matrix structural features, such as setting time and hardening, indeed supports the accurate definition of the work sequence as well as the analysis of the capacity of members associated with the activation of the reinforcement effectiveness, and the prediction of the long-term stiffness. Specifically, [PERSON]'s modulus considerably changes during the early age phase after casting basically due to hydration reactions [9]. Various destructive and non-destructive techniques have been proposed in the literature for the early-age mechanical characterization of cement-based materials. The majority of those tests can only be performed after setting time, i.e., after some days of curing [10]. In the second half of the last century, several non-destructive test methodologies to evaluate the mechanical properties of cement-based materials since setting time have been proposed [11]. Among them, maturity methods are based on temperature measurements during curing; they are mainly applied on-site, and their reliability strictly depends on adopted maturity functions. Measurements of the variation of the dielectric properties of the material can also be correlated with the hydration process and mechanical properties evolution. In the case of methods based on ultrasonic waves, the reflection coefficient is used as an indicator of hydration to qualitatively describe the mechanical evolution since setting time. The Radon exhalation method consists of exploiting the properties of this noble gas to monitor the hydration of the cement and identify the setting time. Further details about the abovementioned methods can be found in [11]. A very promising non-destructive method based on vibration measurements has been recently proposed to assess the evolution of [PERSON]'s modulus E in cementitious materials: the so-called E-modulus Measurement through Ambient Response Method (EMM-ARM) [9; 12]. It has been widely applied in the literature and validated using extensive comparisons with the results of destructive as well as non-destructive techniques [13]. The development of chemical reactions in the early ages might be affected by factors such as exposure to moisture, which might cause premature hydration (prehydration) of the cement. Prehydration leads to a considerable delay in hydration reactions with an increase in setting time and reduced mechanical performance. Calcium silicates, calcium aluminates, and calcium sulfates react with water vapor to form hydration products on the surfaces of the cement particles that reduce the reactivity of cement to water during normal hydration [14].