A system and a method of monitoring physical properties of a physical medium over time are provided herein. The method may include the following steps: embedding a plurality of acoustic sensors into a physical medium before curing thereof; transmitting an acoustic wave by at least one transmitter coupled to or embedded within said physical medium; repeatedly calculating, over different points of time, a travel time of said acoustic wave between the at least one transmitter and the plurality of acoustic sensors; and analyzing said travel times, to detect a change over time in physical properties of said physical medium associated with said travel time.