*Article* **Monitoring the Setting Process of Cementitious Materials Using Guided Waves in Thin Rods**

**Dongquan Wang <sup>1</sup> , Guangyun Yu 2,\*, Shukui Liu 1,2 and Ping Sheng <sup>2</sup>**


**Abstract:** Characterizing early-age properties is very important for the quality control and durability of cementitious materials. In this paper, an approach using embedded guided waves was adopted to monitor the changes in the mechanical proprieties of mortar and concrete during setting, and embedded thin rods with low-cost piezoelectric sensors mounted on top were used for guide wave monitoring. Through continuous attenuation monitoring of the guided waves, the evolution of mortar and concrete properties was characterized. Four different kinds of metallic rods were tested at the same time to find out the optimal setup. Meanwhile, shear wave velocities of the mortar and concrete samples were monitored and correlated to the attenuation, and setting time tests were also performed on these samples. Experimental results demonstrate that the proposed approach could monitor the evolution of the setting of cementitious materials quantitatively, and time of the initial setting could be determined by this technique as well. In addition, it is found that the attenuations of fundamental longitudinal guided wave mode are almost the same in concrete samples and mortar samples sieved from concrete, indicating that this technique is able to eliminate the effects of coarse aggregates, which makes it of great potential for in-situ monitoring of early age concrete.

**Keywords:** guided waves; setting time; mortar and concrete; early age
