Dynamic enhancing effect of free water on the dynamic tensile properties of mortar

This study investigates free water effect on the dynamic tensile properties of mortar. Fully saturated and saturated-then-redried mortar specimens with two porosities, namely common and high-porosity, are prepared and tested under quasi-static and dynamic split-tension states covering strain rates between 1.49e−06s⁻¹ and 5.29s⁻¹. The split-tensile strength and elastic modulus at different strain rates are quantified. Comparing the dynamic increase factor (DIF) for mortar tensile strength, a maximum difference of 1.2 at strain rate 5 s⁻¹ is found between saturated and dried high-porosity mortars revealing the influence of free water. The testing data is compared with other existing data which shows the mortar water effect is more similar to concrete than limestone and sandstone. The high-speed camera images during the dynamic tests are analysed which revealed a water retarding effect on the dynamic split-tension failure process, resulting in an initial crack delay of up to 0.4 ms due to free water. The wave speed for different mortar specimens at different strain rates is analysed, which shows that higher porosity is more sensitive to the water effect. Possible mechanisms leading to this water effect is discussed. Overall, the study provides a quantitative measure of the water enhancing effect on the dynamic tensile strength of mortar and offers insights into the practical use of water in the design and construction of mortar structures.