Evaluation of Compressive Properties of Fresh Mortar for Construction of Early-Age Masonry

Masonry is a heterogeneous material with complex behavior. Analyzing the behavior and response of this material is complicated because several parameters, such as the strength of individual elements and the bond between blocks and mortar, affect the properties of masonry. Since the strength of mortar plays an important role in the properties of masonry, international standards, such as CSA-A179 and ASTM-C109, provided a compressive test approach to determine the compressive strength of fully cured mortar. On the other hand, there is a critical time within a few hours after the construction of masonry, when mortar is fresh, and its strength is less than the strength of fully cured mortar considerably. Therefore, fresh masonry structures are vulnerable to lateral loads. However, the above-mentioned compressive tests should be conducted at least 7 days after construction. Therefore, there is no validated data regarding the compressive properties of fresh mortar. The aim of this research is to find out the compressive properties of fresh mortar to address this gap. Totally, 140 cubic mortar samples corresponding to different curing time groups, including 3, 6, 18, 24, 72, and 168 h have been tested to assess the effects of curing time on the strength and modulus of elasticity of fresh mortar. The results show that the compressive strength of fresh mortar (younger than 6 h) is less than 2% of the strength of fully cured mortar samples (7 days samples), and curing time plays an important role in the properties of fresh mortar. The mortar strength increases logarithmically, and the strength of 72 h samples is almost 60% of the strength of fully cured mortar samples. The failure mode and behavior of the material before and after 18 h are completely different, and the damage moment of the early-age samples cannot be determined using the stress–strain plots. Therefore, the surfaces of the samples should be monitored to record the crack initiation moment to find out the strength of the fresh mortar.