The article presents the results of analyzing the structural changes of samples made of cement mortar. In addition to sand, cement with a higher aluminum oxide content was selected as a mortar component. Biochar, obtained as a product of burning production waste in the wood industry, was intended as an additive affecting the variability of the results. Biochar addition amounted to 1%, 3% and 5% by weight of cement. The samples were subjected to temperature changes. For this purpose, the material was subjected to two phenomena: high temperature (400°) and 150 freezing and thawing cycles. In the study, the authors focused on the possible changes occurring in the internal structure of the material. The possible course of the formation of cracks in the material subjected to variable physical factors, as well as the primary structure, studied by means of the SEM method, were presented. The gathered material complements the previously conducted tests focusing on changes in compressive strength and flexural strengths of reference samples and those prepared according to the described formulations. The results of the study indicate the possibility of using biochar as an additive to mortars allowing them to change their response to different temperatures by affecting the process of water transport inside the material.