To make significant advances in concrete engineering, it will be necessary to understand the behavior of cementitious materials at the microscale. To achieve this goal, the nature of damage initiation and growth needs to be understood at very small scales. This research program sought to increase that understanding through the collection of microscale data using X-ray computed tomography (CT). The tensile and compression behavior of both ultra-high performance concrete (UHPC) and conventional concrete were investigated as a part of this program. Relationships were identified between mechanical performance parameters, such as stiffness degradation and work of load, and cracking parameters, such as crack volume and crack surface area, that could be quantified mathematically and implemented into future finite element analysis (FEA) models. The results of this research program have the potential to improve the accuracy and resiliency of numerical models and to provide insight to the materials engineering community concerning the optimal use of UHPC.