I conducted an extensive experimental investigation into the mechanical limits of cementitious mortars to validate fundamental Materials Science concepts, including brittleness, porosity, and the "rule of mixtures". The study focused on the critical relationships between matrix density, aggregate volume fraction, and early-age hydration kinetics. To test this, I engineered two distinct batches from a commercial Sakrete base: an Optimized Mortar with a low water-to-binder ratio (0.36) to simulate a high-strength grout, and a Diluted Mortar with heavily added silica sand and a higher ratio (0.485). The custom prism specimens were cast and kept in sealed silicone molds for 10 days to enforce autogenous curing conditions. Through rigorous mechanical testing, I analyzed how varying specific surface areas of aggregates can overwhelm available cement paste, leading to a "starved" microstructure that ultimately compromises the composite.