Concrete is one of the most important construction materials used in modern engineering. It is widely applied in buildings, bridges, roads, industrial facilities, and many other infrastructure projects. Concrete is mainly composed of cement, water, fine aggregates, coarse aggregates, and, when required, chemical or mineral admixtures. Aggregates form the main skeleton of concrete, while cement reacts with water to form a hardened cement paste that binds the aggregates together. After hardening, the mixture becomes an artificial stone-like material with significant strength and durability. Concrete has excellent compressive strength but relatively low tensile strength. For this reason, reinforcing steel is commonly embedded in concrete structures to carry tensile loads, creating the reinforced concrete structures widely used in modern construction. But what determines the strength of concrete? Why can concrete produced with similar materials sometimes achieve very different strengt...