The Collapse of Massive Concrete Structures: The Case of Boulders for the Breakwater of Augusta’s Harbor in Italy

The brittle failure of a 25 m3 massive concrete block during handling at Augusta’s harbor, Italy, was investigated to identify the root causes and propose improvements for future projects. The study combined experimental, numerical, and on-site analyses to assess the impact of design, manufacturing, and handling procedures on the block’s performance. Experimental tests revealed significant microcracking, high excess voidage (1.5%–3.0%), and a reduced density (average 2,200 kg/m3), primarily caused by insufficient compaction during casting and the lack of curing. These defects amplified thermal gradients resulting from cement hydration and contributed to the structural degradation. Numerical finite-element simulations confirmed that pre-existing continuity issues, coupled with improper handling involving nonsymmetric lifting, resulted in localized tensile stresses approaching the material’s tensile strength. The findings highlight the critical role of proper compaction, curing, and handling protocols in mitigating thermal stress-induced cracking and ensuring the durability of massive concrete structures. Practical recommendations are proposed to enhance the quality and reliability of future concrete boulders for harbor infrastructure.