4.13.2.1 Historical Perspective on Concrete Longevity

Concrete, originally based on lime that hardened by atmospheric carbonation, has been utilized as a con­struction material for several thousand years. Cement has been around for at least 12 My when reactions occurred between limestone and oil shale during spon­taneous combustion in Israel to form a natural deposit of cement compounds.8 The oldest known concrete is from Yugoslavia and is about 7600 years old.9 Gypsum mortars were used by the Egyptians to fabricate the Great Pyramid at Giza about 2500 BC. The Romans were the first to use hydraulic limes and discovered the benefits of pozzolans. The survival of several ancient concrete structures (e. g., Pantheon in Rome, Figure 1) attests to the durability that concrete can attain.

A detailed study involving an examination of sam­ples obtained from several ancient concrete struc­tures utilizing physical and chemical techniques concluded that these structures survived primarily because of careful selection of materials and con­struction, mild climatic conditions, and the lack of steel reinforcement.9 These structures, however, were not fabricated using current ‘hydraulic Portland cement,’ as it did not exist until about 1824. Some information, however, was presented in Mallinson and Davies9 relative to samples that were obtained for testing from several structures fabricated in the mid — to late 1800s. It was concluded that the durabil­ity of these structures was not only due to high cement contents but also due to the relatively slow cement-setting times and high construction quality. These Portland cements differ somewhat from the Portland cements used to fabricate NPP concrete structures in that the formulations have changed as well as the fineness of the cement. Also, modern con­cretes have incorporated admixtures to improve work­ability, modify hardening or setting characteristics, aid in curing, and enhance the performance or durability.