Why was Roman concrete so durable?

Why was Roman concrete so durable?

Roman concrete, also known as opus caementicium, was a highly durable construction material used by the ancient Romans for a variety of structures, including aqueducts, bridges, and buildings. There are several factors that contributed to the durability of Roman concrete:

The use of lime and pozzolanic materials: Roman concrete was made from a mixture of lime, water, and an aggregate such as sand or crushed stone. The lime was derived from the heating of limestone, which produced a highly reactive form of calcium oxide. The Romans also added a pozzolanic material, such as volcanic ash, to the mixture, which improved the durability and strength of the concrete by reacting with the lime to form a cementitious material.

The inclusion of a reinforcement material: Roman concrete was often reinforced with a material such as iron or lead, which helped to increase its structural strength and resist cracking.

The use of a hydraulic setting process: Roman concrete was able to harden underwater due to its hydraulic setting properties, which allowed it to set and cure even in the presence of water.

The construction of thick, monolithic structures: Roman concrete was often used to build thick, monolithic structures such as walls and foundations, which were able to withstand the forces of nature and resist deterioration over time.

Overall, the combination of these factors made Roman concrete a highly durable construction material that has stood the test of time.

My wife served on a sanitary district board. Decent underground sewer mains have an expected service life of 70 years. Some will last longer, some won't hit the expectation. It depends on site conditions, materials, etc, etc. Many will probably last to 100 years, but I wouldn't expect it to be easy. Especially if you had any of the not decent materials (Orangeburg pipe was common in some areas and is basically wood pulp/fibers mixed with hot tar; service life could vary between 10 and 50 years; the major manufacturer went out of business in 1974, as PVC and ABS pipes rapidly replaced Orangeburg in the materials markerplace).

Actually there was a huge nationwide boom in sewer building post WWII, especially in the 50s, and you can expect that infrastructure to need some largescale replacement over the next 20 years or so. Depending on system design and how housing and industry developed, some systems will be able to just inspect periodically and replace as needed, and some systems will probably take the opportunity to do a more modern redesign (older cities tend to have combined sanitary sewers and storm/runoff drainage; if you're tearing up all the streets to replace the sanitary sewer, it might be a good time to put in a parallel storm drain system)

I'm not sure about water mains, I'd guess they need more frequent replacement since they operate at pressure.