[WCityMike]

"It is durable due to its incorporation of pozzolanic ash, which prevents cracks from spreading."

Third sentence in the Wikipedia article. Later:

"The strength and longevity of Roman marine concrete is understood to benefit from a reaction of seawater with a mixture of volcanic ash and quicklime to create a rare crystal called tobermorite, which may resist fracturing. As seawater percolated within the tiny cracks in the Roman concrete, it reacted with phillipsite naturally found in the volcanic rock and created aluminous tobermorite crystals."

Neither seems to have been 'lost data'.