While the Roman buildings have endured 2,000 years or more, modern cement does not survive so well. Modern concrete can decay dangerously within decades. The problem was particularly significant in the Eastern bloc, where planners had seized on concrete as the ideal material to rebuild cities shattered by the war.
In 1957, Ukrainian scientist Victor Glukhovsky investigated why the ancient recipes were so much more durable than modern ones. From the earliest times, various additives were found to make a difference, and the ancients seem to have tried just about everything. The Romans are known to have used animal fat and milk, and more gruesomely, blood. Modern research has found that the blood altered the texture of the cement and introduced air bubbles, which help it to withstand the effects of freezing and thawing.
Glukhovsky discovered that superior cement could be obtained by mixing alkaline activators based on sodium and potassium, which occur in many natural minerals. His findings were quickly taken up in the Ukraine, but attracted little attention elsewhere. However, his work was important in inspiring Joseph Davidovits, a French chemical engineer. Davidovits developed a theory that the Egyptian pyramids were not constructed by assembling stone blocks as had always been assumed, but that the blocks were a type of artificial stone, made using reconstituted limestone, which had been cast in place.
In 1979, Davidovits discovered a new class of materials known as geopolymers, which are similar to Glukhovsky’s building cements and have aluminosilicate mineral powders added. Technically they are formed by condensation polymerisation and (unlike other cements) do not incorporate waters of hydration within their crystal structure. They are significantly stronger than other cements, impermeable to water, and much more durable to erosion caused by temperature change or chemical action. Geopolymers are only very slowly being accepted into the market in spite of their obvious advantages.
Source: Finding concrete evidence