Short answers, pulled from the story.
Cement is an inorganic binder typically based on lime or calcium silicate that acts as the glue holding sand and gravel together in concrete. It is the second most consumed resource on Earth after water and serves as the chemical substance that sets and hardens to create monolithic structures.
The Romans utilized crushed volcanic ash known as pozzolana mixed with lime to create hydraulic cement that could set in the presence of water during ancient times. This mixture enabled the construction of massive structures like the Pantheon and the Baths of Caracalla which still stand today.
William Aspdin is considered the true father of modern Portland cement and he accidentally produced calcium silicates in the 1840s by heating limestone and clay to high temperatures. His father Joseph Aspdin had patented a similar material in 1824 but William's innovation created the alite mineral phase responsible for early strength.
Cement hardens through a chemical process called hydration where calcium silicates and oxides combine to form mineral hydrates within a temperature range of 5 to 30 degrees Celsius. This process requires moisture to proceed and involves the interlocking of hydrates to give the material its strength.
The production of cement is responsible for nearly 8% of global carbon dioxide emissions and involves heating limestone to 1,450 degrees Celsius in a kiln. Approximately 60% of these emissions come from the chemical decomposition of limestone while the remaining 40% result from the energy required to heat the kiln.