Short answers, pulled from the story.
Cement is a hydraulic binder that sets, hardens, and adheres to other materials. It rarely works alone but binds aggregates together to form concrete or mortar. Hydraulic cements like Portland cement set through a chemical reaction between dry ingredients and water.
John Smeaton planned the third Eddystone Lighthouse between 1755 and 1759 in the English Channel. He needed a hydraulic mortar that would develop strength within the twelve-hour period between successive high tides. Experiments with different limestones and additives revealed that hydraulicity related directly to clay content.
Cement manufacturing releases nearly eight percent of global carbon dioxide emissions annually according to 2018 data. Nearly nine hundred kilograms of CO2 emit for every thousand kilograms of Portland cement produced. Sixty percent comes directly from chemical decomposition of limestone into lime while another forty percent stems from burning fuel to heat kilns.
World production reached about 4.4 billion tonnes per year according to 2021 estimates. China manufactures approximately half of all global cement output followed by India and Vietnam. In 2010 three nations produced over half the world total combined with China manufacturing 1.8 billion tonnes.