Short answers, pulled from the story.
Concrete is a composite material composed of aggregate bound together by a fluid cement that cures to a solid. When aggregate is mixed with dry Portland cement and water, the mixture forms a pourable slurry, and the cement reacts with the water through hydration to harden into a durable stone-like material.
More than 10 billion tonnes of concrete are used worldwide every year. As of 2006, about 7.5 billion cubic meters were made annually, more than one cubic meter for every person on Earth. It is the most widely used building material and the most-manufactured material in the world.
Roman concrete owes its durability to pyroclastic volcanic rock and ash in the mix. The crystallization of strätlingite during curing gave it greater fracture resistance, and the pyroclastic materials react with seawater over time to form Al-tobermorite crystals, making it far more resistant to seawater erosion than modern concrete.
Joseph Aspdin patented a method for producing Portland cement in England in 1824, naming it for its likeness to Portland stone. Reinforced concrete was invented by Joseph Monier in 1849, and François Coignet built the first reinforced concrete house in 1853.
On average, every tonne of cement produced releases one tonne of carbon dioxide into the atmosphere. Cement made for concrete accounts for about 8% of worldwide emissions per year, compared with global aviation at 1.9%, with calcination causing roughly 60% of the greenhouse gases and fuel combustion the other 40%.
Concrete is itself a building material and contains both coarse and fine aggregate particles. Mortar contains only fine aggregates and is used mainly as a bonding agent to hold bricks, tiles, and other masonry units together.
Over 90% of a concrete mix's final strength is typically reached within four weeks, with the remaining 10% achieved over years or even decades. The hydration and hardening during the first three days is critical, and the strength can continue increasing for up to three years.