Donald MacIsaac, age 8, of Niagara Falls, Ontario, Canada, for his question:
When did they start using cement?
Cement is supposed to stick things together, and we have all kinds. We have different glues for cementing wood, paper and plastic. But the cement we use to make sidewalks and such is something very special. It cements sands and gravels together to make sturdy slabs of concrete. We call it portland cement. It was invented about 150 years ago. And for the past 100 years or so, builders have been using it in a big way.
The very first builder's cement was dried mud. Ages ago, they mixed mud and water, molded the paste into bricks and let the sun dry them hard. Later they learned to bake their clay bricks in huge ovens. When time came to build, they used mortar to cement the bricks together. As a rule, the mortar was a moist mixture of lime and clay, some sand and perhaps a few horse hairs to bind it together. When it dried it cemented the bricks in fairly firm walls.
About 200 years ago, they needed a better cement to build a mighty lighthouse, strong enough to withstand the surging seas off the shores of England. They made it by baking limy ingredients and chomping the chunks to powder. It was called Roman cement. When mixed with water it formed a very strong mortar. But a brick layer named Joseph Aspdin longed for a still better mortar to cement his bricks together.
Joseph took pride in his work. He also must have been a sensible person because he studied how the earth cements sands and gravels to make enormous slabs of hard rock. About 150 years ago, he tried to copy nature's recipe. He smashed limestone and other earthy ingredients to fragments. Then he baked the mixture to form hard chunks and ground the chunks to powder. He moistened it and used it to cement his bricks. He tried many experiments. Then in 1824, he invented a cement that was harder than nature's own recipe. He named it portland cement because it reminded him of a sturdy building stone that came from the small Isle of Portland.
This sturdy cement also could stick sand and gravel together in slabs of man made rock called concrete. In the 1830s, Joseph's portland cement became very popular in England. Several factories tried to copy it and in the 1880s, they were using 19 different recipes. About 100 years ago, the builders of the United States and Canada began using their own portland cements to make concrete.
But all those different recipes were a problem. So around 1916, the experts got together and decided that there should be only one standard recipe for making port land cement. They listed the ingredients and described the steps to make it. Then people knew that they always could depend on it if they followed the instructions. The pasty colored powder must be mixed with the right amounts of sand, gravel and water. When it dries, it is sure to form sturdy concrete suitable for building sidewalks and buildings, dams and bridges and dozens of other things.