Allan barstow, age 14, of redondo.beach, calif., for his question:
What exactly is portland cement?
Some peop1e suspect that this sturdy stuff is named for the city of Portland in Maine. Others think it might have been invented to pave the sidewalks of one of the other cities or towns named Portland. Actually it was named for a place so small that most maps do not show it.
Stone masonry is an ancient skill, older than recorded history. Builders through the centuries have tried to better their work and improve their skills. The earth provides many building blocks, and the search for the best building stones never ends. The mason must also know how to stick his stones together, and many recipes for pasty mortars have been invented for this cementing work.
The story of portland cement began with an English bricklayer who wanted a better cementing mortar. He powdered a mixture of limestones and clays and baked them in a kiln. Then he ground the hard brick like cinders to powder. When mixed with water, the powder formed the best cementing mortar known in the building business.
The bricklayer was Joseph Aspdin, and he invented his new cement in the year 1824.
Joseph knew his stones well and where the best of them were to be found. His new mortar reminded him of certain natural stones found on the tiny Is1e of Portland off the shores of Britain. He named it portland cement. But it is not likely that his thoughtful man dreamed of the role his invention would come to play in the building of the future.
The united states alone produces 65 million tons of portland cement every year, and the durable paste is used to create countless tons of man made building stones. It is the binding material of our concrete walks and walls, our roads and launching pads. Our recipes for making it have improved, and even better cements will come in the future, but we still use the lime and clay type minerals used by Joseph Aspdin. Our methods of mixing, grinding, baking and powdering them are similar to those he invented. We still use the name he gave it, even when we drop the capital letter and call it simply portland cement.
The basic recipe for portland cement is set by the government, and the material is manufactured in a huge plant. Tons of powdered clays and limes are fed into a monster kiln, maybe 12 feet wide and as long as a city block. This oven becomes hot enough to melt iron. The roasted clinkers are then ground to powder and mixed with traces of gypsum.