Cinder Blocks: a cinderella story

What is a cinder block? It conjures an image: 8 inch by 8 inch by 16 inch rectangular cube, with two or three core holes. Grey and dull, solid and regular, straight walls and square corners: as American as WalMart.

Actual cinder blocks are pretty cool. You can’t get them any more. They used to be made from the cinders which were a waste product of burning coal. Coal combustion is now done much more efficiently, and doesn’t create large cinders but a very fine fly ash. No more cinders, no more cinder blocks.

Around 1910 coal cumbustion produced cinders, and few places burned more coal than Pittsburgh, Pennsylvania. A brick mason from Pittsburgh named Francis Straub realized the potential of this large volume waste product, and experimented with cinders and cement. This led to the discovery of material mix designs for cinder block in 1913.

Cinder blocks are lightweight, insulate, and nails can be driven into them. Mr. Straub had many challengers to his technology, and fought several patent infringement cases on his invention. The crux of the decision on his case was that if you could drive a nail into a block, it was a cinder block: it was his patent, and nobody else could make block like that.

Mr. Straub would show up at competitors he suspected of infringing on his patent, and try to drive a nail into one of their blocks. If he could drive a nail, he would collect royalties or shut them down, or both.

Around 1936 the United States made a decision to streamline construction and manufacturing by making all construction materials based on a modular coordination of design. It was decided to base all construction materials on a 4 inch cube volumetric grid, so that all materials were designed to fit within this grid; everything from sheets of plywood to 2”x4”s, to windows and doors. The block industry settled on the 8’x8”x16” design which we’re so familiar with today.

Eventually coal combustion became more efficient, and cinder blocks were no longer made. The term stuck though, so today people still refer to concrete blocks as cinder blocks. Today the fly ash from coal combustion is used as a pozzolanic material in concrete, creating a higher strength concrete. They are more dense and you can’t drive a nail into them.

“Cinder block” is practically a cultural icon, it is so ubiquitous and familiar. There are musicians calling themselves ‘cinder block’, and certain crude urban interpretations have been applied to the term. All thanks to Francis Straub from Pittsburgh, circa 1913.

Portland Cement

Cement is often confused with concrete. Cement is the glue that holds the other concrete ingredients together (sand, aggregate and rock). Cement is the world’s most widely used construction material, with around 1.25 billion tons produced each year.

Ancient civilizations sought to bind stone together into a solid mass. Assyrians, Babylonians and other civilizations used mud for this purpose. Egyptians began to use lime and gypsum to improve their mortar to a material more durable than simple clay. Romans developed cement to a much higher degree, by including volcanic ash known as Pozzolanic material (named after the town of Puozoli, at the foot of Mt. Vesuvius). This material was used in Roman concrete, or “Opus Caementicium.” Pozzolonic material acts as a cement in the presence of cement. It is basically just ash, and does not work as a cement by itself.

Romans developed cement to a high state, as described by Vitruvius, around 25 BC in his work “Ten Books of Architecture.” With the fall of the Roman Empire, the art of cement making and use was lost. The key feature of Roman cement is that it was hydraulic cement, and would cure or set underwater.

Hydraulic cement was not rediscovered until late in the eighteenth century, when the scientific method led to its rediscovery, as discussed in this article. “Repeated structural failure of the Eddystone Lighthouse off the coast of Cornwall, England, led John Smeaton, a British engineer, to conduct experiments with mortars in both fresh and salt water. In 1756, these tests led to the discovery that cement made from limestone containing a considerable proportion of clay would harden under water.
Making use of this discovery, he rebuilt the Eddystone Lighthouse in 1759. It stood for 126 years before replacement was necessary.

Other men experimenting in the field of cement during the period from 1756 to 1830 include L. J. Vicat and Lesage in France and Joseph Parker and James Frost in England.

Before portland cement was discovered and for some years after its discovery, large quantities of natural cement were used. Natural cement was produced by burning a naturally occurring mixture of lime and clay. Because the ingredients of natural cement were mixed by nature, its properties varied as widely as the natural resources from which it was made.

In 1824, Joseph Aspdin, a bricklayer and mason in Leeds, England, took out a patent on a hydraulic cement that he called portland cement because its color resembled the stone quarried on the Isle of Portland off the British coast. Aspdin's method involved the careful proportioning of limestone and clay, pulverizing them, and burning the mixture into clinker, which was then ground into finished cement.
Portland cement today, as in Aspdin's day, is a predetermined and carefully proportioned chemical combination of calcium, silicon, iron, and aluminum.”

Portland Cement is widely used in construction today. Tomorrow we’ll look at cinder blocks and concrete blocks, and what the difference is between them.