Sometimes, living in these modern times we often take for granted the little things and really how much history and undertaking has passed for us to reach this point. We often walk on our driveways and sidewalks and enjoy the clean aspects of a new patio made from concrete but there is so much more to the story.
The word concrete comes from the Latin word “concretus” which means compact or condensed. The Assyrians and Babylonians used clay as the bonding substance or cement in their day. Egyptians were a little more advanced and used rough or crushed lime and gypsum to create their cement.
In 1756 a British engineer by the name of John Smeaton made the first modern concrete, or hydraulic cement, by adding pebbles as a coarse aggregate and mixing powdered brick into the batch. It was a good effort but better products were coming.
In 1824, an English inventor, Joseph Aspdin, invented Portland Cement named after the Portland Cliffs in England because of its light color, not Portland, Ore. This revolutionary new concrete has remained the dominant and true artificial cement used in production to this day.
The process to make Portland Cement involves burning ground limestone and clay together in large ovens. The burning process thermally changes the chemical properties of the materials and creates stronger cement than cement simply made from crushed limestone and other materials.
The other part of concrete besides the cement is the aggregate composition. Aggregates include sand, crushed stone, grave, ashes, slag, burned shale, and burned clay.
Aggregates give the finished concrete body and great compressibility. Fine aggregates are used in making concrete slabs and smooth surfaces.
Coarse aggregates, big rock or shot-crete, as most pool builders know, are used in large construction or massive structures.
One thing about concrete that I found surprising is that today the manufacture of Portland Cement is responsible for 5 percent to 6 percent of the world wide, man made Co2 gas emissions. Half of this Co2 is from the chemical process of making the cement and 40 percent more from burning fuel in this process.
Ironically however, when we think of concrete, we think of it as lasting forever. It doesn’t, but it does have a 100-year service life. Over this time period, through a process called carbonation, concrete can actually re-absorb Co2 from the atmosphere and remove up to 57 percent of the Co2 that was created upon its original calcinations or manufacture. Being recyclable, it is also a very green and environmentally sustainable building material.
In 1849, a Parisian gardener Joseph Monier came up with the idea to make garden pots and tubs of concrete using wire mesh and reinforcing steel and rods. He received a patent for this many years later in 1867. The advantage concrete has in building is that it can support heavy loads with a high compression strength. The downside is that it has no ductile or tensile strength. When it becomes torqued or placed under tension it will crack and fail.
Today’s reinforced concrete or ferroconcrete combines the tensile strength of steel with the best qualities of concrete. Monier exhibited this same invention at the Paris Exposition of 1867 and promoted reinforced concrete for use in railway ties, pipes, floors, arches and bridges.
When you stop to think about your pool, deck or landscape, none of this comes to mind. But the steel is there. The only problem with using steel in a wall, pool or structure is that oxidation, or rust as I like to call it, never sleeps. When water from some source (usually from behind a wall) penetrates the concrete, the steel will begin to rust from the inside of the wall expanding outwardly and believe it or not can actually exert thousands of pounds of pressure against the interior of the concrete, cracking and destroying it’s integrity.
This is where design and experience come in and are so important in creating a hard-scape that will not only be beautiful for the end recipient but will be durable and lasting in an ever changing environment.
When you choose your contractor, a little grey hair goes a long way.
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