February is the Valentine month, so it seems fitting to talk about the thing we truly love at ISE Logik … concrete. But most people really don’t know the story of concrete. It’s the story of civilization, itself.
Let’s get to the basics: what is concrete? Most people think it is just a slab of hard material that we walk on, but what is it really made of? Concrete is made up of three basic components: water, aggregate (rock, sand, or gravel) and Portland cement. Cement, in powder form, acts as a binding agent when mixed with water and aggregates. The combination of these simple ingredients produces a reaction that creates one of the most important and prolific building materials in human history. Though the use of concrete has accelerated in the last century, it might surprise you to learn that the history of concrete stretches back thousands of years.
The first known users of concrete were the Nabataeans dating back to 6000 BC, centuries before the Romans and the Greeks built their famous structures. Their empire was in modern day Syria and Jordan, and some of the remains of their concrete structures still stand today. With the discovery of hydraulic cement and using kilns, they used ash to mix with lime and heat in their kilns. The Nabataea were known to have concrete underground cisterns and drain water facilities and concrete floors in homes. Their basic concrete formula is still what we use today.
Around 3000 BC, the Egyptians used bricks made from mixing mud and straw. However, with many applications they used gypsum and lime mortars in building. With the Great Pyramid at Giza, they used 500,000 tons of this mortar as a bedding material for the stones that formed the surface of the finished pyramid. This allowed stone masons to carve and set stones with joints open no wider than .5 millimeters.
Classical Era Concrete
During the Roman era (300 BC to 476 AD) concrete was re-discovered. They found that by adding volcanic ash to the mix, concrete could set underwater. As one of the first forays into fiber reinforced concrete, the Romans added horsehair to reduce cracking. During this time, the Romans made concrete from lime, volcanic ash, and an aggregate of pumice. Its widespread use in many Roman structures was a key event in architectural history, termed the Roman Architectural Revolution.
The Romans use of admixtures in concrete was extensive, including milk, blood, lard, molasses, eggs, and rice paste for producing a wide range of performance characteristics and greater workability in cementitious mixtures. Concrete, as the Romans knew it, was a new and revolutionary material. Laid in the shape of arches and domes, it hardened into a rigid mass, free from many constraints that builders of the past had with similar structures in stone or brick. Modern tests show that much of the concrete of the Roman structures had as much compressive strength as modern Portland-cement concrete. However, due to the absence of sufficient reinforcement, its tensile strength was far lower than modern reinforced concrete.
The Pantheon is one of the wonders of the ancient world. Made with pozzolana cement – ash, lime, sand, water – and dense stone aggregate, its exterior foundation walls are 26 feet wide and 15 feet deep.
Another first at that time was the introduction of lightweight concrete. Heavy aggregates were used in the lower levels of the structure, and lighter and less dense aggregates were used higher in the structure.
Modern Age Concrete
Finally, in 1824, Joseph Aspdin invented Portland cement by burning finely ground chalk and clay in a kiln until the carbon dioxide was removed. It was named “Portland” cement because it resembled the high-quality building stones found in Portland, England. Aspdin refined his method by carefully proportioning limestone and clay, pulverizing them, and then burning the mixture into clinker, which was then ground into finished cement.
Modern Portland cement is manufactured to detailed standards by heating a mixture of limestone and clay in a kiln to temperatures between 1,300° F and 1,500° F. The mix forms a clinker, which is then ground into powder. Between 1835 and 1850, tests to determine the compressive and tensile strength of hardened cement and concrete were introduced and performed, along with chemical analyses. By the 1860s, Portland cements of modern composition were first produced.
The early 1900s was an exciting time for concrete technology. The contemporary use of fly ash as a pozzolanic ingredient was recognized as early as 1914. In 1930, air-entraining admixtures were developed that greatly increased concrete’s resistance to freezing – kicking off modern admixture technology with subsequent retarders, accelerators and water reducing admixtures. By the 1950s, these types of admixtures began to see widespread use in concrete. ASTM first published its C494 standard in 1962 which set performance criteria for the initial Five Types of admixtures: A, B, C, D and E. Today in North America, admixtures are used in almost all commercial concrete mix designs.
Concrete is an amazing product that has become the single most widely used building material in the world. The future for concrete is bright as new technologies continually advance and improve sustainability, strength, performance and potential new uses for concrete.