Brief

An engineer must take into account when choosing between balanced concrete, under-reinforced concrete or over-reinforced concrete for a beam to support a building. “In most circumstances, under-reinforced section concrete beams are generally preferred to either balanced or over-reinforced as they are more economical, and are generally safer,” he writes.

 

Insight

Let’s imagine you have been asked to design a concrete beam for some sections of a building. What do you choose? Pure concrete or reinforced concrete?

The latter, right? But what type of reinforced concrete? Balanced, under reinforced, or over reinforced?

Here we answer this question and also talk more generally about the history of concrete and its physical properties. For all those “concrete-philes” out there, eat your hearts out!

How old is concrete?

Before we get into the nitty-gritty of the main topic, let’s take a quick look at the interesting history of concrete.While you might already be more than familiar with concrete, chances are you may not realize just how old it is. In fact, since it is so ubiquitous today, you probably take this wonder material for granted

Some of the first evidence of concrete-like structures is from around 6500 BC. Evidence exists that early structures like floors, some housing elements, and underground cisterns were built in some regions of Syria and Jordan, and along the Danube.

The next time a type of concrete appears to have made a widespread appearance was around 3000 BC. Ancient Egyptians commonly used to mix mud with straw to make dried bricks.To bind these bricks together, ancient Egyptians would use a combination of gypsum mortar and lime mortars — including in the pyramids. Mortar of this kind is a type of cement, which is an essential element of concrete.

The Great Pyramids of Giza, for example, used somewhere in the region of half a million tons of this mortar.Some studies have found that parts of some pyramids may have been built by using a poured concrete building technique. This method appears to have been used in situ on the pyramids, in place of hauling giant stones.

One of the most important innovations in early concrete history was the advent of Roman concrete. While the Romans were certainly not the first to invent concrete, they were the first to use it en masse — as far as we know. By around the 2nd-Century BC, the Romans had, more or less, perfected the technique, using a combination of volcanic ash, lime, and seawater to form the mix. Both the Romans and the Greeks incorporated pozzolanic ash, which prevents cracks from spreading.

 

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