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As recently as 4,000 to 6,000 years ago, the Sahara was covered with grasslands, trees, lakes, and rivers. Hippopotamuses, elephants, giraffes, ostriches, crocodiles, and other animals splashed in the water and roamed across the rich, green landscape.
Why did the climate change? Scientists aren't sure. One theory is that small changes in the rotation and tilt of the earth altered the pattern of wind and rainfall. Before this devastation took place, many more people lived here. These mysterious tribes left behind the weapons, tools, arrowheads, jewelry, and bones that scientists now find.
And long before there were humans, sea creatures swam in what was to become the Sahara. Recently, scientists found a 50-foot-long skeleton of an ancient whale in a desert valley in Egypt known as Wadi Hitan, or the Valley of the Whales. Hundreds of fossil whale skeletons have been found there, along with bones of sharks and other fish. They lie trapped in the sandstone of an ancient sea bed, and are being exposed by the desert wind. The whale, perhaps 40 million years old, didn't have a blowhole, but it did have tiny legs, feet, and toes, signs that the ancestors of whales once dwelled on land.
The term ‘cement’ dates back to the Latin ‘cæmentium’, meaning rough stone. The Romans found that crushed rock mixed with burnt lime and water formed a mixture which hardened to a stone-like consistency. It was an invaluable construction material, and there are many buildings from the Roman era made (partially) with this cement that are still standing today, including the Pantheon and Colosseum (Flavian Amphitheatre) in Rome. (Technically this is ‘hydraulic cement’ because of the hardening action of water in forming it; mud and clay were used in early cements, but these are non-hydraulic and quickly worn down by water). Cement mixed with more stone is concrete and can be used for making building blocks.
Different recipes for cement were discovered independently by the Mesopotamians, Egyptians and Romans. For some reason, the technique kept getting lost – perhaps because of stonemasons’ desire to protect their trade secrets – and the method of producing high-quality mortar was not discovered again in Europe until the 14th century. Modern cement owes a great deal to the chemists of the 18th and 19th centuries. Many great Victorian buildings, including the Houses of Parliament, were made with Portland cement, which was patented in 1824 and is still the basis for most modern cement and concrete. 3
But while the Roman buildings have endured 2,000 years or more, modern cement does not survive so well. Modern concrete can decay dangerously within decades. The problem was particularly significant in the Eastern bloc, where planners had seized on concrete as the ideal material to rebuild cities shattered by the war.
In 1957, Ukrainian scientist Victor Glukhovsky investigated why the ancient recipes were so much more durable than modern ones. From the earliest times, various additives were found to make a difference, and the ancients seem to have tried just about everything. The Romans are known to have used animal fat and milk, and more gruesomely, blood. Modern research has found that the blood altered the texture of the cement and introduced air bubbles, which help it to withstand the effects of freezing and thawing. It would be interesting to know whether the practice of making an animal or human blood sacrifice when laying the foundations of a new building is related to this. The tradition of foundation sacrifices is known across Europe, Asia and North Africa. 4
Glukhovsky discovered that superior cement could be obtained by mixing alkaline activators based on sodium and potassium, which occur in many natural minerals. His findings were quickly taken up in the Ukraine, but attracted little attention elsewhere. However, his work was important in inspiring Joseph Davidovits, a French chemical engineer. Davidovits developed a theory that the Egyptian pyramids were not constructed by assembling stone blocks as had always been assumed, but that the blocks were a type of artificial stone, made using reconstituted limestone, which had been cast in place.
If correct, Davidovits’s theory would solve a number of mysteries concerning the building of the pyramids. Small barrels of liquid concrete would be much easier to move than multi-ton stone blocks, and the casting process would explain how some of the blocks fit together so precisely. It would also remove the need to explain how the Egyptians worked huge quantities of stone using just stone and copper tools. This theory would require the Egyptians to be capable of manufacturing a material that is every bit as strong and resilient as natural limestone, capable of withstanding over 4,000 years of weathering. In other words, far better than any modern cement. Davidovits set out to re-create such a material. The startling thing is that he succeeded.
Newswise — In partially solving a mystery that has baffled archeologists for centuries, a Drexel University professor has determined that the Great Pyramids of Giza are constructed with a combination of not only carved stones but the first blocks of limestone-based concrete cast by any civilization.
Michel Barsoum, professor of materials engineering, shows in a peer-reviewed paper published Dec. 1 in the Journal of the American Ceramic Society how the Egyptian builders of the nearly 5,000-year-old pyramids were exceptional civil and architectural engineers as well as superb chemists and material scientists. Barsoum wrote the paper with Adrish Ganguly, a an alumnus who received a doctoral degree in materials engineering from Drexel, and Gilles Hug of the National Center for Scientific Research in France.
Their conclusions could lead to a seismic shift in the kind of concrete used in construction and provide developing nations a way to build structures utilizing inexpensive and easily accessible materials.
The longstanding belief is that the pyramids were constructed with limestone blocks that were cut to shape in nearby quarries using copper tools, transported to the pyramid sites, hauled up ramps and hoisted in place with the help of wedges and levers. Barsoum argues that although indeed the majority of the stones were carved and hoisted into place, crucial parts were not. The ancient builders cast the blocks of the outer and inner casings and, most likely, the upper parts of the pyramids using a limestone concrete, called a geopolymer.
To arrive at his findings, Barsoum, an Egypt native, and co-workers analyzed more than 1,000 micrographs, chemical analyses and other materials over three years. Barsoum, whose interest in the pyramids and geopolymers was piqued five years ago when he heard theories about the construction of the pyramids, says that to construct them with only cast stone builders would have needed an unattainable amount of wood and fuel to heat lime to 900 degrees Celsius.
Barsoum’s findings provide long-sought answers to some of the questions about how the pyramids were constructed and with such precision. It puts to rest the question of how steep ramps could have extended to the summit of the pyramids; builders could cast blocks on site, without having to transport stones great distances. By using cast blocks, builders were able to level the pyramids’ bases to within an inch. Finally, builders were able to maintain precisely the angles of the pyramids so that the four planes of each arrived at a peak.
Although these findings answer some of the questions about the pyramids, Barsoum says the mystery of how they were built is far from solved. For example, he has been unable to determine how granite beams — spanning kings’ chambers and weighing as much as 70 tons each — were cut with nothing harder than copper and hauled in place.
The type of concrete pyramid builders used could reduce pollution and outlast Portland cement, the most common type of modern cement. Portland cement injects a large amount of the world’s carbon dioxide into the atmosphere and has a lifespan of about 150 years. If widely used, a geopolymer such as the one used in the construction of the pyramids can reduce that amount of pollution by 90 percent and last much longer. The raw materials used to produce the concrete used in the pyramids — lime, limestone and diatomaceous earth — can be found worldwide and is affordable enough to be an important construction material for developing countries, Barsoum said.
Originally posted by ignorant_ape
i could make other points - but time is short so i will leave you to consider my claims
the giaza plateou shows zero signs of recent [ by recent i mean the last few thousand years ]
Were Egypt's great ancient monuments carved from stone or cast like concrete? New fossil evidence, found intact and embedded in the monument walls, reignites the debate.
Originally posted by woodwytch
Because I'm absolutely certain that I read about this a long time ago (at least a decade ago).