Table of Contents
BEST IELTS General Reading Test 496
IELTS GENERAL READING TEST 496 – PASSAGE – 3
IELTS GENERAL READING TEST – 496
READING PASSAGE – 3
Roman Concrete
Ancient Roman concrete has withstood attacks from elements for over 2000 years. Can we learn from the Romans in some way to improve our concrete?
How is it that Roman walls built with their concrete last longer than modern walls? Or is this just a perception? When we build a wall with concrete today, a plywood framework is constructed, concrete is poured into it, and when the concrete is cured, it is removed, leaving the concrete wall. In ancient Rome, two freestanding, parallel walls were built of brick bound with mortar, the combination of which is much, much stronger than plywood.
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A cavity a couple feet wide was left between the brick walls, and then concrete was poured in, along with some small rocks to bolster stability. This method makes a very sturdy wall. Today, we build buildings to last ten years; the Romans built buildings to last for millennia.
A most unusual Roman structure depicting their technical advancement is the Pantheon. This is a brick faced building constructed to praise the Roman gods and has withstood the ravages of weathering in near perfect condition, sitting magnificently in the business district of Rome. Above all, this building humbles the modern engineer not only in its artistic splendour, but also because there are no steel rods to counter the high tensile forces, such as we need to hold our modern concrete together.
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Examining this large circular building tells much of the intelligence of its builders; it was designed to contain a fictional ball, and is some 143 feet in diameter with a wall in the form of skirts dropping from its circumference. In the centre of the dome is a 19-foot opening held in place by a bronze ring backed by a brick ring integrated into the concrete dome. This ingenious opening admitted sunlight to brighten the interior and the slightly curved marble floor provided drainage.
Dusty ancient history books teach us that Roman concrete consisted of just three parts: hydrate lime, pozzolan ash from a nearby volcano and a few pieces of fist-sized rock. If these parts were mixed together today in the manner of modern concrete and placed in a structure, the result would certainly not pass the test of the ages. So, how was it that the Romans so many years ago built such elaborate and ageless structures in concrete as seen on the skyline of Rome?
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Solving the riddle of ancient concrete is about understanding the chemistry. To understand its chemical composition, we must go back further in time. Three millennia ago, people of the Middle East made walls for their fortifications and homes by pounding moist clay between forms, often called pise work. To protect the surfaces of the clay from erosion, the ancients discovered that a coating of thin, white, burnt limestone would chemically combine with the gases in the air to give a hard protecting and moisture proof shield.
We can only guess that the event of discovering this pseudo concrete occurred when a lime coating was applied to a wall made of volcanic, pozzolanic ash near the town of Pozzuoli in Italy. A chemical reaction took place between the chemicals in the wall of volcanic ash (silica and small amounts of alumina and iron oxide) and the layer of lime (calcium hydroxide) applied to the wall. Later, it was found that mixing a little volcanic ash in a fine powder with the moist lime not only made a thicker coat for the ancient concrete, but also produced a durable product that could be submerged in water, something that the plaster product of wet lime and plain sand could not match.
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A new concrete product called roller compacted concrete was developed in the last century and this concrete mimics some of ancient concrete’s characteristics. Roller compacted concrete consists of a mixture of 40 per cent Portland cement and 60 percent fly ash, a byproduct of electric power plants. By coincidence, the fly ash contains the same amorphous silica compounds as the ash from explosive volcanoes, and, when mixed, the hydrated Portland cement releases the same calcium component recognised in the lime mixing part of the ancient concrete formula.
When these two parts were first mixed for roller compacted concrete – for the building of a hydroelectic dam – a bonding gel was formed to tie inert rock pieces together. The calcium hydroxide molecules created in the concrete made with Portland cement and fly ash with amorphous silica can be compared to the composition of the ancient concrete made with wet lime, and volcanic pozzolan with its amorphous silica. Thus, there is a reasonable relationship regarding the concrete components that make the gel for both modern roller compacted concrete and ancient concrete.
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The similarity of the ingredients of modern roller compacted concrete and ancient concrete has been explained, but there is more. The ancients hand mixed their components (wet lime and volcanic ash) in a mortar box with very little water to give a nearly dry composition, carried it to the job site in baskets, placing it over a previously prepared layer of rock pieces, and then proceeded to pound the mortar into the rock layer. Is this important?
Yes! Close packing of the molecular structure by tamping reduces the need for excess water, which is a source of voids and weakness. In addition, close packing produces more bonding gel than might normally be expected. Again, we have a similarity in the ancient and roller compacted concrete practices, which is little water used and tightly compacting the materials in their placement.
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When we review, we can see that the techniques of making ancient concrete have a modern counterpart. The materials (and their ratios) are very similar in both ancient and modern roller compacted concrete and the technique of tamping stiff mortar into the voids of a rock layer to avoid empty spaces are also common to both.
Questions 28-30
Write NO MORE THAN THREE WORDS from the text for each answer.
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Questions 31-36
Do the following statements agree with the information given in the text?
In boxes 31-36 on your answer sheet write:
TRUE – if the statement agrees with the information
FALSE – if the statement contradicts the information
NOT GIVEN – if there is no information on this
31. The Pantheon was constructed for business purposes.
32. When it was first built, light could not penetrate the Pantheon.
33. Pozzolan ash from volcanoes was difficult to mine for the ancients.
34. The limestone coating on ancient concrete created a water-resistant layer.
35. Using a little volcanic ash in the composition of ancient concrete allowed its use under water.
36. Electricity generation was inadvertently very useful in helping make the ingredients for roller compacted concrete.
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Questions 37-40
Choose FOUR letters, AG.
According to the text, which of the following are true for both Roman concrete and roller compacted concrete? Write the correct letter, A-G.
A. The compositions of both concretes were discovered by accident.
B. Both concretes contain amorphous silica compounds.
C. Sulphuric acid derivatives are required in the composition of both concretes.
D. Both concretes release a calcium component during their composition.
E. Both concretes require little water in their composition.
F. Both concretes dry quickly, even in wet conditions.
G. Packing techniques used for making both concretes reduce the threat of vulnerable gaps in the finished product.
IELTS General Reading Test
IELTS General Reading Test
ANSWERS
28. A PLYWOOD FRAMEWORK
29. MORTAR
30. A CAVITY
31. FALSE
32. FALSE
33. NOT GIVEN
34. TRUE
35. TRUE
36. TRUE
37. B*
38. D*
39. E*
40. G⭑
Note: “Answers for qu. 37-40 in any order
IELTS General Reading Test