Testing the strength of structures
Jagvir Goyal

CONCRETE can be singled out as one construction material that has been most used as well as abused by the construction industry. For ages, scientists and engineers have kept themselves engaged in studying its behaviour and reaction with other materials so as to make it more economical strong, durable, and compatible with other materials. At the same time, it has been played with, tempered with and downgraded in quality to satisfy the greed of those having vested interests. A major handicap has been our inability to test it to be as per specified parameters without destroying it. “Rogues” have been taking maximum benefit of this handicap.

To test a structure under doubt by “destroying” it is an extremely bold step for an engineer who is supposed to be a creator and not a destroyer. If the test results of the structure harmed for testing purposes, so as to remove the doubt, are found satisfactory, the guilt that sets in has no treatment. Under such conditions an engineer longs for such testing methods that may indicate the strength and soundness of a structure without destroying or harming it. It is due to this reason that the focus has been over non-destructive testing for the past few years and now significant breakthrough has been made in this direction.

Such tests and instruments can now be listed which can check the strength, soundness or say, full anatomy of a structure without disintegrating it. What needs to be practised by the engineers is that they should become fully conversant with these instruments and should avail them whenever in doubt. A few of them that may find maximum use and may come most handy to the engineers are described below.

Checking corrosion of steel reinforcement; Once the concrete is poured in position and reinforcement is covered, it is not possible to check whether the steel used for reinforcement was free of rust and scales or not. Moreover if the concrete poured is not of sound quality, the steel may get corroded with time. The condition of steel can now be checked by using Corrosion Analysis instrument which given out printouts showing the condition of steel. Use of rod and wheel electrodes known as half-cells enable this instrument to detect the condition of steel. This instrument can display 240 measurements at a time and can store up to 1,20,000 values.

Another instrument called Resistivity Meter can now be used to measure the electrical resistance of a reinforced concrete structure. This resistance helps in assessing the degree of risk of corrosion of steel embedded in concrete.

Checking cover-depth: Providing adequate cover to steel reinforcement embedded in concrete is one of the most important requirements of concrete structures to save steel from corrosion. Less than prescribed cover may lead to deterioration of steel with the passage of time. To find our whether sufficient cover depth has been kept or not without actually chipping off the concrete, cover Meters have now been developed. These can detect the cover depth up to 300 mm while the normal cover to reinforcement varies from 15mm to 50mm. Light in weight, weighing just 200gm and very much portable, these instruments study the variation in electromagnetic field due to presence of steel bars in concrete and work out the cover to reinforcement.

Checking reinforcement bar spacing and size: Nothing can be said to be hidden and beyond reach with the development of instruments that can detect the size and even the spacing of reinforcement bars embedded in concrete. These instruments called Digital Depth Detectors can measure bar size to an accuracy of +1mm. In these instruments, a path measuring device having an integrated computer scan software is used which makes the embedded reinforcement bars visible. Profometers are the other instruments developed for this purpose. These instruments use magnetic or radar technique to detect the spacing and size of reinforcement bars. Use of an integrated cyber scan software by these instruments makes the reinforcement bars visible on the display screen. An area of 10 sq ft can be displayed in just one minute.

Checking quality of concrete: No-uniformity of concrete, honeycombing in concrete, cavities and cracks in concrete are such defects which may lead to its deterioration due to poor strength, lesser density and ingress of moisture. If finishing is done properly, as most of the builders do, the concrete surface may look fine and smooth and these defects may not at all come to anybody’s notice. To check these defects in concrete, Ultrasonic Testers have been developed. These instruments send electro-acoustic pulses through the concrete pured in position. Total time taken by a pulse to travel from a transducer fixed micro-seconds. More is the time taken, denser and better is the concrete. Further, the strength and density of concrete can now be calculated from the graphs created by developing a relationship between the time taken by the pulse to travel and the strength and density of concrete. Ultrasonic testers are portable instruments and site checking can easily be performed.

Checking location of cracks in concrete: While the Ultrasonic testers tell about the health, density and strength of concrete, exact location of cracks hidden below concrete surface and supposed to appear later in an alarming way can be detected by use of Echo Testers which again pass a wave through the concrete. As soon as the wave encounters a crack or void in concrete, it sends a signal to the monitor on which its movement is being watched. These instruments may be of great help in detecting hidden defects and consequent repair of concrete.

Checking Adhesive strength of concrete and mortar: It has been seen many times that the plaster applied to the walls comes off with time. similarly the plastic coatings or paint finishes applied to the plastered or concrete surfaces come off. Such instruments have now been developed which can measure the adhesive strength of a coating or mortar applied upon a surface. These instruments are called Pull of Testers. These may prove highly useful in work as the adhesive strength of a coating can be measured by applying a sample coating and remedial measures can be taken if adhesive strength is found to be insufficient.

Checking Permeability of concrete: Concrete is supposed to be an impervious material. That’s why it is used in damp-proof course also. In actual, the concrete poured may not be fully impervious due to a variety of reasons such as poor workmanship, loos of excessive time in pouring, use of lesser than designed quantity of cement and so on. If concrete is not impermeable, it will not remain durable and may succumb under severe weather conditions. To avoid such a mis-happening, it is important to check the permeability of concrete. Lesser the permeability, better is the quality of concrete.

To check concrete permeability, instruments have now been developed called permeability Testers. These instruments apply a water column pressure upon concrete surface for a fixed period and then check the drop in water pressure. More is the drop, more is the permeability of concrete.

Checking Asphalt content of concrete: Asphalt concrete is finding more common use in construction of pavements today. For the pavements to be durable and resistant to wear and tear, a correct asphalt mix is extremely important. To determine the quantity of asphalt in asphalt concrete, Asphalt content gauges can now be used. These gauges can indicate the aphalt content of concrete at the site of pavement, at the mixing plant site or in the laboratory to an accurate extent and within minutes.

With the advent of so many non-destructive and accurate testing instruments which are easy to operate, give quick results and are not expensive, it now becomes imperative that a structure must be evaluated with the help of these instruments before it is put to use(if newly constructed) or before dismantling (if outlived). Visual assessments and guess-work should now be minimised.

Ethanol as a viable motor fuel
S.S. Verma

ETHANOL used as a product in spirits, beer and wine earlier is becoming an important viable alternative at present to unleaded gasoline fuel.

Ethanol burns with a pale blue, non-luminous flame to form carbon dioxide and steam. It is a high-octane fuel with high oxygen content ( 35% oxygen by weight) and when blended properly in gasoline produces a cleaner and more complete combustion.

In recent years, considerable interest in ethanol as a fuel extender, octane enhancer, oxygenate, and a neat fuel has increased dramatically because of concerns associated with conventional transportation fuels. The elimination of tetra-ethyl lead in gasoline during the mid-1980s and the 1990 Clean Air Act Amendments have required refinery operations to provide oxygenated gasoline in order to “fill the octane gap” and “reduce” carbon monoxide emissions and smog in the polluted areas. Currently, ethanol and methyl tetra-butyl ether (MTBE) are the two oxygenated fuels most widely used in a number of developed countries. However, Ethanol may be considered as the attractive oxygenate over MTBE as it is produced from bio-mass which is a renewable fuel while MTBE requires iso-butene, a fossil fuel, for synthesis, and moreover, ethanol has roughly double the oxygen content than MTBE on an oxygen to carbon basis.

Ethanol advocates base their arguments for promoting the use of this fuel on three main issues. air quality, energy security, and farm income. So, total ethanol combustion in light duty vehicle gasoline will increase. New study documents ethanol’s ability to reduce greenhouse gases. Ethanol eases pressure on fossil energy for its use in various forms in corn transportation, ethanol production, ethanol transportation and distribution and ethanol combustion in motor vehicles. Ethanol is a quality fuel alternative (anti-knock) rating when blended with gasoline. Ethanol improves engine combustion and keeps fuel systems clean. Ethanol production can be achieved with chemicals manufacturing, farming of corn and biomass. Ethanol combustion can also contribute towards the control of global warming. Although, burning of ethanol still releases carbon dioxide during production and combustion, it is recycled by the crops that produce ethanol.

As for ethanol and NOx, while there is some difference of opinion as to degree, it appears that combustion of ethanol does produce more tailpipe emissions of NOx than gasoline, because the ethanol blend can be burned as a leaner air-fuel mixture, resulting in higher combustion temperatures than with gasoline. With regulations on pollutant emissions becoming strict, the amount of oxygenated fuel like ethanol in gasoline could increase. Therefore, we need a full understanding of the reaction pathways by which ethanol is oxidised and of the pollutant species that may be produced. This understanding will allow industry and regulatory agencies to better evaluate the feasibility and relationship between the combustion process and pollutant emissions when using ethanol. Reaction pathway and sensitivity analysis are used to help identify those reactions and their accompanying rate constants that exhibit a strong influence on the ethanol oxidation process.

Giant plane for cargo traffic

ANTICIPATING an increase in cargo traffic passing through conventional airports by 2010, France engineers plan to develop a giant cargo plane.

The design team Hydro 2000 - a giant, multipurpose, cargo plane - would be a viable solution to the anticipated doubling of cargo traffic in the future.

Hydro 2000 is being designed for long-haul cargo flights - 300 metric tons over 12,000 kilometres or more, or 400 metric tons over 8,000 kilometres.

The aircraft’s operating costs per ton kilometre of payload and its cost-benefit ratio are unbeatable, a report in Gifas Info said.

The plane, with a wingspan of 110 metres, would be powered by six turhofans each producing 45 tons of thrust.

Other specifications of the plane include an overall length of 108 metres, height of 25 metres and a wing area of 1300 metres by 1300 metres.

Civil and military versions of the plane would be offered with one or two cargo decks, the report said.

The Hydro 2000 project team has entered into an agreement with the Berely design office of Russia - an acknowledged leader in hydrodynamics, the report added. PTI

NEW PRODUCTS & DISCOVERIES

New chip that saves energy

IT is now possible to operate solar-powered devices in dimly lit rooms and even in twilight, as scientists have come up with a new chip, which functions with minimal power consumption.

Solar cells provide power for small portable devices such as pocket calculators and wristwatches but there are limits to this form of environmentally friendly power supply. The power and size of the solar cell has to inevitably increase in proportion with the power consumption of the device.

To overcome the challenge, the Fraunhofer Institute for Integrated Circuits IIS in Erlangen, Germany, has developed the revolutionary chip. In most cases the chip does not even require battery backup — which adds another part to the device.

The solar battery can be dispensed with if the device’s power consumption is reduced, a report in Fraunhofer Gesellschafi said.

Employed in modern electronic letter scales, the solar cell supplies electricity to a force sensor, a signal-processing and control circuit and a liquid crystal display (LCD).

Hans Hauer, who is responsible for the design of mixed signals at the institute, explains how the scale works: “The power consumption of the chip itself has been minimised. In addition, it is capable of recognised which functions are required at any particular instant.” PTI

High-temperature superconductivity

Researchers have found a chemical that superconducts electricity at higher temperatures than metals or simple metallic compounds thereby opening up the possibility of making cheap superconducting wires and devices that operate at accessible temperatures.

As superconductors offer no resistance to the flow of electric current, they are ideal for power transmission cables and high-speed circuits. The trouble, however, is that they only lose resistance below a critical temperature — below 23 kelvin for metals or simple metallic compounds.

Scientists from Switzerland had discovered, in 1986, a whole new class of ceramic copper oxide superconductors with much higher critical temperatures, sometimes even over 100 kelvin, but these were expensive and difficult to make and use, a report in New Scientist said.

Jun Akimitsu and his colleagues at the Aoyama Gakuin university in Tokyo have now found that magnesium diboride superconducts at 39 kelvin.

Akimitsu believes this to be “the highest yet determined for a non-copper-oxide bulk superconductor.”

“It’s terribly exciting,” says physicist Lesley Cohen of Imperial College, London. She says one big attraction of magnesium diboride is that it is easy to work with at room temperature.

The race is now on to understand how magnesium diboride superconducts, and push it to higher temperatures in conventional materials,” says Robert Cava of Princeton University.

Researchers at the Lowa State university are reported to have already made magnesium diboride superconducting wires. PTI

Multipurpose lighting

Scientists have developed a device that emits a distinctive light that could be put to use in a variety of 21st century equipment ranging from mobile phones, laptop computers to roadside signs.

Developed by scientists in the United Kingdom, the device which exploits the technology of electroluminescence is basically a flexible, ultralightweight foil-like material just one quarter of a millimeter in thickness that emits a distinctive and consistent light when connected to a power supply.

Although Electroluminescent (EL) lamp technology was developed decades ago and is familiar worldwise as the process that lights the display panel in mobile phones, its use had been limited by its relatively low-light output and lack of flexibility.

The new polyster-based material has a coating with chemical compounds that combine to create a lighter and thinner foil producing 30 per cent more light than existing electroluminescent lamps. The coating also produces a wider beam of light and ensures better durability, a report in British Commercial News said.

As the electroluminescent lamps are cold, highly reliable and use minimal electrical power they are ideal for use as safety lighting, for the floors or walls of aircraft cabins, passengers ships and hospital corridors. PTI

Click and chat

Video Chat just went from a pain to a breeze. With the EZPhone Cam, you chat with family and friends over the Internet simply by clicking on a person’s picture.

To get started, just install the EZPhone Cam software, which is free from Ezonics’ website www.exonics.com, Establish and Id and password, log on the Internet, and you’re ready to chat.

For your friends, the camera is optional — you just won’t see them. When someone wants to reach you the EZPhone Cam blinks and rings.

Price: $ 120.
Popular Science

SCIENCE QUIZ
J.P. GARG TESTS YOUR IQ

1. This English astronomer and physicist is known for his theories about stars and wrote great books “Stellar Movements and the Structure of the Universe”, “The Internal Constitution of Stars” and “The Mathematical Theory of Relativity”. Name this scientist who also popularised Einstein’s theory of relativity and provided an experimental proof of the idea that gravity bends light rays.

2. Scientists have recently discovered that a chemical called BDNF produced by the brain could play a crucial role in disorders such as Parkinson’s disease, schizophrenia and drug addiction. What is the full name of BDNF, a protein that helps develop brain cells?

3. What is the branch of veterinary medical science called which deals with the diseases communicable from animals to human beings?

4. A bright yellow toxic crystalline solid, soluble in water but insoluble in alcohol, this salt is used in the laboratory as an analytical reagent and as an indicator, it is used in leather finishing, in enamels and paints, and as a textile mordant. Which is this compound of potassium?

5. When a liquid is bombarded with sound waves of a suitable high frequency, bubbles are formed in the liquid which emit light. What is this process called?

6. Biogas is a good fuel which is formed by the anaerobic fermentation of animal or plant wastes in the presence of water. Which are the four constituents of biogas? What is the main use of the slury left behind?

7. To boost the intensity of optical signals being carried through a fibre optic communication system, an optical fibre is doped with a rare earth element so that the glass fibre can absorb light at one frequency and emit light at another frequency. Which is this element?

8. In a camera, the amount of light reaching the film depends on the ratio of the focal length of the camera lens and the diameter of the lens opening. What is this ratio called?

9. Joule is a unit in which three physical quantities can be measured. Can you name these?

10. Name the famous natural space object which will appear in the sky in 2061.

Answers

1. Sir Arthur Stanley Eddington
2. Brain-derived neurotrophic factor
3. Zoonosis
4. Potassium chromate
5. Sonoluminescence
6. Methane, carbon dioxide, hydrogen and hydrogen sulphide; as manure
7. Erbium
8. f-number or focal ratio
9. Energy, work and quantity of heat
10. Halley’s Comet.